[vlc-devel] [PATCH] stream: add stream_ForcedPeekNew

[Francois Cartegnie]

Creates a stream_Memory like backend
pointing to an existing stream to convert
reads into peek only requests.

Helps dealing with seekable only designed code
(using stream_Readline for exemple)
---
 include/vlc_stream.h      |  7 +++++++
 src/input/stream_memory.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++-
 src/libvlccore.sym        |  1 +
 3 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/include/vlc_stream.h b/include/vlc_stream.h
index cbdd2fa..fa418f4 100644
--- a/include/vlc_stream.h
+++ b/include/vlc_stream.h
@@ -226,6 +226,13 @@ VLC_API stream_t * stream_MemoryNew(vlc_object_t *p_obj, uint8_t *p_buffer, uint
 #define stream_MemoryNew( a, b, c, d ) stream_MemoryNew( VLC_OBJECT(a), b, c, d )
 
 /**
+ * Create a stream_t reading from another stream, without modifying
+ * its read pointer.
+ * You must delete it using stream_Delete.
+ */
+VLC_API stream_t * stream_ForcedPeekNew( stream_t *p_backend );
+
+/**
  * Create a stream_t reading from a URL.
  * You must delete it using stream_Delete.
  */
diff --git a/src/input/stream_memory.c b/src/input/stream_memory.c
index 3fc23a9..7a97893 100644
--- a/src/input/stream_memory.c
+++ b/src/input/stream_memory.c
@@ -33,7 +33,7 @@ struct stream_sys_t
     size_t    i_pos;      /* Current reading offset */
     size_t    i_size;
     uint8_t  *p_buffer;
-
+    stream_t *p_backend_stream; /* Only used by forced peek */
 };
 
 static ssize_t Read( stream_t *, void *p_read, size_t i_read );
@@ -41,6 +41,9 @@ static int Seek( stream_t *, uint64_t );
 static int  Control( stream_t *, int i_query, va_list );
 static void Delete ( stream_t * );
 
+
+static ssize_t PeekBackend( stream_t *, void *p_read, size_t i_read );
+
 #undef stream_MemoryNew
 /**
  * Create a stream from a memory buffer
@@ -70,6 +73,7 @@ stream_t *stream_MemoryNew( vlc_object_t *p_this, uint8_t *p_buffer,
     p_sys->i_size = i_size;
     p_sys->p_buffer = p_buffer;
     p_sys->i_preserve_memory = i_preserve_memory;
+    p_sys->p_backend_stream = NULL;
 
     s->pf_read    = Read;
     s->pf_seek    = Seek;
@@ -79,6 +83,27 @@ stream_t *stream_MemoryNew( vlc_object_t *p_this, uint8_t *p_buffer,
     return s;
 }
 
+/**
+ * Create a virtual stream to issue peek only requests to
+ * an existing stream
+ *
+ * \param p_backend_stream the stream to be used as backend
+ */
+stream_t *stream_ForcedPeekNew( stream_t *p_backend_stream )
+{
+    if( (uint64_t) stream_Size( p_backend_stream ) <= stream_Tell( p_backend_stream ) )
+        return NULL;
+
+    /* Init an empty stream Mem */
+    stream_t *s = stream_MemoryNew( VLC_OBJECT(p_backend_stream), NULL, 0, true );
+    if( !s )
+        return NULL;
+    s->p_sys->i_size = stream_Size( p_backend_stream ) - stream_Tell( p_backend_stream );
+    s->p_sys->p_backend_stream = p_backend_stream;
+    s->pf_read = PeekBackend;
+    return s;
+}
+
 static void Delete( stream_t *s )
 {
     if( !s->p_sys->i_preserve_memory ) free( s->p_sys->p_buffer );
@@ -161,3 +186,26 @@ static int Seek( stream_t *s, uint64_t offset )
     p_sys->i_pos = offset;
     return VLC_SUCCESS;
 }
+
+/* Peek Only Stream */
+static ssize_t PeekBackend( stream_t *s, void *p_read, size_t i_read )
+{
+    stream_sys_t *p_sys = s->p_sys;
+
+    const uint8_t *p_peek;
+    const ssize_t i_peek = stream_Peek( p_sys->p_backend_stream, &p_peek, p_sys->i_pos + i_read );
+    if( i_peek < 0 )
+    {
+        /* error code */
+        return i_peek;
+    }
+    else if( (size_t) i_peek > p_sys->i_pos )
+    {
+        i_read = i_peek - p_sys->i_pos;
+        memcpy( p_read, &p_peek[p_sys->i_pos], i_read );
+        p_sys->i_pos += i_read;
+        return i_read;
+    }
+    else /* returned less than current pos/last read */
+        return VLC_EGENERIC;
+}
diff --git a/src/libvlccore.sym b/src/libvlccore.sym
index 372b312..d0f5111 100644
--- a/src/libvlccore.sym
+++ b/src/libvlccore.sym
@@ -399,6 +399,7 @@ stream_DemuxNew
 stream_DemuxSend
 stream_DemuxControlVa
 stream_FilterNew
+stream_ForcedPeekNew
 stream_MemoryNew
 stream_Peek
 stream_Read
-- 
2.4.3