avformat/http: request more data after partial response

If the Content-Range indicates a smaller range than what we expected,
we should send a new request for the remainder before attempting to read
more.

Again, this commit is theoretically non-functional on its own, since any
conforming HTTP server should give us the entire range we asked for in the
first place, but it is semantically independent from and prepares us for the
following changes.

libavformat/http.c

@@ -1711,6 +1711,8 @@ static int http_buf_read(URLContext *h, uint8_t *buf, int size)
         uint64_t target_end = s->range_end ? s->range_end : file_end;
         if ((!s->willclose || s->chunksize == UINT64_MAX) && s->off >= file_end)
             return AVERROR_EOF;
+        if (s->off == target_end && target_end < file_end)
+            return AVERROR(EAGAIN); /* reached end of content range */
         len = ffurl_read(s->hd, buf, size);
         if ((!len || len == AVERROR_EOF) &&
             (!s->willclose || s->chunksize == UINT64_MAX) && s->off < target_end) {
@@ -1795,6 +1797,16 @@ static int http_read_stream(URLContext *h, uint8_t *buf, int size)
 
         if (read_ret == AVERROR_EXIT)
             break;
+        else if (read_ret == AVERROR(EAGAIN)) {
+            /* send new request for more data on existing connection */
+            AVDictionary *options = NULL;
+            if (s->willclose)
+                ffurl_closep(&s->hd);
+            read_ret = http_open_cnx(h, &options);
+            av_dict_free(&options);
+            if (read_ret == 0)
+                goto retry;
+        }
 
         if (h->is_streamed && !s->reconnect_streamed)
             break;
@@ -1824,6 +1836,7 @@ static int http_read_stream(URLContext *h, uint8_t *buf, int size)
             return read_ret;
         }
 
+retry:
         read_ret = http_buf_read(h, buf, size);
     }