GenHTTP Lambda

Write a C# snippet that returns a GenHTTP IHandler, press deploy, and get a public URL that serves it. The snippet is compiled with Roslyn at runtime and the resulting handler is hosted by the same [GenHTTP][genhttp] server that serves this application.

return Inline.Create()
             .Get(() => "Hello from my lambda!");

Quick start

docker compose up --build

The application is then available at http://localhost:8080/. Its data - the SQLite database, the stored code and the lambda workspaces - lives in a named volume mounted at /data.

Developing locally

Two processes: the .NET server, and Vite serving the frontend with hot reload.

# the server, on http://localhost:8080/
dotnet run --project src/GenHTTP.Lambda

# the frontend, on http://localhost:5173/ (proxies /api and /lambda to the server)
cd src/Frontend && npm install && npm run dev

Work against http://localhost:5173/ while developing. The server on its own answers with a placeholder page until a frontend has been built into its web root, which is what npm run build does:

cd src/Frontend && npm run build   # writes src/GenHTTP.Lambda/wwwroot

Build and test everything the way CI does:

dotnet build GenHTTP.Lambda.slnx -c Release
dotnet test GenHTTP.Lambda.slnx -c Release

The tests compile and execute real lambdas against a real server on a random port, each against its own temporary data directory.

Routes

API

Browsable at /api/v1/scalar/. A lambda is addressed by its editor key, which is also what authorizes the call. Things that can be listed, read, created or changed are resources; what is a process rather than a thing is a verb in the path.

Creating a lambda asks what somebody would like to build and offers the demos in those words - "Keep track of things", "Let people sign up" - next to an empty lambda. Picking a demo starts the new lambda as a copy of it, which is theirs to change. The files are in Resources/Templates and listed in TemplateCatalog.

A lambda has two keys. The public one is part of its URL and may be changed; the private one is the editor link and is shown only to whoever created the lambda - anyone holding it can edit, deploy and delete.

A lambda may also return a websocket rather than a document, in any of the three flavours the module offers - Websocket.Functional(), .Reactive() and .Imperative(). The handshake is an ordinary request and is bounded by the execution timeout like any other; everything after it belongs to the connection, which is why a socket may stay open far longer than a lambda is given to answer. FrameType, which the imperative flavour reads off every frame, is one of the names a lambda is given, so no import is needed.

The editor says when both free tier timers run out: a hint under the public URL for the deployment, and a chip beside the buttons for the lambda itself, which opens an explanation of how each one is extended.

Editing and deploying are separate: saving creates a version, deploying picks one (the latest by default) and makes it live. A lambda has at most one deployment at a time, and older versions stay available to deploy again.

Changing a lambda by asking

Where the installation runs the build agent, the editor has a Change section: the owner says what should be different, and the same agent that builds things on /build changes the lambda - it reads the code and the history, changes only what was asked with change_code, fixes what does not compile, and puts the result online as a new version. Switched off, it saves the version for the owner to look at and deploy themselves.

The section shows it happen: what the agent says it is doing, each tool it calls with what came of it (the version saved, errors from the compiler, the version online), and a clock against its time limit. Afterwards it offers the difference to the version before, the address, and putting the previous version back. The change is followed by the frame of the editor rather than the section, so the sidebar marks it and the lambda is read again when it ends wherever the owner is; and it is kept by the agent under the lambda, so a reload, a second tab or a redeploy of the server finds it where it got to.

It shares the queue and the daily allowance of /build, one change of a lambda runs at a time, and it can be stopped - whatever it saved stays a version. A change runs without create_lambda, and its editor key travels in the brief inside the build container, never in a log line.

How it is put together

A single .NET 11 project hosted by GenHTTP.Full.Ioxide, wired up in Application.cs and divided into services that the API resources talk to through interfaces: