libio: Move istream_t precache logic into backend implementation

The end goal is to remove direct buffer access from the istream_t
interfaces and make that opaque. For the tar implementation, this
already safes us needless buffer copying, as we essentially allow
the user to read-through from the underlying stream.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 14 insertions, 4 deletions

diff --git a/lib/io/src/unix/istream.c b/lib/io/src/unix/istream.c
index f8cffad..24b18d6 100644
--- a/lib/io/src/unix/istream.c
+++ b/lib/io/src/unix/istream.c
@@ -20,15 +20,25 @@ static int file_precache(istream_t *strm)
 	ssize_t ret;
 	size_t diff;
 
-	while (strm->buffer_used < sizeof(file->buffer)) {
+	if (strm->buffer_offset >= strm->buffer_used) {
+		strm->buffer_offset = 0;
+		strm->buffer_used = 0;
+	} else if (strm->buffer_offset > 0) {
+		memmove(strm->buffer,
+			strm->buffer + strm->buffer_offset,
+			strm->buffer_used - strm->buffer_offset);
+
+		strm->buffer_used -= strm->buffer_offset;
+		strm->buffer_offset = 0;
+	}
+
+	while (!strm->eof && strm->buffer_used < sizeof(file->buffer)) {
 		diff = sizeof(file->buffer) - strm->buffer_used;
 
 		ret = read(file->fd, strm->buffer + strm->buffer_used, diff);
 
-		if (ret == 0) {
+		if (ret == 0)
 			strm->eof = true;
-			break;
-		}
 
 		if (ret < 0) {
 			if (errno == EINTR)