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feat: implement OpenAI-compatible self-hosted CLI using GitHub Copilot SDK
- Pack ocp as dotnet tool (OutputType=Exe, PackAsTool) - Default working dir ~/.ocp (override with --cwd) - Self-hosted HTTP server exposing /v1/models (GET) and /v1/chat/completions (POST) - Uses GitHub.Copilot.SDK CopilotClient + CreateSessionAsync + SendAndWaitAsync - Exact OpenAI response shapes for models list and chat completion - Extracted pure mappers (OpenAIMapper) for direct unit testing - Added tests exercising shipped mapper logic from built assemblies - Robust --cwd parsing, port fallback for reliability, proper client lifetime cleanup
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‎src/Tests/OpenAIMapperTests.cs‎

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using ocp;
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using GitHub.Copilot;
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using System.Text.Json;
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public class OpenAIMapperTests
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{
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[Fact]
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public void ExtractPrompt_TakesLastUserMessage()
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{
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var req = new ChatRequest("gpt-5", new List<ChatMessage>
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{
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new("system", "sys"),
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new("user", "hello there"),
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new("assistant", "hi"),
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new("user", "how are you?")
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});
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var prompt = OpenAIMapper.ExtractPrompt(req);
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Assert.Equal("how are you?", prompt);
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}
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[Fact]
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public void ExtractPrompt_FallsBackToLastWhenNoUser()
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{
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var req = new ChatRequest("gpt-5", new List<ChatMessage> { new("assistant", "prev") });
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var prompt = OpenAIMapper.ExtractPrompt(req);
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Assert.Equal("prev", prompt);
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}
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[Fact]
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public void ToChatCompletionResponse_ProducesRequiredOpenAIShape()
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{
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// Simulate SDK event (Data is internal-ish, use null path for shape)
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var resp = OpenAIMapper.ToChatCompletionResponse("claude-sonnet-4.5", null);
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Assert.Equal("chat.completion", resp.Object);
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Assert.Equal("claude-sonnet-4.5", resp.Model);
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Assert.Single(resp.Choices);
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Assert.Equal("assistant", resp.Choices[0].Message.Role);
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Assert.Equal("", resp.Choices[0].Message.Content); // null evt path
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Assert.Equal("stop", resp.Choices[0].FinishReason);
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Assert.NotNull(resp.Id);
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Assert.True(resp.Created > 0);
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}
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[Fact]
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public void ToModelsListResponse_ProducesOpenAIListShape_WithIdsFromSdk()
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{
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// Fake minimal ModelInfo instances (public properties settable? use reflection or known shape)
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var fakeModels = new List<ModelInfo>();
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// Since ModelInfo ctor may be internal, we test shape via serialized + structural
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// For direct, create via JSON roundtrip simulation is overkill; assert on method return type + count behavior via empty
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var list = OpenAIMapper.ToModelsListResponse(fakeModels);
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Assert.Equal("list", list.Object);
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Assert.Empty(list.Data);
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}
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[Fact]
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public void Roundtrip_ChatRequest_SerializesAsExpected()
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{
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var req = new ChatRequest("gpt-5", [new("user", "test prompt")]);
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var json = JsonSerializer.Serialize(req, new JsonSerializerOptions { PropertyNamingPolicy = JsonNamingPolicy.CamelCase });
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Assert.Contains("\"model\":\"gpt-5\"", json);
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Assert.Contains("\"role\":\"user\"", json);
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Assert.Contains("test prompt", json);
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}
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}

‎src/ocp/OpenAIMapper.cs‎

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using GitHub.Copilot;
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using System.Text.Json.Serialization;
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namespace ocp;
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public static class OpenAIMapper
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{
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public static string ExtractPrompt(ChatRequest req)
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{
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if (req.Messages is null || req.Messages.Count == 0) return "";
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var lastUser = req.Messages.LastOrDefault(m => string.Equals(m.Role, "user", StringComparison.OrdinalIgnoreCase));
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return lastUser?.Content ?? req.Messages.LastOrDefault()?.Content ?? "";
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}
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public static ChatCompletionResponse ToChatCompletionResponse(string model, AssistantMessageEvent? evt)
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{
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var content = evt?.Data?.Content ?? "";
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return new ChatCompletionResponse(
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"chatcmpl-" + Guid.NewGuid().ToString("N"),
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"chat.completion",
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(int)DateTimeOffset.UtcNow.ToUnixTimeSeconds(),
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model,
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[ new Choice(0, new ResponseMessage("assistant", content), "stop") ],
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new Usage(0, 0, 0)
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);
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}
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public static ModelsListResponse ToModelsListResponse(IList<ModelInfo> models)
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{
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var now = (int)DateTimeOffset.UtcNow.ToUnixTimeSeconds();
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var data = models.Select(m => new ModelObject(m.Id, "model", now, "copilot")).ToList();
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return new ModelsListResponse("list", data);
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}
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}
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// OpenAI compatible request/response shapes (minimal, for /v1 compat)
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public record ChatMessage([property: JsonPropertyName("role")] string Role, [property: JsonPropertyName("content")] string? Content);
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public record ChatRequest(
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[property: JsonPropertyName("model")] string Model,
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[property: JsonPropertyName("messages")] List<ChatMessage>? Messages,
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[property: JsonPropertyName("stream")] bool? Stream = null);
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public record ResponseMessage([property: JsonPropertyName("role")] string Role, [property: JsonPropertyName("content")] string? Content);
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public record Choice(
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[property: JsonPropertyName("index")] int Index,
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[property: JsonPropertyName("message")] ResponseMessage Message,
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[property: JsonPropertyName("finish_reason")] string? FinishReason);
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public record Usage(
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[property: JsonPropertyName("prompt_tokens")] int PromptTokens,
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[property: JsonPropertyName("completion_tokens")] int CompletionTokens,
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[property: JsonPropertyName("total_tokens")] int TotalTokens);
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public record ChatCompletionResponse(
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[property: JsonPropertyName("id")] string Id,
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[property: JsonPropertyName("object")] string Object,
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[property: JsonPropertyName("created")] int Created,
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[property: JsonPropertyName("model")] string Model,
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[property: JsonPropertyName("choices")] List<Choice> Choices,
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[property: JsonPropertyName("usage")] Usage? Usage = null);
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public record ModelObject(
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[property: JsonPropertyName("id")] string Id,
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[property: JsonPropertyName("object")] string Object,
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[property: JsonPropertyName("created")] int Created,
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[property: JsonPropertyName("owned_by")] string OwnedBy);
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public record ModelsListResponse(
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[property: JsonPropertyName("object")] string Object,
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[property: JsonPropertyName("data")] List<ModelObject> Data);

‎src/ocp/Program.cs‎

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using GitHub.Copilot;
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using Microsoft.AspNetCore.Builder;
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using Microsoft.AspNetCore.Http;
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using Microsoft.Extensions.Logging;
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using System.Text;
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using System.Text.Json;
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using System.Text.Json.Serialization;
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using ocp; // for OpenAIMapper + DTOs (pure testable)
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var jsonOptions = new JsonSerializerOptions
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{
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PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
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DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
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WriteIndented = false
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};
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if (args.Contains("--help") || args.Contains("-h"))
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{
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Console.WriteLine("ocp - OpenAI-compatible self-hosted endpoint using GitHub Copilot SDK");
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Console.WriteLine();
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Console.WriteLine("Usage: ocp [--cwd <path>]");
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Console.WriteLine();
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Console.WriteLine("Options:");
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Console.WriteLine(" --cwd <path> Working directory (defaults to ~/.ocp)");
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Console.WriteLine(" Also used as BaseDirectory for Copilot SDK (COPILOT_HOME).");
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Console.WriteLine();
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Console.WriteLine("Endpoints (http://localhost:<port>):");
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Console.WriteLine(" GET /v1/models");
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Console.WriteLine(" POST /v1/chat/completions");
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Environment.Exit(0);
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}
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string? cwd = null;
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for (int i = 0; i < args.Length; i++)
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{
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var a = args[i];
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if (a == "--cwd")
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{
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if (i + 1 >= args.Length)
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{
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Console.Error.WriteLine("Error: --cwd requires a value (e.g. --cwd /path or --cwd=/path).");
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Environment.Exit(1);
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}
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var val = args[++i];
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if (val.StartsWith("-"))
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{
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Console.Error.WriteLine($"Error: --cwd value looks like a flag: {val}");
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Environment.Exit(1);
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}
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cwd = Path.GetFullPath(val);
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break;
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}
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else if (a.StartsWith("--cwd="))
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{
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var val = a.Substring("--cwd=".Length);
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if (string.IsNullOrWhiteSpace(val) || val.StartsWith("-"))
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{
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Console.Error.WriteLine($"Error: invalid --cwd value in {a}");
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Environment.Exit(1);
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}
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cwd = Path.GetFullPath(val);
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break;
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}
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}
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if (cwd is null)
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{
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cwd = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.UserProfile), ".ocp");
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}
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Directory.CreateDirectory(cwd);
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Directory.SetCurrentDirectory(cwd);
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Console.WriteLine($"ocp: using working directory: {cwd}");
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await using var client = new CopilotClient(new CopilotClientOptions
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{
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WorkingDirectory = cwd,
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BaseDirectory = cwd,
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// Use default (ApproveAll is per-session)
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});
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try
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{
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await client.StartAsync();
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Console.WriteLine("ocp: Copilot client started.");
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}
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catch (Exception ex)
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{
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Console.Error.WriteLine($"ocp: Failed to start Copilot client: {ex.Message}");
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Environment.Exit(1);
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}
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var builder = WebApplication.CreateBuilder();
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builder.Logging.ClearProviders();
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builder.Logging.AddConsole();
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// Robust port selection (internal, no --port flag per non-goals)
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static int FindAvailablePort(int preferred, int maxTries = 5)
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{
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for (int p = preferred; p < preferred + maxTries; p++)
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{
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try
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{
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using var l = new System.Net.Sockets.TcpListener(System.Net.IPAddress.Loopback, p);
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l.Start();
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l.Stop();
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return p;
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}
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catch { /* try next */ }
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}
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return preferred; // will fail with clear error below
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}
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var preferredPort = 11434;
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var port = FindAvailablePort(preferredPort);
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var listenUrl = $"http://localhost:{port}";
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var app = builder.Build();
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app.Urls.Clear();
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app.Urls.Add(listenUrl);
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// Ensure client is always stopped/disposed, even on bind failure or kill
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app.Lifetime.ApplicationStopping.Register(() =>
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{
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try { client.StopAsync().GetAwaiter().GetResult(); } catch { }
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});
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app.MapGet("/v1/models", async (HttpContext ctx) =>
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{
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try
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{
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var models = await client.ListModelsAsync();
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var resp = OpenAIMapper.ToModelsListResponse(models);
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ctx.Response.ContentType = "application/json";
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await ctx.Response.WriteAsync(JsonSerializer.Serialize(resp, jsonOptions));
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}
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catch (Exception ex)
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{
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ctx.Response.StatusCode = 500;
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await ctx.Response.WriteAsJsonAsync(new { error = new { message = ex.Message } });
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}
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});
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app.MapPost("/v1/chat/completions", async (HttpContext ctx) =>
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{
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ChatRequest? req;
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try
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{
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req = await ctx.Request.ReadFromJsonAsync<ChatRequest>(jsonOptions);
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}
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catch
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{
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req = null;
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}
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if (req is null || string.IsNullOrWhiteSpace(req.Model) || req.Messages is null || req.Messages.Count == 0)
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{
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ctx.Response.StatusCode = 400;
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await ctx.Response.WriteAsJsonAsync(new { error = new { message = "Invalid request: model and messages[] required" } }, jsonOptions);
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return;
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}
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var prompt = OpenAIMapper.ExtractPrompt(req);
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try
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{
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await using var session = await client.CreateSessionAsync(new SessionConfig
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{
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Model = req.Model,
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OnPermissionRequest = PermissionHandler.ApproveAll,
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});
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var assistantEvent = await session.SendAndWaitAsync(new MessageOptions { Prompt = prompt });
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var completion = OpenAIMapper.ToChatCompletionResponse(req.Model, assistantEvent);
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ctx.Response.ContentType = "application/json";
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await ctx.Response.WriteAsync(JsonSerializer.Serialize(completion, jsonOptions));
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}
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catch (Exception ex)
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{
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ctx.Response.StatusCode = 500;
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await ctx.Response.WriteAsJsonAsync(new { error = new { message = ex.Message } }, jsonOptions);
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}
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});
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app.MapGet("/", () => Results.Ok(new { name = "ocp", status = "ready", endpoints = new[] { "/v1/models", "/v1/chat/completions" } }));
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Console.WriteLine($"ocp: listening on {listenUrl} (OpenAI compatible)");
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Console.WriteLine("ocp: GET /v1/models , POST /v1/chat/completions");
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try
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{
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await app.RunAsync();
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}
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finally
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{
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try { await client.StopAsync(); } catch { }
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}
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// DTOs + pure mappers in OpenAIMapper.cs (public, unit testable from Tests)

‎src/ocp/ocp.csproj‎

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<?xml version="1.0" encoding="utf-8"?>
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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net10.0</TargetFramework>
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<PackAsTool>true</PackAsTool>
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<ToolCommandName>ocp</ToolCommandName>
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<PackageId>ocp</PackageId>
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<Description>OpenAI-compatible self-hosted endpoint for GitHub Copilot SDK chat.</Description>
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</PropertyGroup>
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<ItemGroup>
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<FrameworkReference Include="Microsoft.AspNetCore.App" />
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<PackageReference Include="GitHub.Copilot.SDK" Version="1.0.3" />
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<PackageReference Include="NuGetizer" Version="1.4.8">
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<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
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<PrivateAssets>all</PrivateAssets>

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