avformat/segment: atomically update list if possible

Fixes Ticket4802
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/segment.c

@@ -114,6 +114,9 @@ typedef struct SegmentContext {
     int   reference_stream_index;
     int   break_non_keyframes;
 
+    int use_rename;
+    char temp_list_filename[1024];
+
     SegmentListEntry cur_entry;
     SegmentListEntry *segment_list_entries;
     SegmentListEntry *segment_list_entries_end;
@@ -259,7 +262,8 @@ static int segment_list_open(AVFormatContext *s)
     SegmentContext *seg = s->priv_data;
     int ret;
 
-    ret = avio_open2(&seg->list_pb, seg->list, AVIO_FLAG_WRITE,
+    snprintf(seg->temp_list_filename, sizeof(seg->temp_list_filename), seg->use_rename ? "%s.tmp" : "%s", seg->list);
+    ret = avio_open2(&seg->list_pb, seg->temp_list_filename, AVIO_FLAG_WRITE,
                      &s->interrupt_callback, NULL);
     if (ret < 0) {
         av_log(s, AV_LOG_ERROR, "Failed to open segment list '%s'\n", seg->list);
@@ -370,6 +374,8 @@ static int segment_end(AVFormatContext *s, int write_trailer, int is_last)
             if (seg->list_type == LIST_TYPE_M3U8 && is_last)
                 avio_printf(seg->list_pb, "#EXT-X-ENDLIST\n");
             avio_closep(&seg->list_pb);
+            if (seg->use_rename)
+                ff_rename(seg->temp_list_filename, seg->list, s);
         } else {
             segment_list_print_entry(seg->list_pb, seg->list_type, &seg->cur_entry, s);
             avio_flush(seg->list_pb);
@@ -646,9 +652,13 @@ static int seg_write_header(AVFormatContext *s)
             else if (av_match_ext(seg->list, "ffcat,ffconcat")) seg->list_type = LIST_TYPE_FFCONCAT;
             else                                      seg->list_type = LIST_TYPE_FLAT;
         }
-        if (!seg->list_size && seg->list_type != LIST_TYPE_M3U8)
+        if (!seg->list_size && seg->list_type != LIST_TYPE_M3U8) {
             if ((ret = segment_list_open(s)) < 0)
                 goto fail;
+        } else {
+            const char *proto = avio_find_protocol_name(s->filename);
+            seg->use_rename = proto && !strcmp(proto, "file");
+        }
     }
     if (seg->list_type == LIST_TYPE_EXT)
         av_log(s, AV_LOG_WARNING, "'ext' list type option is deprecated in favor of 'csv'\n");