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ASP.NET Core › gRPC Services

Why can't browsers natively call gRPC services directly, and what is gRPC-Web, and how does it solve this?

Intermediate

Answer

Standard gRPC requires full HTTP/2 features (particularly trailers, sent after the response body, used to carry the final status) that browser JavaScript fetch/XHR APIs don't expose access to -- gRPC-Web is a protocol variant designed to work within browser HTTP/1.1 and HTTP/2 constraints (encoding trailers differently, within the body), requiring a compatible client library on the frontend and either native gRPC-Web support on the server or a proxy (like Envoy) translating between gRPC-Web and standard gRPC for the backend service.
// Program.cs -- enabling gRPC-Web support directly in ASP.NET Core
builder.Services.AddGrpc();
var app = builder.Build();
app.UseGrpcWeb();
app.MapGrpcService<GreeterService>().EnableGrpcWeb();
Real-world example A single-page application needs to call a gRPC backend service directly from browser JavaScript, so the team enables ASP.NET Core's built-in gRPC-Web support on the server and uses the grpc-web client library on the frontend, avoiding the need for a separate Envoy proxy.

Common follow-ups: What are the streaming limitations of gRPC-Web compared to full native gRPC?;When would you use a separate Envoy proxy instead of ASP.NET Core's built-in gRPC-Web support?

CORS (Cross-Origin Resource Sharing);Hosting Models: Kestrel IIS & Reverse Proxies
All 15 gRPC Services questions