avformat/libcurl: streams with unknown total size (Content-Range: bytes X-Y/*) end with a 416 error instead of EOF

[ronag]

Summary

6be7932 (avformat/libcurl: also continue sending requests on unknown size) treats resources of unknown size as infinite "at least until we see a 416 Range Not Satisfiable". But nothing handles that 416. on_done() keeps issuing follow-up requests while file_end < 0. The follow-up issued after the true end gets a 416, which header_callback() treats as an ordinary HTTP error. So after the whole resource has been delivered correctly, the read returns AVERROR_HTTP_RANGE_NOT_SATISFIABLE instead of EOF. If reconnect_on_http_error contains 4xx or 416, it instead retries the 416 with backoff until max_retries runs out.

This is the libcurl counterpart of #46 (http.c).

Location

• Continuation on unknown size:

  FFmpeg/libavformat/libcurl.c

  Lines 554 to 564 in fe63f8f

  	if (code == CURLE_OK && c->stream_ok) {
  	int64_t file_end = c->content_size > 0 ? c->content_size - 1 : -1;
  	if (c->end_off > 0)
  	file_end = FFMIN(file_end, c->end_off - 1);
  	if (c->seekable && c->request_end >= 0 &&
  	(c->request_end < file_end || file_end < 0))
  	{
  	c->is_initial = 0;
  	start_request(c);
  	return;
  	}

• Error branch in header_callback():

  FFmpeg/libavformat/libcurl.c

  Lines 405 to 418 in fe63f8f

  	} else {
  	c->loop->num_errors++;
  	c->stream_ok = 0;
  	if (!c->status) {
  	if (http_error_is_recoverable(c, status))
  	c->status = AVERROR(EAGAIN);
  	else
  	c->status = ff_http_averror(status, AVERROR(EIO));
  	}
  	curl_off_t retry_after = 0;
  	curl_easy_getinfo(c->easy, CURLINFO_RETRY_AFTER, &retry_after);
  	c->retry_after = retry_after;
  	}

Reproduction

Server replies 206 with Content-Range: bytes 0-1048575/* (harness from #71):

$ t libcurl:http://127.0.0.1:18080/unknown --readall
size: -78 seekable: 1
readall: total=1048576 last=-909194488 (Server returned 416 Range Not Satisfiable) pb->error=-909194488 eof=1

All 1048576 bytes are delivered, and then the stream ends in an error rather than EOF.

Suggested fix

In header_callback(), when a follow-up request gets a 416 and content_size is unknown (probed, request_start equals the bytes delivered so far), set status = AVERROR_EOF and learn content_size = request_start. Exclude this case from the reconnect_on_http_error matching. Doing the same for a seek past the (unknown) end also covers the unknown-size variant of #74.