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kali

Simple, reliable, single-threaded HTTP service in Python. Aimed at serving web application to localhost as alternative to desktop application development.

Quick Start!

There are tutorial demonstrations in the examples folder at the Git repository. Mainly, you should read that source code (start with the intro) because it will show you how this all fits together. You can run the demos from the Windows command line by, for example, demo intro. (If you're on Linux/Mac/Unix, then feel free to contribute a suitable shell script.)

Why This, Then?

I wanted to expose a SINGLE-THREADED WEB APPLICATION over HTTP to LOCALHOST ONLY. Web application, because it's a comfortable style of working with data entry and navigation. Single threaded, to support working well with SQLite, which doesn't play well with multi-threading, and Windows, which is not particularly suited to a forking-model server.

Web browsers lately all expect to open multiple connections and might not send the first request on the first connection. The Python Standard Library offers class "HttpServer", but as currently coded, it only works properly when you're using a forking or threading mix-in. In sequential-service mode, the standard library deadlocks (at least until the end user refreshes the browser a few times).

The essential problem is solved by setting a brief time-out on the first packet from the client. If that time-out expires, the connection is closed and the server accepts the next caller, which will generally have the request data from the browser. The server also only speaks HTTP/1.0 on purpose: it guarantees all requests are served in a timely manner. There is zero packet latency on localhost, so there's not a real performance drain here.

Features! Benefits!

So long as I'm re-inventing the wheel, I might as well do it with the end in sight. Therefore:

  1. The server is a higher-order function called serve_http: you pass in a handler function. In fact, any callable-object will do. The handler call must accept a Request object and return a Response object (or just a content body). There are some convenience methods for creating redirections, serving plain text, etc.

  2. This means routing requests to different response methods is a separate problem. A simple solution is provided in the box, called class Router. It reads the path component of the Request URI to decide which of many sub-functions to call, and which bits of the path correspond to parameters, etc. Several ways are provided to register functionality, ranging from absolute flexibility to complete convenience.

  3. The framework takes (some) pains to avoid excessive copying, drawing inspiration from the iolist facility in the Erlang ecosystem. Rather than building up a big string, supply a list of them, or a funny-shaped nest of them, etc. The rules are somewhat loose.

  4. There's a simple HTML templating facility included: it will do the job without being accidentally quadratic (much) by participating in the above-described iolist game. You can have templates inline or saved in separate files: allowance is made for both styles of working. As feature sets go, it covers the most important bits (substitution, HTML escapes, loops, template extension) but leaves the really creative stuff for your Python code to work out.

  5. There's also a forms-handling library supplied. It offers components that make it extra easy to handle the most common kinds of work flows.

  6. It's really annoying forgetting to commit-or-rollback a transaction in a handler. Changes may appear fine locally (until they vanish) but nobody else sees anything except a locked database. Checking for this a simple matter by wrapping the root handler (application router) and taking corrective measures. (Roll back the transaction and return an error response maybe.)