Support builds on WebAssembly

[xelandernt]

Description

Hi, I am not able to get logfire working on Cloudflare workers (python), because logfire does not work using pyodide

Reproduction

pyproject.toml

[project]
name = "logfire-cf-workers"
version = "0.1.0"
description = "Add your description here"
readme = "README.md"
requires-python = ">=3.13"
dependencies = [
    "fastapi>=0.124.4",
    "logfire[fastapi]>=4.16.0",
]

[dependency-groups]
dev = [
    "workers-py>=1.7.0",
    "workers-runtime-sdk>=0.3.1",
]

main.py

import logfire # this line causes the error
from fastapi import FastAPI


app = FastAPI()


@app.get("/")
async def root():
    return "HELLO WORLD"


try:
    from workers import WorkerEntrypoint
    import asgi

    class Default(WorkerEntrypoint):
        async def fetch(self, request):
            return await asgi.fetch(app, request, self.env)
except (ModuleNotFoundError, ImportError):
    pass

wrangler.jsonc

{
    "$schema": "node_modules/wrangler/config-schema.json",
	"name": "worker",
	"main": "main.py",
    "compatibility_date": "2025-11-02",
    "compatibility_flags": [
		"python_workers"
	],
    "vars": {
    },
	"observability": {
		"enabled": true
	}
}

Then run:

uv run pywrangler dev

Error:

✘ [ERROR] service core:user:worker: Uncaught Error: PythonError: Traceback (most recent call last):

    File "/lib/python313.zip/_pyodide/_base.py", line 666, in pyimport_impl
      res = __import__(stem, fromlist=fromlist)
    File "/session/metadata/main.py", line 1, in <module>
      import logfire
    File "/session/metadata/python_modules/logfire/__init__.py", line 7, in <module>
      from logfire.propagate import attach_context, get_context
    File "/session/metadata/python_modules/logfire/propagate.py", line 20, in <module>
      from opentelemetry import context as otel_context, propagate, trace
    File "/session/metadata/python_modules/opentelemetry/context/__init__.py", line 163, in <module>
      _SUPPRESS_INSTRUMENTATION_KEY = create_key("suppress_instrumentation")
    File "/session/metadata/python_modules/opentelemetry/context/__init__.py", line 82, in
  create_key
      return keyname + "-" + str(uuid4())
                                 ~~~~~^^
    File "/lib/python313.zip/uuid.py", line 712, in uuid4
      return UUID(bytes=os.urandom(16), version=4)
                        ~~~~~~~~~~^^^^
    File "/lib/python3.13/site-packages/_cloudflare/entropy_patches.py", line 49, in patch_urandom
      raise_unless_entropy_allowed()
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
    File "/lib/python3.13/site-packages/_cloudflare/allow_entropy.py", line 34, in
  raise_unless_entropy_allowed
      raise OSError(EIO, "Cannot get entropy outside of request context")
  OSError: [Errno 29] Cannot get entropy outside of request context
  
    at null.<anonymous> (pyodide-internal:generated/emscriptenSetup:19872:14) in new_error
    at [object Object] in $wrap_exception
    at [object Object] in $pythonexc2js
    at null.<anonymous> (pyodide-internal:generated/emscriptenSetup:22390:15) in
  callPyObjectKwargsPromising

[alexmojaki]

Pyodide is fine, you can use logfire in https://pydantic.run/

The problem is cloudflare, as can be seen at the end of the traceback:

    File "/lib/python3.13/site-packages/_cloudflare/allow_entropy.py", line 34, in
  raise_unless_entropy_allowed
      raise OSError(EIO, "Cannot get entropy outside of request context")
  OSError: [Errno 29] Cannot get entropy outside of request context

And this happens when importing opentelemetry, not just logfire.

I suggest opening an issue in https://github.com/open-telemetry/opentelemetry-python to fallback to plain random when uuid/urandom fails in create_key, I don't think it really needs true randomness.