tests/functional/asset: Verify downloaded size

If the server provides a Content-Length header, use that to verify the
size of the downloaded file. This catches cases where the connection
terminates early, and gives the opportunity to retry. Without this, the
checksum will likely mismatch and fail without retry.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Message-ID: <20250312130002.945508-3-npiggin@gmail.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/functional/qemu_test/asset.py

@@ -121,6 +121,20 @@ class Asset:
                 with tmp_cache_file.open("xb") as dst:
                     with urllib.request.urlopen(self.url) as resp:
                         copyfileobj(resp, dst)
+                        length_hdr = resp.getheader("Content-Length")
+
+                # Verify downloaded file size against length metadata, if
+                # available.
+                if length_hdr is not None:
+                    length = int(length_hdr)
+                    fsize = tmp_cache_file.stat().st_size
+                    if fsize != length:
+                        self.log.error("Unable to download %s: "
+                                       "connection closed before "
+                                       "transfer complete (%d/%d)",
+                                       self.url, fsize, length)
+                        tmp_cache_file.unlink()
+                        continue
                 break
             except FileExistsError:
                 self.log.debug("%s already exists, "