smoothstreamingenc: Write to a temp file while updating the manifest

If a client tries to read the file while it's being updated, the client
would get an incomplete manifest. Instead write to a separate temp file
and atomically rename it to replace the previous one.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/smoothstreamingenc.c

@@ -210,14 +210,15 @@ static int write_manifest(AVFormatContext *s, int final)
 {
     SmoothStreamingContext *c = s->priv_data;
     AVIOContext *out;
-    char filename[1024];
+    char filename[1024], temp_filename[1024];
     int ret, i, video_chunks = 0, audio_chunks = 0, video_streams = 0, audio_streams = 0;
     int64_t duration = 0;
 
     snprintf(filename, sizeof(filename), "%s/Manifest", s->filename);
-    ret = avio_open2(&out, filename, AVIO_FLAG_WRITE, &s->interrupt_callback, NULL);
+    snprintf(temp_filename, sizeof(temp_filename), "%s/Manifest.tmp", s->filename);
+    ret = avio_open2(&out, temp_filename, AVIO_FLAG_WRITE, &s->interrupt_callback, NULL);
     if (ret < 0) {
-        av_log(s, AV_LOG_ERROR, "Unable to open %s for writing\n", filename);
+        av_log(s, AV_LOG_ERROR, "Unable to open %s for writing\n", temp_filename);
         return ret;
     }
     avio_printf(out, "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n");
@@ -278,6 +279,7 @@ static int write_manifest(AVFormatContext *s, int final)
     avio_printf(out, "</SmoothStreamingMedia>\n");
     avio_flush(out);
     avio_close(out);
+    rename(temp_filename, filename);
     return 0;
 }