From 2240530f27a9254697ba9739349b52fb83c663de Mon Sep 17 00:00:00 2001
From: Dan Lapid <dan.lapid@gmail.com>
Date: Sun, 13 Apr 2025 22:52:21 +0100
Subject: [PATCH] Move uvicorn import to usage

uvicorn is an optional dependency only used in one function but is imported at the global scope meaning mcp imports will fail if uvicorn is not available.
This commit moves uvicorn import to usage in run_sse_async.
It would be ideal to mark uvicorn as a default-on optional dependency but that isn't supported yet by pyproject.toml.
---
 pyproject.toml                   | 2 +-
 src/mcp/server/fastmcp/server.py | 2 +-
 uv.lock                          | 6 +++---
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/pyproject.toml b/pyproject.toml
index 25514cd6b..4e1c3ac2e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -29,7 +29,7 @@ dependencies = [
     "starlette>=0.27",
     "sse-starlette>=1.6.1",
     "pydantic-settings>=2.5.2",
-    "uvicorn>=0.23.1",
+    "uvicorn>=0.23.1; sys_platform != 'emscripten'",
 ]
 
 [project.optional-dependencies]
diff --git a/src/mcp/server/fastmcp/server.py b/src/mcp/server/fastmcp/server.py
index bf0ce880a..f3bb2586a 100644
--- a/src/mcp/server/fastmcp/server.py
+++ b/src/mcp/server/fastmcp/server.py
@@ -15,7 +15,6 @@
 
 import anyio
 import pydantic_core
-import uvicorn
 from pydantic import BaseModel, Field
 from pydantic.networks import AnyUrl
 from pydantic_settings import BaseSettings, SettingsConfigDict
@@ -466,6 +465,7 @@ async def run_stdio_async(self) -> None:
 
     async def run_sse_async(self) -> None:
         """Run the server using SSE transport."""
+        import uvicorn
         starlette_app = self.sse_app()
 
         config = uvicorn.Config(
diff --git a/uv.lock b/uv.lock
index 424e2d482..78f46f47c 100644
--- a/uv.lock
+++ b/uv.lock
@@ -496,7 +496,7 @@ dependencies = [
     { name = "pydantic-settings" },
     { name = "sse-starlette" },
     { name = "starlette" },
-    { name = "uvicorn" },
+    { name = "uvicorn", marker = "sys_platform != 'emscripten'" },
 ]
 
 [package.optional-dependencies]
@@ -540,7 +540,7 @@ requires-dist = [
     { name = "sse-starlette", specifier = ">=1.6.1" },
     { name = "starlette", specifier = ">=0.27" },
     { name = "typer", marker = "extra == 'cli'", specifier = ">=0.12.4" },
-    { name = "uvicorn", specifier = ">=0.23.1" },
+    { name = "uvicorn", marker = "sys_platform != 'emscripten'", specifier = ">=0.23.1" },
     { name = "websockets", marker = "extra == 'ws'", specifier = ">=15.0.1" },
 ]
 provides-extras = ["cli", "rich", "ws"]
@@ -1618,4 +1618,4 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/2b/fb/c492d6daa5ec067c2988ac80c61359ace5c4c674c532985ac5a123436cec/websockets-15.0.1-pp310-pypy310_pp73-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_17_x86_64.manylinux2014_x86_64.whl", hash = "sha256:b359ed09954d7c18bbc1680f380c7301f92c60bf924171629c5db97febb12f04", size = 174155 },
     { url = "https://files.pythonhosted.org/packages/68/a1/dcb68430b1d00b698ae7a7e0194433bce4f07ded185f0ee5fb21e2a2e91e/websockets-15.0.1-pp310-pypy310_pp73-win_amd64.whl", hash = "sha256:cad21560da69f4ce7658ca2cb83138fb4cf695a2ba3e475e0559e05991aa8122", size = 176884 },
     { url = "https://files.pythonhosted.org/packages/fa/a8/5b41e0da817d64113292ab1f8247140aac61cbf6cfd085d6a0fa77f4984f/websockets-15.0.1-py3-none-any.whl", hash = "sha256:f7a866fbc1e97b5c617ee4116daaa09b722101d4a3c170c787450ba409f9736f", size = 169743 },
-]
\ No newline at end of file
+]