1 files changed, 97 insertions, 0 deletions
diff --git a/src/lib/istream-failure-at.c b/src/lib/istream-failure-at.c
new file mode 100644
index 0000000..7dccdd3
--- /dev/null
+++ b/src/lib/istream-failure-at.c
@@ -0,0 +1,97 @@
+/* Copyright (c) 2015-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "istream-private.h"
+#include "istream-failure-at.h"
+
+struct failure_at_istream {
+	struct istream_private istream;
+	int error_code;
+	char *error_string;
+	uoff_t failure_offset;
+};
+
+static void i_stream_failure_at_destroy(struct iostream_private *stream)
+{
+	struct failure_at_istream *fstream =
+		container_of(stream, struct failure_at_istream,
+			     istream.iostream);
+
+	i_free(fstream->error_string);
+}
+
+static ssize_t
+i_stream_failure_at_read(struct istream_private *stream)
+{
+	struct failure_at_istream *fstream =
+		container_of(stream, struct failure_at_istream, istream);
+	uoff_t new_offset;
+	ssize_t ret;
+
+	i_stream_seek(stream->parent, stream->parent_start_offset +
+		      stream->istream.v_offset);
+
+	ret = i_stream_read_copy_from_parent(&stream->istream);
+	new_offset = stream->istream.v_offset + (stream->pos - stream->skip);
+	if (ret >= 0 && new_offset >= fstream->failure_offset) {
+		if (stream->istream.v_offset >= fstream->failure_offset) {
+			/* we already passed the wanted failure offset,
+			   return error immediately. */
+			stream->pos = stream->skip;
+			stream->istream.stream_errno = errno =
+				fstream->error_code;
+			io_stream_set_error(&stream->iostream, "%s",
+					    fstream->error_string);
+			ret = -1;
+		} else {
+			/* return data up to the wanted failure offset and
+			   on the next read() call return failure */
+			size_t new_pos = fstream->failure_offset -
+				stream->istream.v_offset + stream->skip;
+			i_assert(new_pos >= stream->skip &&
+				 stream->pos >= new_pos);
+			ret -= stream->pos - new_pos;
+			stream->pos = new_pos;
+		}
+	} else if (ret < 0 && stream->istream.stream_errno == 0 &&
+		   fstream->failure_offset == UOFF_T_MAX) {
+		/* failure at EOF */
+		stream->istream.stream_errno = errno =
+			fstream->error_code;
+		io_stream_set_error(&stream->iostream, "%s",
+				    fstream->error_string);
+	}
+	return ret;
+}
+
+struct istream *
+i_stream_create_failure_at(struct istream *input, uoff_t failure_offset,
+			   int stream_errno, const char *error_string)
+{
+	struct failure_at_istream *fstream;
+
+	fstream = i_new(struct failure_at_istream, 1);
+	fstream->istream.max_buffer_size = input->real_stream->max_buffer_size;
+	fstream->istream.stream_size_passthrough = TRUE;
+
+	fstream->istream.read = i_stream_failure_at_read;
+	fstream->istream.iostream.destroy = i_stream_failure_at_destroy;
+
+	fstream->istream.istream.readable_fd = input->readable_fd;
+	fstream->istream.istream.blocking = input->blocking;
+	fstream->istream.istream.seekable = input->seekable;
+
+	fstream->error_code = stream_errno;
+	fstream->error_string = i_strdup(error_string);
+	fstream->failure_offset = failure_offset;
+	return i_stream_create(&fstream->istream, input,
+			       i_stream_get_fd(input), 0);
+}
+
+struct istream *
+i_stream_create_failure_at_eof(struct istream *input, int stream_errno,
+			       const char *error_string)
+{
+	return i_stream_create_failure_at(input, UOFF_T_MAX, stream_errno,
+					  error_string);
+}