fix(tracing): Take first sentry-trace header in case multiple are supplied (#6722)

#### Issues

* Resolves: #6703
* Resolves: PY-2571

Author: sl0thentr0py

sentry_sdk/tracing_utils.py

@@ -437,6 +437,14 @@ def extract_sentrytrace_data(
     if not header:
         return None
 
+    if "," in header:
+        # Multiple headers may have been combined into one comma-separated value (RFC 7230 3.2.2); use the first non-empty one.
+        parts = [part.strip() for part in header.split(",")]
+        header = next((part for part in parts if part), "")
+
+    if not header:
+        return None
+
     if header.startswith("00-") and header.endswith("-00"):
         header = header[3:-3]
 

tests/tracing/test_http_headers.py

@@ -38,6 +38,27 @@ def test_sentrytrace_extraction(sampling_decision):
     }
 
 
+def test_sentrytrace_extraction_multiple_headers():
+    sentrytrace_header = (
+        "12312012123120121231201212312012-0415201309082013-1,"
+        "12312012123120121231201212312012-0000000000000000-0"
+    )
+    assert extract_sentrytrace_data(sentrytrace_header) == {
+        "trace_id": "12312012123120121231201212312012",
+        "parent_span_id": "0415201309082013",
+        "parent_sampled": True,
+    }
+
+
+def test_sentrytrace_extraction_leading_empty_fragment():
+    sentrytrace_header = ",12312012123120121231201212312012-0415201309082013-1"
+    assert extract_sentrytrace_data(sentrytrace_header) == {
+        "trace_id": "12312012123120121231201212312012",
+        "parent_span_id": "0415201309082013",
+        "parent_sampled": True,
+    }
+
+
 def test_iter_headers(monkeypatch):
     monkeypatch.setattr(
         Transaction,