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enable http headers in sse in the context #216

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enable http headers in sse in the context #216

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144db31
enable http headers in sse in the context
abdullahkady Feb 19, 2025
e402103
add todo comment
abdullahkady Feb 19, 2025
b6e4576
type instead of try/except
abdullahkady Feb 19, 2025
1f146f6
Merge branch 'main' into main
abdullahkady Feb 21, 2025
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7 changes: 7 additions & 0 deletions src/mcp/server/lowlevel/server.py
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Expand Up @@ -526,6 +526,12 @@ async def _handle_request(
logger.debug(f"Dispatching request of type {type(req).__name__}")

token = None
headers = {}
try:
# TODO: This try/catch and ignoring the type is wrong.
headers = message.request.root.headers # type: ignore
except Exception:
pass
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I assume we most likely want headers to be extracted from the transport protocol itself. This means providing ways within a session context to access to original request headers for the HTTP Post in the case of SSE. For STDIO this would be empty. If we ever come to the conclusion that headers are absolutely necessary, I think we likely would move to a STDIO transport description that is akin to the header-based JSON-RPC that LSP is doing, which is of the form:

Some-Header: Some-Value
Some-Header: Some-Value
{"jsonrpc": "2.0", ...}

try:
# Set our global state that can be retrieved via
# app.get_request_context()
Expand All @@ -535,6 +541,7 @@ async def _handle_request(
message.request_meta,
session,
lifespan_context,
headers,
)
)
response = await handler(req)
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3 changes: 2 additions & 1 deletion src/mcp/server/sse.py
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Expand Up @@ -160,7 +160,8 @@ async def handle_post_message(
logger.debug(f"Received JSON: {json}")

try:
message = types.JSONRPCMessage.model_validate(json)
message_with_headers = {**json, "headers": dict(request.headers)}
message = types.JSONRPCMessage.model_validate(message_with_headers)
logger.debug(f"Validated client message: {message}")
except ValidationError as err:
logger.error(f"Failed to parse message: {err}")
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3 changes: 2 additions & 1 deletion src/mcp/shared/context.py
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@@ -1,4 +1,4 @@
from dataclasses import dataclass
from dataclasses import dataclass, field
from typing import Generic, TypeVar

from mcp.shared.session import BaseSession
Expand All @@ -14,3 +14,4 @@ class RequestContext(Generic[SessionT, LifespanContextT]):
meta: RequestParams.Meta | None
session: SessionT
lifespan_context: LifespanContextT
headers: dict[str, str] = field(default_factory=dict)
1 change: 1 addition & 0 deletions src/mcp/types.py
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Expand Up @@ -118,6 +118,7 @@ class JSONRPCRequest(Request):
jsonrpc: Literal["2.0"]
id: RequestId
params: dict[str, Any] | None = None
headers: dict[str, str] | None = None
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I don't think we would want to add headers to the types. The types are a direct translation of the schema.ts in the specification. Adding headers here would not be compatible with JSON-RPC in it's most used form.

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@dsp-ant Thank you! That's fair. I was trying to initially do the change such that only the sse file is the one with changes, but here's my problem, and a suggestion for an approach to fix it. Please correct me if my understanding of the code is not complete.

  • The HTTP request is only available in transport layer (sse.py)
  • The only way to pass stuff down from the transport layer to the server implementation is going to be through the streams, which have JSONRPCMessage type
  • We don't want to extend/change the JSONRPCMessage type because it is part of the schema (and honestly it makes sense, since it only applies to certain transports)

To solve this, here are my other 2 suggestions:

  • Inject the metadata (one of which is optional headers) in the params of the JSONRPCMessage
  • Change the streams so that they now hold a new type (a container type with the JSONRPCMessage + meta), where the meta can be anything that is transport-specific?

Let me know what you think.

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@dsp-ant hey, any chance you have given this some thought and have any guidance for the approach? I would love to update the PR



class JSONRPCNotification(Notification):
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