From 5d58f7763e9de3fff5e7785350dfe04c7a315290 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=B6rg=20Hanke?= <joerg.hanke@lionheart-technology.com>
Date: Wed, 5 Aug 2026 19:57:20 +0200
Subject: [PATCH] Use canImport guards for EventSource/FoundationNetworking in
 HTTPClientTransport

The package manifest already limits the EventSource dependency to Apple
platforms, but HTTPClientTransport.swift gates its import and the SSE
code paths on `#if !os(Linux)`. On any other non-Apple platform (e.g.
x86_64-windows-msvc) the module is absent yet the import is still
compiled, so the whole MCP target fails with:

    HTTPClientTransport.swift:5:12: error: no such module 'EventSource'

Gate on capabilities instead of naming Linux:

- `#if canImport(EventSource)` for the import, the SSE listen loop, and
  connectToEventStream -- selects exactly the same code on Apple and
  Linux as before
- `#if canImport(FoundationNetworking)` for the data(for:) vs bytes(for:)
  split and the matching processResponse overloads, since
  URLSession.AsyncBytes only exists in Darwin Foundation
- reword the two log messages that named Linux

No behavior change on Apple or Linux; the MCP target now compiles for
x86_64-unknown-windows-msvc (verified with Swift 6.3.3).
---
 .../MCP/Base/Transports/HTTPClientTransport.swift  | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/Sources/MCP/Base/Transports/HTTPClientTransport.swift b/Sources/MCP/Base/Transports/HTTPClientTransport.swift
index 060cd133..d0dbbdb8 100644
--- a/Sources/MCP/Base/Transports/HTTPClientTransport.swift
+++ b/Sources/MCP/Base/Transports/HTTPClientTransport.swift
@@ -1,7 +1,7 @@
 import Foundation
 import Logging
 
-#if !os(Linux)
+#if canImport(EventSource)
     import EventSource
 #endif
 
@@ -266,7 +266,7 @@ public actor HTTPClientTransport: Transport {
             request = requestModifier(request)
 
             do {
-                #if os(Linux)
+                #if canImport(FoundationNetworking)
                     let (responseData, response) = try await session.data(for: request)
                     try await processResponse(response: response, data: responseData)
                 #else
@@ -304,7 +304,7 @@ public actor HTTPClientTransport: Transport {
         }
     }
 
-    #if os(Linux)
+    #if canImport(FoundationNetworking)
         private func processResponse(response: URLResponse, data: Data) async throws {
             guard let httpResponse = response as? HTTPURLResponse else {
                 throw MCPError.internalError("Invalid HTTP response")
@@ -325,7 +325,7 @@ public actor HTTPClientTransport: Transport {
             guard case 200..<300 = httpResponse.statusCode else { return }
 
             if contentType.contains(ContentType.sse) {
-                logger.warning("SSE responses aren't fully supported on Linux")
+                logger.warning("SSE responses aren't fully supported on this platform")
                 messageContinuation.yield(data)
             } else if contentType.contains(ContentType.json) {
                 logger.trace("Received JSON response", metadata: ["size": "\(data.count)"])
@@ -467,10 +467,10 @@ public actor HTTPClientTransport: Transport {
     // MARK: - SSE
 
     private func startListeningForServerEvents() async {
-        #if os(Linux)
+        #if !canImport(EventSource)
             if streaming {
                 logger.warning(
-                    "SSE streaming was requested but is not fully supported on Linux. SSE connection will not be attempted."
+                    "SSE streaming was requested but is not fully supported on this platform. SSE connection will not be attempted."
                 )
             }
         #else
@@ -563,7 +563,7 @@ public actor HTTPClientTransport: Transport {
         #endif
     }
 
-    #if !os(Linux)
+    #if canImport(EventSource)
         private func connectToEventStream() async throws {
             guard isConnected else {
                 logger.debug("⚠️ Skipping connectToEventStream - transport not connected")