github.com/jackc/pgio v1.0.0: AppendInt16

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.AppendInt16 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.AppendInt16
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:e3255fbdf0d1aac02dacdb8c15fb0ed88f144de8d585370956c8f321d752340d","contract":["pgio.AppendInt16 appends a 16-bit signed integer in big-endian byte order to a byte slice"],"goal":"verify github.com/jackc/pgio.AppendInt16 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.AppendInt16"]},"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/pgio@v1.0.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/jackc/pgio@v1.0.0","symbols":["github.com/jackc/pgio.AppendInt16"],"verifierAdapter":"golang@1"}

module sample

go 1.21

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=

{
  "schemaVersion": 1,
  "goal": "verify github.com/jackc/pgio.AppendInt16 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.AppendInt16"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"math"
	"os"

	"github.com/jackc/pgio"
)

func main() {
	if err := runTests(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract test failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All contract tests passed successfully.")
}

func runTests() error {
	// Test 1: Append positive int16 in big-endian byte order
	{
		var buf []byte
		val := int16(0x1234)
		buf = pgio.AppendInt16(buf, val)
		expected := []byte{0x12, 0x34}
		if !bytes.Equal(buf, expected) {
			return fmt.Errorf("AppendInt16(%d) = %v, expected %v", val, buf, expected)
		}
	}

	// Test 2: Append negative int16 (e.g. -1 => 0xFFFF, -32768 => 0x8000)
	{
		buf := pgio.AppendInt16(nil, -1)
		expected := []byte{0xFF, 0xFF}
		if !bytes.Equal(buf, expected) {
			return fmt.Errorf("AppendInt16(-1) = %v, expected %v", buf, expected)
		}

		buf = pgio.AppendInt16(nil, math.MinInt16)
		expectedMin := []byte{0x80, 0x00}
		if !bytes.Equal(buf, expectedMin) {
			return fmt.Errorf("AppendInt16(MinInt16) = %v, expected %v", buf, expectedMin)
		}

		buf = pgio.AppendInt16(nil, math.MaxInt16)
		expectedMax := []byte{0x7F, 0xFF}
		if !bytes.Equal(buf, expectedMax) {
			return fmt.Errorf("AppendInt16(MaxInt16) = %v, expected %v", buf, expectedMax)
		}
	}

	// Test 3: Append zero
	{
		buf := pgio.AppendInt16([]byte{}, 0)
		expected := []byte{0x00, 0x00}
		if !bytes.Equal(buf, expected) {
			return fmt.Errorf("AppendInt16(0) = %v, expected %v", buf, expected)
		}
	}

	// Test 4: Append to non-empty buffer preserves existing prefix
	{
		buf := []byte{0xAA, 0xBB, 0xCC}
		buf = pgio.AppendInt16(buf, 258) // 0x0102
		expected := []byte{0xAA, 0xBB, 0xCC, 0x01, 0x02}
		if !bytes.Equal(buf, expected) {
			return fmt.Errorf("AppendInt16 with prefix failed: got %v, expected %v", buf, expected)
		}
	}

	// Test 5: Verify exact equivalence to standard library binary.BigEndian
	{
		testValues := []int16{0, 1, -1, 42, -42, 255, 256, math.MinInt16, math.MaxInt16}
		for _, v := range testValues {
			var stdBuf [2]byte
			binary.BigEndian.PutUint16(stdBuf[:], uint16(v))

			got := pgio.AppendInt16(nil, v)
			if !bytes.Equal(got, stdBuf[:]) {
				return fmt.Errorf("pgio.AppendInt16(%d) = %v, binary.BigEndian = %v", v, got, stdBuf[:])
			}
		}
	}

	return nil
}