1 files changed, 55 insertions, 0 deletions
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