Initial project setup - Phases 1-3 complete

ProxyCore/Sources/ProxyEngine/GlueHandler.swift

@@ -0,0 +1,66 @@
+import Foundation
+import NIOCore
+
+/// Bidirectional TCP forwarder. Pairs two channels so bytes flow in both directions.
+/// Used for CONNECT tunneling (passthrough mode, no MITM).
+final class GlueHandler: ChannelInboundHandler, RemovableChannelHandler {
+    typealias InboundIn = ByteBuffer
+    typealias OutboundOut = ByteBuffer
+
+    var partner: GlueHandler?
+    private var context: ChannelHandlerContext?
+    private var pendingRead = false
+
+    func handlerAdded(context: ChannelHandlerContext) {
+        self.context = context
+    }
+
+    func handlerRemoved(context: ChannelHandlerContext) {
+        self.context = nil
+        self.partner = nil
+    }
+
+    func channelRead(context: ChannelHandlerContext, data: NIOAny) {
+        partner?.write(unwrapInboundIn(data))
+    }
+
+    func channelReadComplete(context: ChannelHandlerContext) {
+        partner?.flush()
+    }
+
+    func channelInactive(context: ChannelHandlerContext) {
+        partner?.close()
+    }
+
+    func errorCaught(context: ChannelHandlerContext, error: Error) {
+        context.close(promise: nil)
+    }
+
+    func channelWritabilityChanged(context: ChannelHandlerContext) {
+        if context.channel.isWritable {
+            partner?.read()
+        }
+    }
+
+    // MARK: - Partner operations
+
+    private func write(_ buffer: ByteBuffer) {
+        context?.write(wrapOutboundOut(buffer), promise: nil)
+    }
+
+    private func flush() {
+        context?.flush()
+    }
+
+    private func read() {
+        if let context, !pendingRead {
+            pendingRead = true
+            context.read()
+            pendingRead = false
+        }
+    }
+
+    private func close() {
+        context?.close(promise: nil)
+    }
+}