GitHub Docs Code Example Copier

A GitHub app that automatically copies code examples and files from source repositories to target repositories when pull requests are merged. Features centralized configuration with distributed workflow management, $ref support for reusable components, advanced pattern matching, and comprehensive monitoring.

Features

Core Functionality

• Main Config System - Centralized configuration with distributed workflow management
• Source Context Inference - Workflows automatically inherit source repo/branch
• $ref Support - Reusable components for transformations, strategies, and excludes
• Resilient Loading - Continues processing when individual configs fail (logs warnings)
• Automated File Copying - Copies files from source to target repos on PR merge
• Advanced Pattern Matching - Prefix, glob, and regex patterns with variable extraction
• Path Transformations - Template-based path transformations with variable substitution
• Flexible Commit Strategies - Direct commits or pull requests with auto-merge
• Deprecation Tracking - Automatic tracking of deleted files

Enhanced Features

• Workflow References - Local, remote (repo), or inline workflow configs
• Default Precedence - Workflow > Workflow config > Main config > System defaults
• Message Templating - Template-ized commit messages and PR titles
• PR Template Integration - Fetch and merge PR templates from target repos
• File Exclusion - Exclude patterns to filter out unwanted files
• Audit Logging - MongoDB-based event tracking for all operations
• Health & Metrics - /health, /ready, and /metrics endpoints for monitoring
• Rate Limit Handling - Automatic GitHub API rate limit detection, backoff, and retry
• Webhook Idempotency - Deduplication via X-GitHub-Delivery header tracking
• Structured Logging - JSON structured logging via log/slog (Cloud Logging compatible)
• Development Tools - Dry-run mode, CLI validation, enhanced logging
• Thread-Safe - Concurrent webhook processing with proper state management

🚀 Quick Start

Prerequisites

• Go 1.26+
• GitHub App credentials
• Google Cloud project (for Secret Manager and logging)
• MongoDB Atlas (optional, for audit logging)

Installation

# Clone the repository
git clone https://github.com/your-org/code-example-tooling.git
cd code-example-tooling/github-copier

# Install dependencies
go mod download

# Build the application
go build -o github-copier .

# Build CLI tools
go build -o config-validator ./cmd/config-validator

Local Configuration

1. Copy environment example file

cp env.yaml.example env.yaml

2. Set required environment variables

# GitHub Configuration
GITHUB_APP_ID: "123456"
INSTALLATION_ID: "789012"  # Optional fallback

# Config Repository (where main config lives)
CONFIG_REPO_OWNER: "your-org"
CONFIG_REPO_NAME: "config-repo"
CONFIG_REPO_BRANCH: "main"

# Main Config
MAIN_CONFIG_FILE: ".copier/workflows/main.yaml"
USE_MAIN_CONFIG: "true"

# Secret Manager References
GITHUB_APP_PRIVATE_KEY_SECRET_NAME: "projects/.../secrets/PEM/versions/latest"
WEBHOOK_SECRET_NAME: "projects/.../secrets/webhook-secret/versions/latest"

# Application Settings
WEBSERVER_PATH: "/events"
DEPRECATION_FILE: "deprecated_examples.json"
COMMITTER_NAME: "GitHub Copier App"
COMMITTER_EMAIL: "bot@mongodb.com"

# Feature Flags
AUDIT_ENABLED: "false"
METRICS_ENABLED: "true"

3. Create main configuration file

Create .copier/workflows/main.yaml in your config repository:

# Main config with global defaults and workflow references
defaults:
  commit_strategy:
    type: "pull_request"
    auto_merge: false
  exclude:
    - "**/.env"
    - "**/node_modules/**"

workflow_configs:
  # Reference workflows in source repo
  - source: "repo"
    repo: "your-org/source-repo"
    branch: "main"
    path: ".copier/workflows/config.yaml"
    enabled: true

4. Create workflow config in source repository

Create .copier/workflows/config.yaml in your source repository:

workflows:
  - name: "copy-examples"
    # source.repo and source.branch inherited from workflow config reference
    destination:
      repo: "your-org/target-repo"
      branch: "main"
    transformations:
      - move: { from: "examples", to: "docs/examples" }
    commit_strategy:
      type: "pull_request"
      pr_title: "Update code examples"
      use_pr_template: true

Running the Application

# Run with default settings
./github-copier

# Run with custom environment file
./github-copier -env ./configs/.env.production

# Run in dry-run mode (no actual commits)
./github-copier -dry-run

# Validate configuration only
./github-copier -validate

Configuration

See MAIN-CONFIG-README.md for complete configuration documentation.

Main Config Structure

The application uses a three-tier configuration system:

1. Main Config - Centralized defaults and workflow references
2. Workflow Configs - Collections of workflows (local, remote, or inline)
3. Individual Workflows - Specific source → destination mappings

Transformation Types

Move Transformation

Move files from one directory to another:

transformations:
  - move:
      from: "examples/go"
      to: "code/go"

Moves: examples/go/main.go → code/go/main.go

Copy Transformation

Copy a single file to a new location:

transformations:
  - copy:
      from: "README.md"
      to: "docs/README.md"

Copies: README.md → docs/README.md

Glob Transformation

Wildcard matching with path transformation:

transformations:
  - glob:
      pattern: "examples/*/main.go"
      transform: "code/${relative_path}"

Matches: examples/go/main.go → code/examples/go/main.go

Regex Transformation

Full regex with named capture groups:

transformations:
  - regex:
      pattern: "^examples/(?P<lang>[^/]+)/(?P<file>.+)$"
      transform: "code/${lang}/${file}"

Matches: examples/go/main.go → code/go/main.go (extracts lang=go, file=main.go)

Path Transformations

Transform source paths to target paths using variables:

path_transform: "docs/${lang}/${category}/${file}"

Built-in Variables:

• ${path} - Full source path
• ${filename} - File name only
• ${dir} - Directory path
• ${ext} - File extension

Custom Variables:

• Any named groups from regex patterns
• Example: (?P<lang>[^/]+) creates ${lang}

Commit Strategies

Direct Commit

commit_strategy:
  type: "direct"
  commit_message: "Update examples from ${source_repo}"

Pull Request

commit_strategy:
  type: "pull_request"
  commit_message: "Update examples"
  pr_title: "Update ${category} examples"
  pr_body: "Automated update from ${source_repo}"
  use_pr_template: true  # Fetch and merge PR template from target repo
  auto_merge: true

Advanced Features

$ref Support for Reusable Components

Extract common configurations into separate files:

# Workflow config
workflows:
  - name: "mflix-java"
    destination:
      repo: "mongodb/sample-app-java-mflix"
      branch: "main"
    transformations:
      $ref: "../transformations/mflix-java.yaml"
    commit_strategy:
      $ref: "../strategies/mflix-pr-strategy.yaml"
    exclude:
      $ref: "../common/mflix-excludes.yaml"

Source Context Inference

Workflows automatically inherit source repo/branch from workflow config reference:

# No need to specify source.repo and source.branch!
workflows:
  - name: "my-workflow"
    # source.repo and source.branch inherited automatically
    destination:
      repo: "mongodb/dest-repo"
      branch: "main"
    transformations:
      - move: { from: "src", to: "dest" }

PR Template Integration

Automatically fetch and merge PR templates from target repositories:

commit_strategy:
  type: "pull_request"
  pr_body: "🤖 Automated update"
  use_pr_template: true  # Fetches .github/pull_request_template.md

File Exclusion

Exclude unwanted files at the workflow or workflow config level:

exclude:
  - "**/.gitignore"
  - "**/node_modules/**"
  - "**/.env"
  - "**/dist/**"

Message Templates

Use variables in commit messages and PR titles:

commit_message: "Update ${category} examples from ${lang}"
pr_title: "Update ${category} examples"

Available Variables:

• ${rule_name} - Name of the copy rule
• ${source_repo} - Source repository
• ${target_repo} - Target repository
• ${source_branch} - Source branch
• ${target_branch} - Target branch
• ${file_count} - Number of files being copied
• Any custom variables from pattern matching

CLI Tools

Config Validator

Validate and test configurations before deployment:

# Validate config file
./config-validator validate -config copier-config.yaml -v

# Test pattern matching
./config-validator test-pattern \
  -type regex \
  -pattern "^examples/(?P<lang>[^/]+)/(?P<file>.+)$" \
  -file "examples/go/main.go"

# Test path transformation
./config-validator test-transform \
  -template "docs/${lang}/${file}" \
  -file "examples/go/main.go" \
  -pattern "^examples/(?P<lang>[^/]+)/(?P<file>.+)$"

# Initialize new config from template
./config-validator init -output copier-config.yaml

# Convert between formats
./config-validator convert -input config.json -output copier-config.yaml

Monitoring

Health Endpoint (Liveness)

Basic liveness check:

curl http://localhost:8080/health

Readiness Endpoint

Deep readiness probe (checks GitHub auth, rate limits, MongoDB):

curl http://localhost:8080/ready

Metrics Endpoint

Get performance metrics:

curl http://localhost:8080/metrics

Audit Logging

When enabled, all operations are logged to MongoDB:

// Query recent copy events
db.audit_events.find({
  event_type: "copy",
  success: true
}).sort({timestamp: -1}).limit(10)

// Find failed operations
db.audit_events.find({
  success: false
}).sort({timestamp: -1})

// Statistics by rule
db.audit_events.aggregate([
  {$match: {event_type: "copy"}},
  {$group: {
    _id: "$rule_name",
    count: {$sum: 1},
    avg_duration: {$avg: "$duration_ms"}
  }}
])

Testing

Run Tests

# Run all tests with race detector
go test -race ./...

# Run specific test suite
go test ./services -v -run TestPatternMatcher

# Run with coverage
go test -race ./services -cover
go test -race ./services -coverprofile=coverage.out
go tool cover -html=coverage.out

Development

Dry-Run Mode

Test without making actual changes:

./github-copier -env .env.test -dry-run

In dry-run mode:

• Webhooks are received and processed through the full pipeline
• Files are matched and path transformations are applied
• GitHub auth failures are tolerated (logged as warnings)
• No commits, PRs, or file uploads are created

Structured Logging

The app uses log/slog with JSON output. Enable debug logging:

LOG_LEVEL=debug ./github-copier
# or
COPIER_DEBUG=true ./github-copier

Architecture

Project Structure

github-copier/
├── app.go                    # Main application entry point
├── github-app-manifest.yml   # GitHub App permissions documentation
├── cmd/
│   ├── config-validator/     # CLI validation tool
│   ├── test-pem/             # PEM key validation tool
│   └── test-webhook/         # Webhook testing tool
├── configs/
│   ├── environment.go        # Environment configuration
│   ├── .env.local.example    # Local environment template
│   └── copier-config.example.yaml # Config template
├── scripts/
│   ├── release.sh            # Create versioned releases
│   ├── deploy-cloudrun.sh    # Cloud Run deployment
│   ├── ci-local.sh           # Run CI checks locally
│   ├── integration-test.sh   # End-to-end integration tests
│   └── ...                   # Additional helper scripts
├── services/
│   ├── webhook_handler_new.go # Webhook handler (orchestrator)
│   ├── workflow_processor.go  # ProcessWorkflow() - core logic
│   ├── pattern_matcher.go     # Pattern matching engine
│   ├── config_loader.go       # Config loading & validation
│   ├── main_config_loader.go  # Main config with $ref support
│   ├── github_auth.go         # GitHub App authentication
│   ├── github_read.go         # GitHub read operations (REST + GraphQL)
│   ├── github_write_to_target.go # GitHub write operations
│   ├── github_write_to_source.go # Deprecation file updates
│   ├── token_manager.go       # Thread-safe token state management
│   ├── rate_limit.go          # GitHub API rate limit handling
│   ├── delivery_tracker.go    # Webhook idempotency (deduplication)
│   ├── errors.go              # Sentinel errors & classification
│   ├── logger.go              # Structured logging (slog)
│   ├── service_container.go   # Dependency injection container
│   ├── file_state_service.go  # Thread-safe upload/deprecation queues
│   ├── health_metrics.go      # Health, readiness, metrics & config endpoints
│   ├── slack_notifier.go      # Slack notifications
│   └── pr_template_fetcher.go # PR template resolution
├── types/
│   ├── config.go              # Configuration types
│   └── types.go               # Core types
└── docs/
    ├── DEPLOYMENT.md          # Deployment & rollback guide
    ├── CONFIG-REFERENCE.md    # Environment variables & YAML schema
    ├── WEBHOOK-TESTING.md     # Webhook testing guide
    ├── SLACK-NOTIFICATIONS.md # Slack integration guide
    └── ...                    # Additional documentation

Service Container

The application uses dependency injection for clean architecture:

container := NewServiceContainer(config)
// All services initialized and wired together

Releasing

The project uses semantic versioning (vMAJOR.MINOR.PATCH) with GitHub Releases. Pushing a version tag triggers CI to build, test, and deploy to Cloud Run.

Release Workflow

1. Merge your changes to main.
2. Run the release script:

# Preview what will happen (no changes made)
./scripts/release.sh v1.2.0 --dry-run

# Create the release
./scripts/release.sh v1.2.0

The script:

1. Validates the version format and that the working tree is clean on main
2. Renames the [Unreleased] section in CHANGELOG.md to [v1.2.0] - YYYY-MM-DD
3. Commits the changelog update and creates an annotated git tag
4. Pushes the tag to origin — this triggers the CI deploy job
5. Creates a GitHub Release with the changelog excerpt

CI Deploy Pipeline

The deploy job in .github/workflows/ci.yml runs only on version tag pushes:

• Authenticates to Google Cloud via Workload Identity Federation
• Deploys to Cloud Run with the version stamped as a build arg (VERSION)
• Tags the Cloud Run revision with the version for easy rollback

Version Stamping

The version tag is injected at build time via -ldflags:

go build -ldflags "-X main.Version=v1.2.0" -o github-copier .

The version appears in the startup banner and the /health endpoint response.

Deployment

See DEPLOYMENT.md for the complete deployment and rollback guide.

Security

• Webhook Signature Verification - HMAC-SHA256 validation
• Webhook Idempotency - Duplicate delivery detection via X-GitHub-Delivery
• Secret Management - Google Cloud Secret Manager
• Least Privilege - Minimal GitHub App permissions (see github-app-manifest.yml)

Documentation

Getting Started

• Main Config README - Main config architecture
• Source Repo README - Workflow config guide for source repos
• Pattern Matching Guide - Pattern matching with examples
• Local Testing - Test locally before deploying
• Deployment Guide - Deploy to Cloud Run

Reference

• Config Reference - Environment variables and YAML schema
• Architecture - System design and components
• Troubleshooting - Common issues and solutions
• FAQ - Frequently asked questions
• Changelog - Release history

Features

• Slack Notifications - Slack integration guide
• Webhook Testing - Webhook testing guide
• GitHub App Manifest - Required permissions and events

Tools

• Config Validator - CLI tool for validating configs
• Test Webhook - CLI tool for testing webhooks
• Scripts - Helper scripts for deployment, testing, and releases