CombinedProtocolErrors

Fatal transport-level errors returned when executing a subscription using the multipart HTTP subscription protocol. See the documentation on the multipart HTTP protocol for GraphQL Subscriptions for more information on these errors.

These errors indicate issues with the subscription transport itself, rather than GraphQL-level errors. They typically occur when there are problems communicating with subgraphs from the Apollo Router.

1 import { CombinedProtocolErrors } from "@apollo/client/errors"; 2 3 // Check if an error is a CombinedProtocolErrors instance 4 if (CombinedProtocolErrors.is(error)) { 5 // Access individual protocol errors 6 error.errors.forEach((protocolError) => { 7 console.log(protocolError.message); 8 console.log(protocolError.extensions); 9 }); 10 }

By default, CombinedProtocolErrors formats the message property by joining each error's message field with a newline. To customize the format of the message, such as changing the delimiter or adding a message prefix, override the static formatMessage method.

The following example demonstrates how to format the error message by joining each error with a comma.

1import { CombinedProtocolErrors } from "@apollo/client/errors"; 2 3CombinedProtocolErrors.formatMessage = (errors) => { 4 return errors.map((error) => error.message).join(", "); 5};

See the formatMessage section for details about the parameters provided to the formatMessage function.

To format part of the message using the default message formatter, call the defaultFormatMessage function provided to the options argument of your message formatter.

The following example prepends a string to the message and uses the default message formatter to format the error messages.

1CombinedProtocolErrors.formatMessage = (errors, { defaultFormatMessage }) => { 2 return `[Protocol errors]: ${defaultFormatMessage(errors)}`; 3};

A method that determines whether an error is a CombinedProtocolErrors object. This method enables TypeScript to narrow the error type.

A function that formats the error message used for the error's message property. Override this method to provide your own formatting.

The formatMessage function is called by the CombinedProtocolErrors constructor to provide a formatted message as the message property of the CombinedProtocolErrors object. Follow the "Providing a custom message formatter" guide to learn how to modify the message format.