feat: support hooking into execute stream (defer/stream) #429
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This PR is built upon #428 and serves as a POC for hoking into the phases where execute returns an AsyncIterable (which will be introduced as part of the next GraphQL major release for defer/stream support). Today, returning AsyncIterable from execute is already supported by various GraphQL servers such as graphql-helix, graphql-ws and graphql over Socket.io.
Adding this to envelop is a breaking change as the type signature of the
ExecuteDonehook changes. The result type is nowAsyncIterable<ExecutionResult> | ExecutionResult. Furthermore, the type signature ofexecuteis changed to now returnAsyncIterable<ExecutionResult> | ExecutionResult.