expose an API for constructing a wire error

[jhump]

When using connect.NewError, it is not possible create an error such that err.IsWireError() will return true.

This capability is particularly useful for dealing with bidi streaming APIs that represent a conversation, where each response message correlates with a request message. It is common for these kinds of APIs to support partial success by having a response message indicate a failure just for that one request message. Often such APIs use google.rpc.Status in the response message to indicate a possible failure. Sometimes they do not.

For this sort of use, it is commonplace for the calling Go code to translate that status into an error. Since the error was received over the wire during an RPC call, it should technically be a wire error, so that any other handling/propagation logic higher up the stack can react to it correctly.

This could be addressed as easily as introducing a new NewWireError function with the same signature and semantics as NewError except that the returned error will return true when err.IsWireError() is called.

[akshayjshah]

Huh, I'd never noticed that portion of the reflection API. TIL!

Happy to take a PR for this. I'm 50/50 on whether we ought to special-case NewWireError or anticipate more things down the road and add NewErrorOpt(Code, error, ...ErrorOption) (function name is terrible, but you get the idea).

[akshayjshah]

Here's another example of an API using a similar pattern: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/otlp.md#partial-success