Add server support

ExampleMCPServer/Sources/main.swift

@@ -0,0 +1,43 @@
+import Foundation
+import JSONSchemaBuilder
+import MCPServer
+
+let transport = Transport.stdio()
+func proxy(_ transport: Transport) -> Transport {
+  var sendToDataSequence: AsyncStream<Data>.Continuation?
+  let dataSequence = AsyncStream<Data>.init { continuation in
+    sendToDataSequence = continuation
+  }
+
+  Task {
+    for await data in transport.dataSequence {
+      mcpLogger.info("Reading data from transport: \(String(data: data, encoding: .utf8)!, privacy: .public)")
+      sendToDataSequence?.yield(data)
+    }
+  }
+
+  return Transport(
+    writeHandler: { data in
+      mcpLogger.info("Writing data to transport: \(String(data: data, encoding: .utf8)!, privacy: .public)")
+      try await transport.writeHandler(data)
+    },
+    dataSequence: dataSequence)
+}
+
+// MARK: - RepeatToolInput
+
+@Schemable
+struct RepeatToolInput {
+  let text: String
+}
+
+let server = try await MCPServer(
+  info: Implementation(name: "test-server", version: "1.0.0"),
+  capabilities: ServerCapabilityHandlers(tools: [
+    Tool(name: "repeat") { (input: RepeatToolInput) in
+      [.text(.init(text: input.text))]
+    },
+  ]),
+  transport: proxy(transport))
+
+try await server.waitForDisconnection()

ExampleMCPServer/launch.sh

@@ -0,0 +1,4 @@
+#!/bin/zsh
+
+dir=$(dirname "$0")
+(cd "$dir/.." && swift run ExampleMCPServer -q)

ExampleMCPServer/readme.md

@@ -0,0 +1,11 @@
+# Inspect the server in the debugger:
+
+```
+nvm use 20.18.1
+
+npx @modelcontextprotocol/inspector "$(pwd)/ExampleMCPServer/launch.sh"
+```
+
+
+# Observe console logs:
+- in Console.app, filter by `com.app.mcp` as the subsystem.

MCPClient/Sources/DataChannel+StdioProcess.swift

@@ -63,6 +63,7 @@
       return path.isEmpty ? executable : path
     }
 
+    // TODO: look at how to use /bin/zsh, at least on MacOS, to avoid needing to specify PATH to locate the executable
     let process = Process()
     process.executableURL = URL(fileURLWithPath: try path(for: executable))
     process.arguments = args