CeleryGetter.get() returns non-string values, crashes TraceContext propagator

[DrMeers]

Description

CeleryGetter.get() can return non-string values (e.g. int) from Celery task request attributes, which causes TraceState.from_header() to crash with:

TypeError: expected string or bytes-like object, got 'int'

Stack trace

celery/utils/dispatch/signal.py:280 in send
opentelemetry/instrumentation/celery/__init__.py:174 in _trace_prerun
opentelemetry/propagate/__init__.py:101 in extract
opentelemetry/propagators/composite.py:52 in extract
opentelemetry/trace/propagation/tracecontext.py:76 in extract
opentelemetry/trace/span.py:386 in from_header
re/__init__.py:207 in split
TypeError: expected string or bytes-like object, got 'int'

Root cause

CeleryGetter.get() uses getattr(carrier, key, None) against task.request, which is a Celery Context object. Celery's Context.__init__ copies all message properties as instance attributes via self.__dict__.update(), including numeric values like timelimit.

When the value is an int, the existing type check wraps it in a tuple but doesn't coerce to string:

class CeleryGetter(Getter):
    def get(self, carrier, key):
        value = getattr(carrier, key, None)
        if value is None:
            return None
        if isinstance(value, str) or not isinstance(value, Iterable):
            value = (value,)  # wraps int in tuple, but doesn't convert to str
        return value

The TextMapPropagator contract expects string values, and TraceState.from_header() passes each value directly to re.split() without type-checking.

Suggested fix

Coerce non-string values to strings in CeleryGetter.get():

def get(self, carrier, key):
    value = getattr(carrier, key, None)
    if value is None:
        return None
    if isinstance(value, str):
        value = (value,)
    elif isinstance(value, Iterable):
        value = tuple(str(v) if not isinstance(v, str) else v for v in value)
    else:
        value = (str(value),)
    return value

Alternatively, TraceState.from_header() could validate input types before calling re.split().

Environment

• opentelemetry-instrumentation-celery 0.61b0
• opentelemetry-sdk 1.x
• celery 5.x
• Python 3.12

Related

• celery instrumentation setting a single time limit (soft_time_limit or time_limit) leads to warning: "Attribute 'celery.timelimit' mixes types str and int in attribute value sequence" #2022 (timelimit str/int mixing in span attributes — same root cause, different code path)