fix(propagation): check for span_id and trace_id before creating span link [backport 2.3] (#7724)

Backport 7954661 from #7708 to 2.3.

Fixes: #7701

## Checklist

- [x] Change(s) are motivated and described in the PR description.
- [x] Testing strategy is described if automated tests are not included
in the PR.
- [x] Risk is outlined (performance impact, potential for breakage,
maintainability, etc).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
are followed. If no release note is required, add label
`changelog/no-changelog`.
- [x] Documentation is included (in-code, generated user docs, [public
corp docs](https://github.com/DataDog/documentation/)).
- [x] Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist

- [x] Title is accurate.
- [x] No unnecessary changes are introduced.
- [x] Description motivates each change.
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes unless absolutely necessary.
- [x] Testing strategy adequately addresses listed risk(s).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] Release note makes sense to a user of the library.
- [x] Reviewer has explicitly acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment.
- [x] Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)
- [x] If this PR touches code that signs or publishes builds or
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from `@DataDog/security-design-and-guidance`.
- [x] This PR doesn't touch any of that.

Co-authored-by: Zachary Groves <[email protected]>

Author: github-actions[bot]

ddtrace/propagation/http.py

@@ -839,7 +839,8 @@ def _resolve_contexts(contexts, styles_w_ctx, normalized_headers):
         links = []
         for context in contexts[1:]:
             style_w_ctx = styles_w_ctx[contexts.index(context)]
-            if context.trace_id != primary_context.trace_id:
+            # encoding expects at least trace_id and span_id
+            if context.span_id and context.trace_id and context.trace_id != primary_context.trace_id:
                 links.append(
                     SpanLink(
                         context.trace_id,

releasenotes/notes/propagation_check_id_valid_before_span_link-08be876337762a15.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    propagation: This fix resolves an issue where a ``Context`` generated from extracted headers could
+    lack a span_id or trace_id, leading ``SpanLink`` encoding errors.

tests/tracer/test_propagation.py

@@ -1046,6 +1046,11 @@ def test_extract_tracecontext(headers, expected_context):
     _HTTP_HEADER_B3_SPAN_ID: "NON_HEX",
     _HTTP_HEADER_B3_SAMPLED: "3",  # unexpected sampling value
 }
+B3_HEADERS_VALID_W_OUT_SPAN_ID = {
+    _HTTP_HEADER_B3_TRACE_ID: "80f198ee56343ba864fe8b2a57d3eff7",
+    _HTTP_HEADER_B3_SAMPLED: "1",
+}
+
 B3_SINGLE_HEADERS_VALID = {
     _HTTP_HEADER_B3_SINGLE: "80f198ee56343ba864fe8b2a57d3eff7-e457b5a2e4d86bd1-1",
 }
@@ -1066,11 +1071,18 @@ def test_extract_tracecontext(headers, expected_context):
 DATADOG_TRACECONTEXT_MATCHING_TRACE_ID_HEADERS.update(TRACECONTEXT_HEADERS_VALID_64_bit)
 
 # edge case testing
-ALL_HEADERS_CHAOTIC = {}
-ALL_HEADERS_CHAOTIC.update(DATADOG_HEADERS_VALID_MATCHING_TRACE_CONTEXT_VALID_TRACE_ID)
-ALL_HEADERS_CHAOTIC.update(TRACECONTEXT_HEADERS_VALID_64_bit)
-ALL_HEADERS_CHAOTIC.update(B3_SINGLE_HEADERS_VALID)
-ALL_HEADERS_CHAOTIC.update(B3_HEADERS_INVALID)
+ALL_HEADERS_CHAOTIC_1 = {}
+ALL_HEADERS_CHAOTIC_1.update(DATADOG_HEADERS_VALID_MATCHING_TRACE_CONTEXT_VALID_TRACE_ID)
+ALL_HEADERS_CHAOTIC_1.update(TRACECONTEXT_HEADERS_VALID_64_bit)
+ALL_HEADERS_CHAOTIC_1.update(B3_SINGLE_HEADERS_VALID)
+ALL_HEADERS_CHAOTIC_1.update(B3_HEADERS_INVALID)
+
+# edge case testing
+ALL_HEADERS_CHAOTIC_2 = {}
+ALL_HEADERS_CHAOTIC_2.update(DATADOG_HEADERS_VALID)
+ALL_HEADERS_CHAOTIC_2.update(TRACECONTEXT_HEADERS_VALID_64_bit)
+ALL_HEADERS_CHAOTIC_2.update(B3_HEADERS_VALID_W_OUT_SPAN_ID)
+ALL_HEADERS_CHAOTIC_2.update(B3_SINGLE_HEADERS_INVALID)
 
 EXTRACT_FIXTURES = [
     # Datadog headers
@@ -1786,6 +1798,40 @@ def test_DD_TRACE_PROPAGATION_STYLE_EXTRACT_overrides_DD_TRACE_PROPAGATION_STYLE
             span_links=[],
         ),
     ),
+    # The trace_id from Datadog context will not align with the tracecontext primary context
+    # therefore we get a span link. B3 single headers are invalid so we won't see a trace of them.
+    # The b3 multi headers are missing a span_id, so we will skip creating a span link for it.
+    (
+        "all_headers_all_styles_do_not_create_span_link_for_context_w_out_span_id",
+        [
+            _PROPAGATION_STYLE_W3C_TRACECONTEXT,
+            PROPAGATION_STYLE_DATADOG,
+            PROPAGATION_STYLE_B3_SINGLE,
+            PROPAGATION_STYLE_B3_MULTI,
+        ],
+        ALL_HEADERS_CHAOTIC_2,
+        Context(
+            trace_id=7277407061855694839,
+            span_id=67667974448284343,
+            meta={
+                "traceparent": "00-000000000000000064fe8b2a57d3eff7-00f067aa0ba902b7-01",
+                "tracestate": "dd=s:2;o:rum;t.dm:-4;t.usr.id:baz64,congo=t61rcWkgMzE",
+                "_dd.p.dm": "-4",
+                "_dd.p.usr.id": "baz64",
+                "_dd.origin": "rum",
+            },
+            metrics={"_sampling_priority_v1": 2},
+            span_links=[
+                SpanLink(
+                    trace_id=13088165645273925489,
+                    span_id=5678,
+                    tracestate=None,
+                    flags=1,
+                    attributes={"reason": "terminated_context", "context_headers": "datadog"},
+                )
+            ],
+        ),
+    ),
     # tracecontext, b3, and b3multi all have the same trace_id
     # therefore only datadog SpanLink is added to context
     (
@@ -1872,7 +1918,7 @@ def test_DD_TRACE_PROPAGATION_STYLE_EXTRACT_overrides_DD_TRACE_PROPAGATION_STYLE
             _PROPAGATION_STYLE_W3C_TRACECONTEXT,
             PROPAGATION_STYLE_B3_SINGLE,
         ],
-        ALL_HEADERS_CHAOTIC,
+        ALL_HEADERS_CHAOTIC_1,
         Context(
             trace_id=7277407061855694839,
             span_id=5678,