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fix: resolve compatibility issues with servers sending LSP notifications #413

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Merged
4t145 merged 1 commit into from
Sep 4, 2025
Merged

fix: resolve compatibility issues with servers sending LSP notifications #413

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73 changes: 55 additions & 18 deletions crates/rmcp/src/transport/async_rw.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -179,8 +179,31 @@ fn without_carriage_return(s: &[u8]) -> &[u8] {
}
}

/// Check if a notification method is a standard MCP notification
/// should update this when MCP spec is updated about new notifications
/// Check if a method is a standard MCP method (request, response, or notification).
/// This includes both requests and notifications defined in the MCP specification.
///
/// Based on MCP specification 2025-06-18: https://modelcontextprotocol.io/specification/2025-06-18
fn is_standard_method(method: &str) -> bool {
matches!(
method,
"initialize"
| "ping"
| "prompts/get"
| "prompts/list"
| "resources/list"
| "resources/read"
| "resources/subscribe"
| "resources/unsubscribe"
| "resources/templates/list"
| "tools/call"
| "tools/list"
| "completion/complete"
| "logging/setLevel"
| "roots/list"
| "sampling/createMessage"
) || is_standard_notification(method)
}

fn is_standard_notification(method: &str) -> bool {
matches!(
method,
Expand All @@ -196,6 +219,29 @@ fn is_standard_notification(method: &str) -> bool {
)
}

/// Determines if a notification should be ignored for compatibility.
fn should_ignore_notification(json_value: &serde_json::Value, method: &str) -> bool {
let is_notification = json_value.get("id").is_none();

// Ignore non-MCP notifications (like LSP messages) for compatibility
if is_notification && !is_standard_method(method) {
tracing::trace!(
"Ignoring non-MCP notification '{}' for compatibility",
method
);
return true;
}

// Ignore non-standard MCP notifications
matches!(
(
method.starts_with("notifications/"),
is_standard_notification(method)
),
(true, false)
)
}

/// Try to parse a message with compatibility handling for non-standard notifications
fn try_parse_with_compatibility<T: serde::de::DeserializeOwned>(
line: &[u8],
Expand All @@ -205,22 +251,13 @@ fn try_parse_with_compatibility<T: serde::de::DeserializeOwned>(
match serde_json::from_slice(line) {
Ok(item) => Ok(Some(item)),
Err(e) => {
// Check if this is a non-standard notification that should be ignored
if line_str.contains("\"method\":\"notifications/") {
// Extract the method name to check if it's standard
if let Ok(json_value) = serde_json::from_str::<serde_json::Value>(line_str) {
if let Some(method) = json_value.get("method").and_then(|m| m.as_str()) {
if method.starts_with("notifications/")
&& !is_standard_notification(method)
{
tracing::debug!(
"Ignoring non-standard notification {} {}: {}",
method,
context,
line_str
);
return Ok(None); // Skip this message
}
// Check if this is a notification that should be ignored for compatibility
if let Ok(json_value) = serde_json::from_str::<serde_json::Value>(line_str) {
if let Some(method) =
json_value.get("method").and_then(serde_json::Value::as_str)
{
if should_ignore_notification(&json_value, method) {
return Ok(None);
}
}
}
Expand Down