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Add HeaderName constants for MCP HTTP headers #1202

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69 changes: 61 additions & 8 deletions crates/rmcp/src/transport/common/http_header.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,21 @@ pub const JSON_MIME_TYPE: &str = "application/json";
pub const HEADER_MCP_METHOD: &str = "Mcp-Method";
pub const HEADER_MCP_NAME: &str = "Mcp-Name";
pub const HEADER_MCP_PARAM_PREFIX: &str = "Mcp-Param-";
pub const HEADER_MCP_PARAM_PREFIX_LOWER: &str = "mcp-param-";

#[cfg(any(feature = "client-side-sse", feature = "server-side-http"))]
pub const HEADER_NAME_SESSION_ID: http::HeaderName =
http::HeaderName::from_static("mcp-session-id");
#[cfg(any(feature = "client-side-sse", feature = "server-side-http"))]
pub const HEADER_NAME_LAST_EVENT_ID: http::HeaderName =
http::HeaderName::from_static("last-event-id");
#[cfg(any(feature = "client-side-sse", feature = "server-side-http"))]
pub const HEADER_NAME_MCP_PROTOCOL_VERSION: http::HeaderName =
http::HeaderName::from_static("mcp-protocol-version");
#[cfg(any(feature = "client-side-sse", feature = "server-side-http"))]
pub const HEADER_NAME_MCP_METHOD: http::HeaderName = http::HeaderName::from_static("mcp-method");
#[cfg(any(feature = "client-side-sse", feature = "server-side-http"))]
pub const HEADER_NAME_MCP_NAME: http::HeaderName = http::HeaderName::from_static("mcp-name");

/// Sentinel wrapping a Base64-encoded SEP-2243 header value (`=?base64?<b64>?=`).
pub const BASE64_HEADER_PREFIX: &str = "=?base64?";
Expand All @@ -29,21 +44,23 @@ pub(crate) const RESERVED_HEADERS: &[&str] = &[
/// `MCP-Protocol-Version` is reserved but allowed through (the worker injects it post-init).
#[cfg(feature = "client-side-sse")]
pub(crate) fn validate_custom_header(name: &http::HeaderName) -> Result<(), String> {
if RESERVED_HEADERS
.iter()
.any(|&r| name.as_str().eq_ignore_ascii_case(r))
{
if name
.as_str()
.eq_ignore_ascii_case(HEADER_MCP_PROTOCOL_VERSION)
{
if is_reserved_header_name(name) {
if name == HEADER_NAME_MCP_PROTOCOL_VERSION {
return Ok(());
}
return Err(name.to_string());
}
Ok(())
}

#[cfg(feature = "client-side-sse")]
fn is_reserved_header_name(name: &http::HeaderName) -> bool {
name == http::header::ACCEPT
|| name == HEADER_NAME_SESSION_ID
|| name == HEADER_NAME_MCP_PROTOCOL_VERSION
|| name == HEADER_NAME_LAST_EVENT_ID
}

/// Extracts the `scope=` parameter from a `WWW-Authenticate` header value.
/// Handles both quoted (`scope="files:read files:write"`) and unquoted (`scope=read:data`) forms.
#[cfg(feature = "client-side-sse")]
Expand Down Expand Up @@ -74,6 +91,9 @@ pub(crate) fn extract_scope_from_header(header: &str) -> Option<String> {

#[cfg(test)]
mod tests {
#[cfg(any(feature = "client-side-sse", feature = "server-side-http"))]
use http::{HeaderMap, HeaderName, HeaderValue};

#[cfg(feature = "client-side-sse")]
use super::*;

Expand Down Expand Up @@ -137,4 +157,37 @@ mod tests {
let name = http::HeaderName::from_static("x-custom");
assert!(validate_custom_header(&name).is_ok());
}

#[cfg(any(feature = "client-side-sse", feature = "server-side-http"))]
#[test]
fn header_name_constants_match_case_insensitively() {
let cases = [
(HEADER_NAME_SESSION_ID, "McP-SeSsIoN-Id"),
(HEADER_NAME_LAST_EVENT_ID, "LaSt-EvEnT-Id"),
(HEADER_NAME_MCP_PROTOCOL_VERSION, "McP-PrOtOcOl-VeRsIoN"),
(HEADER_NAME_MCP_METHOD, "McP-MeThOd"),
(HEADER_NAME_MCP_NAME, "McP-NaMe"),
];

for (constant, mixed_case) in cases {
let mut headers = HeaderMap::new();
headers.insert(
HeaderName::from_bytes(mixed_case.as_bytes()).expect("valid header name"),
HeaderValue::from_static("value"),
);

assert_eq!(
headers.get(constant),
Some(&HeaderValue::from_static("value"))
);
}
}

#[cfg(any(feature = "client-side-sse", feature = "server-side-http"))]
#[test]
fn mcp_param_lower_prefix_matches_header_names() {
let name = HeaderName::from_static("mcp-param-user");

assert!(name.as_str().starts_with(HEADER_MCP_PARAM_PREFIX_LOWER));
}
}
7 changes: 4 additions & 3 deletions crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,8 +11,9 @@ use crate::{
common::{
client_side_sse::{DEFAULT_MAX_SSE_EVENT_SIZE, bounded_sse_stream},
http_header::{
EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_SESSION_ID, JSON_MIME_TYPE,
extract_scope_from_header, validate_custom_header,
EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_NAME_SESSION_ID,
HEADER_SESSION_ID, JSON_MIME_TYPE, extract_scope_from_header,
validate_custom_header,
},
},
streamable_http_client::*,
Expand Down Expand Up @@ -257,7 +258,7 @@ impl StreamableHttpClient for reqwest::Client {
let content_length = response.content_length();
let session_id = response
.headers()
.get(HEADER_SESSION_ID)
.get(HEADER_NAME_SESSION_ID)
.and_then(|v| v.to_str().ok())
.map(|s| s.to_string());
// Spec requires 202 Accepted for these, but some servers return an empty 200.
Expand Down
7 changes: 4 additions & 3 deletions crates/rmcp/src/transport/common/unix_socket.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,8 +15,9 @@ use crate::{
common::{
client_side_sse::{DEFAULT_MAX_SSE_EVENT_SIZE, bounded_sse_stream},
http_header::{
EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_SESSION_ID, JSON_MIME_TYPE,
extract_scope_from_header, validate_custom_header,
EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_NAME_SESSION_ID,
HEADER_SESSION_ID, JSON_MIME_TYPE, extract_scope_from_header,
validate_custom_header,
},
},
streamable_http_client::*,
Expand Down Expand Up @@ -287,7 +288,7 @@ impl StreamableHttpClient for UnixSocketHttpClient {
.and_then(|v| v.parse::<u64>().ok());
let session_id = response
.headers()
.get(HEADER_SESSION_ID)
.get(HEADER_NAME_SESSION_ID)
.and_then(|v| v.to_str().ok())
.map(|s| s.to_string());

Expand Down
13 changes: 7 additions & 6 deletions crates/rmcp/src/transport/streamable_http_client.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,10 @@ use crate::{
},
service::InboundStreamOrigin,
transport::{
common::{client_side_sse::SseAutoReconnectStream, mcp_headers},
common::{
client_side_sse::SseAutoReconnectStream, http_header::HEADER_NAME_MCP_PROTOCOL_VERSION,
mcp_headers,
},
worker::{Worker, WorkerQuitReason, WorkerSendRequest, WorkerTransport},
},
};
Expand Down Expand Up @@ -78,7 +81,7 @@ fn request_version_headers(
};
let mut headers = build_request_headers(base, message, tool_cache, &version);
if let Ok(value) = HeaderValue::from_str(version.as_str()) {
headers.insert(HeaderName::from_static("mcp-protocol-version"), value);
headers.insert(HEADER_NAME_MCP_PROTOCOL_VERSION, value);
}
(version, headers)
}
Expand Down Expand Up @@ -117,9 +120,8 @@ fn negotiate_version_headers(
&& let ServerResult::InitializeResult(init_result) = &response.result
{
version = init_result.protocol_version.clone();
// HeaderName::from_static requires lowercase
if let Ok(hv) = HeaderValue::from_str(init_result.protocol_version.as_str()) {
headers.insert(HeaderName::from_static("mcp-protocol-version"), hv);
headers.insert(HEADER_NAME_MCP_PROTOCOL_VERSION, hv);
}
}
(version, headers)
Expand Down Expand Up @@ -1137,8 +1139,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
if inline_version.is_some() {
negotiated_version = request_version.clone();
if let Ok(value) = HeaderValue::from_str(request_version.as_str()) {
protocol_headers
.insert(HeaderName::from_static("mcp-protocol-version"), value);
protocol_headers.insert(HEADER_NAME_MCP_PROTOCOL_VERSION, value);
}
if let Some(cleanup) = &mut session_cleanup_info {
cleanup.protocol_headers = protocol_headers.clone();
Expand Down
29 changes: 15 additions & 14 deletions crates/rmcp/src/transport/streamable_http_server/tower.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,8 +39,9 @@ use crate::{
OneshotTransport, TransportAdapterIdentity,
common::{
http_header::{
EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_MCP_PROTOCOL_VERSION,
HEADER_SESSION_ID, JSON_MIME_TYPE,
EVENT_STREAM_MIME_TYPE, HEADER_NAME_LAST_EVENT_ID,
HEADER_NAME_MCP_PROTOCOL_VERSION, HEADER_NAME_SESSION_ID, HEADER_SESSION_ID,
JSON_MIME_TYPE,
},
mcp_headers,
server_side_http::{
Expand Down Expand Up @@ -260,7 +261,7 @@ fn validate_protocol_version_header(
headers: &http::HeaderMap,
allow_unknown: bool,
) -> Result<(), BoxResponse> {
if let Some(value) = headers.get(HEADER_MCP_PROTOCOL_VERSION) {
if let Some(value) = headers.get(HEADER_NAME_MCP_PROTOCOL_VERSION) {
let version_str = value.to_str().map_err(|_| {
Response::builder()
.status(http::StatusCode::BAD_REQUEST)
Expand Down Expand Up @@ -396,7 +397,7 @@ fn is_legacy_request(
let version = from_body
.or_else(|| {
headers
.get(HEADER_MCP_PROTOCOL_VERSION)
.get(HEADER_NAME_MCP_PROTOCOL_VERSION)
.and_then(|value| value.to_str().ok())
.and_then(|s| serde_json::from_value(serde_json::Value::String(s.to_owned())).ok())
})
Expand Down Expand Up @@ -466,7 +467,7 @@ fn validate_header_matches_init_body(
body_version: &str,
request_id: Option<RequestId>,
) -> Result<(), BoxResponse> {
let Some(header_value) = headers.get(HEADER_MCP_PROTOCOL_VERSION) else {
let Some(header_value) = headers.get(HEADER_NAME_MCP_PROTOCOL_VERSION) else {
return Ok(());
};
let header_str = header_value.to_str().map_err(|_| {
Expand Down Expand Up @@ -508,7 +509,7 @@ fn validate_request_protocol_version_meta(
let is_discover = matches!(&request.request, ClientRequest::DiscoverRequest(_));
let meta = request.request.get_meta();
let header_version = headers
.get(HEADER_MCP_PROTOCOL_VERSION)
.get(HEADER_NAME_MCP_PROTOCOL_VERSION)
.and_then(|value| value.to_str().ok());
let Some(meta_version) = meta.protocol_version() else {
let requires_request_metadata = is_discover
Expand Down Expand Up @@ -569,7 +570,7 @@ fn validate_required_protocol_header(
// Initialize keeps its own header-matching rule.
return Ok(());
}
if headers.contains_key(HEADER_MCP_PROTOCOL_VERSION) {
if headers.contains_key(HEADER_NAME_MCP_PROTOCOL_VERSION) {
return Ok(());
}
Err(header_mismatch_jsonrpc_response(
Expand Down Expand Up @@ -676,7 +677,7 @@ fn validate_standard_headers(
tool_schema: impl Fn(&str) -> Option<Arc<JsonObject>>,
) -> Result<(), BoxResponse> {
let version_requires_headers = headers
.get(HEADER_MCP_PROTOCOL_VERSION)
.get(HEADER_NAME_MCP_PROTOCOL_VERSION)
.and_then(|value| value.to_str().ok())
.is_some_and(|version| version >= ProtocolVersion::STANDARD_HEADERS.as_str());
if !version_requires_headers {
Expand Down Expand Up @@ -1562,7 +1563,7 @@ where
if !legacy_request {
let Some(last_event_id) = request
.headers()
.get(HEADER_LAST_EVENT_ID)
.get(HEADER_NAME_LAST_EVENT_ID)
.and_then(|value| value.to_str().ok())
else {
return Ok(method_not_allowed_response());
Expand All @@ -1586,7 +1587,7 @@ where
// check session id
let session_id = request
.headers()
.get(HEADER_SESSION_ID)
.get(HEADER_NAME_SESSION_ID)
.and_then(|v| v.to_str().ok())
.map(|s| s.to_owned().into());
let Some(session_id) = session_id else {
Expand Down Expand Up @@ -1622,7 +1623,7 @@ where
// check if last event id is provided
let last_event_id = parts
.headers
.get(HEADER_LAST_EVENT_ID)
.get(HEADER_NAME_LAST_EVENT_ID)
.and_then(|v| v.to_str().ok())
.map(|s| s.to_owned());
if let Some(last_event_id) = last_event_id {
Expand Down Expand Up @@ -1730,7 +1731,7 @@ where
// do we have a session id?
let session_id = part
.headers
.get(HEADER_SESSION_ID)
.get(HEADER_NAME_SESSION_ID)
.and_then(|v| v.to_str().ok());
if let Some(session_id) = session_id {
let session_id = session_id.to_owned().into();
Expand Down Expand Up @@ -2048,7 +2049,7 @@ where
// check session id
let session_id = request
.headers()
.get(HEADER_SESSION_ID)
.get(HEADER_NAME_SESSION_ID)
.and_then(|v| v.to_str().ok())
.map(|s| s.to_owned().into());
let Some(session_id) = session_id else {
Expand Down Expand Up @@ -2092,7 +2093,7 @@ where
init.params.protocol_version.clone()
} else {
headers
.get(HEADER_MCP_PROTOCOL_VERSION)
.get(HEADER_NAME_MCP_PROTOCOL_VERSION)
.and_then(|v| v.to_str().ok())
.and_then(|s| serde_json::from_value(serde_json::Value::String(s.to_owned())).ok())
.unwrap_or(ProtocolVersion::V_2025_03_26)
Expand Down