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Learning gRPC

Victor Martinez

First, what is RPC?

An idea to extend transfer of control and transmission of data from one machine to another.

http://birrell.org/andrew/papers/ImplementingRPC.pdf

note:

The concept dates back to 1976 [1]
Paper written by ANDREW D. BIRRELL and BRUCE JAY NELSON
Back in the days building network application required big expertise and was not user friendly
They wanted to make it as easy to call a remote service as a local one, very user friendly
They wanted to make it efficient (Networks were very slow)
They wanted to make it secure (Networks were not secure)
RPCRuntime is also known as RPC communications package
One of the most important work the server developers must do is to define the interface
In that lab, the user-stub and server-stub used to be generated by a program called Lupine.

[1] WHITE, J. E. A high-level framework for network-based resource sharing. In Proc. National Computer Conference, (June 1976).

gRPC is a modern open source high performance Remote Procedure Call (RPC) framework that can run in any environment.

https://grpc.io/

note:

google Remote procedure calls
Initially created by Google
Used to connect microservices across data centers
It used to be called Stubby
In march 2015 they decided to build and publish a next version called gRPC and make it open source

Why a framework?

gRPC dictates how you will build your network interface.

Code is generated for you batteries included, you must only fill the gaps.

note:

All the underlying details about networking, encoding & more is handled for you.
For clients the feeling must be more of a library one.
Some implementations wrap the original C library, some don't.

Built on top of HTTP2

So we get for free

Multiplexing
Header compression
Server push
TLS

note:

Multiplexing & server push are especially relevant in gRPC

4 types of RPC supported

Metadata

Key-value pairs of data used to provide additional information about a call.

Implemented using HTTP/2 headers.

https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md

note:

gRPC metadata can be sent and received by both the client and the server.
Headers are sent from the client to the server before the initial request.
Headers are sent from the server to the client before the initial response of an RPC call.
The links shows a document specifying supported values as metadata.
Can be useful for: Authentication & tracing.

And many more features

Service-specific health checking
Request interceptors
Reflection for better debugging & discoverability
Configurable call retries via retry policies
RPC cancellations
Flow control for streaming
Client RPC load balancing
...

note:

Features might differ from language to language
Flow control: mechanism to ensure that a receiver of messages does not get overwhelmed by a fast sender
Reflection: Allows for clients without the generated client code to discover the gRPC services on the fly
Health check: A service is provided to monitor the health of specific services in your server
Retries:
- Enabled by default, with no default retry policy.
- By default retries low-level race conditions
- By default transparent retries are made:
  - If the RPC never left the client
  - If the RPC never reached the server application logic

Protocol buffers

Protocol Buffers are language-neutral, platform-neutral extensible mechanisms for serializing structured data.

https://protobuf.dev/

note:

Also developed by google
Default serialization format supported by gRPC
Interface Definition Language supported by gRPC

[2] https://en.wikipedia.org/wiki/Interface_description_language

They are a combination of

The Interface Definition Language
The compiler that generates code from IDL files
Language-specific runtimes
The serialization format

note:

In this section we focus on the IDL and the tooling

Remarkable features of Protocol buffers

Strongly typed data
Language and platform neutral
Compact binary format
Support for RPC service definition
Backward and Forward compatibility

note:

Compatibility notes

Field deletion compatibility is supported at a syntax level
- Via the use of a special keyword
Fields not found will be set a default value always
Extra not supported fields will be ignored

Defining messages

syntax = "proto3";

package decline_renewal.request.v1;

import "google/protobuf/timestamp.proto";

message DeclineRenewalRequest {
  string policy_id = 1;
  google.protobuf.Timestamp requested_at = 2;
  optional string description = 3;
  oneof reason {
    CustomerDeclineRenewalReason customer = 4;
  }
}

enum CustomerDeclineRenewalReason {
  CUSTOMER_DECLINE_RENEWAL_REASON_UNSPECIFIED = 0;
  CUSTOMER_DECLINE_RENEWAL_REASON_COMPETITOR_OFFER = 1;
  CUSTOMER_DECLINE_RENEWAL_REASON_VEHICLE_SOLD = 2;
  CUSTOMER_DECLINE_RENEWAL_REASON_VEHICLE_NOT_PURCHASED = 3;
  CUSTOMER_DECLINE_RENEWAL_REASON_VEHICLE_DEREGISTRATION = 4;
  CUSTOMER_DECLINE_RENEWAL_REASON_NO_INSURANCE_WANTED = 5;
  CUSTOMER_DECLINE_RENEWAL_REASON_DOES_NOT_KNOW = 6;
  CUSTOMER_DECLINE_RENEWAL_REASON_WANTS_GREEN_CARD = 7;
  CUSTOMER_DECLINE_RENEWAL_REASON_INCORRECT_EFFECTIVE_DATE = 8;
  CUSTOMER_DECLINE_RENEWAL_REASON_INCORRECT_PERSONAL_DATA = 9;
  CUSTOMER_DECLINE_RENEWAL_REASON_INCORRECT_DATA_OTHER = 10;
}

note:

We use the IDL to define the structure of our protos
Fields are uniquely identified with a numeric tag.
When deleting fields, their tag must be marked as reserved to ensure its never used again
Enums must always have a 0 variant "UNSPECIFIED" to be used as the default value
The engineer must follow a set of good practices to ensure backward/forward compatibility, not everything can be enforced by the compiler

Defining messages

syntax = "proto3";

package decline_renewal.response.v1;

message DeclineRenewalResponse {
  string policy_id = 1;
}

Defining a service

syntax = "proto3";

package service.v1;

import "es_policy_grpc/messages/amend_termination/request/v1/request.proto";
import "es_policy_grpc/messages/amend_termination/response/v1/response.proto";
// Skipping other imports for the sake of the slide

service PolicyManagementService {
  rpc AmendTermination(amend_termination.request.v1.AmendTerminationRequest)
    returns (amend_termination.response.v1.AmendTerminationResponse);

  rpc TerminatePolicy(terminate_policy.request.v1.TerminatePolicyRequest)
    returns (terminate_policy.response.v1.TerminatePolicyResponse);

  rpc WithdrawPolicy(withdraw_policy.request.v1.WithdrawPolicyRequest)
    returns (withdraw_policy.response.v1.WithdrawPolicyResponse);

  rpc DeclineRenewal(decline_renewal.request.v1.DeclineRenewalRequest)
    returns (decline_renewal.response.v1.DeclineRenewalResponse);
}

note:

Importing other definitions is allowed
"proto3" is the recommended edition to use
Packages have to define a namespace
Service definition is supported by the language as we see above
The 4 types of RPC are supported, above we only see Unary RPCs

The protoc compiler

Compiles .proto files into code. Supports plugins for different languages.

protoc --proto_path=src --python_out=build/gen src/foo.proto

note:

--proto_path specifies the source directory, --*_out the destination directory, and the rest is the path to your .proto

Buf CLI

A linter for proto files
A formatter for proto files
A system to organize your proto files by workspaces
A feature to check for breaking changes in your definitions
A plugin system to compile proto files into multiple formats
Editor integration
And more!

https://buf.build/product/cli

note:

Builds on top of protoc
Provides a very easy to use plugin and build system

gRPC in the Rust ecosystem

❤️

Tower

Library of modular and reusable components for building robust networking clients and servers

note:

It provides a set of basic reusable services such as timeouts and rate limiting.

Tower service

pub trait Service<Request> {
    type Response;
    type Error;
    type Future: Future<Output = Result<Self::Response, Self::Error>>;

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>>;
  
    fn call(&mut self, req: Request) -> Self::Future;
}

note:

Tower’s fundamental abstraction.
An asynchronous function from a Request to a Response.
It immediately returns a Future representing the eventual completion of processing the request.
It is a simplified interface making it easy to write network applications in a modular and reusable way, decoupled from the underlying protocol.

Layers

pub trait Layer<S> {
    type Service;
    
    fn layer(&self, inner: S) -> Self::Service;
}

note:

A mechanism to layer services.
It is used to wrap services building this way a "layer" pattern

Building a layered service

ServiceBuilder::new()
    .layer(TimeoutLayer::new(Duration::from_secs(10)))
    .layer(OpenTelemetryTracingLayer::new())
    .layer(JwtAuthLayer::new(jwks_client, "starsky"))
    .service(PolicyManagementServerStub::new(service));

note:

An example of the Tower builder pattern to build layered services
Slightly simplified for the sake of the presentation.

Building a layered service

Tonic

A gRPC over HTTP/2 rust implementation focused on high performance, interoperability, and flexibility

https://github.com/hyperium/tonic

note:

Build on top of Tower
It has first class support for async/await.

Features

Health check of services
Interceptors
Reflection
Stub generation from protos
RPC cancellation via timeouts
Request/Response compression
Extensible via Tower services
...

note:

We will focus on code generation, service implementation and client-server implementation
Later we will see examples of implementing middleware using Tower Layers

Let's build a library with generated Rust code

Generating code from Proto definitions ⚙️

// build.rs
let mut prost_build = prost_build::Config::new();
prost_build.protoc_arg("--experimental_allow_proto3_optional");
prost_build.compile_protos(
    &[
        "proto/es_policy_grpc/messages/terminate_policy/request/v1/request.proto",
        "proto/es_policy_grpc/messages/terminate_policy/response/v1/response.proto",
        "proto/es_policy_grpc/messages/withdraw_policy/request/v1/request.proto",
        "proto/es_policy_grpc/messages/withdraw_policy/response/v1/response.proto",
        "proto/es_policy_grpc/messages/decline_renewal/request/v1/request.proto",
        "proto/es_policy_grpc/messages/decline_renewal/response/v1/response.proto",
        "proto/es_policy_grpc/messages/amend_termination/request/v1/request.proto",
        "proto/es_policy_grpc/messages/amend_termination/response/v1/response.proto",
    ],
    &["proto"],
)?;

tonic_build::configure()
    .protoc_arg("--experimental_allow_proto3_optional")
    .compile_protos(
        &["proto/es_policy_grpc/service/v1/service.proto"],
        &["proto"],
    )
    .unwrap();

note:

prost_build generates types from the message definitions
tonic_build generates the Client & Server stubs

Generated types

// Generated Request
pub struct DeclineRenewalRequest {
    pub policy_id: String,
    pub requested_at: Option<Timestamp>,
    pub description: Option<String>,
    pub reason: Option<Reason>,
}

pub enum Reason {
    Customer(i32),
}

// Generated Response
pub struct DeclineRenewalResponse {
    pub policy_id: String,
}

#[repr(i32)]
pub enum CustomerDeclineRenewalReason {
    Unspecified = 0,
    CompetitorOffer = 1,
    VehicleSold = 2,
    VehicleNotPurchased = 3,
    VehicleDeregistration = 4,
    NoInsuranceWanted = 5,
    DoesNotKnow = 6,
    WantsGreenCard = 7,
    IncorrectEffectiveDate = 8,
    IncorrectPersonalData = 9,
    IncorrectDataOther = 10,
    PaymentMethodOrDate = 11,
    DeceasedPolicyHolder = 12,
    CoverageChange = 13,
    DissatisfactionService = 14,
    UnderwritingRules = 15,
    MovingToAnotherCountry = 16,
    ProductService = 17,
    PolicyHolderChange = 18,
    PriceIncrease = 19,
    Other = 20,
}

note:

Most fields are generated as Option due to the backward/forward compatibility nature of Protobuf

Generated types

pub trait PolicyManagementService {
    async fn decline_renewal(
        &self,
        request: Request<DeclineRenewalRequest>,
    ) -> Result<Response<DeclineRenewalResponse>, Status>
	// ...
}

Exposing the generated code as a library

// lib.rs

pub mod messages {
    pub mod decline_renewal {
        pub mod request {
            pub mod v1 {
                include!(concat!(env!("OUT_DIR"), "/es_policy_grpc.messages.decline_renewal.request.v1.rs"));
            }
        }

        pub mod response {
            pub mod v1 {
                include!(concat!(env!("OUT_DIR"), "/es_policy_grpc.messages.decline_renewal.response.v1.rs"));
            }
        }
    }
    // ..
}

pub mod policy_service {
    pub mod v1 {
        include!(concat!(env!("OUT_DIR"), "/es_policy_grpc.service.v1.rs"));
    }
}

note:

We must expose the generated code through our lib.rs when building a library

Let's build a gRPC application

Filling the gaps

use es_policy_grpc::policy_service::v1::PolicyManagementService;
use es_policy_grpc::messages::decline_renewal::request::v1::DeclineRenewalyRequest;
use es_policy_grpc::messages::decline_renewal::response::v1::DeclineRenewalResponse;
use tonic::{Request, Response, Status};

pub struct PolicyManagementServiceImpl {
    application: Arc<dyn ApplicationServices>,
}

impl PolicyManagementService for PolicyManagementServiceImpl {
    async fn decline_renewal(
        &self,
        request: Request<DeclineRenewalRequest>,
    ) -> Result<Response<DeclineRenewalResponse>, Status> {
        let request = request.into_inner();

        let policy_id = Uuid::parse_str(&request.policy_id).unwrap();

        let policy = self.application.find_policy(policy_id).await.unwrap();

        let details: TerminateDetails = request.try_to_domain(policy.expiration_date()).unwrap()

        self.application.cancel_policy(policy_id.into(), details).await;

        Ok(Response::new(DeclineRenewalResponse {
            policy_id: policy_id.to_string(),
        }))
    }
    // ..
}

Building the server

use tonic::Server as GrpcServer;
use es_policy_grpc::policy_service::v1::PolicyManagementServiceServer as PolicyManagementServerStub;

let server = 
	// gRPC server provided by Tonic
	GrpcServer::builder() 
		.add_service(
			// Generated Policy Management Server Stub
			PolicyManagementServerStub::new(
				// Implementation of the service
				PolicyManagementServiceImpl::new(application)
			)
    ).add_service(
        QuotingServerStub::new(
            QuoteServiceImpl::new(application)
        )
    );

let listener = TcpListener::bind(("0.0.0.0", grpc_port)).await?;

server.serve(listener).await?;

note:

Simple build of a Tonic Server.

The GrpcServer acts as a Router.
The GrpcServer doesn't know how to unpack-pack messages, that is handled by each specific server stub.
The GrpcServer will be listening to a TCP port like an HTTP2 server.

Building the client

use es_policy_grpc::policy_service::v1::PolicyManagementServiceClient as PolicyManagementClientStub;
use tonic::{metadata::MetadataValue, Request};
use es_policy_grpc::messages::decline_renewal::request::v1::{
    DeclineRenewalRequest,
    DeclineRenewalReason,
    CustomerDeclineRenewalReason
};

// Auto-generated client stub
let mut client = PolicyManagementClientStub::connect("http://localhost:50051").await?;

let mut request = Request::new(DeclineRenewalRequest {
    policy_id: uuid::Uuid::new_v4(),
    requested_at: DateTime::now(),
    description: Some("dummy".into()),
    reason: DeclineRenewalReason::Customer(
        CustomerDeclineRenewalReason::VehicleSold
    )
});

let token: MetadataValue<_> = "Bearer some-auth-token".parse()?;

request.metadata_mut.insert(http::AUTHORIZATION, token);

let _response = client.generate_contract(request).await?;

note:

We use the Metadata feature to set authorization headers to the request
The ClientStub exposes the same API we defined in our protobuf service definition
It handles all the packing-unpacking as well as the network

Building middleware with Tower

So, how can we take advantage of Tower in gRPC?

Authorization middleware

Auth0 M2M authorization

Authorization service

// Tower Service used as a JWT Auth middleware.
pub struct JwtAuth<T: JwtDecoder, S> {
    jwt_decoder: Arc<T>,
    audience: String,
    inner: S,
}

note:

This service acts as a middleware intercepting incoming requests before it gets to the inner service S.
The audience represents the Auth0 audience, which is our API identifier.
The jwt_decoder is able to verify tokens.

Authorization service

impl<T: JwtDecoder, S> JwtAuth<T, S> {
    async fn authorize<Req, Res>(&self, req: http::Request<Req>) -> Result<http::Request<Req>, http::Response<Res>>
    where
        Res: Default,
    {
        let token = req.headers()
            .get(http::AUTHORIZATION)
            .ok_or_else(make_unauthorized_response)?
            .strip_prefix("Bearer ")
            .ok_or_else(make_unauthorized_response)?

        if let Err(_err) = self.jwt_decoder.decode::<serde_json::Value>(token, &self.audience).await {
            return Err(make_unauthorized_response());
        }

        Ok(req)
    }
}

note:

Code is simplified for the sake of the slide.
let's assume that make_unauthorized_response will build an unauthorized response.

Authorization service

use std::task::{Context, Poll};
use http::{Request, Response};

impl<Req, Res, S, T> Service<Request<Req>> for JwtAuth<T, S>
where
    S: Service<Request<Req>, Response = Response<Res>>,
    T: JwtDecoder,
    // .. Skipping other constraints
{
    type Response = S::Response;
    type Error = S::Error;
    type Future = BoxFuture<'static, Result<Self::Response, Self::Error>>;

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.inner.poll_ready(cx)
    }

    fn call(&mut self, req: Request<Req>) -> Self::Future {
        let mut this = self.clone();

        async move {
            match this.authorize(req).await {
                Ok(req) => this.inner.call(req).await,
                Err(res) => Ok(res),
            }
        }
        .boxed()
    }
}

note:

async move is used inside call because we need to return a Future

Authorization layer

// Reusable Tower Layer meant to wrap
// a JWT Auth middleware Service around a generic service
pub struct JwtAuthLayer<T: JwtDecoder> {
    jwt_decoder: Arc<T>,
    audience: String,
}

impl<T: JwtDecoder> JwtAuthLayer<T> {
    pub fn new(jwt_decoder: T, audience: impl Into<String>) -> Self {
        Self {
            jwt_decoder: Arc::new(jwt_decoder),
            audience: audience.into(),
        }
    }
}

Authorization layer

impl<T, S> Layer<S> for JwtAuthLayer<T>
where
    T: JwtDecoder,
{
    type Service = JwtAuth<T, S>;

    fn layer(&self, inner: S) -> Self::Service {
        JwtAuth {
            jwt_decoder: self.jwt_decoder.clone(),
            audience: self.audience.clone(),
            inner,
        }
    }
}

note:

The purpose of the layer is to take advantage of the Tower modularity features that the Layer trait offers

Attaching it to our gRPC server

use es_policy_grpc::policy_service::v1::PolicyManagementServiceServer as PolicyManagementServerStub;
use tonic::Server as GrpcServer;
use tower::ServiceBuilder;

// ...

let authenticated_apis = ServiceBuilder::new()
    .layer(JwtAuthLayer::new(jwks_client, AUDIENCE))
    .service(PolicyManagementServerStub::new(
        PolicyManagementServiceImpl::new(application),
    ));

let server = GrpcServer::builder().add_service(authenticated_apis);

note:

Simplified version of our real server implementation in es-be

Tracing middleware

Building a span from a request

fn make_span<B>(request: &http::Request<B>) -> tracing::Span {
    // We'll assume server_info() works
    let ServerInfo { host, port, .. } = server_info(request);

    let mut headers = request.headers();

    let name = request.uri().path().trim_start_matches('/');

    let (service, method) = name
        .split_once('/')
        .expect("gRPC paths should be formatted as $service/$method");

    tracing::info_span!(
        "gRPC request",
        otel.name = %name,
        rpc.grpc.request.metadata = ?headers,
        rpc.method = method,
        rpc.service = service,
        rpc.system = "grpc",
        server.address = %host,
        server.port = port,
        span.kind = "server",
        // set by the response span
        otel.status_code = tracing::field::Empty,
        rpc.grpc.response.metadata = tracing::field::Empty,
        rpc.grpc.status_code = tracing::field::Empty,
    )
}

note:

Slightly simplified version of the real implementation

Updating the span with the response

fn on_response<B>(response: &http::Response<B>, span: &tracing::Span) {
    let mut headers = response.headers().clone();
    redact_sensitive_headers(&mut headers);

    let code = tonic::Status::from_header_map(&headers)
        .map(|status| status.code())
        .unwrap_or(tonic::Code::Ok);

    span.record("rpc.grpc.status_code", code as i32);
    span.record("grpc.response.header", format!("{:?}", headers));

    if matches!(
        code,
        tonic::Code::Unknown
            | tonic::Code::DeadlineExceeded
            | tonic::Code::Unimplemented
            | tonic::Code::Internal
            | tonic::Code::Unavailable
            | tonic::Code::DataLoss
    ) {
        span.record("otel.status_code", "ERROR");
    }
}

note:

We attach the response metadata to the current span

Tracing service

// Tower Service acting as a Tracing middleware
// for gRPC requests and responses
pub struct OpenTelemetryTracer<S> {
    inner: S,
}

note:

This service will act as tracing middleware

Tracing service

use std::task::{Context, Poll};
use http::{Request, Response};
use opentelemetry_http::HeaderExtractor;
use opentelemetry_sdk::propagation::TraceContextPropagator;

impl<Req, Res, S> Service<Request<Req>> for OpenTelemetryTracer<S>
where
    S: Service<Request<Req>, Response = Response<Res>>,
    S::Future: Send + 'static,
{
    type Response = S::Response;
    type Error = S::Error;
    type Future = BoxFuture<'static, Result<Self::Response, Self::Error>>;

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.inner.poll_ready(cx)
    }

    fn call(&mut self, req: Request<Req>) -> Self::Future {
        let parent_context = TraceContextPropagator::new().extract(&HeaderExtractor(req.headers()));

        let span = make_span(&req);
        span.set_parent(parent_context);

        self.inner.call(req).instrument(span.clone()).inspect_ok(move |response| {
            on_response(response, &span);
        })
        .boxed()
    }
}

note:

The code is simplified for the slides purpose.
The same span is used to track the request and response.
That span is used as the parent span for the inner service call.

Tracing layer

pub struct OpenTelemetryTracingLayer {}

impl OpenTelemetryTracingLayer {
    pub fn new() -> Self {
        Self {}
    }
}

note:

We need the layer if we want to take advantage of the Tower's builder pattern
This layer doesn't need any data to be passed to the OpenTelemetry service

Tracing layer

impl<S> Layer<S> for OpenTelemetryTracingLayer {
    type Service = OpenTelemetryTracer<S>;

    fn layer(&self, inner: S) -> Self::Service {
        OpenTelemetryServerTracing { inner }
    }
}

Attaching it to our gRPC server

use tonic::Server as GrpcServer;

GrpcServer::builder()
    .layer(OpenTelemetryTracingLayer::new())
    // layer other services to benefit from tracing
    .serve(addr)
    .await?;

Extras

Did we get here? 👀

Health checking gRPC services

Tonic provides a health check service implementing a standard gRPC health checking protocol.

https://github.com/grpc/grpc/blob/master/doc/health-checking.md

note:

A GRPC service is used as the health checking mechanism.
Doing a health check is in the same format as a normal rpc.
Per-service health monitoring
The server has full control over the access of the health checking service.

Health service definition

syntax = "proto3";

package grpc.health.v1;

message HealthCheckRequest {
  string service = 1;
}

message HealthCheckResponse {
  enum ServingStatus {
    UNKNOWN = 0;
    SERVING = 1;
    NOT_SERVING = 2;
    SERVICE_UNKNOWN = 3; // Used only by the Watch method.
  }
  ServingStatus status = 1;
}

service Health {
  rpc Check(HealthCheckRequest) returns (HealthCheckResponse);
  rpc Watch(HealthCheckRequest) returns (stream HealthCheckResponse);
}

https://github.com/grpc/grpc/blob/master/doc/health-checking.md

note:

Official service definition from the gRPC documentation
Some languages might implement it and others might not

Enabling the health service

use es_policy_grpc::policy_service::v1::PolicyManagementServiceServer as PolicyManagementServerStub;
use tonic_health::server::health_reporter;
use tonic::Server as GrpcServer;

let (health_reporter, health_service) = health_reporter();

health_reporter
    .set_serving::<PolicyManagementServerStub<PolicyManagementServiceImpl>>()
    .await;

GrpcServer::builder()
	// Add other layers
	.layer(..)
	.add_service(health_service)
	.serve(addr)
	.await?;

note:

tonic-health has to be imported as a separate crate

Interceptors

Interceptors are similar to middleware but with less flexibility.

They allow you to:

Add/remove/check items in the metadata of each request.
Cancel a request with a Status.

Interceptors in practice

use es_policy_grpc::policy_service::v1::PolicyManagementServiceServer as PolicyManagementServerStub;
use tonic::{metadata::MetadataValue, Request, Response, Status};

fn check_auth(req: Request<()>) -> Result<Request<()>, Status> {
    match req.metadata().get(http::AUTHORIZATION) {
        Some(t) if is_valid(t) => Ok(req),
        _ => Err(Status::unauthenticated("No valid auth token")),
    }
}

let svc = PolicyManagementServerStub::with_interceptor(
	PolicyManagementServiceImpl::new(application),
	check_auth
);

Thank you for your time

❤️

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Learning gRPC

First, what is RPC?

Why a framework?

Built on top of HTTP2

4 types of RPC supported

Metadata

And many more features

Protocol buffers

They are a combination of

Remarkable features of Protocol buffers

Defining messages

Defining messages

Defining a service

The protoc compiler

Buf CLI

gRPC in the Rust ecosystem

Tower

Tower service

Layers

Building a layered service

Building a layered service

Tonic

Features

Let's build a library with generated Rust code

Generating code from Proto definitions ⚙️

Generated types

Generated types

Exposing the generated code as a library

Let's build a gRPC application

Filling the gaps

Building the server

Building the client

Building middleware with Tower

Authorization middleware

Authorization service

Authorization service

Authorization service

Authorization layer

Authorization layer

Attaching it to our gRPC server

Tracing middleware

Building a span from a request

Updating the span with the response

Tracing service

Tracing service

Tracing layer

Tracing layer

Attaching it to our gRPC server

Extras

Health checking gRPC services

Health service definition

Enabling the health service

Interceptors

Interceptors in practice

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