github.com/go-logfmt/logfmt v0.6.0: NewDecoder

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify github.com/go-logfmt/logfmt.NewDecoder in pkg:golang/github.com/go-logfmt/logfmt@v0.6.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/go-logfmt/logfmt@v0.6.0
Demonstrate these symbols/APIs:
  - github.com/go-logfmt/logfmt.NewDecoder
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:3d4265f564c058e2ca5c1ebe0b538933a7f7168af5a1080cd3e0a196674c76ff","contract":["logfmt.NewDecoder parses key-value pairs from an io.Reader and scans records and keyvals sequentially","logfmt.NewDecoder correctly unquotes quoted values and decodes escaped characters","logfmt.NewDecoder returns keys and values as byte slices accessible via Key() and Value() methods","logfmt.NewDecoder handles empty inputs without error returning false on initial ScanRecord"],"goal":"verify github.com/go-logfmt/logfmt.NewDecoder in pkg:golang/github.com/go-logfmt/logfmt@v0.6.0","kind":"HOW","packages":["pkg:golang/github.com/go-logfmt/logfmt@v0.6.0"],"schemaVersion":1,"symbols":["github.com/go-logfmt/logfmt.NewDecoder"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/go-logfmt/logfmt@v0.6.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/go-logfmt/logfmt@v0.6.0","symbols":["github.com/go-logfmt/logfmt.NewDecoder"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require github.com/go-logfmt/logfmt v0.6.0

github.com/go-logfmt/logfmt v0.6.0 h1:wGYYu3uicYdqXVgoYbvnkrPVXkuLM1p1ifugDMEdRi4=
github.com/go-logfmt/logfmt v0.6.0/go.mod h1:WYhtIu8zTZfxdn5+rREduYbwxfcBr/Vr6KEVveWlfTs=

package main

import (
	"fmt"
	"strings"

	"github.com/go-logfmt/logfmt"
)

func main() {
	input := "ts=2026-08-23T17:50:00Z level=info msg=\"service started\" port=8080\n"
	dec := logfmt.NewDecoder(strings.NewReader(input))

	for dec.ScanRecord() {
		for dec.ScanKeyval() {
			fmt.Printf("key: %s, val: %s\n", dec.Key(), dec.Value())
		}
	}
	if err := dec.Err(); err != nil {
		fmt.Printf("error: %v\n", err)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/go-logfmt/logfmt.NewDecoder in pkg:golang/github.com/go-logfmt/logfmt@v0.6.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/go-logfmt/logfmt@v0.6.0"
  ],
  "symbols": [
    "github.com/go-logfmt/logfmt.NewDecoder"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"bytes"
	"fmt"
	"os"
	"strings"

	"github.com/go-logfmt/logfmt"
)

func main() {
	// Assertion 1: logfmt.NewDecoder parses key-value pairs from an io.Reader and scans records and keyvals sequentially
	in1 := "level=info msg=hello\nlevel=error msg=world\n"
	dec1 := logfmt.NewDecoder(strings.NewReader(in1))
	var lines []map[string]string
	for dec1.ScanRecord() {
		m := make(map[string]string)
		for dec1.ScanKeyval() {
			m[string(dec1.Key())] = string(dec1.Value())
		}
		lines = append(lines, m)
	}
	if err := dec1.Err(); err != nil {
		fmt.Fprintf(os.Stderr, "assertion 1 error: %v\n", err)
		os.Exit(1)
	}
	if len(lines) != 2 || lines[0]["level"] != "info" || lines[0]["msg"] != "hello" || lines[1]["level"] != "error" || lines[1]["msg"] != "world" {
		fmt.Fprintf(os.Stderr, "assertion 1 failed: lines=%+v\n", lines)
		os.Exit(1)
	}

	// Assertion 2: logfmt.NewDecoder correctly unquotes quoted values and decodes escaped characters
	in2 := "msg=\"hello \\\"world\\\"\" path=\"foo/bar\"\n"
	dec2 := logfmt.NewDecoder(strings.NewReader(in2))
	if !dec2.ScanRecord() {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: expected record\n")
		os.Exit(1)
	}
	kv2 := make(map[string]string)
	for dec2.ScanKeyval() {
		kv2[string(dec2.Key())] = string(dec2.Value())
	}
	if kv2["msg"] != `hello "world"` || kv2["path"] != "foo/bar" {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: unquoted mismatch %+v\n", kv2)
		os.Exit(1)
	}

	// Assertion 3: logfmt.NewDecoder returns keys and values as byte slices accessible via Key() and Value() methods
	in3 := "key=val"
	dec3 := logfmt.NewDecoder(strings.NewReader(in3))
	if !dec3.ScanRecord() || !dec3.ScanKeyval() {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: expected scan\n")
		os.Exit(1)
	}
	if !bytes.Equal(dec3.Key(), []byte("key")) || !bytes.Equal(dec3.Value(), []byte("val")) {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: key=%s, val=%s\n", dec3.Key(), dec3.Value())
		os.Exit(1)
	}

	// Assertion 4: logfmt.NewDecoder handles empty inputs without error returning false on initial ScanRecord
	dec4 := logfmt.NewDecoder(strings.NewReader(""))
	if dec4.ScanRecord() {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: expected false on empty input\n")
		os.Exit(1)
	}
	if err := dec4.Err(); err != nil {
		fmt.Fprintf(os.Stderr, "assertion 4 failed: unexpected error %v\n", err)
		os.Exit(1)
	}

	fmt.Println("All contract assertions passed.")
}