gRPC & ASP.NET Core 3.1: What’s gRPC ? (introduction)

What’s gRPC?

gRPC is an RPC (Remote procedure call) framework and not a Microsoft framework. It runs on HTTP/2 and it uses Protocol Buffers serialization format. gRPC provides bi-directional data transport and allows flow control (cancellation and waiting times). gRPC has been created by Google around 2003/2004 and they open sourced it in 2015. Many languages had implemented it except .NET, Finally Microsoft released a .NET version with ASP.NET Core 3.0 in September 2019.

In gRPC, a client application can directly call a method on a server application on a different machine as if it were a local object, making it easier for you to create distributed applications and services.

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What are Protocol Buffers?

Protocol Buffer is a data structuring language and contract descriptor (services and entities), like WSDL for WCF. Current version of Protocol Buffer is proto 3, (proto 2 is obsolete) and files are named “.proto”.

A Protocol Buffer looks like this:

Protocol Buffer support many types (with their related type in C#)

TypeC# Type


What type of services does gRPC provide ?

gRPC provide four service types:

  • Unary services: A client sends a single request to the server and gets a single response back
  • Server streaming services: A client sends a request to the server and gets a stream to read a sequence of messages back
  • Client streaming services: A client writes a sequence of messages and sends them to the server, again using a provided stream. Once the client has finished writing the messages, it waits for the server to read them and return its response
  • Bidirectionnal streaming services: Both sides send a sequence of messages using a read-write stream. The two streams operate independently, so clients and servers can read and write in whatever order they like


How does gRPC work ?

gRPC breaks REST API “codes”, there is no longer debates on how to write an Url, what verb to use what HttpStatus to manage. gRPC works like this:

  • Uses always POST verb
  • Return always (when the request is handled by gRPC) HTTP 200 OK
  • Uses Content-Type “application/grpc”
  • Uses classical Headers (like any HTTP Request)
  • Uses Trailers (custom metadata)
  • Return a grpc-status
  • Data are transported in binary,then it’s hsard to debug

To learn more about gRPC over HTTP/2 you can go here:

gRPC is also not compatible with a browser, there are some workarounds, we’ll see that further is this serie of articles.

Implementation in .NET Core

There are a lot of packages, gRPC team has develop packages in C# to be able to consume gRPC services in C#, Microsoft reused them to make a .NET Core / ASP.NET Core version. The role of each packages is described on the picture below:



This article was only a quick introduction to gRPC and its concept. The Because the topic is huge I provided you many links to learn more about it. gRPC has also its strenghs and weaknesses, to learn more about it you read this article:, Anyway in this serie of articles we’ll see what we can do with, what we can’t do with.

In the next article we’ll see how to create a gRPC service in ASP.NET Core 3.1

Written by


Anthony is a specialist in Web technologies (14 years of experience), in particular Microsoft .NET and learns the Cloud Azure platform. He has received twice the Microsoft MVP award and he is also certified Microsoft MCSD and Azure Fundamentals.
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