Make hammer agent-friendly: zero-config URL mode, JSON stdout, SLO exit codes

[chenchaoyi]

Reshape hammer so any agent (or CI job) can run a meaningful load test in one command, parse the result without scraping human text, and branch on a stable exit code — while staying a single, dependency-free binary and keeping the existing profile format fully backward-compatible.

What's new

1. Zero-config one-shot mode — no profile file needed:

hammer -url https://api/users -method POST -header 'Authorization: Bearer t' -body '{"x":1}' -content-type REST

Templating ({{ uuid }}, {{ randInt N }}) still works in -url / -body.

2. Machine-readable stdout — -output json emits the whole report to stdout; all logs stay on stderr, so stdout is always clean to pipe into jq.

3. SLO assertions + meaningful exit codes — -max-error-rate, -max-p50/p95/p99 produce a checks block and drive the exit code:

Code	Meaning
0	completed, all checks passed (or none set)
1	SLO threshold violated
2	usage / argument error
3	setup error (bad profile, etc.)

So hammer -url … -max-p99 500ms -max-error-rate 0 || alert just works.

4. Profile from stdin — … | hammer -profile - for generated traffic mixes, no temp file.

5. Quieter for automation — -quiet silences the live monitor; the /stats HTTP endpoint is now opt-in (was :9001 by default) so runs never bind a surprise port in CI/sandboxes.

6. Richer report — added error_rate, achieved_rps, and checks to the JSON, plus a self-documenting -h banner with examples and exit codes.

Implementation notes

• profile/: factored per-call init into Profile.add, then added LoadFromReader (stdin) and SingleCall (URL mode) on top of it — shared validation/templating path.
• hammer.go: split main into run() int so exit codes are explicit and deferred cleanup still runs; report() now writes to an io.Writer and appends check results.
• Added tests for SingleCall/LoadFromReader, header parsing, error-rate, threshold evaluation, and the new derived JSON fields. README rewritten with a dedicated For agents section.

Compatibility

Everything is additive except one deliberate, documented default change: -stats-addr now defaults to disabled (was :9001). The profile format, existing flags, and JSON fields are unchanged.

Verification

go build ./..., go vet ./..., and go test -race ./... all pass; every new flow was exercised end-to-end against the local test server (zero-config mode, JSON-to-stdout, stdin profile, POST with headers, and exit codes for pass/fail/usage/setup).

🤖 Generated with Claude Code

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Generated by Claude Code