Revert "Add support for MCP's Streamable HTTP transport (#1716)"

This reverts commit 8f83407.

# Conflicts:
#	pydantic_ai_slim/pydantic_ai/mcp.py
#	pydantic_ai_slim/pyproject.toml
#	tests/test_mcp.py
#	uv.lock

Author: DouweM

docs/mcp/client.md

@@ -18,23 +18,24 @@ pip/uv-add "pydantic-ai-slim[mcp]"
 
 PydanticAI comes with two ways to connect to MCP servers:
 
-- [`MCPServerHTTP`][pydantic_ai.mcp.MCPServerHTTP] which connects to an MCP server using the [Streamable HTTP transport](https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http) transport
+- [`MCPServerHTTP`][pydantic_ai.mcp.MCPServerHTTP] which connects to an MCP server using the [HTTP SSE](https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#http-with-sse) transport
 - [`MCPServerStdio`][pydantic_ai.mcp.MCPServerStdio] which runs the server as a subprocess and connects to it using the [stdio](https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#stdio) transport
 
 Examples of both are shown below; [mcp-run-python](run-python.md) is used as the MCP server in both examples.
 
-### HTTP Client
+### SSE Client
 
-[`MCPServerHTTP`][pydantic_ai.mcp.MCPServerHTTP] connects over HTTP using the [Streamable HTTP transport](https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http) to a server.
+[`MCPServerHTTP`][pydantic_ai.mcp.MCPServerHTTP] connects over HTTP using the [HTTP + Server Sent Events transport](https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#http-with-sse) to a server.
 
 !!! note
     [`MCPServerHTTP`][pydantic_ai.mcp.MCPServerHTTP] requires an MCP server to be running and accepting HTTP connections before calling [`agent.run_mcp_servers()`][pydantic_ai.Agent.run_mcp_servers]. Running the server is not managed by PydanticAI.
 
-The StreamableHTTP Transport is able to connect to both stateless HTTP and older Server Sent Events (SSE) servers.
+The name "HTTP" is used since this implemented will be adapted in future to use the new
+[Streamable HTTP](https://github.com/modelcontextprotocol/specification/pull/206) currently in development.
 
-Before creating the HTTP client, we need to run the server (docs [here](run-python.md)):
+Before creating the SSE client, we need to run the server (docs [here](run-python.md)):
 
-```bash {title="terminal (run http server)"}
+```bash {title="terminal (run sse server)"}
 deno run \
   -N -R=node_modules -W=node_modules --node-modules-dir=auto \
   jsr:@pydantic/mcp-run-python sse
@@ -55,7 +56,7 @@ async def main():
     #> There are 9,208 days between January 1, 2000, and March 18, 2025.
 ```
 
-1. Define the MCP server with the URL used to connect. This will typically end in `/mcp` for HTTP servers and `/sse` for SSE.
+1. Define the MCP server with the URL used to connect.
 2. Create an agent with the MCP server attached.
 3. Create a client session to connect to the server.
 

pydantic_ai_slim/pydantic_ai/mcp.py

@@ -6,18 +6,17 @@
 from collections.abc import AsyncIterator, Sequence
 from contextlib import AsyncExitStack, asynccontextmanager
 from dataclasses import dataclass
-from datetime import timedelta
 from pathlib import Path
 from types import TracebackType
 from typing import Any
 
 import anyio
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
-from mcp.shared.message import SessionMessage
 from mcp.types import (
     BlobResourceContents,
     EmbeddedResource,
     ImageContent,
+    JSONRPCMessage,
     LoggingLevel,
     TextContent,
     TextResourceContents,
@@ -30,8 +29,8 @@
 
 try:
     from mcp.client.session import ClientSession
+    from mcp.client.sse import sse_client
     from mcp.client.stdio import StdioServerParameters, stdio_client
-    from mcp.client.streamable_http import streamablehttp_client
 except ImportError as _import_error:
     raise ImportError(
         'Please install the `mcp` package to use the MCP server, '
@@ -57,16 +56,19 @@ class MCPServer(ABC):
     """
 
     _client: ClientSession
-    _read_stream: MemoryObjectReceiveStream[SessionMessage | Exception]
-    _write_stream: MemoryObjectSendStream[SessionMessage]
+    _read_stream: MemoryObjectReceiveStream[JSONRPCMessage | Exception]
+    _write_stream: MemoryObjectSendStream[JSONRPCMessage]
     _exit_stack: AsyncExitStack
 
     @abstractmethod
     @asynccontextmanager
     async def client_streams(
         self,
     ) -> AsyncIterator[
-        tuple[MemoryObjectReceiveStream[SessionMessage | Exception], MemoryObjectSendStream[SessionMessage]]
+        tuple[
+            MemoryObjectReceiveStream[JSONRPCMessage | Exception],
+            MemoryObjectSendStream[JSONRPCMessage],
+        ]
     ]:
         """Create the streams for the MCP server."""
         raise NotImplementedError('MCP Server subclasses must implement this method.')
@@ -263,7 +265,10 @@ async def main():
     async def client_streams(
         self,
     ) -> AsyncIterator[
-        tuple[MemoryObjectReceiveStream[SessionMessage | Exception], MemoryObjectSendStream[SessionMessage]]
+        tuple[
+            MemoryObjectReceiveStream[JSONRPCMessage | Exception],
+            MemoryObjectSendStream[JSONRPCMessage],
+        ]
     ]:
         server = StdioServerParameters(command=self.command, args=list(self.args), env=self.env, cwd=self.cwd)
         async with stdio_client(server=server) as (read_stream, write_stream):
@@ -283,11 +288,11 @@ def _get_client_initialize_timeout(self) -> float:
 class MCPServerHTTP(MCPServer):
     """An MCP server that connects over streamable HTTP connections.
 
-    This class implements the Streamable HTTP transport from the MCP specification.
-    See <https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http> for more information.
+    This class implements the SSE transport from the MCP specification.
+    See <https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#http-with-sse> for more information.
 
-    The Streamable HTTP transport is intended to replace the SSE transport from the previous protocol, but it is fully
-    backwards compatible with SSE-based servers.
+    The name "HTTP" is used since this implemented will be adapted in future to use the new
+    [Streamable HTTP](https://github.com/modelcontextprotocol/specification/pull/206) currently in development.
 
     !!! note
         Using this class as an async context manager will create a new pool of HTTP connections to connect
@@ -298,7 +303,7 @@ class MCPServerHTTP(MCPServer):
     from pydantic_ai import Agent
     from pydantic_ai.mcp import MCPServerHTTP
 
-    server = MCPServerHTTP('http://localhost:3001/mcp')  # (1)!
+    server = MCPServerHTTP('http://localhost:3001/sse')  # (1)!
     agent = Agent('openai:gpt-4o', mcp_servers=[server])
 
     async def main():
@@ -311,13 +316,13 @@ async def main():
     """
 
     url: str
-    """The URL of the SSE or MCP endpoint on the MCP server.
+    """The URL of the SSE endpoint on the MCP server.
 
-    For example for a server running locally, this might be `http://localhost:3001/mcp`.
+    For example for a server running locally, this might be `http://localhost:3001/sse`.
     """
 
     headers: dict[str, Any] | None = None
-    """Optional HTTP headers to be sent with each request to the endpoint.
+    """Optional HTTP headers to be sent with each request to the SSE endpoint.
 
     These headers will be passed directly to the underlying `httpx.AsyncClient`.
     Useful for authentication, custom headers, or other HTTP-specific configurations.
@@ -330,8 +335,8 @@ async def main():
     If the connection cannot be established within this time, the operation will fail.
     """
 
-    sse_read_timeout: float = 300
-    """Maximum time as in seconds to wait for new SSE messages before timing out.
+    sse_read_timeout: float = 5 * 60
+    """Maximum time in seconds to wait for new SSE messages before timing out.
 
     This timeout applies to the long-lived SSE connection after it's established.
     If no new messages are received within this time, the connection will be considered stale
@@ -353,28 +358,21 @@ async def main():
     For example, if `tool_prefix='foo'`, then a tool named `bar` will be registered as `foo_bar`
     """
 
-    def __post_init__(self):
-        # streamablehttp_client expects timedeltas, so we accept them too to match,
-        # but primarily work with floats for a simpler user API.
-
-        if isinstance(self.timeout, timedelta):
-            self.timeout = self.timeout.total_seconds()
-
-        if isinstance(self.sse_read_timeout, timedelta):
-            self.sse_read_timeout = self.sse_read_timeout.total_seconds()
-
     @asynccontextmanager
     async def client_streams(
         self,
     ) -> AsyncIterator[
-        tuple[MemoryObjectReceiveStream[SessionMessage | Exception], MemoryObjectSendStream[SessionMessage]]
+        tuple[
+            MemoryObjectReceiveStream[JSONRPCMessage | Exception],
+            MemoryObjectSendStream[JSONRPCMessage],
+        ]
     ]:  # pragma: no cover
-        async with streamablehttp_client(
+        async with sse_client(
             url=self.url,
             headers=self.headers,
-            timeout=timedelta(seconds=self.timeout),
-            sse_read_timeout=timedelta(seconds=self.sse_read_timeout),
-        ) as (read_stream, write_stream, _):
+            timeout=self.timeout,
+            sse_read_timeout=self.sse_read_timeout,
+        ) as (read_stream, write_stream):
             yield read_stream, write_stream
 
     def _get_log_level(self) -> LoggingLevel | None:

tests/test_mcp.py

@@ -1,7 +1,6 @@
 """Tests for the MCP (Model Context Protocol) server implementation."""
 
 import re
-from datetime import timedelta
 from pathlib import Path
 
 import pytest
@@ -71,40 +70,25 @@ async def test_stdio_server_with_cwd():
         assert len(tools) == 10
 
 
-def test_http_server():
-    http_server = MCPServerHTTP(url='http://localhost:8000/sse')
-    assert http_server.url == 'http://localhost:8000/sse'
-    assert http_server._get_log_level() is None  # pyright: ignore[reportPrivateUsage]
+def test_sse_server():
+    sse_server = MCPServerHTTP(url='http://localhost:8000/sse')
+    assert sse_server.url == 'http://localhost:8000/sse'
+    assert sse_server._get_log_level() is None  # pyright: ignore[reportPrivateUsage]
 
 
-def test_http_server_with_header_and_timeout():
-    http_server = MCPServerHTTP(
+def test_sse_server_with_header_and_timeout():
+    sse_server = MCPServerHTTP(
         url='http://localhost:8000/sse',
         headers={'my-custom-header': 'my-header-value'},
         timeout=10,
         sse_read_timeout=100,
         log_level='info',
     )
-    assert http_server.url == 'http://localhost:8000/sse'
-    assert http_server.headers is not None and http_server.headers['my-custom-header'] == 'my-header-value'
-    assert http_server.timeout == 10
-    assert http_server.sse_read_timeout == 100
-    assert http_server._get_log_level() == 'info'  # pyright: ignore[reportPrivateUsage]
-
-
-def test_http_server_with_timedelta_arguments():
-    http_server = MCPServerHTTP(
-        url='http://localhost:8000/sse',
-        headers={'my-custom-header': 'my-header-value'},
-        timeout=timedelta(seconds=10),  # type: ignore[arg-type]
-        sse_read_timeout=timedelta(seconds=100),  # type: ignore[arg-type]
-        log_level='info',
-    )
-    assert http_server.url == 'http://localhost:8000/sse'
-    assert http_server.headers is not None and http_server.headers['my-custom-header'] == 'my-header-value'
-    assert http_server.timeout == 10
-    assert http_server.sse_read_timeout == 100
-    assert http_server._get_log_level() == 'info'  # pyright: ignore[reportPrivateUsage]
+    assert sse_server.url == 'http://localhost:8000/sse'
+    assert sse_server.headers is not None and sse_server.headers['my-custom-header'] == 'my-header-value'
+    assert sse_server.timeout == 10
+    assert sse_server.sse_read_timeout == 100
+    assert sse_server._get_log_level() == 'info'  # pyright: ignore[reportPrivateUsage]
 
 
 @pytest.mark.vcr()