[FFmpeg-devel] [PATCH v2 2/8] avformat/udp: make recv addr of each packet available

[Timo Rothenpieler]

On 07/07/2025 10:03, Jack Lau wrote:
> 
> 
>> On Jul 7, 2025, at 02:36, Timo Rothenpieler <timo at rothenpieler.org> wrote:
>>
>> ---
>> libavformat/network.h |  2 ++
>> libavformat/udp.c     | 25 +++++++++++++++++--------
>> 2 files changed, 19 insertions(+), 8 deletions(-)
>>
>> diff --git a/libavformat/network.h b/libavformat/network.h
>> index ca214087fc..48bb75a758 100644
>> --- a/libavformat/network.h
>> +++ b/libavformat/network.h
>> @@ -338,4 +338,6 @@ int ff_connect_parallel(struct addrinfo *addrs, int timeout_ms_per_address,
>>                          int parallel, URLContext *h, int *fd,
>>                          int (*customize_fd)(void *, int, int), void *customize_ctx);
>>
>> +void ff_udp_get_last_recv_addr(URLContext *h, struct sockaddr_storage *addr);
>> +
>> #endif /* AVFORMAT_NETWORK_H */
>> diff --git a/libavformat/udp.c b/libavformat/udp.c
>> index 30f075de8e..7d64ff07ed 100644
>> --- a/libavformat/udp.c
>> +++ b/libavformat/udp.c
>> @@ -107,7 +107,7 @@ typedef struct UDPContext {
>>      pthread_cond_t cond;
>>      int thread_started;
>> #endif
>> -    uint8_t tmp[UDP_MAX_PKT_SIZE+4];
>> +    uint8_t tmp[UDP_MAX_PKT_SIZE + 4 + sizeof(struct sockaddr_storage)];
>>      int remaining_in_dg;
>>      char *localaddr;
>>      int timeout;
>> @@ -115,6 +115,7 @@ typedef struct UDPContext {
>>      char *sources;
>>      char *block;
>>      IPSourceFilters filters;
>> +    struct sockaddr_storage last_recv_addr;
>> } UDPContext;
>>
>> #define OFFSET(x) offsetof(UDPContext, x)
>> @@ -467,6 +468,12 @@ int ff_udp_get_local_port(URLContext *h)
>>      return s->local_port;
>> }
>>
>> +void ff_udp_get_last_recv_addr(URLContext *h, struct sockaddr_storage *addr)
>> +{
>> +    UDPContext *s = h->priv_data;
>> +    *addr = s->last_recv_addr;
>> +}
>> +
>> /**
>>   * Return the udp file handle for select() usage to wait for several RTP
>>   * streams at the same time.
>> @@ -498,13 +505,14 @@ static void *circular_buffer_task_rx( void *_URLContext)
>>          int len;
>>          struct sockaddr_storage addr;
>>          socklen_t addr_len = sizeof(addr);
>> +        const int header_sz = 4 + addr_len;
>>
>>          pthread_mutex_unlock(&s->mutex);
>>          /* Blocking operations are always cancellation points;
>>             see "General Information" / "Thread Cancelation Overview"
>>             in Single Unix. */
>>          pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &old_cancelstate);
>> -        len = recvfrom(s->udp_fd, s->tmp+4, sizeof(s->tmp)-4, 0, (struct sockaddr *)&addr, &addr_len);
>> +        len = recvfrom(s->udp_fd, s->tmp + header_sz, sizeof(s->tmp) - header_sz, 0, (struct sockaddr *)&addr, &addr_len);
>>          pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old_cancelstate);
>>          pthread_mutex_lock(&s->mutex);
>>          if (len < 0) {
>> @@ -517,8 +525,9 @@ static void *circular_buffer_task_rx( void *_URLContext)
>>          if (ff_ip_check_source_lists(&addr, &s->filters))
>>              continue;
>>          AV_WL32(s->tmp, len);
>> +        memcpy(s->tmp + 4, &addr, sizeof(addr));
>>
>> -        if (av_fifo_can_write(s->fifo) < len + 4) {
>> +        if (av_fifo_can_write(s->fifo) < len + header_sz) {
>>              /* No Space left */
>>              if (s->overrun_nonfatal) {
>>                  av_log(h, AV_LOG_WARNING, "Circular buffer overrun. "
>> @@ -532,7 +541,7 @@ static void *circular_buffer_task_rx( void *_URLContext)
>>                  goto end;
>>              }
>>          }
>> -        av_fifo_write(s->fifo, s->tmp, len + 4);
>> +        av_fifo_write(s->fifo, s->tmp, len + header_sz);
>>          pthread_cond_signal(&s->cond);
>>      }
>>
>> @@ -991,8 +1000,7 @@ static int udp_read(URLContext *h, uint8_t *buf, int size)
>> {
>>      UDPContext *s = h->priv_data;
>>      int ret;
>> -    struct sockaddr_storage addr;
>> -    socklen_t addr_len = sizeof(addr);
>> +    socklen_t addr_len = sizeof(s->last_recv_addr);
>> #if HAVE_PTHREAD_CANCEL
>>      int avail, nonblock = h->flags & AVIO_FLAG_NONBLOCK;
>>
>> @@ -1004,6 +1012,7 @@ static int udp_read(URLContext *h, uint8_t *buf, int size)
>>                  uint8_t tmp[4];
>>
>>                  av_fifo_read(s->fifo, tmp, 4);
>> +                av_fifo_read(s->fifo, &s->last_recv_addr, sizeof(s->last_recv_addr));
>>                  avail = AV_RL32(tmp);
>>                  if(avail > size){
>>                      av_log(h, AV_LOG_WARNING, "Part of datagram lost due to insufficient buffer size\n");
>> @@ -1043,10 +1052,10 @@ static int udp_read(URLContext *h, uint8_t *buf, int size)
>>          if (ret < 0)
>>              return ret;
>>      }
>> -    ret = recvfrom(s->udp_fd, buf, size, 0, (struct sockaddr *)&addr, &addr_len);
>> +    ret = recvfrom(s->udp_fd, buf, size, 0, (struct sockaddr *)&s->last_recv_addr, &addr_len);
>>      if (ret < 0)
>>          return ff_neterrno();
>> -    if (ff_ip_check_source_lists(&addr, &s->filters))
>> +    if (ff_ip_check_source_lists(&s->last_recv_addr, &s->filters))
>>          return AVERROR(EINTR);
>>      return ret;
>> }
>> -- 
>> 2.49.0
>>
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> I think it’s necessary to add "socklen_t last_recv_len".
> I’ve send the fixes to your GitHub repo https://github.com/BtbN/FFmpeg/pull/3 because my fixes depends your patchset.

Anything that needs the len can just get sizeof(sockaddr_storage), can't it?
Getting bigger than neccesary of a size won't break anything, as long as 
it isn't too small.