On Fri, Jul 3, 2015 at 12:32 PM, Nicolas George <geo...@nsup.org> wrote:
> Le quintidi 15 messidor, an CCXXIII, Stephan Holljes a écrit :
>> Signed-off-by: Stephan Holljes <klaxa1...@googlemail.com>
>> ---
>> doc/examples/Makefile | 1 +
>> doc/examples/http_multiclient.c | 101
>> ++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 102 insertions(+)
>> create mode 100644 doc/examples/http_multiclient.c
>>
>> diff --git a/doc/examples/Makefile b/doc/examples/Makefile
>> index 9699f11..8c9501b 100644
>> --- a/doc/examples/Makefile
>> +++ b/doc/examples/Makefile
>> @@ -18,6 +18,7 @@ EXAMPLES= avio_list_dir \
>> extract_mvs \
>> filtering_video \
>> filtering_audio \
>> + http_multiclient \
>> metadata \
>> muxing \
>> remuxing \
>> diff --git a/doc/examples/http_multiclient.c
>> b/doc/examples/http_multiclient.c
>> new file mode 100644
>> index 0000000..fdecab4
>> --- /dev/null
>> +++ b/doc/examples/http_multiclient.c
>> @@ -0,0 +1,101 @@
>> +/*
>> + * copyright (c) 2015 Stephan Holljes
>> + *
>> + * 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
>> + */
>> +
>> +/**
>> + * @file
>> + * libavformat multi-client network API usage example.
>> + *
>> + * @example http_multiclient.c
>> + * This example will serve a file without decoding or demuxing it over http.
>
>> + * Multiple clients can connect and will receive the same file.
>
> Did you test several simultaneous clients? It should work, because fork() is
> a strong isolation, so it if works for one it works for many, but testing is
> always better.
Yes, I tested it with multiple simultaneous wget instances and with
siege (a benchmark tool for webservers).
>
>> + */
>> +
>> +#include <libavformat/avformat.h>
>> +#include <unistd.h>
>> +
>> +int main(int argc, char **argv)
>> +{
>> + AVDictionary *options = NULL;
>> + AVIOContext *input = NULL, *client = NULL, *server = NULL;
>> + const char *in_uri, *out_uri;
>> + int ret, pid, n;
>> + uint8_t buf[1024];
>> +
>> + if (argc < 3) {
>> + printf("usage: %s input http://hostname[:port]\n";
>> + "API example program to serve http to multiple clients.\n"
>
>> + "The output format is guessed according to the input file
>> extension.\n"
>
> I suspect this sentence is outdated.
>
>> + "\n", argv[0]);
>> + return 1;
>> + }
>> +
>> + in_uri = argv[1];
>> + out_uri = argv[2];
>> +
>> + av_register_all();
>> + avformat_network_init();
>> +
>> + if ((ret = av_dict_set(&options, "listen", "2", 0)) < 0)
>> + goto end;
>> + if ((ret = avio_open2(&server, out_uri, AVIO_FLAG_READ_WRITE, NULL,
>> &options)) < 0)
>> + goto end;
>> + fprintf(stderr, "Entering main loop.\n");
>> + for(;;) {
>> + if ((ret = avio_accept(server, &client)) < 0)
>> + goto end;
>> + fprintf(stderr, "Accepted client, forking process.\n");
>
>> + pid = fork();
>
> Zombie apocalypse ahead!
>
> Well, setting SIGCHLD to SIG_IGN is hardly portable, double-fork is ugly and
> proper waiting is painful, so I guess we can leave the zombies for now in a
> simple testing program, but a comment stating it would be useful.
>
>> + if (pid == 0) {
>
> Maybe also:
>
> if (pid < 0) {
> perror("Fork failed");
> err = AVERROR(errno);
> goto end;
> }
>
>> + fprintf(stderr, "Opening input file.\n");
>> + if ((ret = avio_open2(&input, in_uri, AVIO_FLAG_READ, NULL,
>> NULL)) < 0)
>> + goto end;
>> + fprintf(stderr, "In child.\n");
>> + avio_handshake(client);
>> + fprintf(stderr, "Handshake performed.\n");
>
> It would feel more natural to perform the handshake before opening the input
> file. Note that since this is your code, you are free to reject this kind of
> stylistic remark. In this particular case, it will be necessary when
> extending the code, because avio_handshake() will be responsible for getting
> the request file name from the client.
>
> Also: since this is fork()ing instead of pthread_create()ing, you probably
> should close the server context in the client process. And you definitely
> must close the client context in the server process.
I see that I missed closing the client context in the server process,
but I think the server context is being closed when the client process
reaches the end label.
>
>> + for(;;) {
>> + n = avio_read(input, buf, sizeof(buf));
>> + fprintf(stderr, "Read %d bytes from input.\n", n);
>
>> + if (n <= 0) {
>> + fprintf(stderr, "n is negative, abort.\n");
>> + break;
>> + }
>
> n == 0 is not possible and not supposed to be possible according to the API.
>
> n < 0 is a proper error code, but the particular code AVERROR_EOF should not
> be treated as an error, i.e. not print an alarming error message. It usually
> goes something like that:
>
> if (n < 0) {
> if (n == AVERROR_EOF)
> break;
> av_log(ctx, AV_LOG_ERROR, "Error reading from input: %s\n",
> av_err2str(n));
> goto fail;
> }
>
>> + fprintf(stderr, "Writing %d bytes of data.\n", n);
>> + avio_write(client, buf, n);
>> + avio_flush(client);
>> + }
>> + fprintf(stderr, "Flushing client\n");
>> + avio_flush(client);
>> + fprintf(stderr, "Closing client\n");
>> + avio_close(client);
>> + break;
>> + }
>> + }
>> +
>> +end:
>
>> + if (ret)
>> + fprintf(stderr, "Some errors occured.\n");
>
> av_err2str() to know what exactly. And knowing where the error happened
> would be nicer.
>
>> + if (server)
>> + avio_close(server);
>> + if (input)
>> + avio_close(input);
>
> No need to check, avio_close() works for NULL.
>
>> + if (ret < 0 && ret != AVERROR_EOF)
>> + return 1;
>> + return 0;
>> +}
>
> Regards,
>
> --
> Nicolas George
Regards,
Stephan
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