examples: Add streaming ChatGPT proxy from FOSDEM 2025

.licenseignore

@@ -1,6 +1,7 @@
 .gitignore
 .licenseignore
 .swiftformatignore
+.unacceptablelanguageignore
 .spi.yml
 .swift-format
 .github/*
@@ -37,6 +38,8 @@ Examples/HelloWorldiOSClientAppExample/HelloWorldiOSClientApp.*
 Examples/HelloWorldiOSClientAppExample/HelloWorldiOSClientApp/Assets.xcassets/*
 Examples/HelloWorldiOSClientAppExample/HelloWorldiOSClientApp/Preview*
 Examples/**/Generated*
+Examples/streaming-chatgpt-proxy/.env.example
+Examples/streaming-chatgpt-proxy/players.txt
 **/Makefile
 **/*.html
 .editorconfig

.swiftformatignore

@@ -2,4 +2,5 @@ Tests/OpenAPIGeneratorReferenceTests/Resources
 Sources/swift-openapi-generator/Documentation.docc
 Examples/**/Generated/*
 Examples/**/GeneratedSources/*
+Examples/streaming-chatgpt-proxy/**
 **Package.swift

.unacceptablelanguageignore

@@ -0,0 +1 @@
+Examples/streaming-chatgpt-proxy/Sources/ChatGPT/openapi.yaml

Examples/streaming-chatgpt-proxy/.devcontainer/devcontainer.json

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+{
+    "name": "Swift",
+    "image": "swift:6.0",
+    "features": {
+        "ghcr.io/devcontainers/features/common-utils:2": {},
+        "ghcr.io/devcontainers/features/git:1": {}
+    },
+    "runArgs": [
+        "--cap-add=SYS_PTRACE",
+        "--security-opt",
+        "seccomp=unconfined"
+    ],
+    "customizations": {
+        "vscode": {
+            "settings": {
+                "lldb.library": "/usr/lib/liblldb.so"
+            },
+            "extensions": [
+                "sswg.swift-lang",
+                "42Crunch.vscode-openapi"
+            ]
+        }
+    },
+    // Use 'forwardPorts' to make a list of ports inside the container available locally.
+    // "forwardPorts": [],
+
+    // Set `remoteUser` to `root` to connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
+    "remoteUser": "root"
+}

Examples/streaming-chatgpt-proxy/.env.example

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+# Rename this file to just .env and paste your token below.
+OPENAI_TOKEN=PASTE_YOUR_TOKEN_HERE

Examples/streaming-chatgpt-proxy/.gitignore

@@ -0,0 +1,13 @@
+.DS_Store
+.build/
+.build-linux/
+.env
+/Packages
+/*.xcodeproj
+xcuserdata/
+DerivedData/
+.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
+.vscode
+/Package.resolved
+.ci/
+.docc-build/

Examples/streaming-chatgpt-proxy/.vscode/settings.json

@@ -0,0 +1,31 @@
+{
+    "editor.lightbulb.enabled": "off",
+    "explorer.decorations.badges": false,
+    "explorer.decorations.colors": false,
+    "files.exclude": {
+        "**/.build": true,
+        "**/.build-linux": true,
+        "**/.gitignore": true,
+        "**/.swiftpm": true,
+        "**/.vscode": true,
+        ".env": true,
+        "*.o": true,
+        "*.d": true,
+        "*.swiftdeps": true,
+        "*.swiftdeps~": true,
+    },
+    "outline.problems.colors": false,
+    "outline.problems.badges": false,
+    "lldb.library": "/usr/lib/liblldb.so",
+    "lldb.launch.expressions": "native",
+    "swift.diagnosticsStyle": "default",
+    "swift.disableAutoResolve": true,
+    "swift.sourcekit-lsp.backgroundIndexing": "off",
+    "swift.sourcekit-lsp.disable": true,
+    "swift.buildPath": ".build-linux",
+    "workbench.colorCustomizations": {
+        "editorError.foreground": "#00000000",
+        "editorWarning.foreground": "#00000000",
+    },
+    "workbench.startupEditor": "none"
+}

Examples/streaming-chatgpt-proxy/Package.swift

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+// swift-tools-version: 5.9
+import PackageDescription
+
+let package = Package(
+    name: "fosdem-2025-demo",
+    platforms: [.macOS(.v14)],
+    dependencies: [
+        .package(url: "https://github.com/apple/swift-openapi-generator", from: "1.6.0"),
+        .package(url: "https://github.com/apple/swift-openapi-runtime", from: "1.6.0"),
+        .package(url: "https://github.com/apple/swift-openapi-urlsession", from: "1.0.2"),
+        .package(url: "https://github.com/swift-server/swift-openapi-vapor", from: "1.0.1"),
+        .package(url: "https://github.com/swift-server/swift-openapi-async-http-client", from: "1.1.0"),
+    ],
+    targets: [
+        .target(
+            name: "ChatGPT",
+            dependencies: [
+                .product(name: "OpenAPIRuntime", package: "swift-openapi-runtime"),
+            ],
+            plugins: [
+                .plugin(name: "OpenAPIGenerator", package: "swift-openapi-generator"),
+            ]
+        ),
+        .executableTarget(
+            name: "ClientCLI",
+            dependencies: [
+                .product(name: "OpenAPIURLSession", package: "swift-openapi-urlsession"),
+            ],
+            plugins: [
+                .plugin(name: "OpenAPIGenerator", package: "swift-openapi-generator"),
+            ]
+        ),
+        .executableTarget(
+            name: "ProxyServer",
+            dependencies: [
+                "ChatGPT",
+                .product(name: "OpenAPIAsyncHTTPClient", package: "swift-openapi-async-http-client"),
+                .product(name: "OpenAPIVapor", package: "swift-openapi-vapor"),
+            ],
+            plugins: [
+                .plugin(name: "OpenAPIGenerator", package: "swift-openapi-generator"),
+            ]
+        ),
+    ]
+)

Examples/streaming-chatgpt-proxy/README.md

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+# Streaming ChatGPT Proxy
+
+An example project using [Swift OpenAPI Generator](https://github.com/apple/swift-openapi-generator).
+
+> **Disclaimer:** This example is deliberately simplified and is intended for illustrative purposes only.
+
+## Overview
+
+A tailored API server, backed by ChatGPT, and client CLI, with end-to-end
+streaming.
+
+This package is the reference sources for the demo presented at [FOSDEM 2025:
+_Live coding a streaming ChatGPT proxy with Swift OpenAPI—from
+scratch!_][fosdem25-swift-openapi]
+
+> Join us as we build a ChatGPT client, from scratch, using Swift OpenAPI Generator. We’ll take advantage of Swift OpenAPI’s pluggable HTTP transports to reuse the same generated client to make upstream calls from a Linux server, providing end-to-end streaming, backed by async sequences, without buffering upstream responses.
+>
+> In this session you’ll learn how to:
+>
+> * Generate a type-safe ChatGPT macOS client and use URLSession OpenAPI transport.
+> * Stream LLM responses using Server Sent Events (SSE).
+> * Bootstrap a Linux proxy server using the Vapor OpenAPI transport.
+> * Use the same generated ChatGPT client within the proxy by switching to the AsyncHTTPClient transport.
+> * Efficiently transform responses from SSE to JSON Lines, maintaining end-to-end streaming.
+
+The example provides an API for a fictitious _ChantGPT_ service, which produces
+creative chants to sing at basketball games. 🙌 🏀 🙌
+
+## Usage
+
+The upstream calls to ChatGPT require an API token, which is configured using the `OPENAI_TOKEN` environment variable.
+Rename `.env.example` to `.env` and replace the placeholder with your token.
+
+Build and run the server using:
+
+```console
+% swift run ProxyServer
+2025-01-30T09:12:23+0000 notice codes.vapor.application : [Vapor] Server starting on http://127.0.0.1:8080
+...
+```
+
+Then, from another terminal, run the proxy client using:
+
+```console
+% swift run ClientCLI "That team with the Bull logo"
+Build of product 'ClientCLI' complete! (7.24s)
+🧑‍💼: That one with the bull logo
+---
+🤖: **"Charge Ahead, Chicago Bulls!"**
+
+(Verse 1)
+Red and black, we’re on the prowl,
+Chicago Bulls, hear us growl!
+From the Windy City, we take the lead,
+Charging forward with lightning speed!
+
+(Chorus)
+B-U-L-L-S, Bulls! Bulls! Bulls!
+We’re the team that never dulls!
+Hoops and hustle, heart and soul,
+Chicago Bulls, we’re on a roll!
+...
+```
+
+## Linux development with VS Code Dev Containers
+
+The package also contains configuration for developing with VS Code [Dev
+Containers][dev-containers].
+
+If you have the Dev Containers extension installed, use the `Dev Containers: Reopen in Container` command to switch to build and run for Linux.
+
+[fosdem25-swift-openapi]: https://fosdem.org/2025/schedule/event/fosdem-2025-5230-live-coding-a-streaming-chatgpt-proxy-with-swift-openapi-from-scratch-/
+[dev-containers]: https://code.visualstudio.com/docs/devcontainers/containers

Examples/streaming-chatgpt-proxy/Sources/ChatGPT/Middleware.swift

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+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftOpenAPIGenerator open source project
+//
+// Copyright (c) 2025 Apple Inc. and the SwiftOpenAPIGenerator project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftOpenAPIGenerator project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+import Foundation
+import HTTPTypes
+import OpenAPIRuntime
+
+package struct HeaderFieldMiddleware: ClientMiddleware {
+    var name: HTTPField.Name
+    var value: String
+
+    package static func authTokenFromEnvironment(_ environmentVariable: String) -> Self {
+        guard let token = ProcessInfo.processInfo.environment[environmentVariable] else {
+            fatalError("Please set \(environmentVariable) environment variable.")
+        }
+        return Self(name: .authorization, value: "Bearer \(token)")
+    }
+
+    package func intercept(
+        _ request: HTTPRequest,
+        body: HTTPBody?,
+        baseURL: URL,
+        operationID: String,
+        next: @Sendable (HTTPRequest, HTTPBody?, URL) async throws -> (HTTPResponse, HTTPBody?)
+    ) async throws -> (HTTPResponse, HTTPBody?) {
+        var request = request
+        request.headerFields[name] = value
+        return try await next(request, body, baseURL)
+    }
+}

Examples/streaming-chatgpt-proxy/Sources/ChatGPT/openapi-generator-config.yaml

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+generate: [types, client]
+accessModifier: package
+filter:
+  paths:
+    - /chat/completions
+namingStrategy: idiomatic