Files

Jan Novak 3affc05996 feat(go): step 4 — --json output flag

Add --json flag that emits all results as a JSON array. Schema always
uses min/avg/max per phase (consistent regardless of -n); phases absent
from the request are omitted from the phases object. Output is buffered
until all URLs complete, then printed as one pretty-printed array.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

2026-07-01 00:31:54 +02:00

2.3 KiB

Raw Blame History

Step 4 — JSON Output

What this step delivers

A --json flag that emits all results as a JSON array instead of the text table. The text format remains the default.

The JSON schema is always the aggregate shape (min/avg/max per phase), even for a single sample — so the schema is stable regardless of -n.

Phases absent from the request (e.g. TLS for http://) are omitted from the phases object.

Build

cd go
go build -o latprobe .

Usage

latprobe --json [other flags] <url> [url ...]

JSON Schema

[
  {
    "url":     "https://example.com",
    "status":  200,
    "samples": 1,
    "phases": {
      "dns":      { "min_ms": 17.17, "avg_ms": 17.17, "max_ms": 17.17 },
      "connect":  { "min_ms": 12.01, "avg_ms": 12.01, "max_ms": 12.01 },
      "tls":      { "min_ms": 22.78, "avg_ms": 22.78, "max_ms": 22.78 },
      "ttfb":     { "min_ms": 12.99, "avg_ms": 12.99, "max_ms": 12.99 },
      "transfer": { "min_ms":  0.18, "avg_ms":  0.18, "max_ms":  0.18 },
      "total":    { "min_ms": 66.19, "avg_ms": 66.19, "max_ms": 66.19 }
    }
  }
]

Phase keys: dns, connect, tls (HTTPS only), ttfb, transfer, total. All *_ms values are floating-point milliseconds.

Examples

Single URL, single sample

$ ./latprobe --json https://example.com
[
  {
    "url": "https://example.com",
    "status": 200,
    "samples": 1,
    "phases": { ... }
  }
]

Multiple samples — min/avg/max diverge

$ ./latprobe --json -n 5 https://example.com
[
  {
    "url": "https://example.com",
    "status": 200,
    "samples": 5,
    "phases": {
      "total": { "min_ms": 45.00, "avg_ms": 52.30, "max_ms": 61.80 },
      ...
    }
  }
]

Pipe to jq

# Extract avg total latency for each URL
$ ./latprobe --json -n 3 https://example.com https://www.google.com \
  | jq '.[] | {url, avg_total_ms: .phases.total.avg_ms}'

{
  "url": "https://example.com",
  "avg_total_ms": 52.3
}
{
  "url": "https://www.google.com",
  "avg_total_ms": 82.8
}

Notes

Output is buffered until all URLs are measured, then printed as one array. Errors for individual URLs are written to stderr; that URL is excluded from the JSON array, and the process exits with code 1.
The text format is unchanged and remains the default (no --json flag).

2.3 KiB Raw Blame History