GenHTTP Lambda

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 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 workspaces and databases of the lambdas - lives in a named volume mounted at /data. The lambdas answer at subdomains of LAMBDA_HOSTING_URL, one each (see Where the lambdas answer).

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, /lambda and /features to the server)

cd src/Frontend && npm install && npm run dev

Work against http://localhost:5173/ while developing. The lambdas answer at subdomains of localhost named after their keys - http://quiz.localhost:8080/ - which browsers resolve without a record. 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

English is the source of every page; the other languages are translated by script and agent, so that only what changed is read and written:

cd src/Frontend

npm run translations -- extract # a request per language in .translations/

one translator agent per request (.claude/agents/translator.md, on Sonnet)

npm run translations -- apply # the answers into the catalogs, checked npm run translations -- check # every language against English

CLAUDE.md ("How a change is translated") has the rules.

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/, described by /api/v1/openapi.json (or .yaml). The description is the reference for whoever calls the API: it opens with an introduction (getting started, keys, files, limits, errors), groups the operations by what they are about, and says of each what it does, what it leaves alone and every way it is refused. It is written with GenHTTP's documentation attributes beside the code (see ApiDocumentation), and ApiDocumentationTests keeps it complete.

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. A refusal is answered with a status and { status, error, message }, where error is Invalid (400), Forbidden (403), NotFound (404), Conflict (409) or TooMany (429).

| GET /sources/:publicKey/versions/:version | the files of a version as its project has them, packed on the first reque