Documentation Index
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Overview
Transport errors are thrown by the MCP transport layer — the component responsible for managing HTTP connections, sessions, and message framing. Most are internal errors except UnsupportedContentTypeError, which is a client-facing 400 error.
Error Reference
MethodNotImplementedError
Thrown when calling an abstract or placeholder method that has not been implemented.
| Property | Type | Value |
|---|
code | string | METHOD_NOT_IMPLEMENTED |
statusCode | number | 500 |
isPublic | boolean | false |
new MethodNotImplementedError(className?: string, methodName?: string)
import { MethodNotImplementedError } from '@frontmcp/sdk';
throw new MethodNotImplementedError('CustomTransport', 'send');
// "CustomTransport.send() is not implemented"
UnsupportedTransportTypeError
Thrown when an unsupported transport type is specified in configuration.
| Property | Type | Value |
|---|
code | string | UNSUPPORTED_TRANSPORT_TYPE |
statusCode | number | 500 |
isPublic | boolean | false |
new UnsupportedTransportTypeError(transportType: string)
import { UnsupportedTransportTypeError } from '@frontmcp/sdk';
throw new UnsupportedTransportTypeError('websocket');
// "Unsupported transport type: "websocket""
TransportBusRequiredError
Thrown when a transport bus is required but not provided.
| Property | Type | Value |
|---|
code | string | TRANSPORT_BUS_REQUIRED |
statusCode | number | 500 |
isPublic | boolean | false |
new TransportBusRequiredError()
InvalidTransportSessionError
Thrown when a transport session is invalid or missing.
| Property | Type | Value |
|---|
code | string | INVALID_TRANSPORT_SESSION |
statusCode | number | 500 |
isPublic | boolean | false |
new InvalidTransportSessionError(message: string)
import { InvalidTransportSessionError } from '@frontmcp/sdk';
throw new InvalidTransportSessionError('Session ID missing from request headers');
TransportNotConnectedError
Thrown when an operation is attempted on a transport that is not connected.
| Property | Type | Value |
|---|
code | string | TRANSPORT_NOT_CONNECTED |
statusCode | number | 500 |
isPublic | boolean | false |
new TransportNotConnectedError(context?: string)
import { TransportNotConnectedError } from '@frontmcp/sdk';
throw new TransportNotConnectedError('SSE channel closed');
TransportAlreadyStartedError
Thrown when attempting to start a transport that is already running.
| Property | Type | Value |
|---|
code | string | TRANSPORT_ALREADY_STARTED |
statusCode | number | 500 |
isPublic | boolean | false |
new TransportAlreadyStartedError(message?: string)
UnsupportedContentTypeError
Thrown when a request uses an unsupported Content-Type header. This is a public error since it represents a client-side issue.
| Property | Type | Value |
|---|
code | string | UNSUPPORTED_CONTENT_TYPE |
statusCode | number | 400 |
isPublic | boolean | true |
contentType | string | The unsupported content type |
new UnsupportedContentTypeError(contentType: string)
import { UnsupportedContentTypeError } from '@frontmcp/sdk';
throw new UnsupportedContentTypeError('text/xml');
// "Unsupported content-type: text/xml"
