fix test case and invalid algo fallback logic

Author: BYK

sentry_sdk/transport.py

@@ -234,28 +234,38 @@ def __init__(self, options):
             experiments.get("transport_zlib_compression_level"),
         )
         compression_algo = experiments.get(
-            "transport_compression_algo", "br" if brotli is not None else "gzip"
+            "transport_compression_algo",
+            (
+                "gzip"
+                # if only compression level is set, assume gzip for backwards compatibility
+                # if we don't have brotli available, fallback to gzip
+                if compression_level is not None or brotli is None
+                else "br"
+            ),
         )
+
         if compression_algo == "br" and brotli is None:
             logger.warning(
                 "You asked for brotli compression without the Brotli module, falling back to gzip -9"
             )
             compression_algo = "gzip"
             compression_level = None
 
-        self._compression_algo = compression_algo
-        if compression_level is not None:
-            self._compression_level = compression_level
-        elif compression_algo == "gzip":
-            self._compression_level = 9
-        elif compression_algo == "br":
-            self._compression_level = 4
-        else:
+        if compression_algo not in ("br", "gzip"):
             logger.warning(
                 "Unknown compression algo %s, disabling compression", compression_algo
             )
             self._compression_level = 0
             self._compression_algo = None
+        else:
+            self._compression_algo = compression_algo
+
+        if compression_level is not None:
+            self._compression_level = compression_level
+        elif self._compression_algo == "gzip":
+            self._compression_level = 9
+        elif self._compression_algo == "br":
+            self._compression_level = 4
 
     def record_lost_event(
         self,

tests/test_transport.py

@@ -123,7 +123,7 @@ def mock_transaction_envelope(span_count):
 @pytest.mark.parametrize("client_flush_method", ["close", "flush"])
 @pytest.mark.parametrize("use_pickle", (True, False))
 @pytest.mark.parametrize("compression_level", (0, 9, None))
-@pytest.mark.parametrize("compression_algo", ("gzip", "br", None))
+@pytest.mark.parametrize("compression_algo", ("gzip", "br", "<invalid>", None))
 @pytest.mark.parametrize(
     "http2", [True, False] if sys.version_info >= (3, 8) else [False]
 )
@@ -175,16 +175,19 @@ def test_transport_works(
     assert not err and not out
     assert capturing_server.captured
     should_compress = (
-        (
-            compression_level is None
-        )  # default is to compress with bortli if available, gzip otherwise
-        or (
-            compression_level > 0
-        )  # setting compression level to 0 means don't compress
+        # default is to compress with brotli if available, gzip otherwise
+        (compression_level is None)
         or (
-            compression_algo is None
-        )  # if we couldn't resolve to a known algo, we don't compress
+            # setting compression level to 0 means don't compress
+            compression_level
+            > 0
+        )
+    ) and (
+        # if we couldn't resolve to a known algo, we don't compress
+        compression_algo
+        != "<invalid>"
     )
+
     assert capturing_server.captured[0].compressed == should_compress
 
     assert any("Sending envelope" in record.msg for record in caplog.records) == debug