[ffmpeg] - backport - avio: Add an internal function for reading without copying

As long as there is enough contiguous data in the avio buffer,
just return a pointer to it instead of copying it to the caller
provided buffer.

Signed-off-by: Martin Storsjö <martin@martin.st>

2 files changed, 29 insertions, 0 deletions

diff --git a/lib/ffmpeg/libavformat/avio_internal.h b/lib/ffmpeg/libavformat/avio_internal.h
index cf3676402b..e9ece571b9 100644
--- a/lib/ffmpeg/libavformat/avio_internal.h
+++ b/lib/ffmpeg/libavformat/avio_internal.h
@@ -38,6 +38,23 @@ int ffio_init_context(AVIOContext *s,
 
 
 /**
+ * Read size bytes from AVIOContext, returning a pointer.
+ * Note that the data pointed at by the returned pointer is only
+ * valid until the next call that references the same IO context.
+ * @param s IO context
+ * @param buf pointer to buffer into which to assemble the requested
+ *    data if it is not available in contiguous addresses in the
+ *    underlying buffer
+ * @param size number of bytes requested
+ * @param data address at which to store pointer: this will be a
+ *    a direct pointer into the underlying buffer if the requested
+ *    number of bytes are available at contiguous addresses, otherwise
+ *    will be a copy of buf
+ * @return number of bytes read or AVERROR
+ */
+int ffio_read_indirect(AVIOContext *s, unsigned char *buf, int size, unsigned char **data);
+
+/**
  * Read size bytes from AVIOContext into buf.
  * This reads at most 1 packet. If that is not enough fewer bytes will be
  * returned.
diff --git a/lib/ffmpeg/libavformat/aviobuf.c b/lib/ffmpeg/libavformat/aviobuf.c
index 7a73a1791f..465c46d53c 100644
--- a/lib/ffmpeg/libavformat/aviobuf.c
+++ b/lib/ffmpeg/libavformat/aviobuf.c
@@ -522,6 +522,18 @@ int avio_read(AVIOContext *s, unsigned char *buf, int size)
     return size1 - size;
 }
 
+int ffio_read_indirect(AVIOContext *s, unsigned char *buf, int size, unsigned char **data)
+{
+    if (s->buf_end - s->buf_ptr >= size && !s->write_flag) {
+        *data = s->buf_ptr;
+        s->buf_ptr += size;
+        return size;
+    } else {
+        *data = buf;
+        return avio_read(s, buf, size);
+    }
+}
+
 int ffio_read_partial(AVIOContext *s, unsigned char *buf, int size)
 {
     int len;