stream: move file forward skipping to common stream implementation

stream_file.c contains some code meant for forward seeking with pipes.
This simply reads data until the seek position is reached. Move this
code to stream.c. This stops stream_file from doing strange things
(messing with stream internals), and removes the code duplication too.

We also make stream_seek_long() use the new skip code. This is shorter
and much easier to follow than the old code, which basically did strange
things.

stream/stream.c

@@ -249,6 +249,9 @@ static stream_t *open_stream_plugin(const stream_info_t *sinfo,
     if (s->seek && !(s->flags & MP_STREAM_SEEK))
         s->flags |= MP_STREAM_SEEK;
 
+    if (s->flags & MP_STREAM_FAST_SKIPPING)
+        s->flags |= MP_STREAM_SEEK_FW;
+
     s->mode = mode;
 
     s->uncached_type = s->type;
@@ -512,6 +515,23 @@ int stream_write_buffer(stream_t *s, unsigned char *buf, int len)
     return rd;
 }
 
+static int stream_skip_read(struct stream *s, int64_t len)
+{
+    while (len > 0) {
+        int x = s->buf_len - s->buf_pos;
+        if (x == 0) {
+            if (!stream_fill_buffer(s))
+                return 0; // EOF
+            x = s->buf_len - s->buf_pos;
+        }
+        if (x > len)
+            x = len;
+        s->buf_pos += x;
+        len -= x;
+    }
+    return 1;
+}
+
 // Seek function bypassing the local stream buffer.
 static int stream_seek_unbuffered(stream_t *s, int64_t newpos)
 {
@@ -556,26 +576,16 @@ static int stream_seek_long(stream_t *s, int64_t pos)
            "  new_bufpos=%" PRIX64 "  buflen=%X  \n",
            (int64_t)s->pos, (int64_t)newpos, (int64_t)pos, s->buf_len);
 
-    pos -= newpos;
+    if (!s->seek && (s->flags & MP_STREAM_FAST_SKIPPING) && pos >= s->pos) {
-
+        // skipping is handled by generic code below
-    if (stream_seek_unbuffered(s, newpos) >= 0) {
+    } else if (stream_seek_unbuffered(s, newpos) >= 0) {
         s->pos = oldpos;
         return 0;
     }
 
-    while (s->pos < newpos) {
+    if (pos >= s->pos && stream_skip_read(s, pos - s->pos) > 0)
-        if (stream_fill_buffer(s) <= 0)
+        return 1; // success
-            break; // EOF
-    }
 
-    while (stream_fill_buffer(s) > 0) {
-        if (pos <= s->buf_len) {
-            s->buf_pos = pos; // byte position in sector
-            s->eof = 0;
-            return 1;
-        }
-        pos -= s->buf_len;
-    }
     // Fill failed, but seek still is a success (partially).
     s->buf_pos = 0;
     s->buf_len = 0;
@@ -624,19 +634,7 @@ int stream_skip(stream_t *s, int64_t len)
         }
         return r;
     }
-    while (len > 0) {
+    return stream_skip_read(s, len);
-        int x = s->buf_len - s->buf_pos;
-        if (x == 0) {
-            if (!stream_fill_buffer(s))
-                return 0; // EOF
-            x = s->buf_len - s->buf_pos;
-        }
-        if (x > len)
-            x = len;
-        s->buf_pos += x;
-        len -= x;
-    }
-    return 1;
 }
 
 int stream_control(stream_t *s, int cmd, void *arg)

stream/stream.h

@@ -58,6 +58,7 @@ enum streamtype {
 #define STREAM_WRITE 1
 
 // stream->flags
+#define MP_STREAM_FAST_SKIPPING 1 // allow forward seeks by skipping
 #define MP_STREAM_SEEK_BW  2
 #define MP_STREAM_SEEK_FW  4
 #define MP_STREAM_SEEK  (MP_STREAM_SEEK_BW | MP_STREAM_SEEK_FW)

stream/stream_file.c

@@ -69,26 +69,6 @@ static int seek(stream_t *s, int64_t newpos)
     return 1;
 }
 
-static int seek_forward(stream_t *s, int64_t newpos)
-{
-    if (newpos < s->pos) {
-        mp_msg(MSGT_STREAM, MSGL_INFO,
-               "Cannot seek backward in linear streams!\n");
-        return 0;
-    }
-    while (s->pos < newpos) {
-        int len = s->fill_buffer(s, s->buffer, STREAM_BUFFER_SIZE);
-        if (len <= 0) { // EOF
-            s->buf_pos = s->buf_len = 0;
-            break;
-        }
-        s->buf_pos = 0;
-        s->buf_len = len;
-        s->pos += len;
-    }
-    return 1;
-}
-
 static int control(stream_t *s, int cmd, void *arg)
 {
     struct priv *p = s->priv;
@@ -192,10 +172,8 @@ static int open_f(stream_t *stream, int mode)
         len = -1;
 #endif
     stream->type = STREAMTYPE_FILE;
-    if (len == -1 && mode == STREAM_READ) {
+    stream->flags = MP_STREAM_FAST_SKIPPING;
-        stream->seek = seek_forward;
+    if (len >= 0) {
-        stream->flags = MP_STREAM_SEEK_FW;
-    } else if (len >= 0) {
         stream->seek = seek;
         stream->end_pos = len;
     }