Share one fake HTTP body that enforces the net/http lifecycle in every test

[shawnburke]

Follow-up to #165.

Why

#165 was caught by a one-off body fake that fails reads after the request context is cancelled. Neither existing fake could have caught it:

• The trackedBody copies in server/api and server/snykbroker are backed by a strings.Reader, which has no idea a request context exists. They verify drain and close, and nothing about cancellation.
• The httptest.NewServer tests use a real transport, but every body in them is a few bytes. net/http serves bytes it already buffered even after cancel, so small bodies pass by accident. Against a real server, cancelling between Do and ReadAll succeeds for an 11-byte body and fails with context canceled for a 1 MiB body after somewhere between 8 and 20 KB, varying run to run.

What

Commit 1. A new test/httpfake package owns a single Body and Transport. Every body served:

• fails Read once the request's context is done (strictly, since the real buffered threshold is not something a test can control),
• fails Read after Close, as net/http does,
• records whether it was read to EOF and closed.

Both test files now build their client on it, so every test through that path gets all three rules without opting in. The package has its own tests, including one that caught a flaw in my first draft (reusing one canned response served an exhausted reader).

Commit 2. HttpBackend in grpctunnel is the only other http.Client consumer in the agent and had no tests; every tunnel test stubs the Backend interface above the HTTP layer. It hands the raw body to the call handler, which streams it under a context the handler cancels in a defer, which is the same shape as the #165 bug. A new test drives a multi-frame body through startCall with a real HttpBackend over an httpfake client and checks the body is streamed in full, the call ends with End not Cancel, and the body hit EOF and was closed. httpfake.NewBody lets the existing tunnel stubs hand out tracked bodies instead of io.NopCloser.

Proof

• With cortex_api.go and http_helper.go reverted to the pre-Keep the default Cortex API deadline active until the body is read, and clear curl CVEs #165 versions, the two pre-existing tests TestCall_ReadsDrainsAndClosesResponseBody and TestCall_RateLimitedBodyIsDrainedAndClosed both fail with context canceled. The dedicated regression test from Keep the default Cortex API deadline active until the body is read, and clear curl CVEs #165 is therefore folded into the first of them.
• With the call context cancelled right after backend.Do returns in runCall, the new TestHttpBackend_StreamsWholeBodyAndClosesItBeforeCallContextEnds fails with upstream read failed: context canceled.

All four packages pass go vet and go test -race.

🤖 Generated with Claude Code

[keithfz]

nice