feat: Send transactions in envelopes (#729)

This matches what the JS SDK does and what the Tracing dev docs
indicates.

sentry_sdk/client.py

@@ -7,11 +7,12 @@
 
 from sentry_sdk._compat import string_types, text_type, iteritems
 from sentry_sdk.utils import (
-    handle_in_app,
-    get_type_name,
     capture_internal_exceptions,
     current_stacktrace,
     disable_capture_event,
+    format_timestamp,
+    get_type_name,
+    handle_in_app,
     logger,
 )
 from sentry_sdk.serializer import serialize
@@ -20,7 +21,7 @@
 from sentry_sdk.integrations import setup_integrations
 from sentry_sdk.utils import ContextVar
 from sentry_sdk.sessions import SessionFlusher
-from sentry_sdk.envelope import Envelope
+from sentry_sdk.envelope import Envelope, Item, PayloadRef
 
 from sentry_sdk._types import MYPY
 
@@ -334,7 +335,22 @@ def capture_event(
         if session:
             self._update_session_from_event(session, event)
 
-        self.transport.capture_event(event_opt)
+        if event_opt.get("type") == "transaction":
+            # Transactions should go to the /envelope/ endpoint.
+            self.transport.capture_envelope(
+                Envelope(
+                    headers={
+                        "event_id": event_opt["event_id"],
+                        "sent_at": format_timestamp(datetime.utcnow()),
+                    },
+                    items=[
+                        Item(payload=PayloadRef(json=event_opt), type="transaction"),
+                    ],
+                )
+            )
+        else:
+            # All other events go to the /store/ endpoint.
+            self.transport.capture_event(event_opt)
         return event_id
 
     def capture_session(

tests/conftest.py

@@ -211,12 +211,20 @@ def inner():
         events = []
         test_client = sentry_sdk.Hub.current.client
         old_capture_event = test_client.transport.capture_event
+        old_capture_envelope = test_client.transport.capture_envelope
 
-        def append(event):
+        def append_event(event):
             events.append(event)
             return old_capture_event(event)
 
-        monkeypatch.setattr(test_client.transport, "capture_event", append)
+        def append_envelope(envelope):
+            for item in envelope:
+                if item.headers.get("type") in ("event", "transaction"):
+                    events.append(item.payload.json)
+            return old_capture_envelope(envelope)
+
+        monkeypatch.setattr(test_client.transport, "capture_event", append_event)
+        monkeypatch.setattr(test_client.transport, "capture_envelope", append_envelope)
         return events
 
     return inner

tests/test_tracing.py

@@ -22,7 +22,8 @@ def test_basic(sentry_init, capture_events, sample_rate):
             pass
 
     if sample_rate:
-        (event,) = events
+        assert len(events) == 1
+        event = events[0]
 
         span1, span2 = event["spans"]
         parent_span = event