Webmachine state machine and resource callbacks

webmachine.markdown

Webmachine State Machine

General

• Service available?
  • callback: service_available?
  • false: 503 Service Unavailable
• Known method?
  • callback: known_methods
  • absent: 501 Not Implemented
• URI too long?
  • callback: uri_too_long?
  • true: 414 Request URI Too Long
• Method allowed?
  • callback: allowed_methods
  • absent: 405 Method Not Allowed
• Malformed request?
  • callbacks: validate_content_checksum, malformed_request?
  • true: 400 Bad Request
• Authorized?
  • callback: is_authorized?
  • false: 401 Unauthorized
• Forbidden?
  • callback: forbidden?
  • true: 403 Forbidden
• Valid Content-* headers?
  • callback: valid_content_headers?
  • false: 501 Not Implemented
• Known content type?
  • callback: known_content_type?
  • false: 415 Unsupported Media Type
• Request entity too large?
  • callback: valid_entity_length?
  • false: 413 Request Entity Too Large
• OPTIONS?
  • callback: options
  • true: 200 OK

Content Negotiation

• Accept exists?
  • true: Acceptable media type available?
    • callback: content_types_provided
    • absent: 406 Not Acceptable
• Accept-Language exists?
  • true: Acceptable language available?
    • callback: languages_provided
    • absent: 406 Not Acceptable
• Accept-Charset exists?
  • true: Acceptable character set available?
    • callback: charsets_provided
    • absent: 406 Not Acceptable
• Accept-Encoding exists?
  • true: Acceptable encoding available?
    • callback: encodings_available
    • absent: 406 Not Acceptable
• Set Content-Type header
• Set Vary Header

Resource Exists?

• Resource exists?
  • callback: resource_exists?

Exists

Conditional Request

• If-Match exists?
  • true: If-Match: * exists?
    • false: ETag in If-Match?
      • callback: generate_etag
      • false: 412 Precondition Failed
• If-Unmodified-Since exists?
  • true: If-Unmodified-Since is valid date?
    • true: Last-Modified > If-Modified-Since?
      • callback: last_modified
      • true: 412 Precondition Failed
• If-None-Match exists?
  • true: If-None-Match: * exists?
    • false: ETag in If-None-Match?
      • callback: generate_etag
      • true: 304 Not Modified
      • false: 412 Precondition Failed
    • true: GET/HEAD?
      • true: 304 Not Modified (efficient cache updates)
      • false: 412 Precondition Failed (avoid PUT race conditions)
• If-Modified-Since exists?
  • true: If-Modified-Since is valid date?
    • true: If-Modified-Since > now?
      • false: Last-Modified > If-Modified-Since?
        • callback: last_modified
        • false: 304 Not Modified

Verb

• DELETE?

  • true: Delete
    • callback: delete_resource
    • false: 500 Internal Server Error
    • true: Delete enacted?
      • callbacks: delete_completed?
      • false: 202 Accepted
      • true: Response includes an entity?
        • false: 204 No Content
        • true: Multiple Choices?
          • callback: multiple_choices?
          • false: 200 OK
          • true: 300 Multiple Choices

• POST?

  • true: Redirect?
    • callback: post_is_create?
    • true: Create
      • callbacks: base_uri, create_path, content_types_accepted -> handler
      • true: 303 See Other
    • false: Process
      • callbacks: process_post
      • true: New Resource?
        • true: 201 Created
        • false: Response includes an entity?
          • false: 204 No Content
          • true: Multiple Choices?
            • callback: multiple_choices?
            • false: 200 OK
            • true: 300 Multiple Choices

• PUT?

  • true: Conflict?
    • callback: is_conflict?
    • true: 409 Conflict
    • false: New Resource?
      • true: 201 Created
      • false: Response includes an entity?
        • false: 204 No Content
        • true: Multiple Choices?
          • callback: multiple_choices?
          • false: 200 OK
          • true: 300 Multiple Choices

• (GET/HEAD)

  • Generate body
    • callback: content_types_provided -> handler
  • Multiple Choices?
    • callback: multiple_choices?
    • false: 200 OK
    • true: 300 Multiple Choices

Does not exist

• If-Match: * Exists?
  • true: 412 Precondition Failed (PUT race conditions)
  • false: PUT?

PUT

• Apply PUT to a different URL?
  • callback: moved_permanently?
  • true: 301 Moved Permanently
  • false: Conflict?
    • callback: is_conflict?
    • true: 409 Conflict
    • false: New Resource?
      • true: 201 Created
      • false: Response includes an entity?
        • false: 204 No Content
        • true: Multiple Choices?
          • callback: multiple_choices?
            • false: 200 OK
            • true: 300 Multiple Choices

GET/HEAD/POST

• Resource previously existed?
  • callback: previously_existed?

Existed

• Resource moved permanently?
  • callback: moved_permanently?
  • true: 301 Moved Permanently
• Resource moved temporarily?
  • callback: moved_temporarily?
  • true: 307 Moved Temporarily

Never existed

• POST?
  • false: 404 Not Found
  • true: Permit POST to missing resource?
    • callback: allow_missing_post?
    • false: 404 Not Found
    • true: Redirect?
      • callback: post_is_create?
      • true: Create
        • callbacks: base_uri, create_path, content_types_accepted -> handler
        • true: 303 See Other
      • false: Process
        • callbacks: process_post
        • true: New Resource?
          • true: 201 Created
          • false: Response includes an entity?
            • false: 204 No Content
            • true: Multiple Choices?
              • callback: multiple_choices?
              • false: 200 OK
              • true: 300 Multiple Choices