FOSMVVM ServerRequest Generator

Generate ServerRequest types for client-server communication.

Architecture context: See FOSMVVMArchitecture.md

STOP AND READ THIS

ServerRequest is THE way to communicate with an FOSMVVM server. No exceptions.

┌──────────────────────────────────────────────────────────────────────┐
│                 ALL CLIENTS USE ServerRequest                         │
├──────────────────────────────────────────────────────────────────────┤
│                                                                       │
│  iOS App:         Button tap    →  request.processRequest(mvvmEnv:)   │
│  macOS App:       Button tap    →  request.processRequest(mvvmEnv:)   │
│  WebApp:          JS → WebApp   →  request.processRequest(mvvmEnv:)   │
│  CLI Tool:        main()        →  request.processRequest(mvvmEnv:)   │
│  Data Collector:  timer/event   →  request.processRequest(mvvmEnv:)   │
│  Background Job:  cron trigger  →  request.processRequest(mvvmEnv:)   │
│                                                                       │
│  MVVMEnvironment holds: baseURL, headers, version, error handling     │
│  Configure ONCE at startup, use EVERYWHERE via processRequest()       │
│                                                                       │
└──────────────────────────────────────────────────────────────────────┘

What You Must NEVER Do

// ❌ WRONG - hardcoded URL
let url = URL(string: "http://server/api/users/123")!
var request = URLRequest(url: url)

// ❌ WRONG - string path
try await client.get("/api/users/\(id)")

// ❌ WRONG - manual JSON encoding
let json = try JSONEncoder().encode(body)
request.httpBody = json

// ❌ WRONG - hardcoded fetch path
fetch('/api/users/123')

// ❌ WRONG - constructing URLs manually
fetch(`/api/ideas/${ideaId}/move`)

What You Must ALWAYS Do

Step 1: Configure MVVMEnvironment once at startup

// CLI tool, background job, data collector - configure at startup
// Import your shared module to get SystemVersion.currentApplicationVersion
import ViewModels  // ← Your shared module (see FOSMVVMArchitecture.md)

let mvvmEnv = await MVVMEnvironment(
    currentVersion: .currentApplicationVersion,  // From shared module
    appBundle: Bundle.module,
    deploymentURLs: [.debug: URL(string: "http://localhost:8080")!]
)
// NOTE: Version headers (X-FOS-Version) are AUTOMATIC via SystemVersion.current

The shared module contains

SystemVersion+App.swift

// In your shared ViewModels module
public extension SystemVersion {
    static var currentApplicationVersion: Self { .v1_0 }
    static var v1_0: Self { .init(major: 1, minor: 0, patch: 0) }
}

Step 2: Use processRequest(mvvmEnv:) everywhere

// ✅ RIGHT - ServerRequest with MVVMEnvironment
let request = UserShowRequest(query: .init(userId: id))
try await request.processRequest(mvvmEnv: mvvmEnv)
let user = request.responseBody

// ✅ RIGHT - Create operation
let createRequest = CreateIdeaRequest(requestBody: .init(content: content))
try await createRequest.processRequest(mvvmEnv: mvvmEnv)
let newId = createRequest.responseBody?.id

// ✅ RIGHT - Update operation
let updateRequest = MoveIdeaRequest(requestBody: .init(ideaId: id, newStatus: status))
try await updateRequest.processRequest(mvvmEnv: mvvmEnv)

The path is derived from the type name. The HTTP method comes from the protocol. You NEVER write URL strings. Configuration lives in MVVMEnvironment - you NEVER pass baseURL/headers to individual requests.

When to Use This Skill

• Implementing any client-server communication
• Adding CRUD operations (Create, Read, Update, Delete)
• Building data collectors or sync tools
• Any Swift code that needs to talk to the server

If you're about to write

URLRequest

What ServerRequest Provides

Self.path

MoveIdeaRequest

/move_idea

action.httpMethod

RequestBody

requestBody?.toJSONData()

ResponseBody

responseBody

ResponseError

ResponseBody

RequestBody: ValidatableModel

RequestBody.maxBodySize

Request Protocol Selection

Choose based on the operation:

ShowRequest

ViewModelRequest

CreateRequest

UpdateRequest

.replace

DeleteRequest

DestroyRequest

What This Skill Generates

Core Files (Always)

{Action}Request.swift

{ViewModelsTarget}/Requests/

{Action}Controller.swift

{WebServerTarget}/Controllers/

Optional: WebApp Bridge (for web clients)

How to Use This Skill

Invocation: /fosmvvm-serverrequest-generator

Prerequisites:

• Operation requirements understood from conversation context
• RequestBody and ResponseBody structures discussed or documented
• Client type identified (iOS app, WebApp, CLI tool, background job, etc.)

Workflow integration: This skill is typically used when implementing client-server communication. The skill references conversation context automatically—no file paths or Q&A needed. Often follows fosmvvm-viewmodel-generator (for ResponseBody ViewModels) and fosmvvm-fields-generator (for RequestBody validation).

Pattern Implementation

This skill references conversation context to determine ServerRequest structure:

Operation Type Detection

From conversation context, the skill identifies:

• CRUD operation (create, read, update, delete)
• HTTP semantics (GET for read, POST for create, PATCH/PUT for update, DELETE for delete)
• Protocol choice (ShowRequest, ViewModelRequest, CreateRequest, UpdateRequest, DeleteRequest)

Request Structure Design

From requirements already in context:

• RequestBody fields (what data the client sends)
• Query parameters (URL query string data)
• Fragment parameters (URL fragment/anchor data)
• Validation requirements (ValidatableModel for write operations)

Response Structure Design

From requirements already in context:

• ResponseBody type (often a ViewModel, sometimes just an ID)
• ResponseError type (custom error structure or EmptyError)
• Success scenarios (what indicates successful operation)
• Error scenarios (known failure modes requiring structured errors)

Client Detection

From conversation context:

• Target platform (iOS/macOS app, WebApp browser, CLI tool, background job)
• Bridge requirements (whether WebApp route needed for browser clients)
• MVVMEnvironment setup (how client configures baseURL and headers)

File Generation

Core files:

1. ServerRequest type with RequestBody, ResponseBody, ResponseError
2. Controller with action handler
3. Route registration

Optional (for WebApp clients): 4. WebApp route bridging JS to ServerRequest 5. JavaScript handler guidance

Context Sources

Skill references information from:

• Prior conversation: Operation requirements, data structures discussed
• Specification files: If Claude has read API specs or feature docs into context
• Existing patterns: From codebase analysis of similar requests

ServerRequest Type Template

// {Action}Request.swift
import FOSMVVM

public final class {Action}Request: {Protocol}, @unchecked Sendable {
    public typealias Query = EmptyQuery       // or custom Query type
    public typealias Fragment = EmptyFragment
    // ResponseError: use EmptyError OR define nested ResponseError struct (see below)

    public let requestBody: RequestBody?
    public var responseBody: ResponseBody?

    // What the client sends
    public struct RequestBody: ServerRequestBody, ValidatableModel {
        // Fields...
    }

    // What the server returns
    public struct ResponseBody: {Protocol}ResponseBody {
        // Fields (often contains a ViewModel)
    }

    // Optional: Custom error type (nested, not top-level!)
    // public struct ResponseError: ServerRequestError { ... }

    public init(
        query: Query? = nil,
        fragment: Fragment? = nil,
        requestBody: RequestBody? = nil,
        responseBody: ResponseBody? = nil
    ) {
        self.requestBody = requestBody
        self.responseBody = responseBody
    }
}

Note: All subtypes (RequestBody, ResponseBody, ResponseError) are nested inside the request class. This avoids namespace pollution and provides unique YAML localization keys automatically.

Controller Template

Controller action = Protocol name (minus "Request")

ShowRequest

.show

ViewModelRequest

.show

CreateRequest

.create

UpdateRequest

.update

DeleteRequest

.delete

DestroyRequest

.destroy

The pattern is mechanical:

UpdateRequest

.update

CreateRequest

.create

// {Action}Controller.swift
import Vapor
import FOSMVVM
import FOSMVVMVapor

final class {Action}Controller: ServerRequestController {
    typealias TRequest = {Action}Request

    let actions: [ServerRequestAction: ActionProcessor] = [
        .{action}: {Action}Request.performAction
    ]
}

private extension {Action}Request {
    static func performAction(
        _ request: Vapor.Request,
        _ serverRequest: {Action}Request,
        _ requestBody: RequestBody
    ) async throws -> ResponseBody {
        let db = request.db

        // 1. Fetch/validate
        // 2. Perform operation
        // 3. Build response (often a ViewModel)

        return .init(...)
    }
}

Controller Registration

// In WebServer routes.swift
try versionedGroup.register(collection: {Action}Controller())

Client Invocation

All Swift clients (iOS, macOS, CLI, background jobs, etc.):

// MVVMEnvironment configured once at app/tool startup (see "What You Must ALWAYS Do")
let request = {Action}Request(requestBody: .init(...))
try await request.processRequest(mvvmEnv: mvvmEnv)
let result = request.responseBody

WebApp (browser clients): See WebApp Bridge Pattern below.

WebApp Bridge Pattern

When the client is a web browser, you need a bridge between JavaScript and ServerRequest:

Browser                    WebApp (Swift)                      WebServer
   │                            │                                  │
   │  POST /action-name         │                                  │
   │  (JSON body)               │                                  │
   │ ─────────────────────────► │                                  │
   │                            │  request.processRequest(mvvmEnv:)│
   │                            │ ────────────────────────────────►│
   │                            │ ◄────────────────────────────────│
   │  ◄──────────────────────── │  (ResponseBody)                  │
   │  (HTML fragment or JSON)   │                                  │

The WebApp route is internal wiring - it's how browsers invoke ServerRequest, just like a button tap invokes it in iOS.

WebApp Route

// WebApp routes.swift
app.post("{action-name}") { req async throws -> Response in
    // 1. Decode what JS sent
    let body = try req.content.decode({Action}Request.RequestBody.self)

    // 2. Call server via ServerRequest (NOT hardcoded URL!)
    // mvvmEnv is configured at WebApp startup
    let serverRequest = {Action}Request(requestBody: body)
    try await serverRequest.processRequest(mvvmEnv: req.application.mvvmEnv)

    // 3. Return response (HTML fragment or JSON)
    guard let response = serverRequest.responseBody else {
        throw Abort(.internalServerError, reason: "No response from server")
    }
    // ...
}

JavaScript Handler

async function handle{Action}(data) {
    const response = await fetch('/{action-name}', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify(data)
    });
    // Handle response...
}

Note: The JS fetches to the WebApp (same origin), which then uses ServerRequest to talk to the WebServer. The browser NEVER talks directly to the WebServer.

Common Patterns

ViewModel Response

Most operations return a ViewModel for UI update:

public struct ResponseBody: UpdateResponseBody {
    public let viewModel: IdeaCardViewModel
}

ID-Only Response

Some operations just need confirmation:

public struct ResponseBody: CreateResponseBody {
    public let id: ModelIdType
}

Empty Response

Delete operations often return nothing:

// Use EmptyBody as ResponseBody
public typealias ResponseBody = EmptyBody

ResponseError - Typed Error Handling

Each

ServerRequest

ResponseError

How It Works

When processing a response:

1. Framework tries to decode as

   ResponseBody

2. If that fails, tries to decode as

   ResponseError

3. If

   ResponseError

   decode succeeds, that error is thrown
4. Client catches with try/catch at the call site

When to Use Custom ResponseError

Use custom

ResponseError

• Operation has known failure modes (validation, quota, permissions)
• Server returns structured error details (field names, error codes)
• Client needs to take specific action based on error type
• You want field-level validation error display

Use

EmptyError

• Operation rarely fails
• Failures are exceptional (network down, server crash)
• No structured error response expected
• You only need success/failure, not why

Nesting Pattern

ResponseError MUST be nested inside the request class, just like RequestBody and ResponseBody:

public final class CreateIdeaRequest: CreateRequest, @unchecked Sendable {
    public typealias Query = EmptyQuery
    public typealias Fragment = EmptyFragment
    // No typealias needed - ResponseError is nested

    public let requestBody: RequestBody?
    public var responseBody: ResponseBody?

    // ✅ All subtypes nested inside the request
    public struct RequestBody: ServerRequestBody, ValidatableModel { ... }
    public struct ResponseBody: CreateResponseBody { ... }
    public struct ResponseError: ServerRequestError { ... }  // ← Nested, not top-level

    public init(...) { ... }
}

Why nesting matters:

• Consistent with RequestBody/ResponseBody pattern
• Avoids namespace pollution (no

  CreateIdeaError

  ,

  MoveIdeaError

  , etc. at top level)
• YAML localization keys are scoped:

  CreateIdeaRequest.ResponseError.ErrorCode.quotaExceeded

• No need for unique type names like

  GovernanceLessonCreateError

  - nesting provides uniqueness

Pattern 1: Errors with Associated Values

For errors that need dynamic data in their messages, use

LocalizableSubstitutions

public final class CreateIdeaRequest: CreateRequest, @unchecked Sendable {
    // ... other typealiases and properties ...

    public struct ResponseError: ServerRequestError {
        public let code: ErrorCode
        public let message: LocalizableSubstitutions

        public enum ErrorCode: Codable, Sendable {
            case duplicateContent
            case quotaExceeded(requestedSize: Int, maximumSize: Int)
            case invalidCategory(category: String)

            var message: LocalizableSubstitutions {
                switch self {
                case .duplicateContent:
                    .init(
                        baseString: .localized(for: Self.self, parentType: ResponseError.self, propertyName: "duplicateContent"),
                        substitutions: [:]
                    )
                case .quotaExceeded(let requestedSize, let maximumSize):
                    .init(
                        baseString: .localized(for: Self.self, parentType: ResponseError.self, propertyName: "quotaExceeded"),
                        substitutions: [
                            "requestedSize": LocalizableInt(value: requestedSize),
                            "maximumSize": LocalizableInt(value: maximumSize)
                        ]
                    )
                case .invalidCategory(let category):
                    .init(
                        baseString: .localized(for: Self.self, parentType: ResponseError.self, propertyName: "invalidCategory"),
                        substitutions: [
                            "category": LocalizableString.constant(category)
                        ]
                    )
                }
            }
        }

        public init(code: ErrorCode) {
            self.code = code
            self.message = code.message  // Required to localize properly via Codable
        }
    }
}

en:
  CreateIdeaRequest:
    ResponseError:
      ErrorCode:
        duplicateContent: "The requested content is a duplicate of an existing idea."
        quotaExceeded: "The requested content size %{requestedSize} exceeds the maximum allowed size %{maximumSize}."
        invalidCategory: "The category %{category} is not valid."

Pattern 2: Simple Errors (String-Based Codes)

For simpler errors without associated values, use a

String

public final class MoveIdeaRequest: UpdateRequest, @unchecked Sendable {
    // ... other typealiases and properties ...

    public struct ResponseError: ServerRequestError {
        public let code: ErrorCode
        public let message: LocalizableString

        public enum ErrorCode: String, Codable, Sendable {
            case ideaNotFound
            case invalidTransition

            var message: LocalizableString {
                .localized(for: Self.self, parentType: ResponseError.self, propertyName: rawValue)
            }
        }

        public init(code: ErrorCode) {
            self.code = code
            self.message = code.message  // Required to localize properly via Codable
        }
    }
}

en:
  MoveIdeaRequest:
    ResponseError:
      ErrorCode:
        ideaNotFound: "The idea was not found"
        invalidTransition: "Cannot move to the requested status"

Type Safety Means You Already Know

STOP. Before you panic about "how do I know what error type I have?"

This isn't JavaScript. The type system tells you everything at compile time:

// When you write this request...
let request = MoveIdeaRequest(requestBody: body)

// ...you KNOW:
// - MoveIdeaRequest.ResponseError exists (it's declared in the type)
// - It has exactly the cases you defined (ideaNotFound, invalidTransition)
// - Each case has whatever properties you gave it

// So when you catch, you catch THE SPECIFIC TYPE:
do {
    try await request.processRequest(mvvmEnv: mvvmEnv)
} catch let error as MoveIdeaRequest.ResponseError {
    // I KNOW this is MoveIdeaRequest.ResponseError
    // I KNOW it has .code
    // I KNOW .code is ErrorCode enum with ideaNotFound, invalidTransition
    // No mystery. No runtime discovery. No "what if?"
}

The anti-pattern (JavaScript brain):

// ❌ WRONG - treating typed errors as unknown
catch let error as ServerRequestError {
    // "How do I get the message? What properties does it have?"
    // This thinking is WRONG. You're not in a typeless world.
}

The pattern (Swift brain):

// ✅ RIGHT - you know the exact type
catch let error as MoveIdeaRequest.ResponseError {
    switch error.code {
    case .ideaNotFound: // I know this exists
    case .invalidTransition: // I know this exists
    }
}

The

ServerRequestError

Error, Codable, Sendable

Client Error Handling

The primary pattern is try/catch at the call site:

do {
    try await request.processRequest(mvvmEnv: mvvmEnv)
} catch let error as CreateIdeaError {
    switch error.code {
    case .duplicateContent:
        showDuplicateWarning(message: error.message)
    case .quotaExceeded(let requestedSize, let maximumSize):
        showQuotaError(requested: requestedSize, maximum: maximumSize, message: error.message)
    case .invalidCategory(let category):
        highlightInvalidCategory(category, message: error.message)
    }
} catch {
    showGenericError(error)
}

Built-in ValidationError

FOSMVVM provides

ValidationError

// In controller - use Validations to collect errors
let validations = Validations()

if requestBody.email.isEmpty {
    validations.validations.append(.init(
        status: .error,
        fieldId: "email",
        message: .localized(for: CreateUserRequest.self, propertyName: "emailRequired")
    ))
}

// Throw if any errors
if let error = validations.validationError {
    throw error
}

// Client catches ValidationError
catch let error as ValidationError {
    for validation in error.validations {
        for message in validation.messages {
            for fieldId in message.fieldIds {
                formFields[fieldId]?.showError(message.message)
            }
        }
    }
}

Architecture context: See ServerRequestError - Typed Error Responses for full details.

Testing ServerRequests

Always test via

ServerRequest.processRequest(mvvmEnv:)

See fosmvvm-serverrequest-test-generator for complete testing guidance.

// ✅ RIGHT - tests the actual client code path
let request = Update{Entity}Request(
    query: .init(entityId: id),
    requestBody: .init(name: "New Name")
)
try await request.processRequest(mvvmEnv: testMvvmEnv)
#expect(request.responseBody?.viewModel.name == "New Name")

// ❌ WRONG - manual HTTP bypasses version negotiation
try await app.sendRequest(.PATCH, "/entity/\(id)", body: json)

See Also

• Architecture Patterns - Mental models (errors are data, type safety, etc.)
• FOSMVVMArchitecture.md - Full architecture, especially "Core Principle: ServerRequest Is THE Way"
• fosmvvm-serverrequest-test-generator - For testing ServerRequest types
• fosmvvm-viewmodel-generator - For ViewModels returned by requests
• fosmvvm-fields-generator - For ValidatableModel in RequestBody
• fosmvvm-leaf-view-generator - For Leaf templates that render ViewModels
• reference.md - Complete file templates

Version History

ServerRequestBodySize

maxBodySize