Send one bounded HTTP request

Bound one request in both bytes and time.

Type: Build Languages: Go Stage: 3 of 4 Prerequisites: Stages 1 and 2. Understand Go contexts and io.Reader ownership. Time: ~2 hours

What you build

Implement Attempt(ctx, client, endpoint, payload, maxBytes). Send a JSON POST using a copy of the caller's HTTP client, disable redirects, and always close the response body. Refuse nil clients, request bodies over one MiB and response limits outside 1 through 16 MiB.

Add a five-second context deadline even when the caller passes context.Background(). An earlier caller deadline still wins. The standard HTTP transport observes cancellation while connecting and reading the body.

Worked example

With response limit 5 and body 0123456789, read at most six bytes. Seeing six establishes overflow, so return ErrLimit without retaining the entire response. With exactly five bytes, return the body and status.

A 307 response contains a Location header. Return that response for terminal classification; do not send another request to the new host. The original client's CheckRedirect field remains unchanged after the call.

Implement the contract

func Attempt(ctx context.Context, client *http.Client, endpoint, payload string, maxBytes int64) (Reply, error)

Use io.LimitReader(body, maxBytes+1) so exact-fit and overflow remain distinguishable. A timeout on each request alone is insufficient for the final route: stage 4 also shares one deadline across all attempts. A custom RoundTripper must honor context cancellation just as the standard transport does.

Run your work

From the repository root, initialize once; the grader preserves existing workspace files:

python3 scripts/project_test.py llm-gateway-with-fallbacks --init /tmp/llm-gateway-with-fallbacks-work
python3 scripts/project_test.py llm-gateway-with-fallbacks --stage 3 --path /tmp/llm-gateway-with-fallbacks-work --strict

Your implementation belongs in stage3.go in that workspace. Provided adapters call those learner functions; they do not import the reference solution. Stage tests include cases separate from the Orchard demonstration.

Inspect and extend

Test an exactly full body, a body one byte too large, and a redirect to another local test server. The redirected server's request count must remain zero. After implementing all stages, run the actual loopback demo with go run . in your workspace.

Go standard-library reference. The runnable core uses only Go's standard library. External model calls are optional and do not run during ordinary grading.