google.golang.org/protobuf v1.33.0: proto.Unmarshal

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 proto.Unmarshal in pkg:golang/google.golang.org/protobuf@v1.33.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/google.golang.org/protobuf@v1.33.0
Demonstrate these symbols/APIs:
  - proto.Unmarshal

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:b7c6bdbc2f4d2136b654af11ecee10b0da865b5a30173d7f4ba0eeba0f170049","contract":["proto.Unmarshal parses valid wire-format bytes into a proto.Message","proto.Unmarshal returns an error when unmarshaling invalid wire-format bytes","proto.Unmarshal resets destination message before decoding fields","proto.Unmarshal returns an error on truncated wire-format bytes","proto.Unmarshal unmarshals empty byte slice into default message with nil error"],"goal":"verify proto.Unmarshal in pkg:golang/google.golang.org/protobuf@v1.33.0","kind":"HOW","packages":["pkg:golang/google.golang.org/protobuf@v1.33.0"],"schemaVersion":1,"symbols":["proto.Unmarshal"]},"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/google.golang.org/protobuf@v1.33.0"],"schemaVersion":1,"subject":"pkg:golang/google.golang.org/protobuf@v1.33.0","symbols":["proto.Unmarshal"],"verifierAdapter":"golang@1"}

module sample

go 1.23

require google.golang.org/protobuf v1.33.0

github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
google.golang.org/protobuf v1.33.0 h1:uNO2rsAINq/JlFpSdYEKIZ0uKD/R9cpdv0T+yoGwGmI=
google.golang.org/protobuf v1.33.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=

package main

import (
	"fmt"
	"log"

	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/types/known/wrapperspb"
)

// UnmarshalStringValue unmarshals protobuf wire format bytes into a wrapperspb.StringValue.
func UnmarshalStringValue(data []byte) (*wrapperspb.StringValue, error) {
	msg := &wrapperspb.StringValue{}
	if err := proto.Unmarshal(data, msg); err != nil {
		return nil, err
	}
	return msg, nil
}

func main() {
	original := wrapperspb.String("hello protobuf")
	data, err := proto.Marshal(original)
	if err != nil {
		log.Fatalf("Marshal failed: %v", err)
	}

	decoded, err := UnmarshalStringValue(data)
	if err != nil {
		log.Fatalf("Unmarshal failed: %v", err)
	}

	fmt.Printf("Unmarshaled value: %s\n", decoded.GetValue())
}

{
  "schemaVersion": 1,
  "goal": "verify proto.Unmarshal in pkg:golang/google.golang.org/protobuf@v1.33.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/google.golang.org/protobuf@v1.33.0"
  ],
  "symbols": [
    "proto.Unmarshal"
  ]
}

package main

import (
	"fmt"
	"os"

	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/types/known/timestamppb"
	"google.golang.org/protobuf/types/known/wrapperspb"
)

func main() {
	// 1. proto.Unmarshal parses valid wire-format bytes into a proto.Message
	{
		original := &wrapperspb.StringValue{Value: "contract-test-string"}
		data, err := proto.Marshal(original)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: Marshal failed: %v\n", err)
			os.Exit(1)
		}

		decoded := &wrapperspb.StringValue{}
		if err := proto.Unmarshal(data, decoded); err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: Unmarshal valid bytes failed: %v\n", err)
			os.Exit(1)
		}

		if decoded.GetValue() != "contract-test-string" {
			fmt.Fprintf(os.Stderr, "FAIL: Unmarshaled value mismatch, got %q\n", decoded.GetValue())
			os.Exit(1)
		}
	}

	// 2. proto.Unmarshal returns an error when unmarshaling invalid wire-format bytes
	{
		invalidData := []byte{0xff, 0xff, 0xff, 0xff, 0xff}
		msg := &wrapperspb.StringValue{}
		if err := proto.Unmarshal(invalidData, msg); err == nil {
			fmt.Fprintf(os.Stderr, "FAIL: expected error on corrupted wire data, got nil\n")
			os.Exit(1)
		}
	}

	// 3. proto.Unmarshal resets destination message before decoding fields
	{
		target := &timestamppb.Timestamp{
			Seconds: 1700000000,
			Nanos:   999999,
		}

		newMsg := &timestamppb.Timestamp{Nanos: 54321}
		data, err := proto.Marshal(newMsg)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: Marshal failed: %v\n", err)
			os.Exit(1)
		}

		if err := proto.Unmarshal(data, target); err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: Unmarshal failed: %v\n", err)
			os.Exit(1)
		}

		if target.GetSeconds() != 0 || target.GetNanos() != 54321 {
			fmt.Fprintf(os.Stderr, "FAIL: expected reset target with Seconds=0, Nanos=54321, got Seconds=%d, Nanos=%d\n", target.GetSeconds(), target.GetNanos())
			os.Exit(1)
		}
	}

	// 4. proto.Unmarshal returns an error on truncated wire-format bytes
	{
		original := &wrapperspb.StringValue{Value: "length-delimited-payload"}
		data, err := proto.Marshal(original)
		if err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: Marshal failed: %v\n", err)
			os.Exit(1)
		}

		// Truncate the payload bytes
		truncatedData := data[:len(data)-5]
		msg := &wrapperspb.StringValue{}
		if err := proto.Unmarshal(truncatedData, msg); err == nil {
			fmt.Fprintf(os.Stderr, "FAIL: expected error on truncated wire data, got nil\n")
			os.Exit(1)
		}
	}

	// 5. proto.Unmarshal unmarshals empty byte slice into default message with nil error
	{
		msg := &wrapperspb.Int64Value{Value: 999}
		if err := proto.Unmarshal([]byte{}, msg); err != nil {
			fmt.Fprintf(os.Stderr, "FAIL: expected nil error on empty byte slice, got %v\n", err)
			os.Exit(1)
		}
		if msg.GetValue() != 0 {
			fmt.Fprintf(os.Stderr, "FAIL: expected default zero value after unmarshaling empty slice, got %d\n", msg.GetValue())
			os.Exit(1)
		}
	}

	fmt.Println("PASS: all contract assertions passed")
}