Reduce StripeClient() cold start latency for serverless environments

[jar-stripe]

Why?

Users in serverless environments (AWS Lambda with 128MB memory / 3s timeout) report that stripe.StripeClient() initialization alone can exceed their invocation timeout budget. A major contributor to this is the fact that HTTP client library imports (requests, httpx) happen inside StripeClient.__init__(), putting their cost in the invoke phase (3s budget) rather than the module init phase (10s budget).

Additionally, uuid (used only for generating idempotency keys) pulls in 20 transitive modules including re, enum, and platform, adding 300-700ms at Lambda-scale CPU.

What?

• Move HTTP client library detection to module load time. The available client class is resolved once when stripe._http_client is first imported, so new_default_http_client() and new_http_client_async_fallback() just instantiate the pre-resolved class without any imports.
• Replace uuid.uuid4() with os.urandom(16).hex() for idempotency key generation. Produces an equivalent 32-char cryptographically random hex string without importing the uuid module. os is already imported in _api_requestor.py.

See Also

• Slow invocation of the client causes a timeout in AWS Lambda #1799
• https://go/j/DEVSDK-3167 (follow-up)

Changelog

• Moves HTTP library imports to module load time to better accommodate AWS Lambda and other serverless environments that have separate Init phase and Invoke phase time budgets.

[jar-stripe]

Benchmark Results

Methodology: Each measurement is a separate Docker container (python:3.11-slim) with --cpus=0.1 (approximating a 128-256MB AWS Lambda). Each container does a fresh pip install -e . then runs a single cold-start measurement of import stripe and stripe.StripeClient('sk_test_fake'). 10 iterations per configuration.

Baseline (master)

import stripe: 1.100s  StripeClient(): 2.495s  Total: 3.595s
import stripe: 0.608s  StripeClient(): 0.989s  Total: 1.597s
import stripe: 1.195s  StripeClient(): 1.905s  Total: 3.101s
import stripe: 1.294s  StripeClient(): 2.307s  Total: 3.601s
import stripe: 1.490s  StripeClient(): 2.003s  Total: 3.493s
import stripe: 0.911s  StripeClient(): 1.585s  Total: 2.495s
import stripe: 1.296s  StripeClient(): 2.298s  Total: 3.593s
import stripe: 0.706s  StripeClient(): 2.193s  Total: 2.898s
import stripe: 1.499s  StripeClient(): 2.203s  Total: 3.702s
import stripe: 1.004s  StripeClient(): 2.501s  Total: 3.505s

Mean: import stripe=1.110s  StripeClient()=2.048s  Total=3.158s

Fixed (this PR)

import stripe: 1.705s  StripeClient(): 0.105s  Total: 1.809s
import stripe: 3.893s  StripeClient(): 0.108s  Total: 4.002s
import stripe: 2.797s  StripeClient(): 0.206s  Total: 3.003s
import stripe: 2.698s  StripeClient(): 0.099s  Total: 2.797s
import stripe: 2.099s  StripeClient(): 0.114s  Total: 2.214s
import stripe: 2.904s  StripeClient(): 0.108s  Total: 3.012s
import stripe: 2.705s  StripeClient(): 0.205s  Total: 2.910s
import stripe: 3.098s  StripeClient(): 0.111s  Total: 3.208s
import stripe: 3.009s  StripeClient(): 0.194s  Total: 3.203s
import stripe: 2.800s  StripeClient(): 0.205s  Total: 3.005s

Mean: import stripe=2.771s  StripeClient()=0.145s  Total=2.916s

Summary

Metric	Baseline	Fixed	Delta
import stripe	1.110s	2.771s	+1.661s (moved to init phase, 10s budget)
StripeClient()	2.048s	0.145s	-1.903s (invoke phase, 3s budget)
Total	3.158s	2.916s	-0.242s

The key result: StripeClient() drops from ~2s to ~0.15s. The import cost for HTTP libraries such as requests shifts to import stripe, which is more friendly to environments where import stripe may be run in a different phase than StripeClient(...).