http-request-capture

README

http-request-capture

An HTTP server that records each incoming request as a single line of JSON on stdout.

What it does

http-request-capture listens for HTTP requests on any path and logs the method, path, query parameters, headers, and body of each request as a structured JSON record using log/slog. JSON and form-urlencoded bodies are decoded into structured values; any other body is recorded as a string. A request that declares a JSON content type but cannot be parsed is recorded and answered with 400 Bad Request. Because the output is one JSON object per line, it can be inspected with jq or forwarded to a log pipeline.

Usage

Start the server (defaults to :8000):

$ ./http-request-capture
{"time":"2026-06-02T17:15:54.668175236+09:00","level":"INFO","msg":"HttpRequestCapture starting","addr":":8000"}

Listen on a different address with -addr:

$ ./http-request-capture -addr :9000

Send requests with any HTTP client. Each request produces one JSON line on stdout.

GET request

$ curl "http://localhost:8000/test?param1=value1&param2=value2"
Hello from GET

{"time":"2026-06-02T17:16:17.152773634+09:00","level":"INFO","msg":"request captured","method":"GET","path":"/test","query":{"param1":["value1"],"param2":["value2"]},"headers":{"Accept":["*/*"],"User-Agent":["curl/8.19.0-rc3"]},"body":null,"body_parsed":true}

Any path is accepted and recorded in the path field:

$ curl "http://localhost:8000/test/hello?param1=value1&param2=value2"
Hello from GET

{"time":"2026-06-02T17:16:34.292500152+09:00","level":"INFO","msg":"request captured","method":"GET","path":"/test/hello","query":{"param1":["value1"],"param2":["value2"]},"headers":{"Accept":["*/*"],"User-Agent":["curl/8.19.0-rc3"]},"body":null,"body_parsed":true}

POST request (application/x-www-form-urlencoded)

$ curl -X POST -H "Content-Type: application/x-www-form-urlencoded" -d "username=johndoe&password=secret123" http://localhost:8000/
ok

{"time":"2026-06-02T17:17:07.667334867+09:00","level":"INFO","msg":"request captured","method":"POST","path":"/","query":{},"headers":{"Accept":["*/*"],"Content-Length":["35"],"Content-Type":["application/x-www-form-urlencoded"],"User-Agent":["curl/8.19.0-rc3"]},"body":{"password":["secret123"],"username":["johndoe"]},"body_parsed":true}

POST request (application/json)

$ curl -X POST -H "Content-Type: application/json" -d '{"username":"johndoe","password":"secret123"}' http://localhost:8000/
ok

{"time":"2026-06-02T17:17:31.000000000+09:00","level":"INFO","msg":"request captured","method":"POST","path":"/","query":{},"headers":{"Accept":["*/*"],"Content-Length":["45"],"Content-Type":["application/json"],"User-Agent":["curl/8.19.0-rc3"]},"body":{"password":"secret123","username":"johndoe"},"body_parsed":true}

Malformed JSON body

A body that declares application/json but does not parse is recorded with body_parsed set to false and answered with 400 Bad Request. The raw body is kept in the body field.

$ curl -X POST -H "Content-Type: application/json" -d '{"broken":' http://localhost:8000/
Malformed request body for declared Content-Type

{"time":"2026-06-02T17:18:02.000000000+09:00","level":"INFO","msg":"request captured","method":"POST","path":"/","query":{},"headers":{"Accept":["*/*"],"Content-Length":["10"],"Content-Type":["application/json"],"User-Agent":["curl/8.19.0-rc3"]},"body":"{\"broken\":","body_parsed":false}

Filtering output with jq

$ ./http-request-capture | jq 'select(.msg == "request captured") | {path, body}'

License

This project is licensed under the MIT License.