On Wed, Feb 1, 2017 at 6:03 AM, Bodecs Bela <bode...@vivanet.hu> wrote:
>
>
> 2017.01.31. 21:29 keltezéssel, Aman Gupta írta:
>
>> From: Aman Gupta <a...@tmm1.net>
>>
>> Adds a `-hls_flags +temp_file` which will write segment data to
>> filename.tmp, and then rename to filename when the segment is complete
>> and before the file is added to the m3u8 playlist.
>>
>> This patch is similar in spirit to one used in Plex's ffmpeg fork, and
>> allows a transcoding webserver to ensure incomplete segment files are
>> never served up accidentally.
>> ---
>> libavformat/hlsenc.c | 15 +++++++++++++++
>> 1 file changed, 15 insertions(+)
>>
>> diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
>> index bd1e684..23b9011 100644
>> --- a/libavformat/hlsenc.c
>> +++ b/libavformat/hlsenc.c
>> @@ -76,6 +76,7 @@ typedef enum HLSFlags {
>> HLS_SECOND_LEVEL_SEGMENT_INDEX = (1 << 8), // include segment index
>> in segment filenames when use_localtime e.g.: %%03d
>> HLS_SECOND_LEVEL_SEGMENT_DURATION = (1 << 9), // include segment
>> duration (microsec) in segment filenames when use_localtime e.g.: %%09t
>> HLS_SECOND_LEVEL_SEGMENT_SIZE = (1 << 10), // include segment size
>> (bytes) in segment filenames when use_localtime e.g.: %%014s
>> + HLS_TEMP_FILE = (1 << 11),
>> } HLSFlags;
>> typedef enum {
>> @@ -915,6 +916,10 @@ static int hls_start(AVFormatContext *s)
>> set_http_options(&options, c);
>> + if (c->flags & HLS_TEMP_FILE) {
>> + av_strlcat(oc->filename, ".tmp", sizeof(oc->filename));
>> + }
>> +
>> if (c->key_info_file) {
>> if ((err = hls_encryption_start(s)) < 0)
>> goto fail;
>> @@ -1276,6 +1281,15 @@ static int hls_write_packet(AVFormatContext *s,
>> AVPacket *pkt)
>> av_write_frame(oc, NULL); /* Flush any buffered data */
>> + if (hls->flags & HLS_TEMP_FILE) {
>> + size_t len = strlen(oc->filename);
>> + char final_filename[sizeof(oc->filename)];
>> + av_strlcpy(final_filename, oc->filename, len);
>> + final_filename[len-4] = '\0';
>> + ff_rename(oc->filename, final_filename, s);
>> + oc->filename[len-4] = '\0';
>> + }
>> +
>> new_start_pos = avio_tell(hls->avf->pb);
>> hls->size = new_start_pos - hls->start_pos;
>> ret = hls_append_segment(s, hls, hls->duration, hls->start_pos,
>> hls->size);
>> @@ -1406,6 +1420,7 @@ static const AVOption options[] = {
>> {"hls_subtitle_path", "set path of hls subtitles",
>> OFFSET(subtitle_filename), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0, E},
>> {"hls_flags", "set flags affecting HLS playlist and media file
>> generation", OFFSET(flags), AV_OPT_TYPE_FLAGS, {.i64 = 0 }, 0, UINT_MAX, E,
>> "flags"},
>> {"single_file", "generate a single media file indexed with byte
>> ranges", 0, AV_OPT_TYPE_CONST, {.i64 = HLS_SINGLE_FILE }, 0, UINT_MAX, E,
>> "flags"},
>> + {"temp_file", "write segment to temporary file and rename when
>> complete", 0, AV_OPT_TYPE_CONST, {.i64 = HLS_TEMP_FILE }, 0, UINT_MAX, E,
>> "flags"},
>> {"delete_segments", "delete segment files that are no longer part
>> of the playlist", 0, AV_OPT_TYPE_CONST, {.i64 = HLS_DELETE_SEGMENTS }, 0,
>> UINT_MAX, E, "flags"},
>> {"round_durations", "round durations in m3u8 to whole numbers", 0,
>> AV_OPT_TYPE_CONST, {.i64 = HLS_ROUND_DURATIONS }, 0, UINT_MAX, E,
>> "flags"},
>> {"discont_start", "start the playlist with a discontinuity tag", 0,
>> AV_OPT_TYPE_CONST, {.i64 = HLS_DISCONT_START }, 0, UINT_MAX, E, "flags"},
>>
> I think the phrase in your email subject "to create atomically"
> misleading because another renaming may occur afterwards your temp renaming
> if second_level_segment_size or second_level_segment_duration flag is on.
> But the idea to write segment content into a temp file is good by me. To
> ensure the amoticity the two distinct renamings may be merged.
>
I agree my use of "atomic" is confusing. I removed this from the commit
message in v2 of the patch.
>
> I have never thought of it but after your idea I concluded that the
> segment file names are predictable.
> In live streaming enviroment somebody predicting the segment name may see
> the program some seconds earlier than any other viewer by downloading the
> unpublished segment. (with one segment duration seconds earlier)
> If the temp file name would be random name, then your idea may be seen as
> a security feature.
> What is your opinion about this possibility?
I don't have a strong opinion on this. Presumably if someone is concerned
about this, they can still use my temp_file patch and configure their web
server to reject any requests for *.tmp
>
>
> bb
>
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