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CONTRIBUTING.md

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Contributing

So excited to have you here! If you want any guidance whatsoever with contributing to tRPC, don't hesitate to reach out on Discord!

Development workflow

We use pnpm as our package manager, so make sure to install it first.

git clone git@github.com:trpc/trpc.git
cd trpc
pnpm install
pnpm build

Get it running

Terminal 1:

# in project root directory
pnpm dev

This will start a watcher in parallel which builds all packages/* on any file change.

Terminal 2:

In another terminal, you can for instance navigate to examples/next-prisma-starter and run pnpm dev & it will update whenever code is changed in the packages.

Testing

Open one terminal and run:

pnpm dev

In a second terminal, you can run the tests in watch mode using

pnpm test-watch

# example if you want to test a specific test file:
pnpm test-watch react

# run only a regression test while fixing a bug
pnpm test-watch 3085

Testing is currently coalesced in ./packages/tests; we import the different libs from here, this makes it easier for us to do integration testing + getting test coverage on the whole codebase.

Linting

pnpm lint-fix

Troubleshooting

If you get any cryptic errors you can usually get past them by doing pnpm clean && pnpm install; if this doesn't work, feel free to open an issue.

Documentation

cd www/ && pnpm dev

Project overview

This project is a monorepo of packages with well-defined purposes. All of the following are packages are located in the packages/* directory.

@trpc/server

This package contains the core and server-side functionality. If something is shared between the client and server, it should be here.

Building a Router

This is where tRPC has the most interaction with users, so it should be treated with a great deal of importance. We care about offering a simple, intuitive API in which the HTTP layer disappears for the user. Here the user's entrypoint is initTRPC where root configuration such as a data transformer is set and factory functions for router, procedure, middleware, etc. creation are returned.

The most complex types are also in this area because we must keep track of the context, meta, middleware, and each procedure and its inputs and outputs. If you are ever struggling to understand a type, feel free to ask for help on Discord.

Handling a Request and Forming a Response

The core implementation for HTTP handling is contained in resolveHTTPResponse where requests are handled and an object representing a response is created. This function deals with handling different methods (query and mutation have different specs), batching, streaming, etc. so it is an excellent place to get an overview of the complete process of handling a request and forming a response. If you want to learn more about the specification that we implement, read this docs page.

Adapting Requests and Responses

Adapters are what connect our framework-agnostic HTTP handling into a server response. We offer official adapters for some popular frameworks, although adapters can also be third-party. Adapters "adapt" their framework's request object into a common format and the object response from resolveHTTPResponse into their framework-specific responses. This keeps tRPC framework-agnostic, an important principle that allows it to be used in any environment.

@trpc/client

This is where we use the router types to build a typesafe vanilla client that makes requests to a tRPC API. Client packages (@trpc/client, @trpc/react-query) infer types from the server using the Router generic. In this package, users pass it to createTRPCClient.

Proxy API

In our client packages, we use proxies to offer the most intuitive API for users. They simply type the path of the procedure that they created in their Router and it is called as transparently as a regular function, enabling TypeScript features like jump to definition and easy refactors.

Links

The client is extensible via a "link" architecture. Links handle the parts of a request's lifecycle and hook into them using our observable implementation. By default, we make fetch requests using httpBatchLink, but we offer other useful official links, such as one for WebSockets, and links can also be third-party.

@trpc/react-query

Here we build on top of React Query, using @trpc/client to create fetchers. Working similarly to @trpc/client, we wrap all React Query functions to make them typesafe, inferring them from the Router generic that users pass to createReactQueryHooks. Additionally, it includes some functionality needed for SSR.

We also use proxies here to provide a similar API to @trpc/client.

React Query vs. tRPC Domain

Sometimes it can be confusing to determine if an issue or feature is React Query or tRPC's responsibility. React Query is the library that tRPC builds on top of to gain features like query caching in a way that is familiar to many users. tRPC can be thought of as nothing more than a light wrapper over it, only changing it by adding types for the user's tRPC API and automatically providing a key and fetcher. However this does get more complicated if you factor in SSR.

@trpc/next

This is where SSR magic for Next.js happens. If SSR is enabled in the config, all @trpc/react-query queries are fetched on the server using a prepass render of the component tree. We wrap getInitialProps to hook into the response process and perform a prepass render of the app. This package is subject to change in the future as Next.js improves their page and routing system.