20 files changed, 5658 insertions, 0 deletions
diff --git a/src/lib-compression/Makefile.am b/src/lib-compression/Makefile.am
new file mode 100644
index 0000000..f689b0c
--- /dev/null
+++ b/src/lib-compression/Makefile.am
@@ -0,0 +1,61 @@
+noinst_LTLIBRARIES = libcompression.la
+
+AM_CPPFLAGS = \
+	-I$(top_srcdir)/src/lib \
+	-I$(top_srcdir)/src/lib-test \
+	$(ZSTD_CFLAGS)
+
+libcompression_la_SOURCES = \
+	compression.c \
+	istream-decompress.c \
+	istream-lzma.c \
+	istream-lz4.c \
+	istream-zlib.c \
+	istream-bzlib.c \
+	istream-zstd.c \
+	ostream-lz4.c \
+	ostream-zlib.c \
+	ostream-bzlib.c \
+	ostream-zstd.c
+libcompression_la_LIBADD = \
+	$(COMPRESS_LIBS)
+
+pkginc_libdir = $(pkgincludedir)
+pkginc_lib_HEADERS = \
+	compression.h \
+	iostream-lz4.h \
+	istream-zlib.h \
+	ostream-zlib.h
+
+noinst_HEADERS = \
+	iostream-zstd-private.h
+
+pkglib_LTLIBRARIES = libdovecot-compression.la
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+libdovecot_compression_la_LIBADD = libcompression.la ../lib-dovecot/libdovecot.la $(COMPRESS_LIBS)
+libdovecot_compression_la_DEPENDENCIES = libcompression.la ../lib-dovecot/libdovecot.la
+libdovecot_compression_la_LDFLAGS = -export-dynamic
+
+test_programs = \
+	test-compression
+
+noinst_PROGRAMS = $(test_programs) bench-compression
+
+test_libs = \
+	$(noinst_LTLIBRARIES) \
+	../lib-test/libtest.la \
+	../lib/liblib.la
+test_deps = $(test_libs)
+
+test_compression_SOURCES = test-compression.c
+test_compression_LDADD = $(test_libs)
+test_compression_DEPENDENCIES = $(test_deps)
+
+bench_compression_SOURCES = bench-compression.c
+bench_compression_LDADD = $(test_libs)
+bench_compression_DEPENDENCIES = $(test_deps)
+
+check-local:
+	for bin in $(test_programs); do \
+	  if ! $(RUN_TEST) ./$$bin; then exit 1; fi; \
+	done
diff --git a/src/lib-compression/Makefile.in b/src/lib-compression/Makefile.in
new file mode 100644
index 0000000..9ead33e
--- /dev/null
+++ b/src/lib-compression/Makefile.in
@@ -0,0 +1,976 @@
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+clean: clean-am
+
+clean-am: clean-generic clean-libtool clean-noinstLTLIBRARIES \
+	clean-noinstPROGRAMS clean-pkglibLTLIBRARIES mostlyclean-am
+
+distclean: distclean-am
+		-rm -f ./$(DEPDIR)/bench-compression.Po
+	-rm -f ./$(DEPDIR)/compression.Plo
+	-rm -f ./$(DEPDIR)/istream-bzlib.Plo
+	-rm -f ./$(DEPDIR)/istream-decompress.Plo
+	-rm -f ./$(DEPDIR)/istream-lz4.Plo
+	-rm -f ./$(DEPDIR)/istream-lzma.Plo
+	-rm -f ./$(DEPDIR)/istream-zlib.Plo
+	-rm -f ./$(DEPDIR)/istream-zstd.Plo
+	-rm -f ./$(DEPDIR)/ostream-bzlib.Plo
+	-rm -f ./$(DEPDIR)/ostream-lz4.Plo
+	-rm -f ./$(DEPDIR)/ostream-zlib.Plo
+	-rm -f ./$(DEPDIR)/ostream-zstd.Plo
+	-rm -f ./$(DEPDIR)/test-compression.Po
+	-rm -f Makefile
+distclean-am: clean-am distclean-compile distclean-generic \
+	distclean-tags
+
+dvi: dvi-am
+
+dvi-am:
+
+html: html-am
+
+html-am:
+
+info: info-am
+
+info-am:
+
+install-data-am: install-pkginc_libHEADERS
+
+install-dvi: install-dvi-am
+
+install-dvi-am:
+
+install-exec-am: install-pkglibLTLIBRARIES
+
+install-html: install-html-am
+
+install-html-am:
+
+install-info: install-info-am
+
+install-info-am:
+
+install-man:
+
+install-pdf: install-pdf-am
+
+install-pdf-am:
+
+install-ps: install-ps-am
+
+install-ps-am:
+
+installcheck-am:
+
+maintainer-clean: maintainer-clean-am
+		-rm -f ./$(DEPDIR)/bench-compression.Po
+	-rm -f ./$(DEPDIR)/compression.Plo
+	-rm -f ./$(DEPDIR)/istream-bzlib.Plo
+	-rm -f ./$(DEPDIR)/istream-decompress.Plo
+	-rm -f ./$(DEPDIR)/istream-lz4.Plo
+	-rm -f ./$(DEPDIR)/istream-lzma.Plo
+	-rm -f ./$(DEPDIR)/istream-zlib.Plo
+	-rm -f ./$(DEPDIR)/istream-zstd.Plo
+	-rm -f ./$(DEPDIR)/ostream-bzlib.Plo
+	-rm -f ./$(DEPDIR)/ostream-lz4.Plo
+	-rm -f ./$(DEPDIR)/ostream-zlib.Plo
+	-rm -f ./$(DEPDIR)/ostream-zstd.Plo
+	-rm -f ./$(DEPDIR)/test-compression.Po
+	-rm -f Makefile
+maintainer-clean-am: distclean-am maintainer-clean-generic
+
+mostlyclean: mostlyclean-am
+
+mostlyclean-am: mostlyclean-compile mostlyclean-generic \
+	mostlyclean-libtool
+
+pdf: pdf-am
+
+pdf-am:
+
+ps: ps-am
+
+ps-am:
+
+uninstall-am: uninstall-pkginc_libHEADERS uninstall-pkglibLTLIBRARIES
+
+.MAKE: check-am install-am install-strip
+
+.PHONY: CTAGS GTAGS TAGS all all-am am--depfiles check check-am \
+	check-local clean clean-generic clean-libtool \
+	clean-noinstLTLIBRARIES clean-noinstPROGRAMS \
+	clean-pkglibLTLIBRARIES cscopelist-am ctags ctags-am distclean \
+	distclean-compile distclean-generic distclean-libtool \
+	distclean-tags distdir dvi dvi-am html html-am info info-am \
+	install install-am install-data install-data-am install-dvi \
+	install-dvi-am install-exec install-exec-am install-html \
+	install-html-am install-info install-info-am install-man \
+	install-pdf install-pdf-am install-pkginc_libHEADERS \
+	install-pkglibLTLIBRARIES install-ps install-ps-am \
+	install-strip installcheck installcheck-am installdirs \
+	maintainer-clean maintainer-clean-generic mostlyclean \
+	mostlyclean-compile mostlyclean-generic mostlyclean-libtool \
+	pdf pdf-am ps ps-am tags tags-am uninstall uninstall-am \
+	uninstall-pkginc_libHEADERS uninstall-pkglibLTLIBRARIES
+
+.PRECIOUS: Makefile
+
+
+check-local:
+	for bin in $(test_programs); do \
+	  if ! $(RUN_TEST) ./$$bin; then exit 1; fi; \
+	done
+
+# Tell versions [3.59,3.63) of GNU make to not export all variables.
+# Otherwise a system limit (for SysV at least) may be exceeded.
+.NOEXPORT:
diff --git a/src/lib-compression/bench-compression.c b/src/lib-compression/bench-compression.c
new file mode 100644
index 0000000..655079d
--- /dev/null
+++ b/src/lib-compression/bench-compression.c
@@ -0,0 +1,168 @@
+/* Copyright (c) 2020 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "buffer.h"
+#include "istream.h"
+#include "ostream.h"
+#include "randgen.h"
+#include "time-util.h"
+#include "strnum.h"
+#include "compression.h"
+
+#include <stdio.h>
+#include <unistd.h>
+#include <time.h>
+
+/**
+ * Generates semi-compressible data in blocks of given size, to mimic emails
+ * remotely and then compresses and decompresses it using each algorithm.
+ * It measures the time spent on this giving some estimate how well the data
+ * compressed and how long it took.
+ */
+
+static void bench_compression_speed(const struct compression_handler *handler,
+				    unsigned int level, unsigned long block_count)
+{
+	struct istream *is = i_stream_create_file("decompressed.bin", 1024);
+	struct ostream *os = o_stream_create_file("compressed.bin", 0, 0644, 0);
+	struct ostream *os_compressed = handler->create_ostream(os, level);
+	o_stream_unref(&os);
+
+	const unsigned char *data;
+	uint64_t ts_0, ts_1;
+	size_t siz;
+	double compression_speed, decompression_speed;
+
+	ts_0 = i_nanoseconds();
+
+	while (i_stream_read_more(is, &data, &siz) > 0) {
+		o_stream_nsend(os_compressed, data, siz);
+		i_stream_skip(is, siz);
+	}
+
+	if (is->stream_errno != 0)
+		printf("Error: %s\n", i_stream_get_error(is));
+
+	i_assert(o_stream_finish(os_compressed) == 1);
+	o_stream_unref(&os_compressed);
+	i_stream_unref(&is);
+
+	ts_1 = i_nanoseconds();
+
+	/* check ratio */
+	struct stat st_1, st_2;
+	if (stat("decompressed.bin", &st_1) != 0)
+		i_fatal("stat(decompressed.bin): %m");
+	if (stat("compressed.bin", &st_2) != 0)
+		i_fatal("stat(compressed.bin): %m");
+
+	double ratio = (double)st_2.st_size / (double)st_1.st_size;
+
+	compression_speed = ((double)(ts_1-ts_0))/((double)block_count);
+	compression_speed /= 1000.0L;
+
+	is = i_stream_create_file("compressed.bin", 1024);
+	os = o_stream_create_file("decompressed.bin", 0, 0644, 0);
+	struct istream *is_decompressed = handler->create_istream(is);
+	i_stream_unref(&is);
+
+	ts_0 = i_nanoseconds();
+
+	while (i_stream_read_more(is_decompressed, &data, &siz) > 0) {
+		o_stream_nsend(os, data, siz);
+		i_stream_skip(is_decompressed, siz);
+	}
+
+	if (is_decompressed->stream_errno != 0)
+		printf("Error: %s\n", i_stream_get_error(is_decompressed));
+
+	i_assert(o_stream_finish(os) == 1);
+	o_stream_unref(&os);
+	i_stream_unref(&is_decompressed);
+
+	ts_1 = i_nanoseconds();
+
+	decompression_speed = ((double)(ts_1 - ts_0))/((double)block_count);
+	decompression_speed /= 1000.0L;
+
+	printf("%s\n", handler->name);
+	printf("\tCompression: %0.02lf us/block\n\tSpace Saving: %0.02lf%%\n",
+	       compression_speed, (1.0-ratio)*100.0);
+	printf("\tDecompression: %0.02lf us/block\n\n", decompression_speed);
+
+}
+
+static void print_usage(const char *prog)
+{
+	fprintf(stderr, "Usage: %s block_size count level\n", prog);
+	fprintf(stderr, "Runs with 1000 8k blocks using level 6 if nothing given\n");
+	lib_exit(1);
+}
+
+int main(int argc, const char *argv[])
+{
+	unsigned int level = 6;
+	lib_init();
+
+	unsigned long block_size = 8192UL;
+	unsigned long block_count = 1000UL;
+
+	if (argc >= 3) {
+		if (str_to_ulong(argv[1], &block_size) < 0 ||
+		    str_to_ulong(argv[2], &block_count) < 0) {
+			fprintf(stderr, "Invalid parameters\n");
+			print_usage(argv[0]);
+		}
+		if (argc == 4 &&
+		    str_to_uint(argv[3], &level) < 0) {
+			fprintf(stderr, "Invalid parameters\n");
+			print_usage(argv[0]);
+		}
+		if (argc > 4) {
+			print_usage(argv[0]);
+		}
+	} else if (argc != 1) {
+		print_usage(argv[0]);
+	}
+
+	unsigned char buf[block_size];
+	printf("Input data is %lu blocks of %lu bytes\n\n", block_count, block_size);
+
+	time_t t0 = time(NULL);
+
+	/* create plaintext file */
+	struct ostream *os = o_stream_create_file("decompressed.bin", 0, 0644, 0);
+	for (unsigned long r = 0; r < block_count; r++) {
+		time_t t1 = time(NULL);
+		if (t1 - t0 >= 1) {
+			printf("Building block %8lu / %-8lu\r", r, block_count);
+			fflush(stdout);
+			t0 = t1;
+		}
+		for (size_t i = 0; i < sizeof(buf); i++) {
+			if (i_rand_limit(3) == 0)
+				buf[i] = i_rand_limit(4);
+			else
+				buf[i] = i;
+		}
+		o_stream_nsend(os, buf, sizeof(buf));
+	}
+
+	i_assert(o_stream_finish(os) == 1);
+	o_stream_unref(&os);
+
+	printf("Input data constructed          \n");
+
+	for (unsigned int i = 0; compression_handlers[i].name != NULL; i++) T_BEGIN {
+		if (compression_handlers[i].create_istream != NULL &&
+		    compression_handlers[i].create_ostream != NULL) {
+			bench_compression_speed(&compression_handlers[i], level,
+						block_count);
+		}
+	} T_END;
+
+	i_unlink("decompressed.bin");
+	i_unlink("compressed.bin");
+
+	lib_deinit();
+}
diff --git a/src/lib-compression/compression.c b/src/lib-compression/compression.c
new file mode 100644
index 0000000..e562e73
--- /dev/null
+++ b/src/lib-compression/compression.c
@@ -0,0 +1,250 @@
+/* Copyright (c) 2010-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "istream.h"
+#include "istream-zlib.h"
+#include "ostream-zlib.h"
+#include "iostream-lz4.h"
+#include "compression.h"
+
+#ifndef HAVE_ZLIB
+#  define i_stream_create_gz NULL
+#  define o_stream_create_gz NULL
+#  define i_stream_create_deflate NULL
+#  define o_stream_create_deflate NULL
+#  define compression_get_min_level_gz NULL
+#  define compression_get_default_level_gz NULL
+#  define compression_get_max_level_gz NULL
+#endif
+#ifndef HAVE_BZLIB
+#  define i_stream_create_bz2 NULL
+#  define o_stream_create_bz2 NULL
+#  define compression_get_min_level_bz2 NULL
+#  define compression_get_default_level_bz2 NULL
+#  define compression_get_max_level_bz2 NULL
+#endif
+#ifndef HAVE_LZMA
+#  define i_stream_create_lzma NULL
+#endif
+#ifndef HAVE_LZ4
+#  define i_stream_create_lz4 NULL
+#  define o_stream_create_lz4 NULL
+#  define compression_get_min_level_lz4 NULL
+#  define compression_get_default_level_lz4 NULL
+#  define compression_get_max_level_lz4 NULL
+#endif
+#ifndef HAVE_ZSTD
+#  define i_stream_create_zstd NULL
+#  define o_stream_create_zstd NULL
+#  define compression_get_min_level_zstd NULL
+#  define compression_get_default_level_zstd NULL
+#  define compression_get_max_level_zstd NULL
+#endif
+
+static bool is_compressed_zlib(struct istream *input)
+{
+	const unsigned char *data;
+	size_t size;
+
+	/* Peek in to the stream and see if it looks like it's compressed
+	   (based on its header). This also means that users can try to exploit
+	   security holes in the uncompression library by APPENDing a specially
+	   crafted mail. So let's hope zlib is free of holes. */
+	if (i_stream_read_bytes(input, &data, &size, 2) <= 0)
+		return FALSE;
+	i_assert(size >= 2);
+
+	return data[0] == 31 && data[1] == 139;
+}
+
+static bool is_compressed_bzlib(struct istream *input)
+{
+	const unsigned char *data;
+	size_t size;
+
+	if (i_stream_read_bytes(input, &data, &size, 4) <= 0)
+		return FALSE;
+	if (memcmp(data, "BZh", 3) != 0)
+		return FALSE;
+	if (data[3] < '1' || data[3] > '9')
+		return FALSE;
+	/* The above is enough to be considered as the bzlib magic.
+	   Normally it's followed by data header beginning with 0x31. However,
+	   with empty compressed files it's followed by 0x17. */
+	return TRUE;
+}
+
+static bool is_compressed_xz(struct istream *input)
+{
+	const unsigned char *data;
+	size_t size;
+
+	if (i_stream_read_bytes(input, &data, &size, 6) <= 0)
+		return FALSE;
+	return memcmp(data, "\xfd\x37\x7a\x58\x5a\x00", 6) == 0;
+}
+
+static bool is_compressed_lz4(struct istream *input)
+{
+	const unsigned char *data;
+	size_t size;
+
+	if (i_stream_read_bytes(input, &data, &size, IOSTREAM_LZ4_MAGIC_LEN) <= 0)
+		return FALSE;
+	/* there is no standard LZ4 header, so we've created our own */
+	return memcmp(data, IOSTREAM_LZ4_MAGIC, IOSTREAM_LZ4_MAGIC_LEN) == 0;
+}
+
+#define ZSTD_MAGICNUMBER            0xFD2FB528    /* valid since v0.8.0 */
+static bool is_compressed_zstd(struct istream *input)
+{
+	const unsigned char *data;
+	size_t size = 0;
+
+	if (i_stream_read_bytes(input, &data, &size, sizeof(uint32_t)) <= 0)
+	        return FALSE;
+	i_assert(size >= sizeof(uint32_t));
+
+	return le32_to_cpu_unaligned(data) == ZSTD_MAGICNUMBER;
+}
+
+int compression_lookup_handler(const char *name,
+			       const struct compression_handler **handler_r)
+{
+	unsigned int i;
+
+	for (i = 0; compression_handlers[i].name != NULL; i++) {
+		if (strcmp(name, compression_handlers[i].name) == 0) {
+			if (compression_handlers[i].create_istream == NULL ||
+			    compression_handlers[i].create_ostream == NULL) {
+				/* Handler is known but not compiled in */
+				return 0;
+			}
+			(*handler_r) = &compression_handlers[i];
+			return 1;
+		}
+	}
+	return -1;
+}
+
+const struct compression_handler *
+compression_detect_handler(struct istream *input)
+{
+	unsigned int i;
+
+	for (i = 0; compression_handlers[i].name != NULL; i++) {
+		if (compression_handlers[i].is_compressed != NULL &&
+		    compression_handlers[i].is_compressed(input))
+			return &compression_handlers[i];
+	}
+	return NULL;
+}
+
+int compression_lookup_handler_from_ext(const char *path,
+					const struct compression_handler **handler_r)
+{
+	unsigned int i;
+	size_t len, path_len = strlen(path);
+
+	for (i = 0; compression_handlers[i].name != NULL; i++) {
+		if (compression_handlers[i].ext == NULL)
+			continue;
+
+		len = strlen(compression_handlers[i].ext);
+		if (path_len > len &&
+		    strcmp(path + path_len - len, compression_handlers[i].ext) == 0) {
+			if (compression_handlers[i].create_istream == NULL ||
+			    compression_handlers[i].create_ostream == NULL) {
+				/* Handler is known but not compiled in */
+				return 0;
+			}
+			(*handler_r) = &compression_handlers[i];
+			return 1;
+		}
+	}
+	return -1;
+}
+
+static int compression_get_min_level_unsupported(void)
+{
+	return -1;
+}
+
+static int compression_get_default_level_unsupported(void)
+{
+	return -1;
+}
+
+static int compression_get_max_level_unsupported(void)
+{
+	return -1;
+}
+
+const struct compression_handler compression_handlers[] = {
+	{
+		.name = "gz",
+		.ext = ".gz",
+		.is_compressed = is_compressed_zlib,
+		.create_istream = i_stream_create_gz,
+		.create_ostream = o_stream_create_gz,
+		.get_min_level = compression_get_min_level_gz,
+		.get_default_level = compression_get_default_level_gz,
+		.get_max_level = compression_get_max_level_gz,
+	},
+	{
+		.name = "bz2",
+		.ext = ".bz2",
+		.is_compressed = is_compressed_bzlib,
+		.create_istream = i_stream_create_bz2,
+		.create_ostream = o_stream_create_bz2,
+		.get_min_level = compression_get_min_level_bz2,
+		.get_default_level = compression_get_default_level_bz2,
+		.get_max_level = compression_get_max_level_bz2,
+	},
+	{
+		.name = "deflate",
+		.ext = NULL,
+		.is_compressed = NULL,
+		.create_istream = i_stream_create_deflate,
+		.create_ostream = o_stream_create_deflate,
+		.get_min_level = compression_get_min_level_gz,
+		.get_default_level = compression_get_default_level_gz,
+		.get_max_level = compression_get_max_level_gz,
+	},
+	{
+		.name = "xz",
+		.ext = ".xz",
+		.is_compressed = is_compressed_xz,
+		.create_istream = i_stream_create_lzma,
+		.create_ostream = NULL,
+		.get_min_level = compression_get_min_level_unsupported,
+		.get_default_level = compression_get_default_level_unsupported,
+		.get_max_level = compression_get_max_level_unsupported,
+	},
+	{
+		.name = "lz4",
+		.ext = ".lz4",
+		.is_compressed = is_compressed_lz4,
+		.create_istream = i_stream_create_lz4,
+		.create_ostream = o_stream_create_lz4,
+		.get_min_level = compression_get_min_level_lz4, /* does not actually support any of this */
+		.get_default_level = compression_get_default_level_lz4,
+		.get_max_level = compression_get_max_level_lz4,
+	},
+	{
+		.name = "zstd",
+		.ext = ".zstd",
+		.is_compressed = is_compressed_zstd,
+		.create_istream = i_stream_create_zstd,
+		.create_ostream = o_stream_create_zstd,
+		.get_min_level = compression_get_min_level_zstd,
+		.get_default_level = compression_get_default_level_zstd,
+		.get_max_level = compression_get_max_level_zstd,
+	},
+	{
+		.name = "unsupported",
+	},
+	{
+		.name = NULL,
+	}
+};
diff --git a/src/lib-compression/compression.h b/src/lib-compression/compression.h
new file mode 100644
index 0000000..60d58bf
--- /dev/null
+++ b/src/lib-compression/compression.h
@@ -0,0 +1,55 @@
+#ifndef COMPRESSION_H
+#define COMPRESSION_H
+
+enum istream_decompress_flags {
+	/* If stream isn't detected to be compressed, return it as passthrough
+	   istream. */
+	ISTREAM_DECOMPRESS_FLAG_TRY = BIT(0),
+};
+
+/* Compressed input is always detected once at maximum this many bytes have
+   been read. This value must be smaller than a typical istream max buffer
+   size. */
+#define COMPRESSION_HDR_MAX_SIZE 128
+
+struct compression_handler {
+	const char *name;
+	const char *ext;
+	bool (*is_compressed)(struct istream *input);
+	struct istream *(*create_istream)(struct istream *input);
+	struct ostream *(*create_ostream)(struct ostream *output, int level);
+	/* returns minimum level */
+	int (*get_min_level)(void);
+	/* the default can be -1 (e.g. gz), so the return value of this has to
+	   be used as-is. */
+	int (*get_default_level)(void);
+	/* returns maximum level */
+	int (*get_max_level)(void);
+};
+
+extern const struct compression_handler compression_handlers[];
+
+/* Returns 1 if compression handler was found and is usable, 0 if support isn't
+   compiled in, -1 if unknown. */
+int compression_lookup_handler(const char *name,
+			       const struct compression_handler **handler_r);
+/* Detect handler by looking at the first few bytes of the input stream. */
+const struct compression_handler *
+compression_detect_handler(struct istream *input);
+/* Lookup handler based on filename extension in the path, returns the same
+ * values as compression_lookup_handler. */
+int compression_lookup_handler_from_ext(const char *path,
+					const struct compression_handler **handler_r);
+
+/* Automatically detect the compression format. Note that using tee-istream as
+   one of the parent streams is dangerous here: A decompression istream may
+   have to read a lot of data (e.g. 8 kB isn't enough) before it returns even
+   the first byte as output. If the other tee children aren't read forward,
+   this can cause an infinite loop when i_stream_read() is always returning 0.
+   This is why ISTREAM_DECOMPRESS_FLAG_TRY should be used instead of attempting
+   to implement similar functionality with tee-istream. */
+struct istream *
+i_stream_create_decompress(struct istream *input,
+			   enum istream_decompress_flags flags);
+
+#endif
diff --git a/src/lib-compression/iostream-lz4.h b/src/lib-compression/iostream-lz4.h
new file mode 100644
index 0000000..a0897f5
--- /dev/null
+++ b/src/lib-compression/iostream-lz4.h
@@ -0,0 +1,30 @@
+#ifndef IOSTREAM_LZ4_H
+#define IOSTREAM_LZ4_H
+
+/*
+   Dovecot's LZ4 compressed files contain:
+
+   IOSTREAM_LZ4_HEADER
+   n x (4 byte big-endian: compressed chunk length, compressed chunk)
+*/
+
+#define IOSTREAM_LZ4_MAGIC "Dovecot-LZ4\x0d\x2a\x9b\xc5"
+#define IOSTREAM_LZ4_MAGIC_LEN (sizeof(IOSTREAM_LZ4_MAGIC)-1)
+
+struct iostream_lz4_header {
+	unsigned char magic[IOSTREAM_LZ4_MAGIC_LEN];
+	/* OSTREAM_LZ4_CHUNK_SIZE in big-endian */
+	unsigned char max_uncompressed_chunk_size[4];
+};
+
+/* How large chunks we're buffering into memory before compressing them */
+#define OSTREAM_LZ4_CHUNK_SIZE (1024*64)
+/* How large chunks we allow in input data before returning a failure.
+   This must be at least OSTREAM_LZ4_CHUNK_SIZE, but for future compatibility
+   should be somewhat higher (but not too high to avoid wasting memory for
+   corrupted files). */
+#define ISTREAM_LZ4_CHUNK_SIZE (1024*1024)
+
+#define IOSTREAM_LZ4_CHUNK_PREFIX_LEN 4 /* big-endian size of chunk */
+
+#endif
diff --git a/src/lib-compression/iostream-zstd-private.h b/src/lib-compression/iostream-zstd-private.h
new file mode 100644
index 0000000..e430bbc
--- /dev/null
+++ b/src/lib-compression/iostream-zstd-private.h
@@ -0,0 +1,35 @@
+#ifndef IOSTREAM_ZSTD_PRIVATE_H
+#define IOSTREAM_ZSTD_PRIVATE_H 1
+
+/* a horrible hack to fix issues when the installed libzstd is lot
+   newer than what we were compiled against. */
+static inline ZSTD_ErrorCode zstd_version_errcode(ZSTD_ErrorCode err)
+{
+#if ZSTD_VERSION_NUMBER < 10301
+	if (ZSTD_versionNumber() > 10300) {
+		/* reinterpret them */
+		if (err == 10)
+			return ZSTD_error_prefix_unknown;
+		if (err == 32)
+			return ZSTD_error_dictionary_wrong;
+		if (err == 62)
+			return ZSTD_error_init_missing;
+		if (err == 64)
+			return ZSTD_error_memory_allocation;
+		return ZSTD_error_GENERIC;
+	}
+#endif
+	return err;
+}
+
+static inline void zstd_version_check(void)
+{
+	/* error codes were pinned on 1.3.1, so we only care about
+	   versions before that. */
+	if (ZSTD_VERSION_NUMBER < 10301 || ZSTD_versionNumber() < 10301)
+		if (ZSTD_versionNumber() / 100 != ZSTD_VERSION_NUMBER / 100)
+			i_warning("zstd: Compiled against %u, but %u installed!",
+				  ZSTD_VERSION_NUMBER, ZSTD_versionNumber());
+}
+
+#endif
diff --git a/src/lib-compression/istream-bzlib.c b/src/lib-compression/istream-bzlib.c
new file mode 100644
index 0000000..aae1027
--- /dev/null
+++ b/src/lib-compression/istream-bzlib.c
@@ -0,0 +1,231 @@
+/* Copyright (c) 2010-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+
+#ifdef HAVE_BZLIB
+
+#include "istream-private.h"
+#include "istream-zlib.h"
+#include <bzlib.h>
+
+#define CHUNK_SIZE (1024*64)
+
+struct bzlib_istream {
+	struct istream_private istream;
+
+	bz_stream zs;
+	uoff_t eof_offset;
+	struct stat last_parent_statbuf;
+
+	bool hdr_read:1;
+	bool marked:1;
+	bool zs_closed:1;
+};
+
+static void i_stream_bzlib_close(struct iostream_private *stream,
+				 bool close_parent)
+{
+	struct bzlib_istream *zstream = (struct bzlib_istream *)stream;
+
+	if (!zstream->zs_closed) {
+		(void)BZ2_bzDecompressEnd(&zstream->zs);
+		zstream->zs_closed = TRUE;
+	}
+	if (close_parent)
+		i_stream_close(zstream->istream.parent);
+}
+
+static void bzlib_read_error(struct bzlib_istream *zstream, const char *error)
+{
+	io_stream_set_error(&zstream->istream.iostream,
+			    "bzlib.read(%s): %s at %"PRIuUOFF_T,
+			    i_stream_get_name(&zstream->istream.istream), error,
+			    i_stream_get_absolute_offset(&zstream->istream.istream));
+}
+
+static ssize_t i_stream_bzlib_read(struct istream_private *stream)
+{
+	struct bzlib_istream *zstream = (struct bzlib_istream *)stream;
+	const unsigned char *data;
+	uoff_t high_offset;
+	size_t size, out_size;
+	int ret;
+
+	high_offset = stream->istream.v_offset + (stream->pos - stream->skip);
+	if (zstream->eof_offset == high_offset) {
+		stream->istream.eof = TRUE;
+		return -1;
+	}
+
+	if (!zstream->marked) {
+		if (!i_stream_try_alloc(stream, CHUNK_SIZE, &out_size))
+			return -2; /* buffer full */
+	} else {
+		/* try to avoid compressing, so we can quickly seek backwards */
+		if (!i_stream_try_alloc_avoid_compress(stream, CHUNK_SIZE, &out_size))
+			return -2; /* buffer full */
+	}
+
+	if (i_stream_read_more(stream->parent, &data, &size) < 0) {
+		if (stream->parent->stream_errno != 0) {
+			stream->istream.stream_errno =
+				stream->parent->stream_errno;
+		} else {
+			i_assert(stream->parent->eof);
+			bzlib_read_error(zstream, "unexpected EOF");
+			if (!zstream->hdr_read)
+				stream->istream.stream_errno = EINVAL;
+			else
+				stream->istream.stream_errno = EPIPE;
+		}
+		return -1;
+	}
+	if (size == 0) {
+		/* no more input */
+		i_assert(!stream->istream.blocking);
+		return 0;
+	}
+
+	zstream->zs.next_in = (char *)data;
+	zstream->zs.avail_in = size;
+
+	zstream->zs.next_out = (char *)stream->w_buffer + stream->pos;
+	zstream->zs.avail_out = out_size;
+	ret = BZ2_bzDecompress(&zstream->zs);
+	zstream->hdr_read = TRUE;
+
+	out_size -= zstream->zs.avail_out;
+	stream->pos += out_size;
+
+	i_stream_skip(stream->parent, size - zstream->zs.avail_in);
+
+	switch (ret) {
+	case BZ_OK:
+		break;
+	case BZ_PARAM_ERROR:
+		i_unreached();
+	case BZ_DATA_ERROR:
+		bzlib_read_error(zstream, "corrupted data");
+		stream->istream.stream_errno = EINVAL;
+		return -1;
+	case BZ_DATA_ERROR_MAGIC:
+		bzlib_read_error(zstream,
+			"wrong magic in header (not bz2 file?)");
+		stream->istream.stream_errno = EINVAL;
+		return -1;
+	case BZ_MEM_ERROR:
+		i_fatal_status(FATAL_OUTOFMEM, "bzlib.read(%s): Out of memory",
+			       i_stream_get_name(&stream->istream));
+	case BZ_STREAM_END:
+		zstream->eof_offset = stream->istream.v_offset +
+			(stream->pos - stream->skip);
+		stream->cached_stream_size = zstream->eof_offset;
+		if (out_size == 0) {
+			stream->istream.eof = TRUE;
+			return -1;
+		}
+		break;
+	default:
+		i_fatal("BZ2_bzDecompress() failed with %d", ret);
+	}
+	if (out_size == 0) {
+		/* read more input */
+		return i_stream_bzlib_read(stream);
+	}
+	return out_size;
+}
+
+static void i_stream_bzlib_init(struct bzlib_istream *zstream)
+{
+	int ret;
+
+	ret = BZ2_bzDecompressInit(&zstream->zs, 0, 0);
+	switch (ret) {
+	case BZ_OK:
+		break;
+	case BZ_MEM_ERROR:
+		i_fatal_status(FATAL_OUTOFMEM, "bzlib: Out of memory");
+	case BZ_CONFIG_ERROR:
+		i_fatal("Wrong bzlib library version (broken compilation)");
+	case BZ_PARAM_ERROR:
+		i_fatal("bzlib: Invalid parameters");
+	default:
+		i_fatal("BZ2_bzDecompressInit() failed with %d", ret);
+	}
+}
+
+static void i_stream_bzlib_reset(struct bzlib_istream *zstream)
+{
+	struct istream_private *stream = &zstream->istream;
+
+	i_stream_seek(stream->parent, stream->parent_start_offset);
+	zstream->eof_offset = UOFF_T_MAX;
+	zstream->zs.next_in = NULL;
+	zstream->zs.avail_in = 0;
+
+	stream->parent_expected_offset = stream->parent_start_offset;
+	stream->skip = stream->pos = 0;
+	stream->istream.v_offset = 0;
+	stream->high_pos = 0;
+
+	(void)BZ2_bzDecompressEnd(&zstream->zs);
+	i_stream_bzlib_init(zstream);
+}
+
+static void
+i_stream_bzlib_seek(struct istream_private *stream, uoff_t v_offset, bool mark)
+{
+	struct bzlib_istream *zstream = (struct bzlib_istream *) stream;
+
+	if (i_stream_nonseekable_try_seek(stream, v_offset))
+		return;
+
+	/* have to seek backwards - reset state and retry */
+	i_stream_bzlib_reset(zstream);
+	if (!i_stream_nonseekable_try_seek(stream, v_offset))
+		i_unreached();
+
+	if (mark)
+		zstream->marked = TRUE;
+}
+
+static void i_stream_bzlib_sync(struct istream_private *stream)
+{
+	struct bzlib_istream *zstream = (struct bzlib_istream *) stream;
+	const struct stat *st;
+
+	if (i_stream_stat(stream->parent, FALSE, &st) == 0) {
+		if (memcmp(&zstream->last_parent_statbuf,
+			   st, sizeof(*st)) == 0) {
+			/* a compressed file doesn't change unexpectedly,
+			   don't clear our caches unnecessarily */
+			return;
+		}
+		zstream->last_parent_statbuf = *st;
+	}
+	i_stream_bzlib_reset(zstream);
+}
+
+struct istream *i_stream_create_bz2(struct istream *input)
+{
+	struct bzlib_istream *zstream;
+
+	zstream = i_new(struct bzlib_istream, 1);
+	zstream->eof_offset = UOFF_T_MAX;
+
+	i_stream_bzlib_init(zstream);
+
+	zstream->istream.iostream.close = i_stream_bzlib_close;
+	zstream->istream.max_buffer_size = input->real_stream->max_buffer_size;
+	zstream->istream.read = i_stream_bzlib_read;
+	zstream->istream.seek = i_stream_bzlib_seek;
+	zstream->istream.sync = i_stream_bzlib_sync;
+
+	zstream->istream.istream.readable_fd = FALSE;
+	zstream->istream.istream.blocking = input->blocking;
+	zstream->istream.istream.seekable = input->seekable;
+
+	return i_stream_create(&zstream->istream, input,
+			       i_stream_get_fd(input), 0);
+}
+#endif
diff --git a/src/lib-compression/istream-decompress.c b/src/lib-compression/istream-decompress.c
new file mode 100644
index 0000000..2021a01
--- /dev/null
+++ b/src/lib-compression/istream-decompress.c
@@ -0,0 +1,258 @@
+/* Copyright (c) 2020 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "istream-private.h"
+#include "compression.h"
+
+struct decompress_istream {
+	struct istream_private istream;
+	struct istream *compressed_input;
+	struct istream *decompressed_input;
+	enum istream_decompress_flags flags;
+};
+
+static void copy_compressed_input_error(struct decompress_istream *zstream)
+{
+	struct istream_private *stream = &zstream->istream;
+
+	stream->istream.stream_errno = zstream->compressed_input->stream_errno;
+	stream->istream.eof = zstream->compressed_input->eof;
+	if (zstream->compressed_input->stream_errno != 0) {
+		io_stream_set_error(&stream->iostream, "%s",
+			i_stream_get_error(&zstream->compressed_input->real_stream->istream));
+	}
+}
+
+static void copy_decompressed_input_error(struct decompress_istream *zstream)
+{
+	struct istream_private *stream = &zstream->istream;
+
+	stream->istream.stream_errno = zstream->decompressed_input->stream_errno;
+	stream->istream.eof = zstream->decompressed_input->eof;
+	if (zstream->decompressed_input->stream_errno != 0) {
+		io_stream_set_error(&stream->iostream, "%s",
+			i_stream_get_error(&zstream->decompressed_input->real_stream->istream));
+	}
+}
+
+static void
+i_stream_decompress_close(struct iostream_private *_stream, bool close_parent)
+{
+	struct istream_private *stream =
+		container_of(_stream, struct istream_private, iostream);
+	struct decompress_istream *zstream =
+		container_of(stream, struct decompress_istream, istream);
+
+	if (zstream->decompressed_input != NULL)
+		i_stream_close(zstream->decompressed_input);
+	if (close_parent)
+		i_stream_close(zstream->compressed_input);
+}
+
+static void
+i_stream_decompress_destroy(struct iostream_private *_stream)
+{
+	struct istream_private *stream =
+		container_of(_stream, struct istream_private, iostream);
+	struct decompress_istream *zstream =
+		container_of(stream, struct decompress_istream, istream);
+
+	i_stream_unref(&zstream->decompressed_input);
+	i_stream_unref(&zstream->compressed_input);
+}
+
+static int
+i_stream_decompress_not_compressed(struct decompress_istream *zstream)
+{
+	if ((zstream->flags & ISTREAM_DECOMPRESS_FLAG_TRY) == 0) {
+		zstream->istream.istream.stream_errno = EINVAL;
+		io_stream_set_error(&zstream->istream.iostream,
+				    "Stream isn't compressed");
+		return -1;
+	} else {
+		zstream->decompressed_input = zstream->compressed_input;
+		i_stream_ref(zstream->decompressed_input);
+		return 1;
+	}
+}
+
+static int i_stream_decompress_detect(struct decompress_istream *zstream)
+{
+	const struct compression_handler *handler;
+	ssize_t ret;
+
+	ret = i_stream_read(zstream->compressed_input);
+	handler = compression_detect_handler(zstream->compressed_input);
+	if (handler == NULL) {
+		switch (ret) {
+		case -1:
+			if (zstream->compressed_input->stream_errno != 0) {
+				copy_compressed_input_error(zstream);
+				return -1;
+			}
+			/* fall through */
+		case -2:
+			/* we've read a full buffer or we reached EOF -
+			   the stream isn't compressed */
+			return i_stream_decompress_not_compressed(zstream);
+		case 0:
+			return 0;
+		default:
+			if (!zstream->istream.istream.blocking)
+				return 0;
+			return i_stream_decompress_detect(zstream);
+		}
+	}
+	if (handler->create_istream == NULL) {
+		zstream->istream.istream.stream_errno = EINVAL;
+		io_stream_set_error(&zstream->istream.iostream,
+			"Compression handler %s not supported", handler->name);
+		return -1;
+	}
+
+	zstream->decompressed_input =
+		handler->create_istream(zstream->compressed_input);
+	return 1;
+}
+
+static ssize_t i_stream_decompress_read(struct istream_private *stream)
+{
+	struct decompress_istream *zstream =
+		container_of(stream, struct decompress_istream, istream);
+	ssize_t ret;
+	size_t pos;
+
+	if (zstream->decompressed_input == NULL) {
+		if ((ret = i_stream_decompress_detect(zstream)) <= 0)
+			return ret;
+	}
+
+	i_stream_seek(zstream->decompressed_input, stream->istream.v_offset);
+	stream->pos -= stream->skip;
+	stream->skip = 0;
+
+	stream->buffer = i_stream_get_data(zstream->decompressed_input, &pos);
+	if (pos > stream->pos)
+		ret = 0;
+	else do {
+		ret = i_stream_read_memarea(zstream->decompressed_input);
+		copy_decompressed_input_error(zstream);
+		stream->buffer = i_stream_get_data(zstream->decompressed_input,
+						   &pos);
+	} while (pos <= stream->pos && ret > 0);
+	if (ret == -2)
+		return -2;
+
+	if (pos <= stream->pos)
+		ret = ret == 0 ? 0 : -1;
+	else
+		ret = (ssize_t)(pos - stream->pos);
+	stream->pos = pos;
+	i_assert(ret != -1 || stream->istream.eof ||
+		 stream->istream.stream_errno != 0);
+	return ret;
+}
+
+static void i_stream_decompress_reset(struct istream_private *stream)
+{
+	stream->skip = stream->pos = 0;
+	stream->istream.v_offset = 0;
+	stream->istream.eof = FALSE;
+}
+
+static void
+i_stream_decompress_seek(struct istream_private *stream,
+			 uoff_t v_offset, bool mark)
+{
+	struct decompress_istream *zstream =
+		container_of(stream, struct decompress_istream, istream);
+
+	if (zstream->decompressed_input == NULL) {
+		if (!i_stream_nonseekable_try_seek(stream, v_offset))
+			i_panic("seeking backwards before detecting compression format");
+	} else {
+		i_stream_decompress_reset(stream);
+		stream->istream.v_offset = v_offset;
+		if (mark)
+			i_stream_seek_mark(zstream->decompressed_input, v_offset);
+		else
+			i_stream_seek(zstream->decompressed_input, v_offset);
+		copy_decompressed_input_error(zstream);
+	}
+}
+
+static void i_stream_decompress_sync(struct istream_private *stream)
+{
+	struct decompress_istream *zstream =
+		container_of(stream, struct decompress_istream, istream);
+
+	i_stream_decompress_reset(stream);
+	if (zstream->decompressed_input != NULL)
+		i_stream_sync(zstream->decompressed_input);
+}
+
+static int i_stream_decompress_stat(struct istream_private *stream, bool exact)
+{
+	struct decompress_istream *zstream =
+		container_of(stream, struct decompress_istream, istream);
+	const struct stat *st;
+
+	if (!exact) {
+		if (i_stream_stat(zstream->compressed_input, exact, &st) < 0) {
+			copy_compressed_input_error(zstream);
+			return -1;
+		}
+		stream->statbuf = *st;
+		return 0;
+	}
+	if (zstream->decompressed_input == NULL) {
+		(void)i_stream_read(&stream->istream);
+		if (zstream->decompressed_input == NULL) {
+			if (stream->istream.stream_errno == 0) {
+				zstream->istream.istream.stream_errno = EINVAL;
+				io_stream_set_error(&zstream->istream.iostream,
+					"Stream compression couldn't be detected during stat");
+			}
+			return -1;
+		}
+	}
+
+	if (i_stream_stat(zstream->decompressed_input, exact, &st) < 0) {
+		copy_decompressed_input_error(zstream);
+		return -1;
+	}
+	i_stream_decompress_reset(stream);
+	stream->statbuf = *st;
+	return 0;
+}
+
+struct istream *
+i_stream_create_decompress(struct istream *input,
+			   enum istream_decompress_flags flags)
+{
+	struct decompress_istream *zstream;
+
+	zstream = i_new(struct decompress_istream, 1);
+	zstream->compressed_input = input;
+	zstream->flags = flags;
+	i_stream_ref(input);
+
+	zstream->istream.iostream.close = i_stream_decompress_close;
+	zstream->istream.iostream.destroy = i_stream_decompress_destroy;
+	zstream->istream.max_buffer_size = input->real_stream->max_buffer_size;
+	zstream->istream.read = i_stream_decompress_read;
+	zstream->istream.seek = i_stream_decompress_seek;
+	zstream->istream.sync = i_stream_decompress_sync;
+	zstream->istream.stat = i_stream_decompress_stat;
+
+	zstream->istream.istream.readable_fd = FALSE;
+	zstream->istream.istream.blocking = input->blocking;
+	zstream->istream.istream.seekable = input->seekable;
+
+	struct istream *ret = i_stream_create(&zstream->istream, NULL,
+					      i_stream_get_fd(input), 0);
+	/* input isn't used as our parent istream, so need to copy the stream
+	   name to preserve it. */
+	i_stream_set_name(ret, i_stream_get_name(input));
+	return ret;
+}
diff --git a/src/lib-compression/istream-lz4.c b/src/lib-compression/istream-lz4.c
new file mode 100644
index 0000000..24d539a
--- /dev/null
+++ b/src/lib-compression/istream-lz4.c
@@ -0,0 +1,281 @@
+/* Copyright (c) 2013-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+
+#ifdef HAVE_LZ4
+
+#include "buffer.h"
+#include "istream-private.h"
+#include "istream-zlib.h"
+#include "iostream-lz4.h"
+#include <lz4.h>
+
+struct lz4_istream {
+	struct istream_private istream;
+
+	struct stat last_parent_statbuf;
+
+	buffer_t *chunk_buf;
+	uint32_t chunk_size, chunk_left, max_uncompressed_chunk_size;
+
+	bool marked:1;
+	bool header_read:1;
+};
+
+static void i_stream_lz4_close(struct iostream_private *stream,
+			       bool close_parent)
+{
+	struct lz4_istream *zstream = (struct lz4_istream *)stream;
+
+	buffer_free(&zstream->chunk_buf);
+	if (close_parent)
+		i_stream_close(zstream->istream.parent);
+}
+
+static void lz4_read_error(struct lz4_istream *zstream, const char *error)
+{
+	io_stream_set_error(&zstream->istream.iostream,
+			    "lz4.read(%s): %s at %"PRIuUOFF_T,
+			    i_stream_get_name(&zstream->istream.istream), error,
+			    i_stream_get_absolute_offset(&zstream->istream.istream));
+}
+
+static int i_stream_lz4_read_header(struct lz4_istream *zstream)
+{
+	const struct iostream_lz4_header *hdr;
+	const unsigned char *data;
+	size_t size;
+	int ret;
+
+	ret = i_stream_read_bytes(zstream->istream.parent, &data,
+				  &size, sizeof(*hdr));
+	size = I_MIN(size, sizeof(*hdr));
+	buffer_append(zstream->chunk_buf, data, size);
+	i_stream_skip(zstream->istream.parent, size);
+	if (ret < 0 || (ret == 0 && zstream->istream.istream.eof)) {
+		i_assert(ret != -2);
+		if (zstream->istream.istream.stream_errno == 0) {
+			lz4_read_error(zstream, "missing header (not lz4 file?)");
+			zstream->istream.istream.stream_errno = EINVAL;
+		} else
+			zstream->istream.istream.stream_errno =
+				zstream->istream.parent->stream_errno;
+		return ret;
+	}
+	if (zstream->chunk_buf->used < sizeof(*hdr)) {
+		i_assert(!zstream->istream.istream.blocking);
+		return 0;
+	}
+
+	hdr = zstream->chunk_buf->data;
+	if (ret == 0 || memcmp(hdr->magic, IOSTREAM_LZ4_MAGIC,
+			       IOSTREAM_LZ4_MAGIC_LEN) != 0) {
+		lz4_read_error(zstream, "wrong magic in header (not lz4 file?)");
+		zstream->istream.istream.stream_errno = EINVAL;
+		return -1;
+	}
+	zstream->max_uncompressed_chunk_size =
+		be32_to_cpu_unaligned(hdr->max_uncompressed_chunk_size);
+	buffer_set_used_size(zstream->chunk_buf, 0);
+	if (zstream->max_uncompressed_chunk_size > ISTREAM_LZ4_CHUNK_SIZE) {
+		lz4_read_error(zstream, t_strdup_printf(
+			"lz4 max chunk size too large (%u > %u)",
+			zstream->max_uncompressed_chunk_size,
+			ISTREAM_LZ4_CHUNK_SIZE));
+		zstream->istream.istream.stream_errno = EINVAL;
+		return -1;
+	}
+	return 1;
+}
+
+static int i_stream_lz4_read_chunk_header(struct lz4_istream *zstream)
+{
+	int ret;
+	size_t size;
+	const unsigned char *data;
+	struct istream_private *stream = &zstream->istream;
+
+	i_assert(zstream->chunk_buf->used <= IOSTREAM_LZ4_CHUNK_PREFIX_LEN);
+	ret = i_stream_read_more(stream->parent, &data, &size);
+	size = I_MIN(size, IOSTREAM_LZ4_CHUNK_PREFIX_LEN - zstream->chunk_buf->used);
+	buffer_append(zstream->chunk_buf, data, size);
+	i_stream_skip(stream->parent, size);
+	if (ret < 0) {
+		i_assert(ret != -2);
+		stream->istream.stream_errno = stream->parent->stream_errno;
+		if (stream->istream.stream_errno == 0) {
+			stream->istream.eof = TRUE;
+			stream->cached_stream_size =
+				stream->istream.v_offset +
+				stream->pos - stream->skip;
+		}
+		return ret;
+	}
+	i_assert(ret != 0 || !stream->istream.blocking);
+	if (ret == 0)
+		return ret;
+	if (zstream->chunk_buf->used < IOSTREAM_LZ4_CHUNK_PREFIX_LEN)
+		return 0;
+	zstream->chunk_size = zstream->chunk_left =
+		be32_to_cpu_unaligned(zstream->chunk_buf->data);
+	if (zstream->chunk_size == 0 ||
+	    zstream->chunk_size > ISTREAM_LZ4_CHUNK_SIZE) {
+		lz4_read_error(zstream, t_strdup_printf(
+			"invalid lz4 chunk size: %u", zstream->chunk_size));
+		stream->istream.stream_errno = EINVAL;
+		return -1;
+	}
+	buffer_set_used_size(zstream->chunk_buf, 0);
+	return 1;
+}
+
+static ssize_t i_stream_lz4_read(struct istream_private *stream)
+{
+	struct lz4_istream *zstream = (struct lz4_istream *)stream;
+	const unsigned char *data;
+	size_t size;
+	int ret;
+
+	/* if we already have max_buffer_size amount of data, fail here */
+	if (stream->pos - stream->skip >= i_stream_get_max_buffer_size(&stream->istream))
+		return -2;
+
+	if (!zstream->header_read) {
+		if ((ret = i_stream_lz4_read_header(zstream)) <= 0) {
+			stream->istream.eof = TRUE;
+			return ret;
+		}
+		zstream->header_read = TRUE;
+	}
+
+	if (zstream->chunk_left == 0) {
+		while ((ret = i_stream_lz4_read_chunk_header(zstream)) == 0) {
+			if (!stream->istream.blocking)
+				return 0;
+		}
+		if (ret < 0)
+			return ret;
+	}
+
+	/* read the whole compressed chunk into memory */
+	while (zstream->chunk_left > 0 &&
+	       (ret = i_stream_read_more(zstream->istream.parent, &data, &size)) > 0) {
+		if (size > zstream->chunk_left)
+			size = zstream->chunk_left;
+		buffer_append(zstream->chunk_buf, data, size);
+		i_stream_skip(zstream->istream.parent, size);
+		zstream->chunk_left -= size;
+	}
+	if (zstream->chunk_left > 0) {
+		if (ret == -1 && zstream->istream.parent->stream_errno == 0) {
+			lz4_read_error(zstream, "truncated lz4 chunk");
+			stream->istream.stream_errno = EPIPE;
+			return -1;
+		}
+		zstream->istream.istream.stream_errno =
+			zstream->istream.parent->stream_errno;
+		i_assert(ret != 0 || !stream->istream.blocking);
+		return ret;
+	}
+	/* if we already have max_buffer_size amount of data, fail here */
+	if (stream->pos - stream->skip >= i_stream_get_max_buffer_size(&stream->istream))
+		return -2;
+	if (i_stream_get_data_size(zstream->istream.parent) > 0) {
+		/* Parent stream was only partially consumed. Set the stream's
+		   IO as pending to avoid hangs. */
+		i_stream_set_input_pending(&zstream->istream.istream, TRUE);
+	}
+	/* allocate enough space for the old data and the new
+	   decompressed chunk. we don't know the original compressed size,
+	   so just allocate the max amount of memory. */
+	void *dest = i_stream_alloc(stream, zstream->max_uncompressed_chunk_size);
+	ret = LZ4_decompress_safe(zstream->chunk_buf->data, dest,
+				  zstream->chunk_buf->used,
+				  zstream->max_uncompressed_chunk_size);
+	i_assert(ret <= (int)zstream->max_uncompressed_chunk_size);
+	if (ret < 0) {
+		lz4_read_error(zstream, "corrupted lz4 chunk");
+		stream->istream.stream_errno = EINVAL;
+		return -1;
+	}
+	i_assert(ret > 0);
+	stream->pos += ret;
+	i_assert(stream->pos <= stream->buffer_size);
+
+	/* we are going to get next chunk after this, so reset here
+	   so we can reuse the chunk buf for reading next buffer prefix */
+	if (zstream->chunk_left == 0)
+		buffer_set_used_size(zstream->chunk_buf, 0);
+
+	return ret;
+}
+
+static void i_stream_lz4_reset(struct lz4_istream *zstream)
+{
+	struct istream_private *stream = &zstream->istream;
+
+	i_stream_seek(stream->parent, stream->parent_start_offset);
+	zstream->header_read = FALSE;
+	zstream->chunk_size = zstream->chunk_left = 0;
+
+	stream->parent_expected_offset = stream->parent_start_offset;
+	stream->skip = stream->pos = 0;
+	stream->istream.v_offset = 0;
+	buffer_set_used_size(zstream->chunk_buf, 0);
+}
+
+static void
+i_stream_lz4_seek(struct istream_private *stream, uoff_t v_offset, bool mark)
+{
+	struct lz4_istream *zstream = (struct lz4_istream *) stream;
+
+	if (i_stream_nonseekable_try_seek(stream, v_offset))
+		return;
+
+	/* have to seek backwards - reset state and retry */
+	i_stream_lz4_reset(zstream);
+	if (!i_stream_nonseekable_try_seek(stream, v_offset))
+		i_unreached();
+
+	if (mark)
+		zstream->marked = TRUE;
+}
+
+static void i_stream_lz4_sync(struct istream_private *stream)
+{
+	struct lz4_istream *zstream = (struct lz4_istream *) stream;
+	const struct stat *st;
+
+	if (i_stream_stat(stream->parent, FALSE, &st) == 0) {
+		if (memcmp(&zstream->last_parent_statbuf,
+			   st, sizeof(*st)) == 0) {
+			/* a compressed file doesn't change unexpectedly,
+			   don't clear our caches unnecessarily */
+			return;
+		}
+		zstream->last_parent_statbuf = *st;
+	}
+	i_stream_lz4_reset(zstream);
+}
+
+struct istream *i_stream_create_lz4(struct istream *input)
+{
+	struct lz4_istream *zstream;
+
+	zstream = i_new(struct lz4_istream, 1);
+
+	zstream->istream.iostream.close = i_stream_lz4_close;
+	zstream->istream.max_buffer_size = input->real_stream->max_buffer_size;
+	zstream->istream.read = i_stream_lz4_read;
+	zstream->istream.seek = i_stream_lz4_seek;
+	zstream->istream.sync = i_stream_lz4_sync;
+
+	zstream->istream.istream.readable_fd = FALSE;
+	zstream->istream.istream.blocking = input->blocking;
+	zstream->istream.istream.seekable = input->seekable;
+	zstream->chunk_buf = buffer_create_dynamic(default_pool, 1024);
+
+	return i_stream_create(&zstream->istream, input,
+			       i_stream_get_fd(input), 0);
+}
+#endif
diff --git a/src/lib-compression/istream-lzma.c b/src/lib-compression/istream-lzma.c
new file mode 100644
index 0000000..7b0c2a6
--- /dev/null
+++ b/src/lib-compression/istream-lzma.c
@@ -0,0 +1,264 @@
+/* Copyright (c) 2010-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+
+#ifdef HAVE_LZMA
+
+#include "istream-private.h"
+#include "istream-zlib.h"
+#include <lzma.h>
+
+#define CHUNK_SIZE (1024*64)
+
+#define LZMA_MEMORY_LIMIT (1024*1024*80)
+
+struct lzma_istream {
+	struct istream_private istream;
+
+	lzma_stream strm;
+	uoff_t eof_offset;
+	struct stat last_parent_statbuf;
+
+	bool hdr_read:1;
+	bool marked:1;
+	bool strm_closed:1;
+};
+
+static void i_stream_lzma_close(struct iostream_private *stream,
+				 bool close_parent)
+{
+	struct lzma_istream *zstream = (struct lzma_istream *)stream;
+
+	if (!zstream->strm_closed) {
+		lzma_end(&zstream->strm);
+		zstream->strm_closed = TRUE;
+	}
+	if (close_parent)
+		i_stream_close(zstream->istream.parent);
+}
+
+static void lzma_read_error(struct lzma_istream *zstream, const char *error)
+{
+	io_stream_set_error(&zstream->istream.iostream,
+			    "lzma.read(%s): %s at %"PRIuUOFF_T,
+			    i_stream_get_name(&zstream->istream.istream), error,
+			    i_stream_get_absolute_offset(&zstream->istream.istream));
+}
+
+static int lzma_handle_error(struct lzma_istream *zstream, lzma_ret lzma_err)
+{
+	struct istream_private *stream = &zstream->istream;
+	switch (lzma_err) {
+	case LZMA_OK:
+		break;
+	case LZMA_DATA_ERROR:
+	case LZMA_BUF_ERROR:
+		lzma_read_error(zstream, "corrupted data");
+		stream->istream.stream_errno = EINVAL;
+		return -1;
+	case LZMA_FORMAT_ERROR:
+		lzma_read_error(zstream, "wrong magic in header (not xz file?)");
+		stream->istream.stream_errno = EINVAL;
+		return -1;
+	case LZMA_OPTIONS_ERROR:
+		lzma_read_error(zstream, "Unsupported xz options");
+		stream->istream.stream_errno = EIO;
+		return -1;
+	case LZMA_MEM_ERROR:
+		i_fatal_status(FATAL_OUTOFMEM, "lzma.read(%s): Out of memory",
+			       i_stream_get_name(&stream->istream));
+	case LZMA_STREAM_END:
+		break;
+	default:
+		lzma_read_error(zstream, t_strdup_printf(
+			"lzma_code() failed with %d", lzma_err));
+		stream->istream.stream_errno = EIO;
+		return -1;
+	}
+	return 0;
+}
+
+static void lzma_stream_end(struct lzma_istream *zstream)
+{
+	zstream->eof_offset = zstream->istream.istream.v_offset +
+		(zstream->istream.pos - zstream->istream.skip);
+	zstream->istream.cached_stream_size = zstream->eof_offset;
+}
+
+static ssize_t i_stream_lzma_read(struct istream_private *stream)
+{
+	struct lzma_istream *zstream = (struct lzma_istream *)stream;
+	const unsigned char *data;
+	uoff_t high_offset;
+	size_t size, out_size;
+	lzma_ret ret;
+
+	high_offset = stream->istream.v_offset + (stream->pos - stream->skip);
+	if (zstream->eof_offset == high_offset) {
+		stream->istream.eof = TRUE;
+		return -1;
+	}
+
+	if (!zstream->marked) {
+		if (!i_stream_try_alloc(stream, CHUNK_SIZE, &out_size))
+			return -2; /* buffer full */
+	} else {
+		/* try to avoid compressing, so we can quickly seek backwards */
+		if (!i_stream_try_alloc_avoid_compress(stream, CHUNK_SIZE, &out_size))
+			return -2; /* buffer full */
+	}
+
+	if (i_stream_read_more(stream->parent, &data, &size) < 0) {
+		if (stream->parent->stream_errno != 0) {
+			stream->istream.stream_errno =
+				stream->parent->stream_errno;
+		} else {
+			i_assert(stream->parent->eof);
+			lzma_stream_end(zstream);
+			ret = lzma_code(&zstream->strm, LZMA_FINISH);
+			if (lzma_handle_error(zstream, ret) < 0)
+				;
+			else if (!zstream->hdr_read) {
+				lzma_read_error(zstream, "file too small (not xz file?)");
+				stream->istream.stream_errno = EINVAL;
+			} else if (ret != LZMA_STREAM_END) {
+				lzma_read_error(zstream, "unexpected EOF");
+				stream->istream.stream_errno = EPIPE;
+			}
+			stream->istream.eof = TRUE;
+		}
+		return -1;
+	}
+	if (size == 0) {
+		/* no more input */
+		i_assert(!stream->istream.blocking);
+		return 0;
+	}
+
+	zstream->strm.next_in = data;
+	zstream->strm.avail_in = size;
+
+	zstream->strm.next_out = stream->w_buffer + stream->pos;
+	zstream->strm.avail_out = out_size;
+	if (!zstream->hdr_read && size > LZMA_STREAM_HEADER_SIZE)
+		zstream->hdr_read = TRUE;
+	ret = lzma_code(&zstream->strm, LZMA_RUN);
+
+	out_size -= zstream->strm.avail_out;
+	stream->pos += out_size;
+
+	size_t bytes_consumed = size - zstream->strm.avail_in;
+	i_stream_skip(stream->parent, bytes_consumed);
+	if (i_stream_get_data_size(stream->parent) > 0 &&
+	    (bytes_consumed > 0 || out_size > 0)) {
+		/* Parent stream was only partially consumed. Set the stream's
+		   IO as pending to avoid hangs. */
+		i_stream_set_input_pending(&stream->istream, TRUE);
+	}
+
+	if (lzma_handle_error(zstream, ret) < 0) {
+		return -1;
+	} else if (ret == LZMA_STREAM_END) {
+		lzma_stream_end(zstream);
+		if (out_size == 0) {
+			stream->istream.eof = TRUE;
+			return -1;
+		}
+	}
+	if (out_size == 0) {
+		/* read more input */
+		return i_stream_lzma_read(stream);
+	}
+	return out_size;
+}
+
+static void i_stream_lzma_init(struct lzma_istream *zstream)
+{
+	lzma_ret ret;
+
+	ret = lzma_stream_decoder(&zstream->strm, LZMA_MEMORY_LIMIT,
+				  LZMA_CONCATENATED);
+	switch (ret) {
+	case LZMA_OK:
+		break;
+	case LZMA_MEM_ERROR:
+		i_fatal_status(FATAL_OUTOFMEM, "lzma: Out of memory");
+	default:
+		i_fatal("lzma_stream_decoder() failed with ret=%d", ret);
+	}
+}
+
+static void i_stream_lzma_reset(struct lzma_istream *zstream)
+{
+	struct istream_private *stream = &zstream->istream;
+
+	i_stream_seek(stream->parent, stream->parent_start_offset);
+	zstream->eof_offset = UOFF_T_MAX;
+	zstream->strm.next_in = NULL;
+	zstream->strm.avail_in = 0;
+
+	stream->parent_expected_offset = stream->parent_start_offset;
+	stream->skip = stream->pos = 0;
+	stream->istream.v_offset = 0;
+
+	lzma_end(&zstream->strm);
+	i_stream_lzma_init(zstream);
+}
+
+static void
+i_stream_lzma_seek(struct istream_private *stream, uoff_t v_offset, bool mark)
+{
+	struct lzma_istream *zstream = (struct lzma_istream *) stream;
+
+	if (i_stream_nonseekable_try_seek(stream, v_offset))
+		return;
+
+	/* have to seek backwards - reset state and retry */
+	i_stream_lzma_reset(zstream);
+	if (!i_stream_nonseekable_try_seek(stream, v_offset))
+		i_unreached();
+
+	if (mark)
+		zstream->marked = TRUE;
+}
+
+static void i_stream_lzma_sync(struct istream_private *stream)
+{
+	struct lzma_istream *zstream = (struct lzma_istream *) stream;
+	const struct stat *st;
+
+	if (i_stream_stat(stream->parent, FALSE, &st) == 0) {
+		if (memcmp(&zstream->last_parent_statbuf,
+			   st, sizeof(*st)) == 0) {
+			/* a compressed file doesn't change unexpectedly,
+			   don't clear our caches unnecessarily */
+			return;
+		}
+		zstream->last_parent_statbuf = *st;
+	}
+	i_stream_lzma_reset(zstream);
+}
+
+struct istream *i_stream_create_lzma(struct istream *input)
+{
+	struct lzma_istream *zstream;
+
+	zstream = i_new(struct lzma_istream, 1);
+	zstream->eof_offset = UOFF_T_MAX;
+
+	i_stream_lzma_init(zstream);
+
+	zstream->istream.iostream.close = i_stream_lzma_close;
+	zstream->istream.max_buffer_size = input->real_stream->max_buffer_size;
+	zstream->istream.read = i_stream_lzma_read;
+	zstream->istream.seek = i_stream_lzma_seek;
+	zstream->istream.sync = i_stream_lzma_sync;
+
+	zstream->istream.istream.readable_fd = FALSE;
+	zstream->istream.istream.blocking = input->blocking;
+	zstream->istream.istream.seekable = input->seekable;
+
+	return i_stream_create(&zstream->istream, input,
+			       i_stream_get_fd(input), 0);
+}
+#endif
diff --git a/src/lib-compression/istream-zlib.c b/src/lib-compression/istream-zlib.c
new file mode 100644
index 0000000..3a975c3
--- /dev/null
+++ b/src/lib-compression/istream-zlib.c
@@ -0,0 +1,431 @@
+/* Copyright (c) 2010-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+
+#ifdef HAVE_ZLIB
+
+#include "crc32.h"
+#include "istream-private.h"
+#include "istream-zlib.h"
+#include <zlib.h>
+
+#define CHUNK_SIZE (1024*64)
+
+#define GZ_HEADER_MIN_SIZE 10
+#define GZ_TRAILER_SIZE 8
+
+#define GZ_MAGIC1	0x1f
+#define GZ_MAGIC2	0x8b
+#define GZ_FLAG_FHCRC	0x02
+#define GZ_FLAG_FEXTRA	0x04
+#define GZ_FLAG_FNAME	0x08
+#define GZ_FLAG_FCOMMENT 0x10
+
+struct zlib_istream {
+	struct istream_private istream;
+
+	z_stream zs;
+	uoff_t eof_offset;
+	size_t prev_size;
+	uint32_t crc32;
+	struct stat last_parent_statbuf;
+
+	bool gz:1;
+	bool marked:1;
+	bool header_read:1;
+	bool trailer_read:1;
+	bool zs_closed:1;
+	bool starting_concated_output:1;
+};
+
+static void i_stream_zlib_init(struct zlib_istream *zstream);
+
+static void i_stream_zlib_close(struct iostream_private *stream,
+				bool close_parent)
+{
+	struct zlib_istream *zstream = (struct zlib_istream *)stream;
+
+	if (!zstream->zs_closed) {
+		(void)inflateEnd(&zstream->zs);
+		zstream->zs_closed = TRUE;
+	}
+	if (close_parent)
+		i_stream_close(zstream->istream.parent);
+}
+
+static void zlib_read_error(struct zlib_istream *zstream, const char *error)
+{
+	io_stream_set_error(&zstream->istream.iostream,
+			    "zlib.read(%s): %s at %"PRIuUOFF_T,
+			    i_stream_get_name(&zstream->istream.istream), error,
+			    i_stream_get_absolute_offset(&zstream->istream.istream));
+}
+
+static int i_stream_zlib_read_header(struct istream_private *stream)
+{
+	struct zlib_istream *zstream = (struct zlib_istream *)stream;
+	const unsigned char *data;
+	size_t size;
+	unsigned int pos, fextra_size;
+	int ret;
+
+	ret = i_stream_read_bytes(stream->parent, &data, &size,
+				  zstream->prev_size + 1);
+	if (size == zstream->prev_size) {
+		stream->istream.stream_errno = stream->parent->stream_errno;
+		if (ret == -1 && stream->istream.stream_errno == 0) {
+			zlib_read_error(zstream, "missing gz header");
+			stream->istream.stream_errno = EINVAL;
+		}
+		if (ret == -2) {
+			zlib_read_error(zstream, "gz header is too large");
+			stream->istream.stream_errno = EINVAL;
+			ret = -1;
+		}
+		return ret;
+	}
+	zstream->prev_size = size;
+
+	if (size < GZ_HEADER_MIN_SIZE)
+		return 0;
+	pos = GZ_HEADER_MIN_SIZE;
+
+	if (data[0] != GZ_MAGIC1 || data[1] != GZ_MAGIC2) {
+		/* missing gzip magic header */
+		zlib_read_error(zstream, "wrong magic in header (not gz file?)");
+		stream->istream.stream_errno = EINVAL;
+		return -1;
+	}
+	if ((data[3] & GZ_FLAG_FEXTRA) != 0) {
+		if (pos + 2 > size)
+			return 0;
+
+		fextra_size = le16_to_cpu_unaligned(&data[pos]);
+		pos += 2;
+		if (pos + fextra_size > size)
+			return 0;
+		pos += fextra_size;
+	}
+	if ((data[3] & GZ_FLAG_FNAME) != 0) {
+		do {
+			if (pos == size)
+				return 0;
+		} while (data[pos++] != '\0');
+	}
+	if ((data[3] & GZ_FLAG_FCOMMENT) != 0) {
+		do {
+			if (pos == size)
+				return 0;
+		} while (data[pos++] != '\0');
+	}
+	if ((data[3] & GZ_FLAG_FHCRC) != 0) {
+		if (pos + 2 > size)
+			return 0;
+		pos += 2;
+	}
+	i_stream_skip(stream->parent, pos);
+	zstream->prev_size = 0;
+	return 1;
+}
+
+static int i_stream_zlib_read_trailer(struct zlib_istream *zstream)
+{
+	struct istream_private *stream = &zstream->istream;
+	const unsigned char *data;
+	size_t size;
+	int ret;
+
+	ret = i_stream_read_bytes(stream->parent, &data, &size,
+				  GZ_TRAILER_SIZE);
+	if (size == zstream->prev_size) {
+		stream->istream.stream_errno = stream->parent->stream_errno;
+		if (ret == -1 && stream->istream.stream_errno == 0) {
+			zlib_read_error(zstream, "missing gz trailer");
+			stream->istream.stream_errno = EINVAL;
+		}
+		return ret;
+	}
+	zstream->prev_size = size;
+
+	if (size < GZ_TRAILER_SIZE)
+		return 0;
+
+	if (le32_to_cpu_unaligned(data) != zstream->crc32) {
+		zlib_read_error(zstream, "gz trailer has wrong CRC value");
+		stream->istream.stream_errno = EINVAL;
+		return -1;
+	}
+	i_stream_skip(stream->parent, GZ_TRAILER_SIZE);
+	zstream->prev_size = 0;
+	zstream->trailer_read = TRUE;
+	return 1;
+}
+
+static ssize_t i_stream_zlib_read(struct istream_private *stream)
+{
+	struct zlib_istream *zstream = (struct zlib_istream *)stream;
+	const unsigned char *data;
+	uoff_t high_offset;
+	size_t size, out_size;
+	int ret;
+
+	high_offset = stream->istream.v_offset + (stream->pos - stream->skip);
+	if (zstream->eof_offset == high_offset) {
+		/* zlib library returned EOF. */
+		if (!zstream->gz) {
+			/* deflate - ignore if there's still more data */
+			stream->istream.eof = TRUE;
+			return -1;
+		}
+		/* gz format - read the trailer */
+		if (!zstream->trailer_read) {
+			do {
+				ret = i_stream_zlib_read_trailer(zstream);
+			} while (ret == 0 && stream->istream.blocking);
+			if (ret <= 0)
+				return ret;
+		}
+		/* See if there's another concatenated gz stream. */
+		if (i_stream_read_eof(stream->parent)) {
+			/* EOF or error */
+			stream->istream.stream_errno =
+				stream->parent->stream_errno;
+			stream->istream.eof = TRUE;
+			return -1;
+		}
+		/* Multiple gz streams concatenated together */
+		zstream->starting_concated_output = TRUE;
+	}
+	if (zstream->starting_concated_output) {
+		/* make sure there actually is something in parent stream.
+		   we don't want to reset the stream unless we actually see
+		   some concated output. */
+		ret = i_stream_read_more(stream->parent, &data, &size);
+		if (ret <= 0) {
+			if (ret == 0)
+				return 0;
+			if (stream->parent->stream_errno != 0) {
+				stream->istream.stream_errno =
+					stream->parent->stream_errno;
+			}
+			stream->istream.eof = TRUE;
+			return -1;
+		}
+
+		/* gzip file with concatenated content */
+		stream->cached_stream_size = UOFF_T_MAX;
+		zstream->eof_offset = UOFF_T_MAX;
+		zstream->header_read = FALSE;
+		zstream->trailer_read = FALSE;
+		zstream->crc32 = 0;
+		zstream->starting_concated_output = FALSE;
+
+		(void)inflateEnd(&zstream->zs);
+		i_stream_zlib_init(zstream);
+	}
+
+	if (!zstream->header_read) {
+		do {
+			ret = i_stream_zlib_read_header(stream);
+		} while (ret == 0 && stream->istream.blocking);
+		if (ret <= 0)
+			return ret;
+		zstream->header_read = TRUE;
+	}
+
+	if (!zstream->marked) {
+		if (!i_stream_try_alloc(stream, CHUNK_SIZE, &out_size))
+			return -2; /* buffer full */
+	} else {
+		/* try to avoid compressing, so we can quickly seek backwards */
+		if (!i_stream_try_alloc_avoid_compress(stream, CHUNK_SIZE, &out_size))
+			return -2; /* buffer full */
+	}
+
+	if (i_stream_read_more(stream->parent, &data, &size) < 0) {
+		if (stream->parent->stream_errno != 0) {
+			stream->istream.stream_errno =
+				stream->parent->stream_errno;
+		} else {
+			i_assert(stream->parent->eof);
+			zlib_read_error(zstream, "unexpected EOF");
+			stream->istream.stream_errno = EPIPE;
+		}
+		return -1;
+	}
+	if (size == 0) {
+		/* no more input */
+		i_assert(!stream->istream.blocking);
+		return 0;
+	}
+
+	zstream->zs.next_in = (void *)data;
+	zstream->zs.avail_in = size;
+
+	zstream->zs.next_out = stream->w_buffer + stream->pos;
+	zstream->zs.avail_out = out_size;
+	ret = inflate(&zstream->zs, Z_SYNC_FLUSH);
+
+	out_size -= zstream->zs.avail_out;
+	zstream->crc32 = crc32_data_more(zstream->crc32,
+					 stream->w_buffer + stream->pos,
+					 out_size);
+	stream->pos += out_size;
+
+	size_t bytes_consumed = size - zstream->zs.avail_in;
+	i_stream_skip(stream->parent, bytes_consumed);
+	if (i_stream_get_data_size(stream->parent) > 0 &&
+	    (bytes_consumed > 0 || out_size > 0)) {
+		/* Parent stream was only partially consumed. Set the stream's
+		   IO as pending to avoid hangs. */
+		i_stream_set_input_pending(&stream->istream, TRUE);
+	}
+
+	switch (ret) {
+	case Z_OK:
+		break;
+	case Z_NEED_DICT:
+		zlib_read_error(zstream, "can't read file without dict");
+		stream->istream.stream_errno = EIO;
+		return -1;
+	case Z_DATA_ERROR:
+		zlib_read_error(zstream, "corrupted data");
+		stream->istream.stream_errno = EINVAL;
+		return -1;
+	case Z_MEM_ERROR:
+		i_fatal_status(FATAL_OUTOFMEM, "zlib.read(%s): Out of memory",
+			       i_stream_get_name(&stream->istream));
+	case Z_STREAM_END:
+		zstream->eof_offset = stream->istream.v_offset +
+			(stream->pos - stream->skip);
+		stream->cached_stream_size = zstream->eof_offset;
+		zstream->zs.avail_in = 0;
+
+		if (!zstream->trailer_read) {
+			/* try to read and verify the trailer, we might not
+			   be called again. */
+			if (i_stream_zlib_read_trailer(zstream) < 0)
+				return -1;
+		}
+		break;
+	default:
+		i_fatal("inflate() failed with %d", ret);
+	}
+	if (out_size == 0) {
+		/* read more input */
+		return i_stream_zlib_read(stream);
+	}
+	return out_size;
+}
+
+static void i_stream_zlib_init(struct zlib_istream *zstream)
+{
+	int ret;
+
+	ret = inflateInit2(&zstream->zs, -15);
+	switch (ret) {
+	case Z_OK:
+		break;
+	case Z_MEM_ERROR:
+		i_fatal_status(FATAL_OUTOFMEM, "zlib: Out of memory");
+	case Z_VERSION_ERROR:
+		i_fatal("Wrong zlib library version (broken compilation)");
+	case Z_STREAM_ERROR:
+		i_fatal("zlib: Invalid parameters");
+	default:
+		i_fatal("inflateInit() failed with %d", ret);
+	}
+	zstream->header_read = !zstream->gz;
+	zstream->trailer_read = !zstream->gz;
+}
+
+static void i_stream_zlib_reset(struct zlib_istream *zstream)
+{
+	struct istream_private *stream = &zstream->istream;
+
+	i_stream_seek(stream->parent, stream->parent_start_offset);
+	zstream->eof_offset = UOFF_T_MAX;
+	zstream->crc32 = 0;
+
+	zstream->zs.next_in = NULL;
+	zstream->zs.avail_in = 0;
+
+	stream->parent_expected_offset = stream->parent_start_offset;
+	stream->skip = stream->pos = 0;
+	stream->istream.v_offset = 0;
+	stream->high_pos = 0;
+	zstream->prev_size = 0;
+
+	(void)inflateEnd(&zstream->zs);
+	i_stream_zlib_init(zstream);
+}
+
+static void
+i_stream_zlib_seek(struct istream_private *stream, uoff_t v_offset, bool mark)
+{
+	struct zlib_istream *zstream = (struct zlib_istream *) stream;
+
+	if (i_stream_nonseekable_try_seek(stream, v_offset))
+		return;
+
+	/* have to seek backwards - reset state and retry */
+	i_stream_zlib_reset(zstream);
+	if (!i_stream_nonseekable_try_seek(stream, v_offset))
+		i_unreached();
+
+	if (mark)
+		zstream->marked = TRUE;
+}
+
+static void i_stream_zlib_sync(struct istream_private *stream)
+{
+	struct zlib_istream *zstream = (struct zlib_istream *) stream;
+	const struct stat *st;
+
+	if (i_stream_stat(stream->parent, FALSE, &st) == 0) {
+		if (memcmp(&zstream->last_parent_statbuf,
+			   st, sizeof(*st)) == 0) {
+			/* a compressed file doesn't change unexpectedly,
+			   don't clear our caches unnecessarily */
+			return;
+		}
+		zstream->last_parent_statbuf = *st;
+	}
+	i_stream_zlib_reset(zstream);
+}
+
+static struct istream *
+i_stream_create_zlib(struct istream *input, bool gz)
+{
+	struct zlib_istream *zstream;
+
+	zstream = i_new(struct zlib_istream, 1);
+	zstream->eof_offset = UOFF_T_MAX;
+	zstream->gz = gz;
+
+	i_stream_zlib_init(zstream);
+
+	zstream->istream.iostream.close = i_stream_zlib_close;
+	zstream->istream.max_buffer_size = input->real_stream->max_buffer_size;
+	zstream->istream.read = i_stream_zlib_read;
+	zstream->istream.seek = i_stream_zlib_seek;
+	zstream->istream.sync = i_stream_zlib_sync;
+
+	zstream->istream.istream.readable_fd = FALSE;
+	zstream->istream.istream.blocking = input->blocking;
+	zstream->istream.istream.seekable = input->seekable;
+
+	return i_stream_create(&zstream->istream, input,
+			       i_stream_get_fd(input), 0);
+}
+
+struct istream *i_stream_create_gz(struct istream *input)
+{
+	return i_stream_create_zlib(input, TRUE);
+}
+
+struct istream *i_stream_create_deflate(struct istream *input)
+{
+	return i_stream_create_zlib(input, FALSE);
+}
+#endif
diff --git a/src/lib-compression/istream-zlib.h b/src/lib-compression/istream-zlib.h
new file mode 100644
index 0000000..041fbf3
--- /dev/null
+++ b/src/lib-compression/istream-zlib.h
@@ -0,0 +1,11 @@
+#ifndef ISTREAM_ZLIB_H
+#define ISTREAM_ZLIB_H
+
+struct istream *i_stream_create_gz(struct istream *input);
+struct istream *i_stream_create_deflate(struct istream *input);
+struct istream *i_stream_create_bz2(struct istream *input);
+struct istream *i_stream_create_lzma(struct istream *input);
+struct istream *i_stream_create_lz4(struct istream *input);
+struct istream *i_stream_create_zstd(struct istream *input);
+
+#endif
diff --git a/src/lib-compression/istream-zstd.c b/src/lib-compression/istream-zstd.c
new file mode 100644
index 0000000..9e059bc
--- /dev/null
+++ b/src/lib-compression/istream-zstd.c
@@ -0,0 +1,268 @@
+/* Copyright (c) 2020 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+
+#ifdef HAVE_ZSTD
+
+#include "buffer.h"
+#include "istream-private.h"
+#include "istream-zlib.h"
+
+#include "zstd.h"
+#include "zstd_errors.h"
+#include "iostream-zstd-private.h"
+
+#ifndef HAVE_ZSTD_GETERRORCODE
+ZSTD_ErrorCode ZSTD_getErrorCode(size_t functionResult)
+{
+	ssize_t errcode = (ssize_t)functionResult;
+	if (errcode < 0)
+		return -errcode;
+	return ZSTD_error_no_error;
+}
+#endif
+
+struct zstd_istream {
+	struct istream_private istream;
+
+	ZSTD_DStream *dstream;
+	ZSTD_inBuffer input;
+	ZSTD_outBuffer output;
+
+	struct stat last_parent_statbuf;
+
+	/* ZSTD input size */
+	size_t input_size;
+
+	/* storage for frames */
+	buffer_t *frame_buffer;
+
+	/* storage for data */
+	buffer_t *data_buffer;
+
+	bool hdr_read:1;
+	bool marked:1;
+	bool zs_closed:1;
+	/* is there data remaining */
+	bool remain:1;
+};
+
+static void i_stream_zstd_init(struct zstd_istream *zstream)
+{
+	zstream->dstream = ZSTD_createDStream();
+	if (zstream->dstream == NULL)
+		i_fatal_status(FATAL_OUTOFMEM, "zstd: Out of memory");
+	ZSTD_initDStream(zstream->dstream);
+	zstream->input_size = ZSTD_DStreamInSize();
+	if (zstream->frame_buffer == NULL)
+		zstream->frame_buffer = buffer_create_dynamic(default_pool, ZSTD_DStreamInSize());
+	else
+		buffer_set_used_size(zstream->frame_buffer, 0);
+	if (zstream->data_buffer == NULL)
+		zstream->data_buffer = buffer_create_dynamic(default_pool, ZSTD_DStreamOutSize());
+	else
+		buffer_set_used_size(zstream->data_buffer, 0);
+	zstream->zs_closed = FALSE;
+}
+
+static void i_stream_zstd_deinit(struct zstd_istream *zstream, bool reuse_buffers)
+{
+	(void)ZSTD_freeDStream(zstream->dstream);
+	zstream->dstream = NULL;
+	if (!reuse_buffers) {
+		buffer_free(&zstream->frame_buffer);
+		buffer_free(&zstream->data_buffer);
+	}
+	zstream->zs_closed = TRUE;
+	i_zero(&zstream->input);
+}
+
+static void i_stream_zstd_close(struct iostream_private *stream,
+				bool close_parent)
+{
+	struct istream_private *_istream =
+		container_of(stream, struct istream_private, iostream);
+	struct zstd_istream *zstream =
+		container_of(_istream, struct zstd_istream, istream);
+	if (!zstream->zs_closed)
+		i_stream_zstd_deinit(zstream, FALSE);
+	buffer_free(&zstream->frame_buffer);
+	if (close_parent)
+		i_stream_close(zstream->istream.parent);
+}
+
+static void i_stream_zstd_read_error(struct zstd_istream *zstream, size_t err)
+{
+	ZSTD_ErrorCode errcode = zstd_version_errcode(ZSTD_getErrorCode(err));
+	const char *error = ZSTD_getErrorName(err);
+	if (errcode == ZSTD_error_memory_allocation)
+		i_fatal_status(FATAL_OUTOFMEM, "zstd.read(%s): Out of memory",
+			       i_stream_get_name(&zstream->istream.istream));
+	else if (errcode == ZSTD_error_prefix_unknown ||
+#if HAVE_DECL_ZSTD_ERROR_PARAMETER_UNSUPPORTED == 1
+		 errcode == ZSTD_error_parameter_unsupported ||
+#endif
+
+		 errcode == ZSTD_error_dictionary_wrong ||
+		 errcode == ZSTD_error_init_missing)
+		zstream->istream.istream.stream_errno = EINVAL;
+	else
+		zstream->istream.istream.stream_errno = EIO;
+
+	io_stream_set_error(&zstream->istream.iostream,
+			    "zstd.read(%s): %s at %"PRIuUOFF_T,
+			    i_stream_get_name(&zstream->istream.istream), error,
+			    i_stream_get_absolute_offset(&zstream->istream.istream));
+}
+
+static ssize_t i_stream_zstd_read(struct istream_private *stream)
+{
+	struct zstd_istream *zstream =
+		container_of(stream, struct zstd_istream, istream);
+	const unsigned char *data;
+	size_t size;
+
+	if (stream->istream.eof)
+		return -1;
+
+	for (;;) {
+		if (zstream->data_buffer->used > 0) {
+			if (!i_stream_try_alloc(stream, stream->max_buffer_size, &size))
+				return -2;
+			size = I_MIN(zstream->data_buffer->used, size);
+			memcpy(PTR_OFFSET(stream->w_buffer,stream->pos),
+			       zstream->data_buffer->data, size);
+			stream->pos += size;
+			buffer_delete(zstream->data_buffer, 0, size);
+			return size;
+		}
+
+		/* see if we can get more */
+		if (zstream->input.pos == zstream->input.size) {
+			ssize_t ret;
+			buffer_set_used_size(zstream->frame_buffer, 0);
+			/* need to read more */
+			if ((ret = i_stream_read_more(stream->parent, &data, &size)) < 0) {
+				stream->istream.stream_errno =
+					stream->parent->stream_errno;
+				stream->istream.eof = stream->parent->eof;
+				if (stream->istream.stream_errno != 0)
+					;
+				else if (!zstream->hdr_read)
+					stream->istream.stream_errno = EINVAL;
+				else if (zstream->remain)
+					/* truncated data */
+					stream->istream.stream_errno = EPIPE;
+				return ret;
+			}
+			if (ret == 0)
+				return 0;
+			buffer_append(zstream->frame_buffer, data, size);
+			/* NOTE: All of the parent stream input is skipped
+			   over here. This is why there's no need to call
+			   i_stream_set_input_pending() here like with other
+			   compression istreams. */
+			i_stream_skip(stream->parent, size);
+			zstream->input.src = zstream->frame_buffer->data;
+			zstream->input.size = zstream->frame_buffer->used;
+			zstream->input.pos = 0;
+		}
+
+		i_assert(zstream->input.size > 0);
+		i_assert(zstream->data_buffer->used == 0);
+		zstream->output.dst = buffer_append_space_unsafe(zstream->data_buffer,
+								 ZSTD_DStreamOutSize());
+		zstream->output.pos = 0;
+		zstream->output.size = ZSTD_DStreamOutSize();
+
+		size_t zret = ZSTD_decompressStream(zstream->dstream, &zstream->output,
+						    &zstream->input);
+		if (ZSTD_isError(zret) != 0) {
+			i_stream_zstd_read_error(zstream, zret);
+			return -1;
+		}
+		/* ZSTD magic number is 4 bytes, but it's only defined after v0.8 */
+		if (!zstream->hdr_read && zstream->input.size > 4)
+			zstream->hdr_read = TRUE;
+		zstream->remain = zret > 0;
+		buffer_set_used_size(zstream->data_buffer, zstream->output.pos);
+	}
+	i_unreached();
+}
+
+static void i_stream_zstd_reset(struct zstd_istream *zstream)
+{
+	struct istream_private *stream = &zstream->istream;
+
+	i_stream_seek(stream->parent, stream->parent_start_offset);
+	stream->parent_expected_offset = stream->parent_start_offset;
+	stream->skip = stream->pos = 0;
+	stream->istream.v_offset = 0;
+	stream->high_pos = 0;
+
+	i_stream_zstd_deinit(zstream, TRUE);
+	i_stream_zstd_init(zstream);
+}
+
+static void
+i_stream_zstd_seek(struct istream_private *stream, uoff_t v_offset, bool mark)
+{
+	struct zstd_istream *zstream =
+		container_of(stream, struct zstd_istream, istream);
+
+	if (i_stream_nonseekable_try_seek(stream, v_offset))
+		return;
+
+	/* have to seek backwards - reset state and retry */
+	i_stream_zstd_reset(zstream);
+	if (!i_stream_nonseekable_try_seek(stream, v_offset))
+		i_unreached();
+
+	if (mark)
+		zstream->marked = TRUE;
+}
+
+static void i_stream_zstd_sync(struct istream_private *stream)
+{
+	struct zstd_istream *zstream =
+		container_of(stream, struct zstd_istream, istream);
+	const struct stat *st;
+
+	if (i_stream_stat(stream->parent, FALSE, &st) == 0) {
+		if (memcmp(&zstream->last_parent_statbuf,
+			   st, sizeof(*st)) == 0) {
+			/* a compressed file doesn't change unexpectedly,
+			   don't clear our caches unnecessarily */
+			return;
+		}
+		zstream->last_parent_statbuf = *st;
+	}
+	i_stream_zstd_reset(zstream);
+}
+
+struct istream *
+i_stream_create_zstd(struct istream *input)
+{
+	struct zstd_istream *zstream;
+
+	zstd_version_check();
+
+	zstream = i_new(struct zstd_istream, 1);
+
+	i_stream_zstd_init(zstream);
+
+	zstream->istream.iostream.close = i_stream_zstd_close;
+	zstream->istream.max_buffer_size = input->real_stream->max_buffer_size;
+	zstream->istream.read = i_stream_zstd_read;
+	zstream->istream.seek = i_stream_zstd_seek;
+	zstream->istream.sync = i_stream_zstd_sync;
+
+	zstream->istream.istream.readable_fd = FALSE;
+	zstream->istream.istream.blocking = input->blocking;
+	zstream->istream.istream.seekable = input->seekable;
+
+	return i_stream_create(&zstream->istream, input,
+			       i_stream_get_fd(input), 0);
+}
+
+#endif
diff --git a/src/lib-compression/ostream-bzlib.c b/src/lib-compression/ostream-bzlib.c
new file mode 100644
index 0000000..4d072b2
--- /dev/null
+++ b/src/lib-compression/ostream-bzlib.c
@@ -0,0 +1,307 @@
+/* Copyright (c) 2010-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+
+#ifdef HAVE_BZLIB
+
+#include "ostream-private.h"
+#include "ostream-zlib.h"
+#include <bzlib.h>
+
+#define CHUNK_SIZE (1024*64)
+
+struct bzlib_ostream {
+	struct ostream_private ostream;
+	bz_stream zs;
+
+	char outbuf[CHUNK_SIZE];
+	unsigned int outbuf_offset, outbuf_used;
+
+	bool flushed:1;
+};
+
+/* in bzlib, level is actually block size. From bzlib manual:
+
+   The block size affects both the compression ratio achieved,
+   and the amount of memory needed for compression and decompression.
+
+   BlockSize 1 through BlockSize 9 specify the block size to be 100,000 bytes
+   through 900,000 bytes respectively. The default is to use the maximum block
+   size.
+
+   Larger block sizes give rapidly diminishing marginal returns.
+   Most of the compression comes from the first two or three hundred k of
+   block size, a fact worth bearing in mind when using bzip2 on small machines.
+   It is also important to appreciate that the decompression memory
+   requirement is set at compression time by the choice of block size.
+
+   * In general, try and use the largest block size memory constraints
+     allow, since that maximises the compression achieved.
+   * Compression and decompression speed are virtually unaffected by block
+     size.
+
+   Another significant point applies to files which fit in a single block -
+   that means most files you'd encounter using a large block size. The
+   amount of real memory touched is proportional to the size of the file,
+   since the file is smaller than a block. For example, compressing a file
+   20,000 bytes long with the flag BlockSize 9 will cause the compressor to
+   allocate around 7600k of memory, but only touch 400k + 20000 * 8 = 560 kbytes
+   of it. Similarly, the decompressor will allocate 3700k but only
+   touch 100k + 20000 * 4 = 180 kbytes.
+*/
+
+int compression_get_min_level_bz2(void)
+{
+	return 1;
+}
+
+int compression_get_default_level_bz2(void)
+{
+	/* default is maximum level */
+	return 9;
+}
+
+int compression_get_max_level_bz2(void)
+{
+	return 9;
+}
+
+static void o_stream_bzlib_close(struct iostream_private *stream,
+				 bool close_parent)
+{
+	struct bzlib_ostream *zstream = (struct bzlib_ostream *)stream;
+
+	(void)BZ2_bzCompressEnd(&zstream->zs);
+	if (close_parent)
+		o_stream_close(zstream->ostream.parent);
+}
+
+static int o_stream_zlib_send_outbuf(struct bzlib_ostream *zstream)
+{
+	ssize_t ret;
+	size_t size;
+
+	if (zstream->outbuf_used == 0)
+		return 1;
+
+	size = zstream->outbuf_used - zstream->outbuf_offset;
+	i_assert(size > 0);
+	ret = o_stream_send(zstream->ostream.parent,
+			    zstream->outbuf + zstream->outbuf_offset, size);
+	if (ret < 0) {
+		o_stream_copy_error_from_parent(&zstream->ostream);
+		return -1;
+	}
+	if ((size_t)ret != size) {
+		zstream->outbuf_offset += ret;
+		return 0;
+	}
+	zstream->outbuf_offset = 0;
+	zstream->outbuf_used = 0;
+	return 1;
+}
+
+static ssize_t
+o_stream_bzlib_send_chunk(struct bzlib_ostream *zstream,
+			  const void *data, size_t size)
+{
+	bz_stream *zs = &zstream->zs;
+	int ret;
+
+	i_assert(zstream->outbuf_used == 0);
+
+	zs->next_in = (void *)data;
+	zs->avail_in = size;
+	while (zs->avail_in > 0) {
+		if (zs->avail_out == 0) {
+			/* previous block was compressed. send it and start
+			   compression for a new block. */
+			zs->next_out = zstream->outbuf;
+			zs->avail_out = sizeof(zstream->outbuf);
+
+			zstream->outbuf_used = sizeof(zstream->outbuf);
+			if ((ret = o_stream_zlib_send_outbuf(zstream)) < 0)
+				return -1;
+			if (ret == 0) {
+				/* parent stream's buffer full */
+				break;
+			}
+		}
+
+		switch ((ret = BZ2_bzCompress(zs, BZ_RUN))) {
+		case BZ_RUN_OK:
+			break;
+		case BZ_MEM_ERROR:
+			i_fatal_status(FATAL_OUTOFMEM, "bzip2.write(%s): Out of memory",
+				       o_stream_get_name(&zstream->ostream.ostream));
+		default:
+			i_fatal("BZ2_bzCompress() failed with %d", ret);
+		}
+	}
+	size -= zs->avail_in;
+
+	zstream->flushed = FALSE;
+	return size;
+}
+
+static int o_stream_bzlib_send_flush(struct bzlib_ostream *zstream, bool final)
+{
+	bz_stream *zs = &zstream->zs;
+	size_t len;
+	bool done = FALSE;
+	int ret;
+
+	i_assert(zs->avail_in == 0);
+
+	if (zstream->flushed) {
+		i_assert(zstream->outbuf_used == 0);
+		return 1;
+	}
+
+	if ((ret = o_stream_flush_parent_if_needed(&zstream->ostream)) <= 0)
+		return ret;
+	if ((ret = o_stream_zlib_send_outbuf(zstream)) <= 0)
+		return ret;
+
+	/* do not attempt to finish the stream early */
+	if (!final)
+		return 1;
+
+	i_assert(zstream->outbuf_used == 0);
+	do {
+		len = sizeof(zstream->outbuf) - zs->avail_out;
+		if (len != 0) {
+			zs->next_out = zstream->outbuf;
+			zs->avail_out = sizeof(zstream->outbuf);
+
+			zstream->outbuf_used = len;
+			if ((ret = o_stream_zlib_send_outbuf(zstream)) <= 0)
+				return ret;
+			if (done)
+				break;
+		}
+
+		ret = BZ2_bzCompress(zs, BZ_FINISH);
+		switch (ret) {
+		case BZ_RUN_OK:
+		case BZ_FLUSH_OK:
+		case BZ_STREAM_END:
+			done = TRUE;
+			break;
+		case BZ_FINISH_OK:
+			break;
+                case BZ_MEM_ERROR:
+                        i_fatal_status(FATAL_OUTOFMEM, "bzip2.write(%s): Out of memory",
+                                       o_stream_get_name(&zstream->ostream.ostream));
+                default:
+                        i_fatal("BZ2_bzCompress() failed with %d", ret);
+		}
+	} while (zs->avail_out != sizeof(zstream->outbuf));
+
+	if (final)
+		zstream->flushed = TRUE;
+	i_assert(zstream->outbuf_used == 0);
+	return 1;
+}
+
+static int o_stream_bzlib_flush(struct ostream_private *stream)
+{
+	struct bzlib_ostream *zstream = (struct bzlib_ostream *)stream;
+	int ret;
+	if ((ret = o_stream_bzlib_send_flush(zstream, stream->finished)) < 0)
+		return -1;
+	else if (ret > 0)
+		return o_stream_flush_parent(stream);
+	return ret;
+}
+
+static size_t
+o_stream_bzlib_get_buffer_used_size(const struct ostream_private *stream)
+{
+	const struct bzlib_ostream *zstream =
+		(const struct bzlib_ostream *)stream;
+
+	/* outbuf has already compressed data that we're trying to send to the
+	   parent stream. We're not including bzlib's internal compression
+	   buffer size. */
+	return (zstream->outbuf_used - zstream->outbuf_offset) +
+		o_stream_get_buffer_used_size(stream->parent);
+}
+
+static size_t
+o_stream_bzlib_get_buffer_avail_size(const struct ostream_private *stream)
+{
+	/* FIXME: not correct - this is counting compressed size, which may be
+	   too larger than uncompressed size in some situations. Fixing would
+	   require some kind of additional buffering. */
+	return o_stream_get_buffer_avail_size(stream->parent);
+}
+
+static ssize_t
+o_stream_bzlib_sendv(struct ostream_private *stream,
+		    const struct const_iovec *iov, unsigned int iov_count)
+{
+	struct bzlib_ostream *zstream = (struct bzlib_ostream *)stream;
+	ssize_t ret, bytes = 0;
+	unsigned int i;
+
+	if ((ret = o_stream_zlib_send_outbuf(zstream)) <= 0) {
+		/* error / we still couldn't flush existing data to
+		   parent stream. */
+		return ret;
+	}
+
+	for (i = 0; i < iov_count; i++) {
+		ret = o_stream_bzlib_send_chunk(zstream, iov[i].iov_base,
+						iov[i].iov_len);
+		if (ret < 0)
+			return -1;
+		bytes += ret;
+		if ((size_t)ret != iov[i].iov_len)
+			break;
+	}
+	stream->ostream.offset += bytes;
+
+	/* avail_in!=0 check is used to detect errors. if it's non-zero here
+	   it simply means we didn't send all the data */
+	zstream->zs.avail_in = 0;
+	return bytes;
+}
+
+struct ostream *o_stream_create_bz2(struct ostream *output, int level)
+{
+	struct bzlib_ostream *zstream;
+	int ret;
+
+	i_assert(level >= 1 && level <= 9);
+
+	zstream = i_new(struct bzlib_ostream, 1);
+	zstream->ostream.sendv = o_stream_bzlib_sendv;
+	zstream->ostream.flush = o_stream_bzlib_flush;
+	zstream->ostream.get_buffer_used_size =
+		o_stream_bzlib_get_buffer_used_size;
+	zstream->ostream.get_buffer_avail_size =
+		o_stream_bzlib_get_buffer_avail_size;
+	zstream->ostream.iostream.close = o_stream_bzlib_close;
+
+	ret = BZ2_bzCompressInit(&zstream->zs, level, 0, 0);
+	switch (ret) {
+	case BZ_OK:
+		break;
+	case BZ_MEM_ERROR:
+		i_fatal_status(FATAL_OUTOFMEM,
+			       "bzlib: Out of memory");
+	case BZ_CONFIG_ERROR:
+		i_fatal("Wrong bzlib library version (broken compilation)");
+	case BZ_PARAM_ERROR:
+		i_fatal("bzlib: Invalid parameters");
+	default:
+		i_fatal("BZ2_bzCompressInit() failed with %d", ret);
+	}
+
+	zstream->zs.next_out = zstream->outbuf;
+	zstream->zs.avail_out = sizeof(zstream->outbuf);
+	return o_stream_create(&zstream->ostream, output,
+			       o_stream_get_fd(output));
+}
+#endif
diff --git a/src/lib-compression/ostream-lz4.c b/src/lib-compression/ostream-lz4.c
new file mode 100644
index 0000000..360f475
--- /dev/null
+++ b/src/lib-compression/ostream-lz4.c
@@ -0,0 +1,249 @@
+/* Copyright (c) 2013-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+
+#ifdef HAVE_LZ4
+
+#include "ostream-private.h"
+#include "ostream-zlib.h"
+#include "iostream-lz4.h"
+#include <lz4.h>
+
+#define CHUNK_SIZE OSTREAM_LZ4_CHUNK_SIZE
+
+struct lz4_ostream {
+	struct ostream_private ostream;
+
+	unsigned char compressbuf[CHUNK_SIZE];
+	unsigned int compressbuf_offset;
+
+	/* chunk size, followed by compressed data */
+	unsigned char outbuf[IOSTREAM_LZ4_CHUNK_PREFIX_LEN +
+	                     LZ4_COMPRESSBOUND(CHUNK_SIZE)];
+	unsigned int outbuf_offset, outbuf_used;
+};
+
+/* There is no actual compression level in LZ4, so for legacy
+   reasons we allow 1-9 to avoid breaking anyone's config. */
+int compression_get_min_level_lz4(void)
+{
+	return 1;
+}
+
+int compression_get_default_level_lz4(void)
+{
+	return 1;
+}
+
+int compression_get_max_level_lz4(void)
+{
+	return 9;
+}
+
+static void o_stream_lz4_close(struct iostream_private *stream,
+			       bool close_parent)
+{
+	struct lz4_ostream *zstream = (struct lz4_ostream *)stream;
+
+	if (close_parent)
+		o_stream_close(zstream->ostream.parent);
+}
+
+static int o_stream_lz4_send_outbuf(struct lz4_ostream *zstream)
+{
+	ssize_t ret;
+	size_t size;
+
+	if (zstream->outbuf_used == 0)
+		return 1;
+
+	size = zstream->outbuf_used - zstream->outbuf_offset;
+	i_assert(size > 0);
+	ret = o_stream_send(zstream->ostream.parent,
+			    zstream->outbuf + zstream->outbuf_offset, size);
+	if (ret < 0) {
+		o_stream_copy_error_from_parent(&zstream->ostream);
+		return -1;
+	}
+	if ((size_t)ret != size) {
+		zstream->outbuf_offset += ret;
+		return 0;
+	}
+	zstream->outbuf_offset = 0;
+	zstream->outbuf_used = 0;
+	return 1;
+}
+
+static int o_stream_lz4_compress(struct lz4_ostream *zstream)
+{
+	uint32_t chunk_size;
+	int ret;
+
+	if (zstream->compressbuf_offset == 0)
+		return 1;
+	if ((ret = o_stream_lz4_send_outbuf(zstream)) <= 0)
+		return ret;
+
+	i_assert(zstream->outbuf_offset == 0);
+	i_assert(zstream->outbuf_used == 0);
+
+#if defined(HAVE_LZ4_COMPRESS_DEFAULT)
+	int max_dest_size = LZ4_compressBound(zstream->compressbuf_offset);
+	i_assert(max_dest_size >= 0);
+	if (max_dest_size == 0) {
+		io_stream_set_error(&zstream->ostream.iostream,
+			"lz4-compress: input size %u too large (> %u)",
+			zstream->compressbuf_offset, LZ4_MAX_INPUT_SIZE);
+		zstream->ostream.ostream.stream_errno = EINVAL;
+		return -1;
+	}
+	ret = LZ4_compress_default((void *)zstream->compressbuf,
+				   (void *)(zstream->outbuf +
+				            IOSTREAM_LZ4_CHUNK_PREFIX_LEN),
+				   zstream->compressbuf_offset,
+				   max_dest_size);
+#else
+	ret = LZ4_compress((void *)zstream->compressbuf,
+			   (void *)(zstream->outbuf +
+			            IOSTREAM_LZ4_CHUNK_PREFIX_LEN),
+			   zstream->compressbuf_offset);
+#endif /* defined(HAVE_LZ4_COMPRESS_DEFAULT) */
+	i_assert(ret > 0 && (unsigned int)ret <= sizeof(zstream->outbuf) -
+	         IOSTREAM_LZ4_CHUNK_PREFIX_LEN);
+	zstream->outbuf_used = IOSTREAM_LZ4_CHUNK_PREFIX_LEN + ret;
+	chunk_size = zstream->outbuf_used - IOSTREAM_LZ4_CHUNK_PREFIX_LEN;
+	zstream->outbuf[0] = (chunk_size & 0xff000000) >> 24;
+	zstream->outbuf[1] = (chunk_size & 0x00ff0000) >> 16;
+	zstream->outbuf[2] = (chunk_size & 0x0000ff00) >> 8;
+	zstream->outbuf[3] = (chunk_size & 0x000000ff);
+	zstream->compressbuf_offset = 0;
+	return 1;
+}
+
+static ssize_t
+o_stream_lz4_send_chunk(struct lz4_ostream *zstream,
+			const void *data, size_t size)
+{
+	size_t max_size;
+	ssize_t added_bytes = 0;
+	int ret;
+
+	i_assert(zstream->outbuf_used == 0);
+
+	do {
+		max_size = I_MIN(size, sizeof(zstream->compressbuf) -
+				 zstream->compressbuf_offset);
+		memcpy(zstream->compressbuf + zstream->compressbuf_offset,
+		       data, max_size);
+		zstream->compressbuf_offset += max_size;
+
+		data = CONST_PTR_OFFSET(data, max_size);
+		size -= max_size;
+		added_bytes += max_size;
+
+		if (zstream->compressbuf_offset == sizeof(zstream->compressbuf)) {
+			ret = o_stream_lz4_compress(zstream);
+			if (ret <= 0)
+				return added_bytes != 0 ? added_bytes : ret;
+		}
+	} while (size > 0);
+
+	return added_bytes;
+}
+
+static int o_stream_lz4_flush(struct ostream_private *stream)
+{
+	struct lz4_ostream *zstream = (struct lz4_ostream *)stream;
+
+	if (o_stream_lz4_compress(zstream) < 0)
+		return -1;
+	if (o_stream_lz4_send_outbuf(zstream) < 0)
+		return -1;
+
+	return o_stream_flush_parent(stream);
+}
+
+static size_t
+o_stream_lz4_get_buffer_used_size(const struct ostream_private *stream)
+{
+	const struct lz4_ostream *zstream =
+		(const struct lz4_ostream *)stream;
+
+	/* outbuf has already compressed data that we're trying to send to the
+	   parent stream. compressbuf isn't included in the return value,
+	   because it needs to be filled up or flushed. */
+	return (zstream->outbuf_used - zstream->outbuf_offset) +
+		o_stream_get_buffer_used_size(stream->parent);
+}
+
+static size_t
+o_stream_lz4_get_buffer_avail_size(const struct ostream_private *stream)
+{
+	const struct lz4_ostream *zstream =
+		(const struct lz4_ostream *)stream;
+
+	/* We're only guaranteed to accept data to compressbuf. The parent
+	   stream might have space, but since compressed data gets written
+	   there it's not really known how much we can actually write there. */
+	return sizeof(zstream->compressbuf) - zstream->compressbuf_offset;
+}
+
+static ssize_t
+o_stream_lz4_sendv(struct ostream_private *stream,
+		    const struct const_iovec *iov, unsigned int iov_count)
+{
+	struct lz4_ostream *zstream = (struct lz4_ostream *)stream;
+	ssize_t ret, bytes = 0;
+	unsigned int i;
+
+	if ((ret = o_stream_lz4_send_outbuf(zstream)) <= 0) {
+		/* error / we still couldn't flush existing data to
+		   parent stream. */
+		return ret;
+	}
+
+	for (i = 0; i < iov_count; i++) {
+		ret = o_stream_lz4_send_chunk(zstream, iov[i].iov_base,
+					      iov[i].iov_len);
+		if (ret < 0)
+			return -1;
+		bytes += ret;
+		if ((size_t)ret != iov[i].iov_len)
+			break;
+	}
+	stream->ostream.offset += bytes;
+	return bytes;
+}
+
+struct ostream *o_stream_create_lz4(struct ostream *output, int level)
+{
+	struct iostream_lz4_header *hdr;
+	struct lz4_ostream *zstream;
+
+	i_assert(level >= 1 && level <= 9);
+
+	zstream = i_new(struct lz4_ostream, 1);
+	zstream->ostream.sendv = o_stream_lz4_sendv;
+	zstream->ostream.flush = o_stream_lz4_flush;
+	zstream->ostream.get_buffer_used_size =
+		o_stream_lz4_get_buffer_used_size;
+	zstream->ostream.get_buffer_avail_size =
+		o_stream_lz4_get_buffer_avail_size;
+	zstream->ostream.iostream.close = o_stream_lz4_close;
+
+	i_assert(sizeof(zstream->outbuf) >= sizeof(*hdr));
+	hdr = (void *)zstream->outbuf;
+	memcpy(hdr->magic, IOSTREAM_LZ4_MAGIC, sizeof(hdr->magic));
+	hdr->max_uncompressed_chunk_size[0] =
+		(OSTREAM_LZ4_CHUNK_SIZE & 0xff000000) >> 24;
+	hdr->max_uncompressed_chunk_size[1] =
+		(OSTREAM_LZ4_CHUNK_SIZE & 0x00ff0000) >> 16;
+	hdr->max_uncompressed_chunk_size[2] =
+		(OSTREAM_LZ4_CHUNK_SIZE & 0x0000ff00) >> 8;
+	hdr->max_uncompressed_chunk_size[3] =
+		(OSTREAM_LZ4_CHUNK_SIZE & 0x000000ff);
+	zstream->outbuf_used = sizeof(*hdr);
+	return o_stream_create(&zstream->ostream, output,
+			       o_stream_get_fd(output));
+}
+#endif
diff --git a/src/lib-compression/ostream-zlib.c b/src/lib-compression/ostream-zlib.c
new file mode 100644
index 0000000..7267917
--- /dev/null
+++ b/src/lib-compression/ostream-zlib.c
@@ -0,0 +1,392 @@
+/* Copyright (c) 2010-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+
+#ifdef HAVE_ZLIB
+
+#include "crc32.h"
+#include "ostream-private.h"
+#include "ostream-zlib.h"
+#include <zlib.h>
+
+#define CHUNK_SIZE (1024*32)
+#define ZLIB_OS_CODE 0x03  /* Unix */
+
+struct zlib_ostream {
+	struct ostream_private ostream;
+	z_stream zs;
+
+	unsigned char gz_header[10];
+	unsigned char outbuf[CHUNK_SIZE];
+	unsigned int outbuf_offset, outbuf_used;
+	unsigned int header_bytes_left;
+
+	uint32_t crc, bytes32;
+
+	bool gz:1;
+	bool flushed:1;
+};
+
+int compression_get_min_level_gz(void)
+{
+	return Z_NO_COMPRESSION;
+}
+
+int compression_get_default_level_gz(void)
+{
+	return Z_DEFAULT_COMPRESSION;
+}
+
+int compression_get_max_level_gz(void)
+{
+	return Z_BEST_COMPRESSION;
+}
+
+static void o_stream_zlib_close(struct iostream_private *stream,
+				bool close_parent)
+{
+	struct zlib_ostream *zstream = (struct zlib_ostream *)stream;
+
+	i_assert(zstream->ostream.finished ||
+		 zstream->ostream.ostream.stream_errno != 0 ||
+		 zstream->ostream.error_handling_disabled);
+	(void)deflateEnd(&zstream->zs);
+	if (close_parent)
+		o_stream_close(zstream->ostream.parent);
+}
+
+static int o_stream_zlib_send_gz_header(struct zlib_ostream *zstream)
+{
+	size_t header_send_offset =
+		sizeof(zstream->gz_header) - zstream->header_bytes_left;
+	ssize_t ret;
+
+	i_assert(zstream->header_bytes_left <= sizeof(zstream->gz_header));
+	ret = o_stream_send(zstream->ostream.parent,
+			    zstream->gz_header + header_send_offset,
+			    zstream->header_bytes_left);
+	if (ret < 0) {
+		o_stream_copy_error_from_parent(&zstream->ostream);
+		return -1;
+	}
+	i_assert((size_t)ret <= zstream->header_bytes_left);
+	zstream->header_bytes_left -= ret;
+	return zstream->header_bytes_left == 0 ? 1 : 0;
+}
+
+static int o_stream_zlib_lsb_uint32(struct ostream *output, uint32_t num)
+{
+	unsigned char buf[sizeof(uint32_t)];
+	unsigned int i;
+
+	for (i = 0; i < sizeof(buf); i++) {
+		buf[i] = num & 0xff;
+		num >>= 8;
+	}
+	if (o_stream_send(output, buf, sizeof(buf)) != sizeof(buf))
+		return -1;
+	return 0;
+}
+
+static int o_stream_zlib_send_gz_trailer(struct zlib_ostream *zstream)
+{
+	struct ostream *output = zstream->ostream.parent;
+
+	if (!zstream->gz)
+		return 0;
+
+	if (o_stream_zlib_lsb_uint32(output, zstream->crc) < 0 ||
+	    o_stream_zlib_lsb_uint32(output, zstream->bytes32) < 0) {
+		o_stream_copy_error_from_parent(&zstream->ostream);
+		return -1;
+	}
+	return 0;
+}
+
+static int o_stream_zlib_send_outbuf(struct zlib_ostream *zstream)
+{
+	ssize_t ret;
+	size_t size;
+
+	if (zstream->outbuf_used == 0)
+		return 1;
+
+	size = zstream->outbuf_used - zstream->outbuf_offset;
+	i_assert(size > 0);
+	ret = o_stream_send(zstream->ostream.parent,
+			    zstream->outbuf + zstream->outbuf_offset, size);
+	if (ret < 0) {
+		o_stream_copy_error_from_parent(&zstream->ostream);
+		return -1;
+	}
+	if ((size_t)ret != size) {
+		zstream->outbuf_offset += ret;
+		return 0;
+	}
+	zstream->outbuf_offset = 0;
+	zstream->outbuf_used = 0;
+	return 1;
+}
+
+static ssize_t
+o_stream_zlib_send_chunk(struct zlib_ostream *zstream,
+			 const void *data, size_t size)
+{
+	z_stream *zs = &zstream->zs;
+	int ret, flush;
+
+	i_assert(zstream->outbuf_used == 0);
+
+	flush = zstream->ostream.corked || zstream->gz ?
+		Z_NO_FLUSH : Z_SYNC_FLUSH;
+
+	if (zstream->header_bytes_left > 0) {
+		if ((ret = o_stream_zlib_send_gz_header(zstream)) <= 0)
+			return ret;
+	}
+
+	zs->next_in = (void *)data;
+	zs->avail_in = size;
+	while (zs->avail_in > 0) {
+		if (zs->avail_out == 0) {
+			/* previous block was compressed. send it and start
+			   compression for a new block. */
+			zs->next_out = zstream->outbuf;
+			zs->avail_out = sizeof(zstream->outbuf);
+
+			zstream->outbuf_used = sizeof(zstream->outbuf);
+			if ((ret = o_stream_zlib_send_outbuf(zstream)) < 0)
+				return -1;
+			if (ret == 0) {
+				/* parent stream's buffer full */
+				break;
+			}
+		}
+
+		ret = deflate(zs, flush);
+		switch (ret) {
+		case Z_OK:
+		case Z_BUF_ERROR:
+			break;
+		case Z_MEM_ERROR:
+			i_fatal_status(FATAL_OUTOFMEM, "zlib: Out of memory");
+		case Z_STREAM_ERROR:
+			i_assert(zstream->gz);
+			i_panic("zlib.write(%s) failed: Can't write more data to .gz after flushing",
+				o_stream_get_name(&zstream->ostream.ostream));
+		default:
+			i_panic("zlib.write(%s) failed with unexpected code %d",
+				o_stream_get_name(&zstream->ostream.ostream), ret);
+		}
+	}
+	size -= zs->avail_in;
+
+	zstream->crc = crc32_data_more(zstream->crc, data, size);
+	zstream->bytes32 += size;
+	zstream->flushed = FALSE;
+	return size;
+}
+
+static int
+o_stream_zlib_send_flush(struct zlib_ostream *zstream, bool final)
+{
+	z_stream *zs = &zstream->zs;
+	size_t len;
+	bool done = FALSE;
+	int ret, flush;
+
+	i_assert(zs->avail_in == 0);
+
+	if (zstream->flushed) {
+		i_assert(zstream->outbuf_used == 0);
+		return 1;
+	}
+
+	if ((ret = o_stream_flush_parent_if_needed(&zstream->ostream)) <= 0)
+		return ret;
+	if (zstream->header_bytes_left > 0) {
+		if ((ret = o_stream_zlib_send_gz_header(zstream)) <= 0)
+			return ret;
+	}
+
+	if ((ret = o_stream_zlib_send_outbuf(zstream)) <= 0)
+		return ret;
+
+	flush = final ? Z_FINISH :
+		(!zstream->gz ? Z_SYNC_FLUSH : Z_NO_FLUSH);
+
+	i_assert(zstream->outbuf_used == 0);
+	do {
+		len = sizeof(zstream->outbuf) - zs->avail_out;
+		if (len != 0) {
+			zs->next_out = zstream->outbuf;
+			zs->avail_out = sizeof(zstream->outbuf);
+
+			zstream->outbuf_used = len;
+			if ((ret = o_stream_zlib_send_outbuf(zstream)) <= 0)
+				return ret;
+			if (done)
+				break;
+		}
+
+		switch (deflate(zs, flush)) {
+		case Z_OK:
+		case Z_BUF_ERROR:
+			break;
+		case Z_STREAM_END:
+			done = TRUE;
+			break;
+		case Z_MEM_ERROR:
+			i_fatal_status(FATAL_OUTOFMEM, "zlib: Out of memory");
+		default:
+			i_unreached();
+		}
+	} while (zs->avail_out != sizeof(zstream->outbuf));
+
+	if (final) {
+		if (o_stream_zlib_send_gz_trailer(zstream) < 0)
+			return -1;
+	}
+	if (final)
+		zstream->flushed = TRUE;
+	i_assert(zstream->outbuf_used == 0);
+	return 1;
+}
+
+static int o_stream_zlib_flush(struct ostream_private *stream)
+{
+	struct zlib_ostream *zstream = (struct zlib_ostream *)stream;
+	int ret;
+	if ((ret = o_stream_zlib_send_flush(zstream, stream->finished)) < 0)
+		return -1;
+	else if (ret > 0)
+		return o_stream_flush_parent(stream);
+	return ret;
+}
+
+static size_t
+o_stream_zlib_get_buffer_used_size(const struct ostream_private *stream)
+{
+	const struct zlib_ostream *zstream =
+		(const struct zlib_ostream *)stream;
+
+	/* outbuf has already compressed data that we're trying to send to the
+	   parent stream. We're not including zlib's internal compression
+	   buffer size. */
+	return (zstream->outbuf_used - zstream->outbuf_offset) +
+		o_stream_get_buffer_used_size(stream->parent);
+}
+
+static size_t
+o_stream_zlib_get_buffer_avail_size(const struct ostream_private *stream)
+{
+	/* FIXME: not correct - this is counting compressed size, which may be
+	   too larger than uncompressed size in some situations. Fixing would
+	   require some kind of additional buffering. */
+	return o_stream_get_buffer_avail_size(stream->parent);
+}
+
+static ssize_t
+o_stream_zlib_sendv(struct ostream_private *stream,
+		    const struct const_iovec *iov, unsigned int iov_count)
+{
+	struct zlib_ostream *zstream = (struct zlib_ostream *)stream;
+	ssize_t ret, bytes = 0;
+	unsigned int i;
+
+	if ((ret = o_stream_zlib_send_outbuf(zstream)) <= 0) {
+		/* error / we still couldn't flush existing data to
+		   parent stream. */
+		return ret;
+	}
+
+	for (i = 0; i < iov_count; i++) {
+		ret = o_stream_zlib_send_chunk(zstream, iov[i].iov_base,
+					       iov[i].iov_len);
+		if (ret < 0)
+			return -1;
+		bytes += ret;
+		if ((size_t)ret != iov[i].iov_len)
+			break;
+	}
+	stream->ostream.offset += bytes;
+
+	if (!zstream->ostream.corked && i == iov_count) {
+		if (o_stream_zlib_send_flush(zstream, FALSE) < 0)
+			return -1;
+	}
+	/* avail_in!=0 check is used to detect errors. if it's non-zero here
+	   it simply means we didn't send all the data */
+	zstream->zs.avail_in = 0;
+	return bytes;
+}
+
+static void o_stream_zlib_init_gz_header(struct zlib_ostream *zstream,
+					 int level, int strategy)
+{
+	unsigned char *hdr = zstream->gz_header;
+
+	hdr[0] = 0x1f;
+	hdr[1] = 0x8b;
+	hdr[2] = Z_DEFLATED;
+	hdr[8] = level == 9 ? 2 :
+		(strategy >= Z_HUFFMAN_ONLY ||
+		 (level != Z_DEFAULT_COMPRESSION && level < 2) ? 4 : 0);
+	hdr[9] = ZLIB_OS_CODE;
+	i_assert(sizeof(zstream->gz_header) == 10);
+}
+
+static struct ostream *
+o_stream_create_zlib(struct ostream *output, int level, bool gz)
+{
+	const int strategy = Z_DEFAULT_STRATEGY;
+	struct zlib_ostream *zstream;
+	int ret;
+
+	/* accepted range is 0..9 and -1 is default compression */
+	i_assert(level >= -1 && level <= 9);
+
+	zstream = i_new(struct zlib_ostream, 1);
+	zstream->ostream.sendv = o_stream_zlib_sendv;
+	zstream->ostream.flush = o_stream_zlib_flush;
+	zstream->ostream.get_buffer_used_size =
+		o_stream_zlib_get_buffer_used_size;
+	zstream->ostream.get_buffer_avail_size =
+		o_stream_zlib_get_buffer_avail_size;
+	zstream->ostream.iostream.close = o_stream_zlib_close;
+	zstream->crc = 0;
+	zstream->gz = gz;
+	if (gz)
+		zstream->header_bytes_left = sizeof(zstream->gz_header);
+
+	o_stream_zlib_init_gz_header(zstream, level, strategy);
+	ret = deflateInit2(&zstream->zs, level, Z_DEFLATED, -15, 8, strategy);
+	switch (ret) {
+	case Z_OK:
+		break;
+	case Z_MEM_ERROR:
+		i_fatal_status(FATAL_OUTOFMEM, "deflateInit(): Out of memory");
+	case Z_VERSION_ERROR:
+		i_fatal("Wrong zlib library version (broken compilation)");
+	case Z_STREAM_ERROR:
+		i_fatal("Invalid compression level %d", level);
+	default:
+		i_fatal("deflateInit() failed with %d", ret);
+	}
+
+	zstream->zs.next_out = zstream->outbuf;
+	zstream->zs.avail_out = sizeof(zstream->outbuf);
+	return o_stream_create(&zstream->ostream, output,
+			       o_stream_get_fd(output));
+}
+
+struct ostream *o_stream_create_gz(struct ostream *output, int level)
+{
+	return o_stream_create_zlib(output, level, TRUE);
+}
+
+struct ostream *o_stream_create_deflate(struct ostream *output, int level)
+{
+	return o_stream_create_zlib(output, level, FALSE);
+}
+#endif
diff --git a/src/lib-compression/ostream-zlib.h b/src/lib-compression/ostream-zlib.h
new file mode 100644
index 0000000..ac038b5
--- /dev/null
+++ b/src/lib-compression/ostream-zlib.h
@@ -0,0 +1,26 @@
+#ifndef OSTREAM_ZLIB_H
+#define OSTREAM_ZLIB_H
+
+struct ostream *o_stream_create_gz(struct ostream *output, int level);
+struct ostream *o_stream_create_deflate(struct ostream *output, int level);
+struct ostream *o_stream_create_bz2(struct ostream *output, int level);
+struct ostream *o_stream_create_lz4(struct ostream *output, int level);
+struct ostream *o_stream_create_zstd(struct ostream *output, int level);
+
+int compression_get_min_level_gz(void);
+int compression_get_default_level_gz(void);
+int compression_get_max_level_gz(void);
+
+int compression_get_min_level_bz2(void);
+int compression_get_default_level_bz2(void);
+int compression_get_max_level_bz2(void);
+
+int compression_get_min_level_lz4(void);
+int compression_get_default_level_lz4(void);
+int compression_get_max_level_lz4(void);
+
+int compression_get_min_level_zstd(void);
+int compression_get_default_level_zstd(void);
+int compression_get_max_level_zstd(void);
+
+#endif
diff --git a/src/lib-compression/ostream-zstd.c b/src/lib-compression/ostream-zstd.c
new file mode 100644
index 0000000..e40380b
--- /dev/null
+++ b/src/lib-compression/ostream-zstd.c
@@ -0,0 +1,243 @@
+/* Copyright (c) 2020 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+
+#ifdef HAVE_ZSTD
+
+#include "ostream.h"
+#include "ostream-private.h"
+#include "ostream-zlib.h"
+
+#include "zstd.h"
+#include "zstd_errors.h"
+#include "iostream-zstd-private.h"
+
+struct zstd_ostream {
+	struct ostream_private ostream;
+
+	ZSTD_CStream *cstream;
+	ZSTD_outBuffer output;
+
+	unsigned char *outbuf;
+
+	bool flushed:1;
+	bool closed:1;
+	bool finished:1;
+};
+
+int compression_get_min_level_zstd(void)
+{
+#if HAVE_DECL_ZSTD_MINCLEVEL == 1
+	return ZSTD_minCLevel();
+#else
+	return 1;
+#endif
+}
+
+int compression_get_default_level_zstd(void)
+{
+#ifdef ZSTD_CLEVEL_DEFAULT
+	return ZSTD_CLEVEL_DEFAULT;
+#else
+	/* Documentation says 3 is default */
+	return 3;
+#endif
+}
+
+int compression_get_max_level_zstd(void)
+{
+	return ZSTD_maxCLevel();
+}
+
+static void o_stream_zstd_write_error(struct zstd_ostream *zstream, size_t err)
+{
+	ZSTD_ErrorCode errcode = zstd_version_errcode(ZSTD_getErrorCode(err));
+	const char *error = ZSTD_getErrorName(err);
+	if (errcode == ZSTD_error_memory_allocation)
+		i_fatal_status(FATAL_OUTOFMEM, "zstd.write(%s): Out of memory",
+			       o_stream_get_name(&zstream->ostream.ostream));
+	else if (errcode == ZSTD_error_prefix_unknown ||
+#if HAVE_DECL_ZSTD_ERROR_PARAMETER_UNSUPPORTED == 1
+		 errcode == ZSTD_error_parameter_unsupported ||
+#endif
+		 errcode == ZSTD_error_dictionary_wrong ||
+		 errcode == ZSTD_error_init_missing)
+		zstream->ostream.ostream.stream_errno = EINVAL;
+	else
+		zstream->ostream.ostream.stream_errno = EIO;
+
+	io_stream_set_error(&zstream->ostream.iostream,
+			    "zstd.write(%s): %s at %"PRIuUOFF_T,
+			    o_stream_get_name(&zstream->ostream.ostream), error,
+			    zstream->ostream.ostream.offset);
+}
+
+static ssize_t o_stream_zstd_send_outbuf(struct zstd_ostream *zstream)
+{
+	ssize_t ret;
+	/* nothing to send */
+	if (zstream->output.pos == 0)
+		return 1;
+	ret = o_stream_send(zstream->ostream.parent, zstream->output.dst,
+			    zstream->output.pos);
+	if (ret < 0) {
+		o_stream_copy_error_from_parent(&zstream->ostream);
+		return -1;
+	} else {
+		memmove(zstream->outbuf, zstream->outbuf+ret, zstream->output.pos-ret);
+		zstream->output.pos -= ret;
+	}
+	if (zstream->output.pos > 0)
+		return 0;
+	return 1;
+}
+
+static ssize_t
+o_stream_zstd_sendv(struct ostream_private *stream,
+		    const struct const_iovec *iov, unsigned int iov_count)
+{
+	struct zstd_ostream *zstream =
+		container_of(stream, struct zstd_ostream, ostream);
+	ssize_t total = 0;
+	size_t ret;
+
+	for (unsigned int i = 0; i < iov_count; i++) {
+		/* does it actually fit there */
+		ZSTD_inBuffer input = {
+			.src = iov[i].iov_base,
+			.pos = 0,
+			.size = iov[i].iov_len
+		};
+		bool flush_attempted = FALSE;
+		for (;;) {
+			size_t prev_pos = input.pos;
+			ret = ZSTD_compressStream(zstream->cstream, &zstream->output,
+						  &input);
+			if (ZSTD_isError(ret) != 0) {
+				o_stream_zstd_write_error(zstream, ret);
+				return -1;
+			}
+			size_t new_input_size = input.pos - prev_pos;
+			if (new_input_size == 0 && flush_attempted) {
+				/* non-blocking output buffer full */
+				return total;
+			}
+			stream->ostream.offset += new_input_size;
+			total += new_input_size;
+			if (input.pos == input.size)
+				break;
+			/* output buffer full. try to flush it. */
+			if (o_stream_zstd_send_outbuf(zstream) < 0)
+				return -1;
+			flush_attempted = TRUE;
+		}
+	}
+	if (o_stream_zstd_send_outbuf(zstream) < 0)
+		return -1;
+	return total;
+}
+
+static int o_stream_zstd_send_flush(struct zstd_ostream *zstream, bool final)
+{
+	int ret;
+
+	if (zstream->flushed) {
+		i_assert(zstream->output.pos == 0);
+		return 1;
+	}
+
+	if ((ret = o_stream_flush_parent_if_needed(&zstream->ostream)) <= 0)
+		return ret;
+
+	if (zstream->output.pos == 0)
+		ZSTD_flushStream(zstream->cstream, &zstream->output);
+
+	if ((ret = o_stream_zstd_send_outbuf(zstream)) <= 0)
+		return ret;
+
+	if (!final)
+		return 1;
+
+	if (!zstream->finished) {
+		ret = ZSTD_endStream(zstream->cstream, &zstream->output);
+		if (ZSTD_isError(ret) != 0) {
+			o_stream_zstd_write_error(zstream, ret);
+			return -1;
+		}
+		zstream->finished = TRUE;
+	}
+
+	if ((ret = o_stream_zstd_send_outbuf(zstream)) <= 0)
+		return ret;
+
+	if (final)
+		zstream->flushed = TRUE;
+	i_assert(zstream->output.pos == 0);
+	return 1;
+}
+
+static int o_stream_zstd_flush(struct ostream_private *stream)
+{
+	struct zstd_ostream *zstream =
+		container_of(stream, struct zstd_ostream, ostream);
+
+	int ret;
+	if ((ret = o_stream_zstd_send_flush(zstream, stream->finished)) < 0)
+		return -1;
+	else if (ret > 0)
+		return o_stream_flush_parent(stream);
+	return ret;
+}
+
+static void o_stream_zstd_close(struct iostream_private *stream,
+				bool close_parent)
+{
+	struct ostream_private *_ostream =
+		container_of(stream, struct ostream_private, iostream);
+	struct zstd_ostream *zstream =
+		container_of(_ostream, struct zstd_ostream, ostream);
+
+	i_assert(zstream->ostream.finished ||
+		 zstream->ostream.ostream.stream_errno != 0 ||
+		 zstream->ostream.error_handling_disabled);
+	if (zstream->cstream != NULL) {
+		ZSTD_freeCStream(zstream->cstream);
+		zstream->cstream = NULL;
+	}
+	i_free(zstream->outbuf);
+	i_zero(&zstream->output);
+	if (close_parent)
+		o_stream_close(zstream->ostream.parent);
+}
+
+struct ostream *
+o_stream_create_zstd(struct ostream *output, int level)
+{
+	struct zstd_ostream *zstream;
+	size_t ret;
+
+	i_assert(level >= compression_get_min_level_zstd() &&
+		 level <= compression_get_max_level_zstd());
+
+	zstd_version_check();
+
+	zstream = i_new(struct zstd_ostream, 1);
+	zstream->ostream.sendv = o_stream_zstd_sendv;
+	zstream->ostream.flush = o_stream_zstd_flush;
+	zstream->ostream.iostream.close = o_stream_zstd_close;
+	zstream->cstream = ZSTD_createCStream();
+	if (zstream->cstream == NULL)
+		i_fatal_status(FATAL_OUTOFMEM, "zstd: Out of memory");
+	ret = ZSTD_initCStream(zstream->cstream, level);
+	if (ZSTD_isError(ret) != 0)
+		o_stream_zstd_write_error(zstream, ret);
+	else {
+		zstream->outbuf = i_malloc(ZSTD_CStreamOutSize());
+		zstream->output.dst = zstream->outbuf;
+		zstream->output.size = ZSTD_CStreamOutSize();
+	}
+	return o_stream_create(&zstream->ostream, output,
+			       o_stream_get_fd(output));
+}
+
+#endif
diff --git a/src/lib-compression/test-compression.c b/src/lib-compression/test-compression.c
new file mode 100644
index 0000000..f690c7b
--- /dev/null
+++ b/src/lib-compression/test-compression.c
@@ -0,0 +1,1122 @@
+/* Copyright (c) 2014-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "buffer.h"
+#include "istream.h"
+#include "iostream-temp.h"
+#include "ostream.h"
+#include "sha1.h"
+#include "randgen.h"
+#include "test-common.h"
+#include "compression.h"
+#include "iostream-lz4.h"
+
+#include "hex-binary.h"
+
+#include <unistd.h>
+#include <fcntl.h>
+
+static void test_compression_handler_detect(const struct compression_handler *handler)
+{
+	const unsigned char test_data[] = {'h','e','l','l','o',' ',
+					   'w','o','r','l','d','\n'};
+	const unsigned char *data;
+	size_t size;
+	buffer_t *buffer;
+	struct ostream *test_output;
+	struct ostream *output;
+
+	struct istream *test_input;
+	struct istream *input;
+
+	/* write some amount of data */
+	test_begin(t_strdup_printf("compression handler %s (detect)", handler->name));
+
+	buffer = buffer_create_dynamic(default_pool, 1024);
+
+	test_output = test_ostream_create(buffer);
+	output = handler->create_ostream(test_output, 1);
+	o_stream_unref(&test_output);
+
+	/* write data at once */
+	test_assert(o_stream_send(output, test_data, sizeof(test_data)) == sizeof(test_data));
+	test_assert(o_stream_finish(output) == 1);
+	o_stream_unref(&output);
+
+	test_input = test_istream_create_data(buffer->data, buffer->used);
+	handler = compression_detect_handler(test_input);
+	i_stream_seek(test_input, 0);
+	test_assert(handler != NULL);
+	if (handler != NULL) {
+		input = handler->create_istream(test_input);
+		i_stream_unref(&test_input);
+
+		test_assert(i_stream_read_more(input, &data, &size) > 0);
+		test_assert(size == sizeof(test_data) &&
+			    memcmp(data, test_data, size) == 0);
+
+		i_stream_unref(&input);
+	} else {
+		i_stream_unref(&test_input);
+	}
+
+	buffer_free(&buffer);
+	test_end();
+}
+
+static void
+test_compression_handler_short(const struct compression_handler *handler,
+			       bool autodetect)
+{
+	const unsigned char *data;
+	size_t len, size;
+	buffer_t *test_data;
+	buffer_t *buffer;
+	struct ostream *test_output;
+	struct ostream *output;
+
+	struct istream *test_input;
+	struct istream *input;
+
+	/* write some amount of data */
+	test_begin(t_strdup_printf("compression handler %s (small, autodetect=%s)",
+				   handler->name, autodetect ? "yes" : "no"));
+	len = i_rand_minmax(1, 1024);
+	test_data = buffer_create_dynamic(default_pool, len);
+	random_fill(buffer_append_space_unsafe(test_data, len), len);
+	buffer_set_used_size(test_data, len);
+	buffer_append(test_data, "hello. world.\n", 14);
+
+	buffer = buffer_create_dynamic(default_pool, 1024);
+	test_output = test_ostream_create(buffer);
+	output = handler->create_ostream(test_output, 1);
+	o_stream_unref(&test_output);
+
+	/* write data at once */
+	test_assert(o_stream_send(output, test_data->data, test_data->used) == (ssize_t)test_data->used);
+	test_assert(o_stream_finish(output) == 1);
+	o_stream_unref(&output);
+
+	/* read data at once */
+	test_input = test_istream_create_data(buffer->data, buffer->used);
+	input = !autodetect ? handler->create_istream(test_input) :
+		i_stream_create_decompress(test_input, 0);
+	i_stream_unref(&test_input);
+
+	test_assert(i_stream_read_more(input, &data, &size) > 0);
+	test_assert(size == test_data->used &&
+		    memcmp(data, test_data->data, size) ==0);
+
+	i_stream_unref(&input);
+
+	buffer_free(&buffer);
+	buffer_free(&test_data);
+
+	test_end();
+}
+
+static void
+test_compression_handler_empty(const struct compression_handler *handler,
+			       bool autodetect)
+{
+	buffer_t *buffer;
+	struct ostream *test_output;
+	struct ostream *output;
+
+	struct istream *test_input;
+	struct istream *input;
+
+	/* create stream and finish it without writing anything */
+	test_begin(t_strdup_printf("compression handler %s (empty, autodetect=%s)",
+				   handler->name, autodetect ? "yes" : "no"));
+	buffer = buffer_create_dynamic(default_pool, 128);
+	test_output = test_ostream_create(buffer);
+	output = handler->create_ostream(test_output, 1);
+	o_stream_unref(&test_output);
+	test_assert(o_stream_finish(output) == 1);
+	o_stream_unref(&output);
+
+	/* read the input */
+	test_input = test_istream_create_data(buffer->data, buffer->used);
+	input = !autodetect ? handler->create_istream(test_input) :
+		i_stream_create_decompress(test_input, 0);
+	i_stream_unref(&test_input);
+
+	test_assert(i_stream_read(input) == -1);
+	test_assert(i_stream_get_data_size(input) == 0);
+	i_stream_unref(&input);
+
+	buffer_free(&buffer);
+
+	test_end();
+}
+
+static void
+test_compression_handler_seek(const struct compression_handler *handler,
+			      bool autodetect)
+{
+	const unsigned char *data,*ptr;
+	size_t len, size, pos;
+	buffer_t *test_data;
+	buffer_t *buffer;
+	struct ostream *test_output;
+	struct ostream *output;
+
+	struct istream *test_input;
+	struct istream *input;
+
+	/* write some amount of data */
+	test_begin(t_strdup_printf("compression handler %s (seek, autodetect=%s)",
+				   handler->name, autodetect ? "yes" : "no"));
+	len = i_rand_minmax(1024, 2048);
+	test_data = buffer_create_dynamic(default_pool, len);
+	random_fill(buffer_append_space_unsafe(test_data, len), len);
+	buffer_set_used_size(test_data, len);
+	buffer_append(test_data, "hello. world.\n", 14);
+
+	buffer = buffer_create_dynamic(default_pool, 1024);
+	test_output = test_ostream_create(buffer);
+	output = handler->create_ostream(test_output, 1);
+	o_stream_unref(&test_output);
+
+	/* write data at once */
+	test_assert(o_stream_send(output, test_data->data, test_data->used) == (ssize_t)test_data->used);
+	test_assert(o_stream_finish(output) == 1);
+	o_stream_unref(&output);
+
+	test_input = test_istream_create_data(buffer->data, buffer->used);
+	input = !autodetect ? handler->create_istream(test_input) :
+		i_stream_create_decompress(test_input, 0);
+	i_stream_unref(&test_input);
+
+	/* seek forward */
+	i_stream_seek(input, test_data->used - 14); /* should read 'hello. world.\n' */
+
+	test_assert(i_stream_read_more(input, &data, &size) > 0);
+	test_assert(size >= 14 && memcmp(data, "hello. world.\n", 14) == 0);
+	i_stream_skip(input, size);
+
+	ptr = test_data->data;
+
+	/* seek to random positions and see that we get correct data */
+	for (unsigned int i = 0; i < 1000; i++) {
+		pos = i_rand_limit(test_data->used);
+		i_stream_seek(input, pos);
+		size = 0;
+		test_assert_idx(i_stream_read_more(input, &data, &size) > 0, i);
+		test_assert_idx(size > 0 && memcmp(data,ptr+pos,size) == 0, i);
+	}
+
+	i_stream_unref(&input);
+
+	buffer_free(&buffer);
+	buffer_free(&test_data);
+
+	test_end();
+}
+
+static void
+test_compression_handler_reset(const struct compression_handler *handler,
+			       bool autodetect)
+{
+	const unsigned char *data;
+	size_t len, size;
+	buffer_t *test_data;
+	buffer_t *buffer;
+	struct ostream *test_output;
+	struct ostream *output;
+
+	struct istream *test_input;
+	struct istream *input;
+
+	/* write some amount of data */
+	test_begin(t_strdup_printf("compression handler %s (reset, autodetect=%s)",
+				   handler->name, autodetect ? "yes" : "no"));
+	len = i_rand_minmax(1024, 2048);
+	test_data = buffer_create_dynamic(default_pool, len);
+	random_fill(buffer_append_space_unsafe(test_data, len), len);
+	buffer_set_used_size(test_data, len);
+	buffer_append(test_data, "hello. world.\n", 14);
+
+	buffer = buffer_create_dynamic(default_pool, 1024);
+	test_output = test_ostream_create(buffer);
+	output = handler->create_ostream(test_output, 1);
+	o_stream_unref(&test_output);
+
+	/* write data at once */
+	test_assert(o_stream_send(output, test_data->data, test_data->used) == (ssize_t)test_data->used);
+	test_assert(o_stream_finish(output) == 1);
+	o_stream_unref(&output);
+
+	test_input = test_istream_create_data(buffer->data, buffer->used);
+	input = !autodetect ? handler->create_istream(test_input) :
+		i_stream_create_decompress(test_input, 0);
+	i_stream_unref(&test_input);
+
+	/* seek forward */
+	i_stream_seek(input, test_data->used - 14); /* should read 'hello. world.\n' */
+
+	test_assert(i_stream_read_more(input, &data, &size) > 0);
+	test_assert(size >= 14 && memcmp(data, "hello. world.\n", 14) == 0);
+	i_stream_skip(input, size);
+
+	/* reset */
+	i_stream_sync(input);
+
+	/* see that we still get data, at start */
+	size = 0;
+	test_assert(i_stream_read_more(input, &data, &size) > 0);
+	test_assert(size > 0 && memcmp(data, test_data->data, size) == 0);
+
+	i_stream_unref(&input);
+
+	buffer_free(&buffer);
+	buffer_free(&test_data);
+
+	test_end();
+}
+
+static void
+test_compression_handler(const struct compression_handler *handler,
+			 bool autodetect)
+{
+	const char *path = "test-compression.tmp";
+	struct istream *file_input, *input;
+	struct ostream *file_output, *output;
+	unsigned char buf[IO_BLOCK_SIZE];
+	const unsigned char *data;
+	size_t size;
+	uoff_t stream_size;
+	struct sha1_ctxt sha1;
+	unsigned char output_sha1[SHA1_RESULTLEN], input_sha1[SHA1_RESULTLEN];
+	unsigned int i;
+	int fd;
+	ssize_t ret;
+
+	test_begin(t_strdup_printf("compression handler %s (autodetect=%s)",
+				   handler->name, autodetect ? "yes" : "no"));
+
+	/* write compressed data */
+	fd = open(path, O_TRUNC | O_CREAT | O_RDWR, 0600);
+	if (fd == -1)
+		i_fatal("creat(%s) failed: %m", path);
+	file_output = o_stream_create_fd_file(fd, 0, FALSE);
+	output = handler->create_ostream(file_output, 1);
+	sha1_init(&sha1);
+
+	/* 1) write lots of easily compressible data */
+	memset(buf, 0, sizeof(buf));
+	for (i = 0; i < 1024*1024*4 / sizeof(buf); i++) {
+		sha1_loop(&sha1, buf, sizeof(buf));
+		test_assert(o_stream_send(output, buf, sizeof(buf)) == sizeof(buf));
+	}
+
+	/* 2) write uncompressible data */
+	for (i = 0; i < 1024*128 / sizeof(buf); i++) {
+		random_fill(buf, sizeof(buf));
+		sha1_loop(&sha1, buf, sizeof(buf));
+		test_assert(o_stream_send(output, buf, sizeof(buf)) == sizeof(buf));
+	}
+	/* make sure the input size isn't multiple of something simple */
+	random_fill(buf, sizeof(buf));
+	sha1_loop(&sha1, buf, sizeof(buf) - 5);
+	test_assert(o_stream_send(output, buf, sizeof(buf) - 5) == sizeof(buf) - 5);
+
+	/* 3) write semi-compressible data */
+	for (i = 0; i < sizeof(buf); i++) {
+		if (i_rand_limit(3) == 0)
+			buf[i] = i_rand_limit(4);
+		else
+			buf[i] = i & UCHAR_MAX;
+	}
+	for (i = 0; i < 1024*128 / sizeof(buf); i++) {
+		sha1_loop(&sha1, buf, sizeof(buf));
+		test_assert(o_stream_send(output, buf, sizeof(buf)) == sizeof(buf));
+	}
+
+	test_assert(o_stream_finish(output) > 0);
+	uoff_t uncompressed_size = output->offset;
+	o_stream_destroy(&output);
+	uoff_t compressed_size = file_output->offset;
+	o_stream_destroy(&file_output);
+	sha1_result(&sha1, output_sha1);
+
+	/* read and uncompress the data */
+	file_input = i_stream_create_fd(fd, IO_BLOCK_SIZE);
+	input = !autodetect ? handler->create_istream(file_input) :
+		i_stream_create_decompress(file_input, 0);
+
+	test_assert(i_stream_get_size(input, FALSE, &stream_size) == 1);
+	test_assert(stream_size == compressed_size);
+
+	test_assert(i_stream_get_size(input, TRUE, &stream_size) == 1);
+	test_assert(stream_size == uncompressed_size);
+
+	sha1_init(&sha1);
+	for (bool seeked = FALSE;;) {
+		sha1_init(&sha1);
+		while ((ret = i_stream_read_more(input, &data, &size)) > 0) {
+			sha1_loop(&sha1, data, size);
+			i_stream_skip(input, size);
+		}
+		test_assert(ret == -1);
+		test_assert(input->stream_errno == 0);
+		sha1_result(&sha1, input_sha1);
+		test_assert(memcmp(input_sha1, output_sha1, sizeof(input_sha1)) == 0);
+		if (seeked)
+			break;
+		seeked = TRUE;
+		i_stream_seek(input, 1);
+		(void)i_stream_read(input);
+		i_stream_seek(input, 0);
+	}
+	i_stream_destroy(&input);
+	i_stream_destroy(&file_input);
+
+	i_unlink(path);
+	i_close_fd(&fd);
+
+	test_end();
+}
+
+static void
+test_compression_handler_partial_parent_write(const struct compression_handler *handler,
+					      bool autodetect)
+{
+	test_begin(t_strdup_printf("compression handler %s (partial parent writes, autodetect=%s)",
+				   handler->name, autodetect ? "yes" : "no"));
+
+	int ret;
+	buffer_t *buffer = t_buffer_create(64);
+	buffer_t *compressed_data = t_buffer_create(256);
+	struct ostream *os = test_ostream_create_nonblocking(buffer, 64);
+	struct ostream *os_compressed = handler->create_ostream(os, 9);
+	o_stream_unref(&os);
+
+	unsigned char input_buffer[64];
+	/* create unlikely compressible data */
+	random_fill(input_buffer, sizeof(input_buffer));
+
+	for (unsigned int i = 0; i < 10; i++) {
+		/* write it to stream */
+		test_assert_idx(o_stream_send(os_compressed, input_buffer, sizeof(input_buffer)) == sizeof(input_buffer), i);
+
+		while ((ret = o_stream_flush(os_compressed)) == 0) {
+			/* flush buffer */
+			if (buffer->used > 0)
+				buffer_append(compressed_data, buffer->data, buffer->used);
+			buffer_set_used_size(buffer, 0);
+		}
+		if (buffer->used > 0)
+			buffer_append(compressed_data, buffer->data, buffer->used);
+		buffer_set_used_size(buffer, 0);
+		test_assert_idx(ret == 1, i);
+	}
+	test_assert(o_stream_finish(os_compressed) == 1);
+	o_stream_unref(&os_compressed);
+        if (buffer->used > 0)
+                buffer_append(compressed_data, buffer->data, buffer->used);
+
+	struct istream *is = test_istream_create_data(compressed_data->data, compressed_data->used);
+	struct istream *is_decompressed =
+		!autodetect ? handler->create_istream(is) :
+		i_stream_create_decompress(is, 0);
+	i_stream_unref(&is);
+
+	const unsigned char *data;
+	size_t siz;
+	buffer_t *decompressed_data = t_buffer_create(sizeof(input_buffer)*10);
+
+	while(i_stream_read_more(is_decompressed, &data, &siz) > 0) {
+		buffer_append(decompressed_data, data, siz);
+		i_stream_skip(is_decompressed, siz);
+	}
+	test_assert(decompressed_data->used == sizeof(input_buffer)*10);
+	for(siz = 0; siz < decompressed_data->used; siz+=sizeof(input_buffer)) {
+		test_assert(decompressed_data->used - siz >= sizeof(input_buffer) &&
+			   memcmp(CONST_PTR_OFFSET(decompressed_data->data, siz),
+				  input_buffer, sizeof(input_buffer)) == 0);
+	}
+
+	i_stream_unref(&is_decompressed);
+
+	test_end();
+}
+
+static void
+test_compression_handler_random_io(const struct compression_handler *handler,
+				   bool autodetect)
+{
+	unsigned char in_buf[8192];
+	size_t in_buf_size;
+	buffer_t *enc_buf, *dec_buf;
+	unsigned int i, j;
+	int ret;
+
+	enc_buf = buffer_create_dynamic(default_pool, sizeof(in_buf));
+	dec_buf = buffer_create_dynamic(default_pool, sizeof(in_buf));
+
+	test_begin(t_strdup_printf("compression handler %s (random I/O, autodetect=%s)",
+				   handler->name, autodetect ? "yes" : "no"));
+
+	for (i = 0; !test_has_failed() && i < 300; i++) {
+		struct istream *input1, *input2;
+		struct ostream *output1, *output2;
+		struct istream *top_input;
+		const unsigned char *data;
+		size_t size, in_pos, out_pos;
+
+		/* Initialize test data (semi-compressible) */
+		in_buf_size = i_rand_limit(sizeof(in_buf));
+		for (j = 0; j < in_buf_size; j++) {
+			if (i_rand_limit(3) == 0)
+				in_buf[j] = i_rand_limit(256);
+			else
+				in_buf[j] = (unsigned char)j;
+		}
+
+		/* Reset encode output buffer */
+		buffer_set_used_size(enc_buf, 0);
+
+		/* Create input stream for test data */
+		input1 = test_istream_create_data(in_buf, in_buf_size);
+		i_stream_set_name(input1, "[data]");
+
+		/* Create output stream for compressed data */
+		output1 = test_ostream_create_nonblocking(enc_buf,
+							  i_rand_minmax(1, 512));
+
+		/* Create compressor output stream */
+		output2 = handler->create_ostream(output1, i_rand_minmax(1, 6));
+
+		/* Compress the data incrementally */
+		in_pos = out_pos = 0;
+		ret = 0;
+		test_istream_set_size(input1, in_pos);
+		while (ret == 0) {
+			enum ostream_send_istream_result res;
+
+			res = o_stream_send_istream(output2, input1);
+			switch(res) {
+			case OSTREAM_SEND_ISTREAM_RESULT_ERROR_INPUT:
+			case OSTREAM_SEND_ISTREAM_RESULT_ERROR_OUTPUT:
+				ret = -1;
+				break;
+			case OSTREAM_SEND_ISTREAM_RESULT_WAIT_OUTPUT:
+				out_pos += i_rand_limit(512);
+				test_ostream_set_max_output_size(
+					output1, out_pos);
+				break;
+			case OSTREAM_SEND_ISTREAM_RESULT_WAIT_INPUT:
+				in_pos += i_rand_limit(512);
+				if (in_pos > in_buf_size)
+					in_pos = in_buf_size;
+				test_istream_set_size(input1, in_pos);
+				break;
+			case OSTREAM_SEND_ISTREAM_RESULT_FINISHED:
+				/* finish it */
+				ret = o_stream_finish(output2);
+				break;
+			}
+		}
+
+		/* Clean up */
+		i_stream_unref(&input1);
+		o_stream_unref(&output1);
+		o_stream_unref(&output2);
+
+		/* Reset decode output buffer */
+		buffer_set_used_size(dec_buf, 0);
+
+		/* Create input stream for compressed data */
+		input1 = i_stream_create_from_buffer(enc_buf);
+		i_stream_set_name(input1, "[compressed-data]");
+
+		/* Create decompressor stream */
+		input2 = !autodetect ? handler->create_istream(input1) :
+			i_stream_create_decompress(input1, 0);
+		i_stream_set_name(input2, "[decompressor]");
+
+		/* Assign random buffer sizes */
+		i_stream_set_max_buffer_size(input2, i_rand_minmax(1, 512));
+
+		/* Read the outer stream in full with random increments. */
+		top_input = input2;
+		while ((ret = i_stream_read_more(
+			top_input, &data, &size)) > 0) {
+			size_t ch = i_rand_limit(512);
+
+			size = I_MIN(size, ch);
+			buffer_append(dec_buf, data, size);
+			i_stream_skip(top_input, size);
+		}
+		if (ret < 0 && top_input->stream_errno == 0) {
+			data = i_stream_get_data(top_input, &size);
+			if (size > 0) {
+				buffer_append(dec_buf, data, size);
+				i_stream_skip(top_input, size);
+			}
+		}
+
+		/* Assert stream status */
+		test_assert_idx(ret < 0 && top_input->stream_errno == 0, i);
+		/* Assert input/output equality */
+		test_assert_idx(dec_buf->used == in_buf_size &&
+				memcmp(in_buf, dec_buf->data, in_buf_size) == 0,
+				i);
+
+		if (top_input->stream_errno != 0) {
+			i_error("%s: %s", i_stream_get_name(input1),
+			       i_stream_get_error(input1));
+			i_error("%s: %s", i_stream_get_name(input2),
+			       i_stream_get_error(input2));
+		}
+
+		if (test_has_failed()) {
+			i_info("Test parameters: size=%zu",
+				in_buf_size);
+		}
+
+		/* Clean up */
+		i_stream_unref(&input1);
+		i_stream_unref(&input2);
+	}
+	test_end();
+
+	buffer_free(&enc_buf);
+	buffer_free(&dec_buf);
+}
+
+static void
+test_compression_handler_large_random_io(const struct compression_handler *handler,
+					 bool autodetect)
+{
+#define RANDOMNESS_SIZE (1024*1024)
+	unsigned char *randomness;
+	struct istream *input, *dec_input;
+	struct ostream *temp_output, *output;
+	const unsigned char *data;
+	size_t size;
+	int ret;
+
+	test_begin(t_strdup_printf("compression handler %s (large random io, autodetect=%s)",
+				   handler->name, autodetect ? "yes" : "no"));
+	randomness = i_malloc(RANDOMNESS_SIZE);
+	random_fill(randomness, RANDOMNESS_SIZE);
+
+	/* write 1 MB of randomness to buffer */
+	input = i_stream_create_from_data(randomness, RANDOMNESS_SIZE);
+
+	temp_output = iostream_temp_create(".temp.", 0);
+	output = handler->create_ostream(temp_output, i_rand_minmax(1, 6));
+
+	switch (o_stream_send_istream(output, input)) {
+	case OSTREAM_SEND_ISTREAM_RESULT_ERROR_INPUT:
+	case OSTREAM_SEND_ISTREAM_RESULT_ERROR_OUTPUT:
+		test_assert(FALSE);
+		break;
+	case OSTREAM_SEND_ISTREAM_RESULT_WAIT_OUTPUT:
+	case OSTREAM_SEND_ISTREAM_RESULT_WAIT_INPUT:
+		i_unreached();
+	case OSTREAM_SEND_ISTREAM_RESULT_FINISHED:
+		test_assert(o_stream_finish(output) == 1);
+		break;
+	}
+	test_assert(output->offset == RANDOMNESS_SIZE);
+	test_assert(output->stream_errno == 0);
+	i_stream_unref(&input);
+
+	input = iostream_temp_finish(&temp_output, SIZE_MAX);
+	o_stream_unref(&output);
+
+	/* verify that reading the input works */
+
+	dec_input = !autodetect ? handler->create_istream(input) :
+		i_stream_create_decompress(input, 0);
+
+	while ((ret = i_stream_read_more(dec_input, &data, &size)) > 0) {
+		test_assert(memcmp(data, randomness + dec_input->v_offset, size) == 0);
+		i_stream_skip(dec_input, size);
+	}
+	test_assert(ret == -1);
+	test_assert(dec_input->v_offset == RANDOMNESS_SIZE);
+	test_assert(dec_input->stream_errno == 0);
+
+	i_stream_unref(&dec_input);
+	i_stream_unref(&input);
+	i_free(randomness);
+	test_end();
+}
+
+static void
+test_compression_handler_errors(const struct compression_handler *handler,
+				bool autodetect)
+{
+	test_begin(t_strdup_printf("compression handler %s (errors, autodetect=%s)",
+				   handler->name, autodetect ? "yes" : "no"));
+
+	/* test that zero stream reading errors out */
+	struct istream *is = test_istream_create("");
+	struct istream *input =
+		!autodetect ? handler->create_istream(is) :
+		i_stream_create_decompress(is, 0);
+	i_stream_unref(&is);
+	test_assert(i_stream_read(input) == -1 && input->eof);
+	i_stream_unref(&input);
+
+	/* test that garbage isn't considered valid */
+	is = test_istream_create("dedededededededededededededede"
+				 "dedededeededdedededededededede"
+				 "dedededededededededededededede");
+	is->blocking = TRUE;
+	input = !autodetect ? handler->create_istream(is) :
+		i_stream_create_decompress(is, 0);
+	i_stream_unref(&is);
+	test_assert(i_stream_read(input) == -1 && input->eof);
+	i_stream_unref(&input);
+
+	/* test that truncated data is not considered valid */
+	buffer_t *odata = buffer_create_dynamic(pool_datastack_create(), 65535);
+	unsigned char buf[IO_BLOCK_SIZE];
+	struct ostream *os = test_ostream_create(odata);
+	struct ostream *output = handler->create_ostream(os, 1);
+	o_stream_unref(&os);
+
+	for (unsigned int i = 0; i < 10; i++) {
+		random_fill(buf, sizeof(buf));
+		test_assert(o_stream_send(output, buf, sizeof(buf)) == sizeof(buf));
+	}
+
+	test_assert(o_stream_finish(output) == 1);
+	o_stream_unref(&output);
+
+	/* truncate buffer */
+	is = test_istream_create_data(odata->data, odata->used - sizeof(buf)*2 - 1);
+	input = !autodetect ? handler->create_istream(is) :
+		i_stream_create_decompress(is, 0);
+	i_stream_unref(&is);
+
+	const unsigned char *data ATTR_UNUSED;
+	size_t size;
+	while (i_stream_read_more(input, &data, &size) > 0)
+		i_stream_skip(input, size);
+
+	test_assert(input->stream_errno == EPIPE);
+	i_stream_unref(&input);
+
+	/* Cannot do the next check if we don't know if it's compressed. */
+	if (handler->is_compressed != NULL) {
+		/* test incrementally reading up to 32 bytes of plaintext data
+		   that should not match any handlers' header */
+		for (size_t i = 0; i < 32; i++) {
+			is = test_istream_create_data("dededededededededededededededede", i);
+			input = !autodetect ? handler->create_istream(is) :
+				i_stream_create_decompress(is, 0);
+			i_stream_unref(&is);
+			while (i_stream_read_more(input, &data, &size) >= 0) {
+				test_assert_idx(size == 0, i);
+				i_stream_skip(input, size);
+			}
+			test_assert_idx(input->stream_errno == EINVAL, i);
+			i_stream_unref(&input);
+		}
+	}
+
+	test_end();
+}
+
+static void test_compression_int(bool autodetect)
+{
+	unsigned int i;
+
+	for (i = 0; compression_handlers[i].name != NULL; i++) {
+		if (compression_handlers[i].create_istream != NULL &&
+		    compression_handlers[i].create_ostream != NULL &&
+		    (!autodetect ||
+		     compression_handlers[i].is_compressed != NULL)) T_BEGIN {
+			if (compression_handlers[i].is_compressed != NULL &&
+			    !autodetect)
+				test_compression_handler_detect(&compression_handlers[i]);
+			test_compression_handler_short(&compression_handlers[i], autodetect);
+			test_compression_handler_empty(&compression_handlers[i], autodetect);
+			test_compression_handler(&compression_handlers[i], autodetect);
+			test_compression_handler_seek(&compression_handlers[i], autodetect);
+			test_compression_handler_reset(&compression_handlers[i], autodetect);
+			test_compression_handler_partial_parent_write(&compression_handlers[i], autodetect);
+			test_compression_handler_random_io(&compression_handlers[i], autodetect);
+			test_compression_handler_large_random_io(&compression_handlers[i], autodetect);
+			test_compression_handler_errors(&compression_handlers[i], autodetect);
+		} T_END;
+	}
+}
+
+static void test_compression(void)
+{
+	test_compression_int(FALSE);
+	test_compression_int(TRUE);
+}
+
+static void test_istream_decompression_try(void)
+{
+	const char *tests[] = {
+		"",
+		"1",
+		"12",
+		"12345678901234567890123456789012345678901234567890",
+	};
+	struct istream *is, *input;
+	const unsigned char *data;
+	size_t size;
+
+	test_begin("istream-decompression try");
+
+	for (unsigned int i = 0; i < N_ELEMENTS(tests); i++) {
+		size_t test_len = strlen(tests[i]);
+		is = i_stream_create_from_data(tests[i], test_len);
+		input = i_stream_create_decompress(is, ISTREAM_DECOMPRESS_FLAG_TRY);
+		i_stream_unref(&is);
+
+		ssize_t ret = i_stream_read(input);
+		test_assert_idx((test_len == 0 && ret == -1) ||
+				(test_len > 0 && ret == (ssize_t)test_len), i);
+		data = i_stream_get_data(input, &size);
+		test_assert_idx(size == test_len &&
+				memcmp(data, tests[i], size) == 0, i);
+
+		i_stream_skip(input, size);
+		test_assert_idx(i_stream_read(input) == -1, i);
+		test_assert_idx(input->stream_errno == 0, i);
+		i_stream_unref(&input);
+	}
+	test_end();
+}
+
+static void test_gz(const char *str1, const char *str2, bool autodetect)
+{
+	const struct compression_handler *gz;
+	struct ostream *buf_output, *output;
+	struct istream *test_input, *input;
+	buffer_t *buf = t_buffer_create(512);
+
+	if (compression_lookup_handler("gz", &gz) <= 0 )
+		return; /* not compiled in or unkown*/
+
+	/* write concated output */
+	buf_output = o_stream_create_buffer(buf);
+	o_stream_set_finish_via_child(buf_output, FALSE);
+
+	output = gz->create_ostream(buf_output, 6);
+	o_stream_nsend_str(output, str1);
+	test_assert(o_stream_finish(output) > 0);
+	o_stream_destroy(&output);
+
+	if (str2[0] != '\0') {
+		output = gz->create_ostream(buf_output, 6);
+		o_stream_nsend_str(output, "world");
+		test_assert(o_stream_finish(output) > 0);
+		o_stream_destroy(&output);
+	}
+
+	o_stream_destroy(&buf_output);
+
+	/* read concated input */
+	const unsigned char *data;
+	size_t size;
+	test_input = test_istream_create_data(buf->data, buf->used);
+	test_istream_set_allow_eof(test_input, FALSE);
+	input = !autodetect ? gz->create_istream(test_input) :
+		i_stream_create_decompress(test_input, 0);
+	for (size_t i = 0; i <= buf->used; i++) {
+		test_istream_set_size(test_input, i);
+		test_assert(i_stream_read(input) >= 0);
+	}
+	test_istream_set_allow_eof(test_input, TRUE);
+	test_assert(i_stream_read(input) == -1);
+	test_assert(input->stream_errno == 0);
+
+	data = i_stream_get_data(input, &size);
+	test_assert(size == strlen(str1)+strlen(str2) &&
+		    memcmp(data, str1, strlen(str1)) == 0 &&
+		    memcmp(data+strlen(str1), str2, strlen(str2)) == 0);
+	i_stream_unref(&input);
+	i_stream_unref(&test_input);
+}
+
+static void test_gz_concat(void)
+{
+	test_begin("gz concat (autodetect=no)");
+	test_gz("hello", "world", FALSE);
+	test_end();
+
+	test_begin("gz concat (autodetect=yes)");
+	test_gz("hello", "world", TRUE);
+	test_end();
+}
+
+static void test_gz_no_concat(void)
+{
+	test_begin("gz no concat (autodetect=no)");
+	test_gz("hello", "", FALSE);
+	test_end();
+
+	test_begin("gz no concat (autodetect=yes)");
+	test_gz("hello", "", TRUE);
+	test_end();
+}
+
+static void test_gz_header_int(bool autodetect)
+{
+	const struct compression_handler *gz;
+	const char *input_strings[] = {
+		"\x1F\x8B",
+		"\x1F\x8B\x01\x02"/* GZ_FLAG_FHCRC */"\xFF\xFF\x01\x01\x01\x01",
+		"\x1F\x8B\x01\x04"/* GZ_FLAG_FEXTRA */"\xFF\xFF\x01\x01\x01\x01",
+		"\x1F\x8B\x01\x08"/* GZ_FLAG_FNAME */"\x01\x01\x01\x01\x01\x01",
+		"\x1F\x8B\x01\x10"/* GZ_FLAG_FCOMMENT */"\x01\x01\x01\x01\x01\x01",
+		"\x1F\x8B\x01\x0C"/* GZ_FLAG_FEXTRA | GZ_FLAG_FNAME */"\xFF\xFF\x01\x01\x01\x01",
+	};
+	struct istream *file_input, *input;
+	if (compression_lookup_handler("gz", &gz) <= 0 )
+		return; /* not compiled in or unkown*/
+
+	test_begin(t_strdup_printf(
+		"gz header (autodetect=%s)", autodetect ? "yes" : "no"));
+	for (unsigned int i = 0; i < N_ELEMENTS(input_strings); i++) {
+		file_input = test_istream_create_data(input_strings[i],
+						      strlen(input_strings[i]));
+		file_input->blocking = TRUE;
+		input = !autodetect ? gz->create_istream(file_input) :
+			i_stream_create_decompress(file_input, 0);
+		test_assert_idx(i_stream_read(input) == -1, i);
+		test_assert_idx(input->stream_errno == EINVAL, i);
+		i_stream_unref(&input);
+		i_stream_unref(&file_input);
+	}
+	test_end();
+}
+
+static void test_gz_header(void)
+{
+	test_gz_header_int(FALSE);
+	test_gz_header_int(TRUE);
+}
+
+static void test_gz_large_header_int(bool autodetect)
+{
+	const struct compression_handler *gz;
+	static const unsigned char gz_input[] = {
+		0x1f, 0x8b, 0x08, 0x08,
+		'a','a','a','a','a','a','a','a','a','a','a',
+		0
+	};
+	struct istream *file_input, *input;
+	size_t i;
+
+	if (compression_lookup_handler("gz", &gz) <= 0 )
+		return; /* not compiled in or unkown*/
+
+	test_begin(t_strdup_printf(
+		"gz large header (autodetect=%s)", autodetect ? "yes" : "no"));
+
+	/* max buffer size smaller than gz header */
+	for (i = 1; i < sizeof(gz_input); i++) {
+		file_input = test_istream_create_data(gz_input, sizeof(gz_input));
+		test_istream_set_size(file_input, i);
+		test_istream_set_max_buffer_size(file_input, i);
+
+		input = !autodetect ? gz->create_istream(file_input) :
+			i_stream_create_decompress(file_input, 0);
+		test_assert_idx(i_stream_read(input) == 0, i);
+		test_assert_idx(i_stream_read(input) == -1 &&
+				input->stream_errno == EINVAL, i);
+		i_stream_unref(&input);
+		i_stream_unref(&file_input);
+	}
+
+	/* max buffer size is exactly the gz header */
+	file_input = test_istream_create_data(gz_input, sizeof(gz_input));
+	input = !autodetect ? gz->create_istream(file_input) :
+		i_stream_create_decompress(file_input, 0);
+	test_istream_set_size(file_input, i);
+	test_istream_set_allow_eof(file_input, FALSE);
+	test_istream_set_max_buffer_size(file_input, i);
+	test_assert(i_stream_read(input) == 0);
+	i_stream_unref(&input);
+	i_stream_unref(&file_input);
+
+	test_end();
+}
+
+static void test_gz_large_header(void)
+{
+	test_gz_large_header_int(FALSE);
+	test_gz_large_header_int(TRUE);
+}
+
+static void test_lz4_small_header(void)
+{
+	const struct compression_handler *lz4;
+	struct iostream_lz4_header lz4_input;
+	struct istream *file_input, *input;
+
+	if (compression_lookup_handler("lz4", &lz4) <= 0)
+		return; /* not compiled in or unkown */
+
+	test_begin("lz4 small header");
+
+	memcpy(lz4_input.magic, IOSTREAM_LZ4_MAGIC, IOSTREAM_LZ4_MAGIC_LEN);
+	lz4_input.max_uncompressed_chunk_size[0] = 0;
+	lz4_input.max_uncompressed_chunk_size[1] = 1;
+	lz4_input.max_uncompressed_chunk_size[2] = 0;
+	lz4_input.max_uncompressed_chunk_size[3] = 0;
+
+	/* truncated header */
+	file_input = i_stream_create_from_data(&lz4_input, sizeof(lz4_input)-1);
+	input = lz4->create_istream(file_input);
+	test_assert(i_stream_read(input) == -1 &&
+		    input->stream_errno == EINVAL);
+	i_stream_unref(&input);
+	i_stream_unref(&file_input);
+
+	/* partial initial header read */
+	file_input = test_istream_create_data(&lz4_input, sizeof(lz4_input));
+	file_input->blocking = TRUE;
+
+	test_istream_set_max_buffer_size(file_input, sizeof(lz4_input)-1);
+	(void)i_stream_read(file_input);
+	test_istream_set_max_buffer_size(file_input, sizeof(lz4_input));
+
+	input = lz4->create_istream(file_input);
+	test_assert(i_stream_read(input) == -1 &&
+		    input->stream_errno == 0);
+	i_stream_unref(&input);
+	i_stream_unref(&file_input);
+
+	test_end();
+}
+
+static void test_uncompress_file(const char *path)
+{
+	const struct compression_handler *handler;
+	struct istream *input, *file_input;
+	const unsigned char *data;
+	size_t size;
+	int ret;
+
+	ret = compression_lookup_handler_from_ext(path, &handler);
+	if (ret < 0)
+		i_fatal("Can't detect compression algorithm from path %s", path);
+	else if (ret == 0)
+		i_fatal("Support not compiled in for %s", handler->name);
+
+	file_input = i_stream_create_file(path, IO_BLOCK_SIZE);
+	input = handler->create_istream(file_input);
+	while (i_stream_read_more(input, &data, &size) > 0) {
+		if (write(STDOUT_FILENO, data, size) < 0)
+			break;
+		i_stream_skip(input, size);
+	}
+	i_stream_destroy(&input);
+}
+
+static void test_compress_file(const char *in_path, const char *out_path)
+{
+	const struct compression_handler *handler;
+	struct istream *input, *file_input;
+	struct ostream *output, *file_output;
+	int fd_in, fd_out;
+	struct sha1_ctxt sha1;
+	unsigned char output_sha1[SHA1_RESULTLEN], input_sha1[SHA1_RESULTLEN];
+	const unsigned char *data;
+	size_t size;
+	int ret;
+
+	ret = compression_lookup_handler_from_ext(out_path, &handler);
+	if (ret < 0)
+		i_fatal("Can't detect compression algorithm from path %s", out_path);
+	if (ret == 0)
+		i_fatal("Support not compiled in for %s", handler->name);
+
+	/* write the compressed output file */
+	fd_in = open(in_path, O_RDONLY);
+	if (fd_in == -1)
+		i_fatal("open(%s) failed: %m", in_path);
+	fd_out = open(out_path, O_TRUNC | O_CREAT | O_RDWR, 0600);
+	if (fd_out == -1)
+		i_fatal("creat(%s) failed: %m", out_path);
+
+	sha1_init(&sha1);
+	file_output = o_stream_create_fd_file(fd_out, 0, FALSE);
+	output = handler->create_ostream(file_output, 1);
+	input = i_stream_create_fd_autoclose(&fd_in, IO_BLOCK_SIZE);
+	while (i_stream_read_more(input, &data, &size) > 0) {
+		sha1_loop(&sha1, data, size);
+		o_stream_nsend(output, data, size);
+		i_stream_skip(input, size);
+	}
+	if (o_stream_finish(output) < 0) {
+		i_fatal("write(%s) failed: %s",
+			out_path, o_stream_get_error(output));
+	}
+	i_stream_destroy(&input);
+	o_stream_destroy(&output);
+	o_stream_destroy(&file_output);
+	sha1_result(&sha1, output_sha1);
+
+	/* verify that we can read the compressed file */
+	sha1_init(&sha1);
+	file_input = i_stream_create_fd(fd_out, IO_BLOCK_SIZE);
+	input = handler->create_istream(file_input);
+	while (i_stream_read_more(input, &data, &size) > 0) {
+		sha1_loop(&sha1, data, size);
+		i_stream_skip(input, size);
+	}
+	i_stream_destroy(&input);
+	i_stream_destroy(&file_input);
+	sha1_result(&sha1, input_sha1);
+
+	if (memcmp(input_sha1, output_sha1, sizeof(input_sha1)) != 0)
+		i_fatal("Decompression couldn't get the original input");
+	i_close_fd(&fd_out);
+}
+
+static void test_compression_ext(void)
+{
+	const struct compression_handler *handler;
+	test_begin("compression handler by extension");
+
+	for (unsigned int i = 0; compression_handlers[i].name != NULL; i++) {
+		if (compression_handlers[i].ext != NULL) {
+			const char *path =
+				t_strconcat("file", compression_handlers[i].ext, NULL);
+			int ret = compression_lookup_handler_from_ext(path, &handler);
+			test_assert(ret == 0 || handler == &compression_handlers[i]);
+		}
+	}
+
+	test_end();
+}
+
+int main(int argc, char *argv[])
+{
+	static void (*const test_functions[])(void) = {
+		test_compression,
+		test_istream_decompression_try,
+		test_gz_concat,
+		test_gz_no_concat,
+		test_gz_header,
+		test_gz_large_header,
+		test_lz4_small_header,
+		test_compression_ext,
+		NULL
+	};
+	if (argc == 2) {
+		test_uncompress_file(argv[1]);
+		return 0;
+	}
+	if (argc == 3) {
+		test_compress_file(argv[1], argv[2]);
+		return 0;
+	}
+	return test_run(test_functions);
+}