add cache protocol

This allows backward seeking on top of some non seekable streams.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/Makefile

@@ -333,6 +333,7 @@ OBJS-$(CONFIG_LIBNUT_MUXER)              += libnut.o riff.o
 OBJS+= avio.o aviobuf.o
 
 OBJS-$(CONFIG_APPLEHTTP_PROTOCOL)        += applehttpproto.o
+OBJS-$(CONFIG_CACHE_PROTOCOL)            += cache.o
 OBJS-$(CONFIG_CONCAT_PROTOCOL)           += concat.o
 OBJS-$(CONFIG_CRYPTO_PROTOCOL)           += crypto.o
 OBJS-$(CONFIG_FILE_PROTOCOL)             += file.o

libavformat/allformats.c

@@ -249,6 +249,7 @@ void av_register_all(void)
 
     /* protocols */
     REGISTER_PROTOCOL (APPLEHTTP, applehttp);
+    REGISTER_PROTOCOL (CACHE, cache);
     REGISTER_PROTOCOL (CONCAT, concat);
     REGISTER_PROTOCOL (CRYPTO, crypto);
     REGISTER_PROTOCOL (FILE, file);

libavformat/cache.c

+/*
+ * Input cache protocol.
+ * Copyright (c) 2011 Michael Niedermayer
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * Based on file.c by Fabrice Bellard
+ */
+
+#include "libavutil/avassert.h"
+#include "libavutil/avstring.h"
+#include "libavutil/file.h"
+#include "avformat.h"
+#include <fcntl.h>
+#if HAVE_SETMODE
+#include <io.h>
+#endif
+#include <unistd.h>
+#include <sys/stat.h>
+#include <stdlib.h>
+#include "os_support.h"
+#include "url.h"
+
+typedef struct Context {
+    int fd;
+    int64_t end;
+    int64_t pos;
+    URLContext *inner;
+} Context;
+
+static int cache_open(URLContext *h, const char *arg, int flags)
+{
+    int access;
+    const char *buffername;
+    Context *c;
+
+    c = av_mallocz(sizeof(Context));
+    if (!c) {
+        return AVERROR(ENOMEM);
+    }
+    h->priv_data = c;
+
+    av_strstart(arg, "cache:", &arg);
+
+    c->fd = av_tempfile("ffcache", &buffername);
+    if (c->fd < 0){
+        av_log(h, AV_LOG_ERROR, "Failed to create tempfile\n");
+        return c->fd;
+    }
+
+    unlink(buffername);
+    av_free(buffername);
+
+    return ffurl_open(&c->inner, arg, flags);
+}
+
+static int cache_read(URLContext *h, unsigned char *buf, int size)
+{
+    Context *c= h->priv_data;
+    int r;
+
+    if(c->pos<c->end){
+        r = read(c->fd, buf, FFMIN(size, c->end - c->pos));
+        if(r>0)
+            c->pos += r;
+        return (-1 == r)?AVERROR(errno):r;
+    }else{
+        r = ffurl_read(c->inner, buf, size);
+        if(r > 0){
+            int r2= write(c->fd, buf, r);
+            av_assert0(r2==r); // FIXME handle cache failure
+            c->pos += r;
+            c->end += r;
+        }
+        return r;
+    }
+}
+
+static int64_t cache_seek(URLContext *h, int64_t pos, int whence)
+{
+    Context *c= h->priv_data;
+
+    if (whence == AVSEEK_SIZE) {
+        return ffurl_seek(c->inner, pos, whence);
+    }
+
+    pos= lseek(c->fd, pos, whence);
+    if(pos<0){
+        return pos;
+    }else if(pos <= c->end){
+        c->pos= pos;
+        return pos;
+    }else{
+        lseek(c->fd, c->pos, SEEK_SET);
+        return AVERROR(EPIPE);
+    }
+}
+
+static int cache_close(URLContext *h)
+{
+    Context *c= h->priv_data;
+    close(c->fd);
+    ffurl_close(c->inner);
+
+    av_freep(&h->priv_data);
+
+    return 0;
+}
+
+URLProtocol ff_cache_protocol = {
+    .name                = "cache",
+    .url_open            = cache_open,
+    .url_read            = cache_read,
+    .url_seek            = cache_seek,
+    .url_close           = cache_close,
+};