Auth Interceptor not working for sync client

[maaft]

according to docs, i can setup an auth interceptor like this:

class AuthInterceptorSync:
    """Synchronous interceptor to add authentication headers to all requests"""

    def __init__(self, token: str):
        self.token = token


    def on_start(self, ctx: RequestContext) -> None:
        """Add authorization header when RPC starts"""
        ctx.request_headers()["authorization"] = self.token

    def on_end(self, token: None, ctx: RequestContext) -> None:
        """Called when RPC ends"""
        pass

But on_start is never called.

When i instead defined intercept_unary_sync, it worked.

class AuthInterceptorSync:
    """Synchronous interceptor to add authentication headers to all requests"""

    def __init__(self, token: str):
        self.token = token

    def intercept_unary_sync(
        self,
        call_next: Callable[[REQ, RequestContext], RES],
        request: REQ,
        ctx: RequestContext,
    ) -> RES:
        """Intercepts a unary RPC.

        Args:
            call_next: A callable to invoke to continue processing, either to another
                interceptor or the actual RPC. Generally will be called with the same
                request the interceptor received but the request can be replaced as
                needed. Can be skipped if returning a response from the interceptor
                directly.
            request: The request message.
            ctx: The request context.

        Returns:
            The response message.
        """
        ctx.request_headers()["authorization"] = self.token
        return call_next(request, ctx)

[maaft]

Found it.

For sync clients the methods are called on_start_sync and on_end_sync:

class AuthInterceptorSync:
    """Synchronous interceptor to add authentication headers to all requests"""

    def __init__(self, token: str):
        self.token = token


    def on_start_sync(self, ctx: RequestContext) -> None:
        """Called when the RPC starts. The return value will be passed to on_end as-is.
        For example, if measuring RPC invocation time, on_start may return the current
        time. If a return value isn't needed or on_end won't be used, return None.
        """
        ctx.request_headers()["authorization"] = self.token

    def on_end_sync(self, token: None, ctx: RequestContext) -> None:
        """Called when the RPC ends."""
        pass

[anuraaga]

Thanks for the report @maaft! This is indeed a bug in the docs, sent #35 to fix it