From fbe2fc353338e2c8e852b1c064e884c2163352f4 Mon Sep 17 00:00:00 2001
From: Jeremiah Lowin <153965+jlowin@users.noreply.github.com>
Date: Fri, 20 Jun 2025 13:12:23 -0400
Subject: [PATCH] Add transport handling for trailing slashes

---
 src/fastmcp/client/transports.py   | 15 +++++++++++++++
 tests/utilities/test_mcp_config.py |  4 ++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/fastmcp/client/transports.py b/src/fastmcp/client/transports.py
index 778c58447..153491029 100644
--- a/src/fastmcp/client/transports.py
+++ b/src/fastmcp/client/transports.py
@@ -9,6 +9,7 @@ import warnings
 from collections.abc import AsyncIterator, Callable
 from pathlib import Path
 from typing import Any, Literal, TypedDict, TypeVar, cast, overload
+from urllib.parse import urlparse, urlunparse
 
 import anyio
 import httpx
@@ -159,6 +160,13 @@ class SSETransport(ClientTransport):
             url = str(url)
         if not isinstance(url, str) or not url.startswith("http"):
             raise ValueError("Invalid HTTP/S URL provided for SSE.")
+
+        # Ensure the URL path ends with a trailing slash to avoid automatic redirects
+        parsed = urlparse(url)
+        if not parsed.path.endswith("/"):
+            parsed = parsed._replace(path=parsed.path + "/")
+            url = urlunparse(parsed)
+
         self.url = url
         self.headers = headers or {}
         self._set_auth(auth)
@@ -227,6 +235,13 @@ class StreamableHttpTransport(ClientTransport):
             url = str(url)
         if not isinstance(url, str) or not url.startswith("http"):
             raise ValueError("Invalid HTTP/S URL provided for Streamable HTTP.")
+
+        # Ensure the URL path ends with a trailing slash to avoid automatic redirects
+        parsed = urlparse(url)
+        if not parsed.path.endswith("/"):
+            parsed = parsed._replace(path=parsed.path + "/")
+            url = urlunparse(parsed)
+
         self.url = url
         self.headers = headers or {}
         self._set_auth(auth)
diff --git a/tests/utilities/test_mcp_config.py b/tests/utilities/test_mcp_config.py
index ec6833b0a..7775e12bc 100644
--- a/tests/utilities/test_mcp_config.py
+++ b/tests/utilities/test_mcp_config.py
@@ -39,7 +39,7 @@ def test_parse_single_remote_config():
     mcp_config = MCPConfig.from_dict(config)
     transport = mcp_config.mcpServers["test_server"].to_transport()
     assert isinstance(transport, StreamableHttpTransport)
-    assert transport.url == "http://localhost:8000"
+    assert transport.url == "http://localhost:8000/"
 
 
 def test_parse_remote_config_with_transport():
@@ -54,7 +54,7 @@ def test_parse_remote_config_with_transport():
     mcp_config = MCPConfig.from_dict(config)
     transport = mcp_config.mcpServers["test_server"].to_transport()
     assert isinstance(transport, SSETransport)
-    assert transport.url == "http://localhost:8000"
+    assert transport.url == "http://localhost:8000/"
 
 
 def test_parse_remote_config_with_url_inference():