github.com/jackc/pgx/v5 v5.10.0: pgproto3.NewBackend

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/jackc/pgx/v5/pgproto3.NewBackend in 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
Demonstrate these symbols/APIs:
  - github.com/jackc/pgx/v5/pgproto3.NewBackend

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 (
	"io"

	"github.com/jackc/pgx/v5/pgproto3"
)

// Session represents a mock PostgreSQL backend session.
type Session struct {
	backend *pgproto3.Backend
}

// NewSession creates a new PostgreSQL backend session wrapping the provided reader and writer.
func NewSession(r io.Reader, w io.Writer) *Session {
	return &Session{
		backend: pgproto3.NewBackend(r, w),
	}
}

// Backend returns the underlying pgproto3.Backend instance.
func (s *Session) Backend() *pgproto3.Backend {
	return s.backend
}

// HandleStartup receives and verifies the startup message from the client.
func (s *Session) HandleStartup() (*pgproto3.StartupMessage, error) {
	msg, err := s.backend.ReceiveStartupMessage()
	if err != nil {
		return nil, err
	}
	if sm, ok := msg.(*pgproto3.StartupMessage); ok {
		return sm, nil
	}
	return nil, nil
}

// SendReady sends an AuthenticationOk and ReadyForQuery message to the client, flushing the buffer.
func (s *Session) SendReady(txStatus byte) error {
	s.backend.Send(&pgproto3.AuthenticationOk{})
	s.backend.Send(&pgproto3.ReadyForQuery{TxStatus: txStatus})
	return s.backend.Flush()
}

{"case":{"caseId":"case:sha256:2c15c9d7f423148f911f8ff6a8d6de020e468a328d850c4a8b1503190dfe5e42","contract":["pgproto3.NewBackend initializes a non-nil PostgreSQL backend protocol handler","Backend.ReceiveStartupMessage decodes client StartupMessage parameters from the stream","Backend.Send and Backend.Flush write backend protocol messages to the writer","Backend.Receive decodes incoming frontend Query messages from the stream"],"goal":"verify github.com/jackc/pgx/v5/pgproto3.NewBackend in 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":["github.com/jackc/pgx/v5/pgproto3.NewBackend"]},"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/jackc/pgx/v5@v5.10.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/jackc/pgx/v5@v5.10.0","symbols":["github.com/jackc/pgx/v5/pgproto3.NewBackend"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/jackc/pgx/v5 v5.10.0

github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
github.com/davecgh/go-spew v1.1.1/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 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
golang.org/x/text v0.29.0 h1:1neNs90w9YzJ9BocxfsQNHKuAT4pkghyXc4nhZ6sJvk=
golang.org/x/text v0.29.0/go.mod h1:7MhJOA9CD2qZyOKYazxdYMF85OwPdEr9jTtBpO7ydH4=
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

{
  "schemaVersion": 1,
  "goal": "verify github.com/jackc/pgx/v5/pgproto3.NewBackend in pkg:golang/github.com/jackc/pgx/v5@v5.10.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/jackc/pgx/v5@v5.10.0"
  ],
  "symbols": [
    "github.com/jackc/pgx/v5/pgproto3.NewBackend"
  ]
}

package main

import (
	"bytes"
	"fmt"
	"os"

	"github.com/jackc/pgx/v5/pgproto3"
	"sample"
)

func main() {
	var in bytes.Buffer
	var out bytes.Buffer

	// 1. pgproto3.NewBackend constructs a non-nil Backend from io.Reader and io.Writer
	backend := pgproto3.NewBackend(&in, &out)
	if backend == nil {
		fmt.Fprintf(os.Stderr, "expected non-nil backend from pgproto3.NewBackend\n")
		os.Exit(1)
	}

	// 2. ReceiveStartupMessage receives a startup message encoded in wire protocol
	startup := &pgproto3.StartupMessage{
		ProtocolVersion: pgproto3.ProtocolVersionNumber,
		Parameters: map[string]string{
			"user":     "sample_user",
			"database": "sample_db",
		},
	}
	rawStartup, err := startup.Encode(nil)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to encode startup message: %v\n", err)
		os.Exit(1)
	}
	in.Write(rawStartup)

	receivedStartup, err := backend.ReceiveStartupMessage()
	if err != nil {
		fmt.Fprintf(os.Stderr, "ReceiveStartupMessage failed: %v\n", err)
		os.Exit(1)
	}
	sm, ok := receivedStartup.(*pgproto3.StartupMessage)
	if !ok || sm.Parameters["user"] != "sample_user" || sm.Parameters["database"] != "sample_db" {
		fmt.Fprintf(os.Stderr, "unexpected startup message content: %+v\n", sm)
		os.Exit(1)
	}

	// 3. Backend.Send queues backend messages and Backend.Flush writes them to the underlying writer
	backend.Send(&pgproto3.AuthenticationOk{})
	backend.Send(&pgproto3.ReadyForQuery{TxStatus: 'I'})
	if err := backend.Flush(); err != nil {
		fmt.Fprintf(os.Stderr, "Flush failed: %v\n", err)
		os.Exit(1)
	}
	if out.Len() == 0 {
		fmt.Fprintf(os.Stderr, "expected output buffer to contain flushed messages\n")
		os.Exit(1)
	}

	// 4. Backend.Receive parses frontend query messages from the stream
	query := &pgproto3.Query{String: "SELECT 1;"}
	rawQuery, err := query.Encode(nil)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to encode query: %v\n", err)
		os.Exit(1)
	}
	in.Write(rawQuery)

	receivedQuery, err := backend.Receive()
	if err != nil {
		fmt.Fprintf(os.Stderr, "Receive failed: %v\n", err)
		os.Exit(1)
	}
	q, ok := receivedQuery.(*pgproto3.Query)
	if !ok || q.String != "SELECT 1;" {
		fmt.Fprintf(os.Stderr, "expected Query message with 'SELECT 1;', got %+v\n", receivedQuery)
		os.Exit(1)
	}

	// 5. Higher-level Session wrapper integrates pgproto3.NewBackend
	sessionIn := bytes.NewBuffer(rawStartup)
	var sessionOut bytes.Buffer
	session := sample.NewSession(sessionIn, &sessionOut)
	if session.Backend() == nil {
		fmt.Fprintf(os.Stderr, "expected non-nil backend from session\n")
		os.Exit(1)
	}
	parsedStartup, err := session.HandleStartup()
	if err != nil || parsedStartup == nil || parsedStartup.Parameters["user"] != "sample_user" {
		fmt.Fprintf(os.Stderr, "session.HandleStartup failed: %v\n", err)
		os.Exit(1)
	}
	if err := session.SendReady('I'); err != nil || sessionOut.Len() == 0 {
		fmt.Fprintf(os.Stderr, "session.SendReady failed: %v\n", err)
		os.Exit(1)
	}

	fmt.Println("All pgproto3.NewBackend contract assertions passed.")
}