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>

7 files changed, 68 insertions, 26 deletions

diff --git a/include/io/istream.h b/include/io/istream.h
index 3280327..9c34678 100644
--- a/include/io/istream.h
+++ b/include/io/istream.h
@@ -96,7 +96,10 @@ SQFS_INTERNAL sqfs_s32 istream_read(istream_t *strm, void *data, size_t size);
  *
  * @return 0 on success, -1 on failure.
  */
-SQFS_INTERNAL int istream_precache(istream_t *strm);
+SQFS_INLINE int istream_precache(istream_t *strm)
+{
+	return strm->precache(strm);
+}
 
 /**
  * @brief Get the underlying filename of an input stream.
diff --git a/lib/io/src/istream.c b/lib/io/src/istream.c
index 64fa478..051fac8 100644
--- a/lib/io/src/istream.c
+++ b/lib/io/src/istream.c
@@ -38,26 +38,6 @@ sqfs_s32 istream_read(istream_t *strm, void *data, size_t size)
 	return total;
 }
 
-int istream_precache(istream_t *strm)
-{
-	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;
-	}
-
-	if (strm->eof)
-		return 0;
-
-	return strm->precache(strm);
-}
-
 int istream_skip(istream_t *strm, sqfs_u64 size)
 {
 	size_t diff;
diff --git a/lib/io/src/mem.c b/lib/io/src/mem.c
index 4e9f9af..d305a83 100644
--- a/lib/io/src/mem.c
+++ b/lib/io/src/mem.c
@@ -26,8 +26,21 @@ typedef struct {
 static int mem_in_precache(istream_t *strm)
 {
 	mem_istream_t *mem = (mem_istream_t *)strm;
-	size_t diff = mem->bufsz - strm->buffer_used;
+	size_t diff;
+
+	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;
+	}
 
+	diff = mem->bufsz - strm->buffer_used;
 	if (diff > mem->size)
 		diff = mem->size;
 
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)
diff --git a/lib/io/src/win32/istream.c b/lib/io/src/win32/istream.c
index be3d829..918b868 100644
--- a/lib/io/src/win32/istream.c
+++ b/lib/io/src/win32/istream.c
@@ -23,6 +23,21 @@ static int file_precache(istream_t *strm)
 	DWORD diff, actual;
 	HANDLE hnd;
 
+	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;
+	}
+
+	if (strm->eof)
+		return 0;
+
 	hnd = file->path == NULL ? GetStdHandle(STD_INPUT_HANDLE) : file->hnd;
 
 	while (strm->buffer_used < sizeof(file->buffer)) {
diff --git a/lib/io/src/xfrm/istream.c b/lib/io/src/xfrm/istream.c
index 4a1ad77..b301209 100644
--- a/lib/io/src/xfrm/istream.c
+++ b/lib/io/src/xfrm/istream.c
@@ -20,6 +20,21 @@ static int xfrm_precache(istream_t *base)
 	istream_xfrm_t *xfrm = (istream_xfrm_t *)base;
 	int ret;
 
+	if (base->buffer_offset >= base->buffer_used) {
+		base->buffer_offset = 0;
+		base->buffer_used = 0;
+	} else if (base->buffer_offset > 0) {
+		memmove(base->buffer,
+			base->buffer + base->buffer_offset,
+			base->buffer_used - base->buffer_offset);
+
+		base->buffer_used -= base->buffer_offset;
+		base->buffer_offset = 0;
+	}
+
+	if (base->eof)
+		return 0;
+
 	ret = istream_precache(xfrm->wrapped);
 	if (ret != 0)
 		return ret;
diff --git a/lib/tar/src/iterator.c b/lib/tar/src/iterator.c
index 0940905..532eb8c 100644
--- a/lib/tar/src/iterator.c
+++ b/lib/tar/src/iterator.c
@@ -104,6 +104,12 @@ static int strm_precache(istream_t *strm)
 	tar_istream_t *tar = (tar_istream_t *)strm;
 	sqfs_u64 diff;
 
+	strm->buffer_used -= strm->buffer_offset;
+	strm->buffer_offset = 0;
+
+	if (strm->eof)
+		return 0;
+
 	tar->parent->offset += tar->parent->last_chunk;
 
 	if (!tar->parent->last_sparse) {