Question: How to set the user-agent (and/or `X-Goog-Api-Client`) header for all requests

[tswast]

Hi, it'd be quite useful for my work to be able to set the user-agent and/or X-Goog-Api-Client as documented in https://cloud.google.com/apis/docs/system-parameters to attribute requests to these libraries and tools built with these libraries.

Per hyperium/tonic#453 (comment) I tried to use an interceptor like this:

    let read_client: GoogleApi<BigQueryReadClient<GoogleAuthMiddleware>> =
        GoogleApi::from_function(
            // Maximum row size in BigQuery is 100 MB, so this should allow for
            // the largest possible row plus some overhead.
            |inner| BigQueryReadClient::with_interceptor(
                inner,  |mut req: tonic::Request<()>| {
                    req.metadata_mut().insert(
                        "user-agent",
                        tonic::metadata::MetadataValue::from_str("some-user-agent").unwrap(),
                    );
                    Ok(req)
                }
            ).max_decoding_message_size(101 * 1024 * 1024),
            "https://bigquerystorage.googleapis.com",
            None,
        )
        .await?;

But I get a type error.

`?` operator has incompatible types
`?` operator cannot convert from `GoogleApiClient<GoogleApiClientBuilderFunction<...>, ...>` to `GoogleApiClient<GoogleApiClientBuilderFunction<...>, ...>`
expected struct `GoogleApiClient<GoogleApiClientBuilderFunction<...>, ...>` (`GoogleAuthMiddlewareService<Channel>`)
   found struct `GoogleApiClient<GoogleApiClientBuilderFunction<...>, ...>` (`InterceptedService<..., ...>`)
the full name for the type has been written to '/usr/local/google/home/swast/src/github.com/pola-rs/polars-bigquery-client/target/debug/deps/polars_bigquery-67ec6568e750e1b9.long-type-13703174448194782730.txt'
consider using `--verbose` to print the full type name to the consolerustc[Click for full compiler diagnostic](rust-analyzer-diagnostics-view:/diagnostic%20message%20[5]?5#file:///usr/local/google/home/swast/src/github.com/pola-rs/polars-bigquery-client/src/bigquery.rs)
`?` operator has incompatible types
`?` operator cannot convert from `GoogleApiClient<GoogleApiClientBuilderFunction<...>, ...>` to `GoogleApiClient<GoogleApiClientBuilderFunction<...>, ...>`
expected struct `GoogleApiClient<GoogleApiClientBuilderFunction<...>, ...>` (`GoogleAuthMiddlewareService<Channel>`)
   found struct `GoogleApiClient<GoogleApiClientBuilderFunction<...>, ...>` (`InterceptedService<..., ...>`)
the full name for the type has been written to '/usr/local/google/home/swast/src/github.com/pola-rs/polars-bigquery-client/target/debug/deps/polars_bigquery-c61b4cad463e858a.long-type-18130587985917432528.txt'
consider using `--verbose` to print the full type name to the consolerustc

In particular,

expected struct `GoogleApiClient<GoogleApiClientBuilderFunction<...>, ...>` (`GoogleAuthMiddlewareService<Channel>`)
   found struct `GoogleApiClient<GoogleApiClientBuilderFunction<...>, ...>` (`InterceptedService<..., ...>`)` 

is coming from from_function.

[tswast]

This seems to work:

    // TODO(tswast): Handle the connection error gracefully.
    let channel =
        GoogleEnvironment::init_google_services_channel("https://bigquerystorage.googleapis.com")
            .await
            .unwrap();
    let read_client =
            // Maximum row size in BigQuery is 100 MB, so this should allow for
            // the largest possible row plus some overhead.
            BigQueryReadClient::with_interceptor(
                channel,  |mut req: tonic::Request<()>| {
                    req.metadata_mut().insert(
                        "user-agent",
                        tonic::metadata::MetadataValue::from_str("some-user-agent").unwrap(),
                    );
                    Ok(req)
                }
            ).max_decoding_message_size(101 * 1024 * 1024);

It compiles once I remove the .get() calls later on in the code sample that I no longer need.

That said, it becomes much more difficult to pass client objects around due to hyperium/tonic#110.

[tswast]

I did figure out a way to pass a client object somewhat reasonably,

async fn read_stream<F: tonic::service::Interceptor + Sized>(
    read_client: Arc<BigQueryReadClient<InterceptedService<Channel, F>>>,
    schema: Arc<Vec<u8>>,
    stream_name: String,
    tx: Arc<tokio::sync::mpsc::Sender<DataFrame>>,
) {

Except this doesn't work because

trait `DerefMut` is required to modify through a dereference, but it is not implemented for `Arc<BigQueryReadClient<InterceptedService<Channel, F>>>

The GoogleApi object was helping us before with sharing a client in spawned tasks.

Not sure 100% how to proceed. I'll try to take another look tomorrow.

[abdolence]

Oh, I didn't notice this for some reason.

Sorry, let me check this and come back to you.