http: make caching of redirect url optional

added "cache_redirect" option to http.
when enabled, requests issued after seek will use the latest redirected
url.
when disabled, each call to seek will revert to the original url that
was sent to http_open.

currently, the default remains 'enabled', until the next major
libavformat bump, where it will change to 'disabled'.

libavformat/http.c

@@ -69,7 +69,9 @@ typedef struct HTTPContext {
     uint64_t chunksize;
     int chunkend;
     uint64_t off, end_off, filesize;
+    char *uri;
     char *location;
+    int cache_redirect;
     HTTPAuthState auth_state;
     HTTPAuthState proxy_auth_state;
     char *http_proxy;
@@ -169,6 +171,7 @@ static const AVOption options[] = {
     { "resource", "The resource requested by a client", OFFSET(resource), AV_OPT_TYPE_STRING, { .str = NULL }, 0, 0, E },
     { "reply_code", "The http status code to return to a client", OFFSET(reply_code), AV_OPT_TYPE_INT, { .i64 = 200}, INT_MIN, 599, E},
     { "short_seek_size", "Threshold to favor readahead over seek.", OFFSET(short_seek_size), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, D },
+    { "cache_redirect", "Save redirected URL for subsequent seek operations", OFFSET(cache_redirect), AV_OPT_TYPE_BOOL, { .i64 = FF_HTTP_CACHE_REDIRECT_DEFAULT }, 0, 1, D },
     { NULL }
 };
 
@@ -432,11 +435,17 @@ int ff_http_do_new_request2(URLContext *h, const char *uri, AVDictionary **opts)
     s->chunkend      = 0;
     s->off           = 0;
     s->icy_data_read = 0;
+
     av_free(s->location);
     s->location = av_strdup(uri);
     if (!s->location)
         return AVERROR(ENOMEM);
 
+    av_free(s->uri);
+    s->uri = av_strdup(uri);
+    if (!s->uri)
+        return AVERROR(ENOMEM);
+
     if ((ret = av_opt_set_dict(s, opts)) < 0)
         return ret;
 
@@ -623,9 +632,15 @@ static int http_open(URLContext *h, const char *uri, int flags,
         h->is_streamed = 1;
 
     s->filesize = UINT64_MAX;
+
     s->location = av_strdup(uri);
     if (!s->location)
         return AVERROR(ENOMEM);
+
+    s->uri = av_strdup(uri);
+    if (!s->uri)
+        return AVERROR(ENOMEM);
+
     if (options)
         av_dict_copy(&s->chained_options, *options, 0);
 
@@ -651,6 +666,7 @@ bail_out:
     if (ret < 0) {
         av_dict_free(&s->chained_options);
         av_dict_free(&s->cookie_dict);
+        av_freep(&s->uri);
     }
     return ret;
 }
@@ -1769,6 +1785,7 @@ static int http_close(URLContext *h)
         ffurl_closep(&s->hd);
     av_dict_free(&s->chained_options);
     av_dict_free(&s->cookie_dict);
+    av_freep(&s->uri);
     return ret;
 }
 
@@ -1810,6 +1827,16 @@ static int64_t http_seek_internal(URLContext *h, int64_t off, int whence, int fo
             return s->off;
     }
 
+    /* if redirect caching is disabled, revert to the original uri */
+    if (!s->cache_redirect && strcmp(s->uri, s->location)) {
+        char *new_uri;
+        new_uri = av_strdup(s->uri);
+        if (!new_uri)
+            return AVERROR(ENOMEM);
+        av_free(s->location);
+        s->location = new_uri;
+    }
+
     /* we save the old context in case the seek fails */
     old_buf_size = s->buf_end - s->buf_ptr;
     memcpy(old_buf, s->buf_ptr, old_buf_size);

libavformat/version.h

@@ -60,6 +60,7 @@
 #define FF_API_AVIOCONTEXT_WRITTEN      (LIBAVFORMAT_VERSION_MAJOR < 60)
 #define FF_HLS_TS_OPTIONS               (LIBAVFORMAT_VERSION_MAJOR < 60)
 #define FF_API_AVSTREAM_CLASS           (LIBAVFORMAT_VERSION_MAJOR > 59)
+#define FF_HTTP_CACHE_REDIRECT_DEFAULT  (LIBAVFORMAT_VERSION_MAJOR < 60)
 
 
 #define FF_API_R_FRAME_RATE            1