github.com/jackc/pgx/v5 v5.10.0: CopyFromRows, CopyFromFunc

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 pkg:golang/github.com/jackc/pgx/v5@v5.10.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/jackc/pgx/v5@v5.10.0
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@11.8.0
  - runtime: node@24.13.1

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:sha256:215bc768564f14da7c211af5adaffe73a851c9d5e2310098f93b60f0e69f0009","contract":["CopyFromRows wraps 2D slice into CopyFromSource iterator","CopyFromFunc streams rows via generator callback until EOF or error"],"goal":"verify pkg:golang/github.com/jackc/pgx/v5@v5.10.0","kind":"HOW","packages":["pkg:golang/github.com/jackc/pgx/v5@v5.10.0"],"schemaVersion":1,"symbols":["CopyFromRows","CopyFromFunc"]},"contractCommand":["go","test","./..."],"environment":{"arch":"x64","ecosystem":"golang","language":"go","os":"windows","osVersionBucket":"11","packageManager":"go","packageManagerVersion":"1.26.5","runtime":"go","runtimeVersion":"1.26.5","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/jackc/pgx/v5@v5.10.0"],"schemaVersion":1,"symbols":["CopyFromRows","CopyFromFunc"],"verifierAdapter":"golang@1"}

module contract

go 1.26.5

require (
	github.com/jackc/pgpassfile v1.0.0 // indirect
	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
	github.com/jackc/pgx/v5 v5.10.0 // indirect
	golang.org/x/text v0.29.0 // indirect
)

github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/jackc/pgpassfile v1.0.0 h1:/6Hmqy13Ss2zCq62VdNG8tM1wchn8zjSGOBJ6icpsIM=
github.com/jackc/pgpassfile v1.0.0/go.mod h1:CEx0iS5ambNFdcRtxPj5JhEz+xB6uRky5eyVu/W2HEg=
github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 h1:iCEnooe7UlwOQYpKFhBabPMi4aNAfoODPEFNiAnClxo=
github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761/go.mod h1:5TJZWKEWniPve33vlWYSoGYefn3gLQRzjfDlhSJ9ZKM=
github.com/jackc/pgx/v5 v5.10.0 h1:VhSvgU2jSli8o3AqIEOTJr7rZwAEUVo4E4XhR94Zfr0=
github.com/jackc/pgx/v5 v5.10.0/go.mod h1:mal1tBGAFfLHvZzaYh77YS/eC6IX9OWbRV1QIIM0Jn4=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
golang.org/x/text v0.29.0 h1:1neNs90w9YzJ9BocxfsQNHKuAT4pkghyXc4nhZ6sJvk=
golang.org/x/text v0.29.0/go.mod h1:7MhJOA9CD2qZyOKYazxdYMF85OwPdEr9jTtBpO7ydH4=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

package main

import (
	"fmt"

	"github.com/jackc/pgx/v5"
)

// RowsCopySource wraps a 2D slice into a pgx.CopyFromSource.
func RowsCopySource(rows [][]any) pgx.CopyFromSource {
	return pgx.CopyFromRows(rows)
}

// StreamCopySource wraps a row generator function into a pgx.CopyFromSource.
func StreamCopySource(generator func() ([]any, error)) pgx.CopyFromSource {
	return pgx.CopyFromFunc(generator)
}

func main() {
	rows := [][]any{
		{"alpha", 1},
		{"beta", 2},
	}
	src := RowsCopySource(rows)
	for src.Next() {
		vals, err := src.Values()
		if err != nil {
			panic(err)
		}
		fmt.Printf("row: %v\n", vals)
	}
	if err := src.Err(); err != nil {
		panic(err)
	}

	idx := 0
	streamSrc := StreamCopySource(func() ([]any, error) {
		if idx >= len(rows) {
			return nil, nil // EOF
		}
		r := rows[idx]
		idx++
		return r, nil
	})
	for streamSrc.Next() {
		vals, err := streamSrc.Values()
		if err != nil {
			panic(err)
		}
		fmt.Printf("stream row: %v\n", vals)
	}
	if err := streamSrc.Err(); err != nil {
		panic(err)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/github.com/jackc/pgx/v5@v5.10.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/jackc/pgx/v5@v5.10.0"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@11.8.0",
    "runtime": "node@24.13.1"
  }
}

package test

import (
	"errors"
	"reflect"
	"testing"

	"github.com/jackc/pgx/v5"
)

func TestCopyFromRows(t *testing.T) {
	rows := [][]any{
		{101, "item1", true},
		{102, "item2", false},
		{103, "item3", true},
	}

	source := pgx.CopyFromRows(rows)

	var collected [][]any
	for source.Next() {
		vals, err := source.Values()
		if err != nil {
			t.Fatalf("unexpected error from Values(): %v", err)
		}
		collected = append(collected, vals)
	}

	if err := source.Err(); err != nil {
		t.Fatalf("unexpected error from Err(): %v", err)
	}

	if len(collected) != len(rows) {
		t.Fatalf("expected %d rows, got %d", len(rows), len(collected))
	}

	for i, r := range collected {
		if !reflect.DeepEqual(r, rows[i]) {
			t.Errorf("row %d mismatch: got %v, expected %v", i, r, rows[i])
		}
	}
}

func TestCopyFromFunc(t *testing.T) {
	data := [][]any{
		{"event_a", 10},
		{"event_b", 20},
	}

	cursor := 0
	source := pgx.CopyFromFunc(func() ([]any, error) {
		if cursor >= len(data) {
			return nil, nil // signals EOF
		}
		row := data[cursor]
		cursor++
		return row, nil
	})

	var collected [][]any
	for source.Next() {
		vals, err := source.Values()
		if err != nil {
			t.Fatalf("unexpected error from Values(): %v", err)
		}
		collected = append(collected, vals)
	}

	if err := source.Err(); err != nil {
		t.Fatalf("unexpected error from Err(): %v", err)
	}

	if len(collected) != len(data) {
		t.Fatalf("expected %d rows, got %d", len(data), len(collected))
	}

	for i, r := range collected {
		if !reflect.DeepEqual(r, data[i]) {
			t.Errorf("row %d mismatch: got %v, expected %v", i, r, data[i])
		}
	}
}

func TestCopyFromFuncError(t *testing.T) {
	expectedErr := errors.New("simulated read failure")

	callCount := 0
	source := pgx.CopyFromFunc(func() ([]any, error) {
		callCount++
		if callCount == 1 {
			return []any{"valid_row"}, nil
		}
		return nil, expectedErr
	})

	if !source.Next() {
		t.Fatalf("expected first Next() to succeed")
	}
	vals, err := source.Values()
	if err != nil || len(vals) != 1 || vals[0] != "valid_row" {
		t.Fatalf("unexpected first row: %v, err: %v", vals, err)
	}

	if source.Next() {
		t.Fatalf("expected second Next() to return false on error")
	}

	if !errors.Is(source.Err(), expectedErr) {
		t.Fatalf("expected error %v, got %v", expectedErr, source.Err())
	}
}