github.com/jackc/pgio v1.0.0: AppendUint16

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/pgio.AppendUint16 in pkg:golang/github.com/jackc/pgio@v1.0.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/jackc/pgio@v1.0.0
Demonstrate these symbols/APIs:
  - github.com/jackc/pgio.AppendUint16
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:sha256:9ec641a2511f6afc5e3c77fa89ec148f4a222a7d76cc86a9979377950477c903","contract":["pgio.AppendUint16 appends a uint16 as 2 bytes in big-endian order to byte slice","pgio.AppendUint16 appends to an existing byte slice preserving preceding bytes","pgio.AppendUint16 handles zero, small, and maximum uint16 boundary values"],"goal":"verify github.com/jackc/pgio.AppendUint16 in pkg:golang/github.com/jackc/pgio@v1.0.0","kind":"HOW","packages":["pkg:golang/github.com/jackc/pgio@v1.0.0"],"schemaVersion":1,"symbols":["github.com/jackc/pgio.AppendUint16"]},"contractCommand":["go","test","./..."],"environment":{"arch":"amd64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","moduleSystem":"go","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/jackc/pgio@v1.0.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/jackc/pgio@v1.0.0","symbols":["github.com/jackc/pgio.AppendUint16"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require github.com/jackc/pgio v1.0.0

github.com/jackc/pgio v1.0.0 h1:g12B9UwVnzGhueNavwioyEEpAmqMe1E/BN9ES+8ovkE=
github.com/jackc/pgio v1.0.0/go.mod h1:oP+2QK2wFfUWgr+gxjoBH9KGBb31Eio69xUb0w5bYf8=

package main

import (
	"fmt"

	"github.com/jackc/pgio"
)

func main() {
	buf := []byte("prefix:")
	buf = pgio.AppendUint16(buf, 0x1234)
	fmt.Printf("buffer length: %d bytes\n", len(buf))
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/jackc/pgio.AppendUint16 in pkg:golang/github.com/jackc/pgio@v1.0.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/jackc/pgio@v1.0.0"
  ],
  "symbols": [
    "github.com/jackc/pgio.AppendUint16"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package test

import (
	"bytes"
	"encoding/binary"
	"math"
	"testing"

	"github.com/jackc/pgio"
)

func TestAppendUint16(t *testing.T) {
	// 1. pgio.AppendUint16 appends a uint16 as 2 bytes in big-endian order to byte slice
	testCases := []uint16{
		0,
		1,
		42,
		255,
		256,
		1000,
		0x1234,
		0xABCD,
		math.MaxUint16,
	}

	for _, val := range testCases {
		var expected [2]byte
		binary.BigEndian.PutUint16(expected[:], val)

		res := pgio.AppendUint16(nil, val)
		if len(res) != 2 {
			t.Fatalf("expected 2 bytes, got %d for val %d", len(res), val)
		}
		if !bytes.Equal(res, expected[:]) {
			t.Fatalf("expected big-endian bytes %v, got %v for val %d", expected[:], res, val)
		}
	}

	// 2. pgio.AppendUint16 appends to an existing byte slice preserving preceding bytes
	prefix := []byte{0xAA, 0xBB, 0xCC}
	val := uint16(0x5678)
	combined := pgio.AppendUint16(prefix, val)

	if len(combined) != len(prefix)+2 {
		t.Fatalf("expected length %d, got %d", len(prefix)+2, len(combined))
	}
	if !bytes.Equal(combined[:len(prefix)], []byte{0xAA, 0xBB, 0xCC}) {
		t.Fatalf("preceding bytes were not preserved: %v", combined[:len(prefix)])
	}

	var expectedVal [2]byte
	binary.BigEndian.PutUint16(expectedVal[:], val)
	if !bytes.Equal(combined[len(prefix):], expectedVal[:]) {
		t.Fatalf("appended uint16 mismatch: expected %v, got %v", expectedVal[:], combined[len(prefix):])
	}

	// 3. pgio.AppendUint16 handles zero, small, and maximum uint16 boundary values
	zeroRes := pgio.AppendUint16([]byte{}, 0)
	if !bytes.Equal(zeroRes, []byte{0x00, 0x00}) {
		t.Fatalf("expected [0x00, 0x00], got %v", zeroRes)
	}

	maxRes := pgio.AppendUint16([]byte{}, math.MaxUint16)
	if !bytes.Equal(maxRes, []byte{0xFF, 0xFF}) {
		t.Fatalf("expected [0xFF, 0xFF], got %v", maxRes)
	}
}