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 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:
  - 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.

package sample

import (
	"strings"
	"testing"

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

func TestContractDecoder(t *testing.T) {
	// 1. Verify logfmt.NewDecoder creates a Decoder from an io.Reader
	input := "level=info msg=\"task started\" count=42\nlevel=error msg=\"task failed\" reason=\"timeout\"\n"
	reader := strings.NewReader(input)
	dec := logfmt.NewDecoder(reader)
	if dec == nil {
		t.Fatal("expected non-nil Decoder from logfmt.NewDecoder")
	}

	// 2. Verify logfmt.Decoder.ScanRecord and ScanKeyval on the first record
	if !dec.ScanRecord() {
		t.Fatalf("expected ScanRecord to return true, got false, err: %v", dec.Err())
	}

	firstRecord := make(map[string]string)
	for dec.ScanKeyval() {
		firstRecord[string(dec.Key())] = string(dec.Value())
	}
	if dec.Err() != nil {
		t.Fatalf("unexpected error scanning keyvals: %v", dec.Err())
	}

	if firstRecord["level"] != "info" {
		t.Errorf("expected level=info, got %q", firstRecord["level"])
	}
	if firstRecord["msg"] != "task started" {
		t.Errorf("expected msg='task started', got %q", firstRecord["msg"])
	}
	if firstRecord["count"] != "42" {
		t.Errorf("expected count='42', got %q", firstRecord["count"])
	}

	// 3. Verify helper functions ParseLogRecord and ParseAllLogRecords
	singleInput := "app=demo env=production status=200"
	rec, err := ParseLogRecord(strings.NewReader(singleInput))
	if err != nil {
		t.Fatalf("ParseLogRecord failed: %v", err)
	}
	if rec["app"] != "demo" || rec["env"] != "production" || rec["status"] != "200" {
		t.Errorf("unexpected ParseLogRecord result: %v", rec)
	}

	allRecords, err := ParseAllLogRecords(strings.NewReader(input))
	if err != nil {
		t.Fatalf("ParseAllLogRecords failed: %v", err)
	}
	if len(allRecords) != 2 {
		t.Fatalf("expected 2 records, got %d", len(allRecords))
	}
	if allRecords[1]["reason"] != "timeout" {
		t.Errorf("expected reason=timeout, got %q", allRecords[1]["reason"])
	}
}

{"case":{"caseId":"case:sha256:61e00cbbaef7e31568fee5b14f4d11fddc19a70318e20d3309eecf0ad1a3f485","contract":["logfmt.NewDecoder creates a Decoder from an io.Reader","logfmt.Decoder.ScanRecord advances through logfmt records","logfmt.Decoder.ScanKeyval parses key-value pairs within a record","logfmt.Decoder handles quoted values containing whitespace"],"goal":"verify 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":["logfmt.NewDecoder"]},"contractCommand":["go","test","./..."],"environment":{"arch":"amd64","compiler":"go","compilerVersion":"1.26.6","distro":"ubuntu","ecosystem":"golang","language":"go","languageVersion":"1.26.6","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","packageManagerVersion":"1.26.6","runtime":"go","runtimeVersion":"1.26.6","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":["logfmt.NewDecoder"],"verifierAdapter":"golang@1"}

package sample

import (
	"io"

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

// ParseLogRecord parses a single logfmt record from an io.Reader and returns key-value pairs.
func ParseLogRecord(r io.Reader) (map[string]string, error) {
	dec := logfmt.NewDecoder(r)
	result := make(map[string]string)
	if dec.ScanRecord() {
		for dec.ScanKeyval() {
			result[string(dec.Key())] = string(dec.Value())
		}
	}
	if err := dec.Err(); err != nil {
		return nil, err
	}
	return result, nil
}

// ParseAllLogRecords parses all logfmt records from an io.Reader and returns a slice of key-value maps.
func ParseAllLogRecords(r io.Reader) ([]map[string]string, error) {
	dec := logfmt.NewDecoder(r)
	var records []map[string]string
	for dec.ScanRecord() {
		rec := make(map[string]string)
		for dec.ScanKeyval() {
			rec[string(dec.Key())] = string(dec.Value())
		}
		records = append(records, rec)
	}
	if err := dec.Err(); err != nil {
		return nil, err
	}
	return records, nil
}

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=

{
  "schemaVersion": 1,
  "goal": "verify 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": [
    "logfmt.NewDecoder"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}