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FAQ & Troubleshooting

Common questions, issues, and solutions when working with Azu.

Frequently Asked Questions

General Questions

Q: What makes Azu different from other web frameworks?

A: Azu emphasizes compile-time type safety and contract-first development. Unlike traditional frameworks that validate at runtime, Azu catches errors during compilation, resulting in more reliable applications with zero runtime overhead for type checking.

Q: Can I use Azu for production applications?

A: Yes! Azu is built for production use with performance optimizations, comprehensive error handling, and scalability features. Many applications are successfully running Azu in production environments.

Q: How does Azu compare to other Crystal web frameworks?

A: Azu focuses on type-safe contracts and real-time features, while frameworks like Kemal prioritize simplicity. Azu provides more structure and compile-time guarantees at the cost of some flexibility.

Q: Do I need to learn Crystal to use Azu?

A: Yes, basic Crystal knowledge is required. However, Crystal's syntax is similar to Ruby, making it approachable for developers from many backgrounds.

Technical Questions

Q: How do I handle database connections in Azu?

A: Azu doesn't include a built-in ORM. You can use any Crystal database library like crystal-db, granite, or jennifer.cr:

require "pg"
require "azu"

struct UserEndpoint
  include Azu::Endpoint(UserRequest, UserResponse)

  get "/users/:id"

  def call : UserResponse
    DB.open("postgres://localhost/mydb") do |db|
      user = db.query_one("SELECT * FROM users WHERE id = $1",
                         params["id"], as: User)
      UserResponse.new(user)
    end
  end
end

Q: Can I use Azu with existing Crystal libraries?

A: Absolutely! Azu is designed to work with the Crystal ecosystem. You can use any Crystal shard or library within your Azu applications.

Q: How do I handle authentication?

A: Implement authentication using middleware:

class AuthenticationHandler
  include HTTP::Handler

  def call(context)
    token = context.request.headers["Authorization"]?

    unless token && valid_token?(token)
      context.response.status = HTTP::Status::UNAUTHORIZED
      context.response.print "Authentication required"
      return
    end

    context.set("current_user", get_user_from_token(token))
    call_next(context)
  end
end

# Add to middleware stack
MyApp.start [
  AuthenticationHandler.new,
  # ... other handlers
]

Q: How do I deploy Azu applications?

A: Compile your application and deploy the binary:

# Build for production
crystal build --release --no-debug src/my_app.cr

# Deploy binary to server
scp my_app user@server:/opt/myapp/

Common Issues

Compilation Issues

Problem: "can't infer type" errors

# ❌ This causes type inference issues
def create_user(request)
  # Crystal can't infer the request type
end

# ✅ Use explicit types
def create_user(request : CreateUserRequest) : UserResponse
  # Clear type information
end

Problem: Template compilation errors

Error: can't find template "users/show.html"

Solution: Check template paths in configuration:

configure do
  templates.path = ["templates", "views"] # Add all template directories
  template_hot_reload = env.development?  # Enable hot reload for development
end

Runtime Issues

Problem: WebSocket connections not working

Symptoms:

  • WebSocket connection fails

  • No error messages in logs

  • Client can't connect

Solutions:

  1. Check WebSocket route registration:

class MyChannel < Azu::Channel
  ws "/websocket" # Make sure this matches client URL

  def on_connect
    # Implementation
  end
end

  1. Verify middleware order:

MyApp.start [
  Azu::Handler::Logger.new,
  # Don't put static handler before WebSocket routes
  # WebSocket handlers should come early in the stack
]

  1. Check client-side connection:

// Make sure URL matches server route
const ws = new WebSocket("ws://localhost:4000/websocket");

Problem: Request validation not working

Symptoms:

  • Validation rules ignored

  • Invalid data passes through

Solutions:

  1. Ensure validation is called:

def call : UserResponse
  # Always validate before processing
  unless create_user_request.valid?
    raise Azu::Response::ValidationError.new(
      create_user_request.errors.group_by(&.field).transform_values(&.map(&.message))
    )
  end

  # Process validated request
  UserResponse.new(create_user(create_user_request))
end

  1. Check validation rules syntax:

struct UserRequest
  include Azu::Request

  getter name : String
  getter email : String

  # ✅ Correct validation syntax
  validate name, presence: true, length: {min: 2}
  validate email, presence: true, format: /@/

  def initialize(@name = "", @email = "")
  end
end

Problem: File uploads not working

Symptoms:

  • File uploads fail silently

  • Uploaded files are empty

  • Memory issues with large files

Solutions:

  1. Configure upload limits:

configure do
  upload.max_file_size = 50.megabytes
  upload.temp_dir = "/tmp/uploads"
end

  1. Handle multipart data correctly:

struct FileUploadRequest
  include Azu::Request

  getter file : Azu::Params::Multipart::File?
  getter description : String

  def initialize(@file = nil, @description = "")
  end
end

def call : FileUploadResponse
  if file = file_upload_request.file
    # Validate file
    raise error("File too large") if file.size > 10.megabytes

    # Save file
    final_path = save_uploaded_file(file)
    file.cleanup # Important: clean up temp file

    FileUploadResponse.new(path: final_path)
  else
    raise error("File is required")
  end
end

Performance Issues

Problem: Slow response times

Diagnosis:

  1. Enable request logging:

MyApp.start [
  Azu::Handler::Logger.new, # Add this first
  # ... other handlers
]

  1. Check for blocking operations:

def call : UserResponse
  # ❌ Blocking database call
  users = database.query("SELECT * FROM users") # Blocks fiber

  # ✅ Use async operations when possible
  users = database.async_query("SELECT * FROM users")
  UserResponse.new(users)
end

Problem: Memory leaks

Common causes:

  • Not cleaning up file uploads

  • Keeping references to WebSocket connections

  • Large object creation in loops

Solutions:

  1. Clean up resources:

def handle_file_upload(file)
  process_file(file)
ensure
  file.cleanup if file # Always cleanup
end

  1. Manage WebSocket connections:

class MyChannel < Azu::Channel
  CONNECTIONS = Set(HTTP::WebSocket).new

  def on_connect
    CONNECTIONS << socket.not_nil!
  end

  def on_close(code, message)
    CONNECTIONS.delete(socket) # Remove on disconnect
  end
end

Development Issues

Problem: Hot reload not working

Solutions:

  1. Enable in configuration:

configure do
  template_hot_reload = env.development? # Make sure this is true
end

  1. Check file permissions and paths:

# Make sure template files are readable
chmod -R 644 templates/

Problem: CORS issues in development

Symptoms:

  • Browser blocks requests from frontend

  • CORS errors in console

Solution:

MyApp.start [
  Azu::Handler::CORS.new(
    allowed_origins: ["http://localhost:3000"], # Add your frontend URL
    allowed_methods: %w(GET POST PUT PATCH DELETE OPTIONS),
    allowed_headers: %w(Accept Content-Type Authorization)
  ),
  # ... other handlers
]

Debugging Tips

Enable Debug Logging

configure do
  log.level = Log::Severity::DEBUG # See all log messages
end

Inspect Request Data

def call : UserResponse
  Log.debug { "Request data: #{create_user_request.inspect}" }
  Log.debug { "Params: #{params.to_hash}" }
  Log.debug { "Headers: #{context.request.headers}" }

  # ... endpoint logic
end

Use Crystal's Built-in Debugging

# Add pp for pretty printing
require "pp"

def call : UserResponse
  pp create_user_request # Pretty print request object
  pp params.to_hash      # Pretty print parameters

  # ... endpoint logic
end

Test Individual Components

# Test request contracts in isolation
user_request = CreateUserRequest.new(name: "test", email: "test@example.com")
puts user_request.valid?
puts user_request.errors.map(&.message)

# Test response objects
user = User.new(name: "test")
response = UserResponse.new(user)
puts response.render

Performance Troubleshooting

Profile Your Application

require "benchmark"

def call : UserResponse
  time = Benchmark.measure do
    # Your endpoint logic here
  end

  Log.info { "Endpoint took #{time.total_seconds}s" }

  # ... return response
end

Monitor Memory Usage

# Check memory usage during runtime
ps aux | grep my_app

# Use Crystal's built-in memory tracking
crystal run --stats src/my_app.cr

Database Query Optimization

# Log slow queries
def call : UserResponse
  start_time = Time.monotonic

  users = database.query("SELECT * FROM users WHERE active = true")

  duration = Time.monotonic - start_time
  if duration > 100.milliseconds
    Log.warn { "Slow query detected: #{duration.total_milliseconds}ms" }
  end

  UserResponse.new(users)
end

Getting Help

Community Resources

Reporting Issues

When reporting issues, include:

  1. Crystal version: crystal version

  2. Azu version: Check shard.yml

  3. Minimal reproduction case

  4. Error messages and stack traces

  5. Environment details (OS, deployment method)

Example Issue Report

**Crystal Version**: 1.10.1
**Azu Version**: 0.5.2
**OS**: macOS 13.0

**Issue**: WebSocket connection fails with "Connection refused"

**Reproduction**:
```crystal
class TestChannel < Azu::Channel
  ws "/test"
  def on_connect
    puts "Connected"
  end
end

Error: Connection refused when trying to connect to ws://localhost:4000/test

Expected: WebSocket connection should succeed


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**Still need help?** Check the [Contributing Guide](contributing.md) for information on getting support from the community.
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