Request-id middleware sketch

log_request_id.py

import logbook

class LogRequestIDMiddleware(object):
    def __init__(self, application):
        self.application = application

    def make_processor(self, request_id):
        @logbook.Processor
        def processor(log_record):
            log_record.extra['request_id'] = request_id
        return processor

    def __call__(self, environ, start_response):
        req_id = environ.get("HTTP_X_REQUEST_ID", "no-request-id")
        with self.make_processor(req_id).threadbound():
            return self.application(environ, start_response)

request_id.py

import uuid

class RequestIDMiddleware(object):
    def __init__(self, application):
        self.application = application

    def __call__(self, environ, start_response):
        req_id = unicode(uuid.uuid4())
        environ["HTTP_X_REQUEST_ID"] = req_id
        def new_start_response(status, response_headers, exc_info=None):
            response_headers.append(("X-Request-ID", req_id))
            return start_response(status, response_headers, exc_info)
        return self.application(environ, new_start_response)

test_app.py

import flask, logbook

from request_id import RequestIDMiddleware
from log_request_id import LogRequestIDMiddleware

app = flask.Flask("testapp")

fstr = (
    "{record.extra[request_id]} [{record.time:%Y-%m-%d %H:%M:%S}] {record.level_name}: "
    "{record.channel}: {record.message}"
)
# Is there a better place to do global configuration like this?
logbook.StderrHandler(format_string=fstr, bubble=False).push_application()

@app.route("/")
def root():
    logbook.Logger("root").info("This is a message")
    return "hi! " + flask.request.headers.get("X-Request-ID", "No Id Set!")

# Plain app: no request ids, logs show no request ids
wsgi_app = app
# Log app: no request ids, logs show request id of "no-request-id"
lid_app = LogRequestIDMiddleware(wsgi_app)
# Request Id app: Request ids are set, but don't appear in logs
rid_app = RequestIDMiddleware(wsgi_app)
# Full app: Request ids are set, and appear in logs
lrid_app = RequestIDMiddleware(LogRequestIDMiddleware(wsgi_app))

Quick correction:

Plain app: no request ids, logs show no request ids

wsgi_app = app.wsgi_app

Log app: no request ids, logs show request id of "no-request-id"

app.wsgi_app = LogRequestIDMiddleware(wsgi_app)

Request Id app: Request ids are set, but don't appear in logs

app.wsgi_app = RequestIDMiddleware(wsgi_app)

Full app: Request ids are set, and appear in logs

app.wsgi_app = RequestIDMiddleware(LogRequestIDMiddleware(wsgi_app))