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Fix: Move receive() outside loop to fix stream consumption #170

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Fix: Move receive() outside loop to fix stream consumption #170

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4 changes: 2 additions & 2 deletions Package.resolved
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63 changes: 30 additions & 33 deletions Sources/MCP/Client/Client.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -179,43 +179,40 @@ public actor Client {
// Start message handling loop
task = Task {
guard let connection = self.connection else { return }
repeat {
// Check for cancellation before starting the iteration
if Task.isCancelled { break }

do {
let stream = await connection.receive()
for try await data in stream {
if Task.isCancelled { break } // Check inside loop too

// Attempt to decode data
// Try decoding as a batch response first
if let batchResponse = try? decoder.decode([AnyResponse].self, from: data) {
await handleBatchResponse(batchResponse)
} else if let response = try? decoder.decode(AnyResponse.self, from: data) {
await handleResponse(response)
} else if let message = try? decoder.decode(AnyMessage.self, from: data) {
await handleMessage(message)
} else {
var metadata: Logger.Metadata = [:]
if let string = String(data: data, encoding: .utf8) {
metadata["message"] = .string(string)
}
await logger?.warning(
"Unexpected message received by client (not single/batch response or notification)",
metadata: metadata
)
// Get the stream once - async streams can only be iterated once.
// Previously, receive() was called inside a repeat loop, which meant
// each iteration tried to create a new stream from an already-consumed one.
let stream = await connection.receive()

do {
for try await data in stream {
if Task.isCancelled { break }

// Attempt to decode data
// Try decoding as a batch response first
if let batchResponse = try? decoder.decode([AnyResponse].self, from: data) {
await handleBatchResponse(batchResponse)
} else if let response = try? decoder.decode(AnyResponse.self, from: data) {
await handleResponse(response)
} else if let message = try? decoder.decode(AnyMessage.self, from: data) {
await handleMessage(message)
} else {
var metadata: Logger.Metadata = [:]
if let string = String(data: data, encoding: .utf8) {
metadata["message"] = .string(string)
}
await logger?.warning(
"Unexpected message received by client (not single/batch response or notification)",
metadata: metadata
)
}
} catch let error where MCPError.isResourceTemporarilyUnavailable(error) {
try? await Task.sleep(for: .milliseconds(10))
continue
} catch {
await logger?.error(
"Error in message handling loop", metadata: ["error": "\(error)"])
break
}
} while true
} catch {
await logger?.error(
"Error in message handling loop", metadata: ["error": "\(error)"])
}

await self.logger?.debug("Client message handling loop task is terminating.")
}

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