fix(propagation): filter out unsupported dd_origin values (#6854)

We ran into situations where public clients were sending HTTP requests
with unsupported non-ascii characters in the `x-datadog-origin` headers.
These headers were being propagated, via the
[`HTTPPropagator.extract`](https://github.com/DataDog/dd-trace-py/blob/fd0820b9d7b561d6b75b75c6865a5b3b5792054d/ddtrace/propagation/http.py#L835)
and [gRPC client
interceptor](https://github.com/DataDog/dd-trace-py/blob/c5dfcec45ae21483171c0ac148f94e61ade0b4d2/ddtrace/contrib/grpc/client_interceptor.py#L203),
to branching gRPC calls. The gRPC calls are then failing on the client
side due to gRPC client side validation which [forbids metadata values
with non-ascii](grpc/grpc-go#5318) characters.

The proposed solution here will prevent these unsupported headers values
from being propagated by preventing them from being set within
`Context`. This approach may impact HTTP propagation to branching HTTP
requests, but my understanding is that non-ascii characters are not
supported in these situations either.

## 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
packages, or handles credentials of any kind, I've requested a review
from `@DataDog/security-design-and-guidance`.
- [x] This PR doesn't touch any of that.

---------

Co-authored-by: ZStriker19 <zach.groves@datadoghq.com>
Co-authored-by: Zachary Groves <32471391+ZStriker19@users.noreply.github.com>

ddtrace/context.py

@@ -32,6 +32,8 @@
     ]
 
 
+_DD_ORIGIN_INVALID_CHARS_REGEX = re.compile(r"[^\x20-\x7E]+")
+
 log = get_logger(__name__)
 
 
@@ -64,7 +66,7 @@ def __init__(
         self.trace_id = trace_id  # type: Optional[int]
         self.span_id = span_id  # type: Optional[int]
 
-        if dd_origin is not None:
+        if dd_origin is not None and _DD_ORIGIN_INVALID_CHARS_REGEX.search(dd_origin) is None:
             self._meta[ORIGIN_KEY] = dd_origin
         if sampling_priority is not None:
             self._metrics[SAMPLING_PRIORITY_KEY] = sampling_priority

docs/spelling_wordlist.txt

@@ -27,6 +27,7 @@ app
 appsec
 aredis
 args
+ascii
 asgi
 async
 asyncio

releasenotes/notes/prevent-propagating-unsupported-headers-ddbb32b101ca2cab.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    propagation: Prevent propagating unsupported non-ascii ``origin`` header values.

tests/tracer/test_context.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 import pickle
+from typing import Optional
 
 import pytest
 
@@ -326,3 +327,20 @@ def test_traceparent(context, expected_traceparent):
 def test_tracestate(context, expected_tracestate):
     # type: (Context,str) -> None
     assert context._tracestate == expected_tracestate
+
+
+@pytest.mark.parametrize(
+    "ctx,expected_dd_origin",
+    [
+        (Context(), None),
+        (Context(dd_origin="abcABC"), "abcABC"),
+        (Context(dd_origin="abcABC123"), "abcABC123"),
+        (Context(dd_origin="!@#$%^&*()>?"), "!@#$%^&*()>?"),
+        (Context(dd_origin="\x00\x10"), None),
+        (Context(dd_origin="\x80"), None),
+        (Context(dd_origin="§¢À"), None),
+    ],
+)
+def test_dd_origin_character_set(ctx, expected_dd_origin):
+    # type: (Context,Optional[str]) -> None
+    assert ctx.dd_origin == expected_dd_origin