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ashd -- A Sane HTTP Daemon Ashd is a HTTP server that follows standard Unix philosophy for modularity. Instead of being a monolithic program with loadable modules, as most other HTTP servers seem to be, Ashd is simply a collection of much simpler programs, passing HTTP requests to each other using a simple protocol. Among the nice properties brought about by such a design, the following might be said to stand out: * Sanity of design -- The clean delineation of functions allows each program to be very small and simple – currently, each of the programs in the collection (including even the core HTTP parser program, htparser, as long as one does not count its, quite optional, SSL implementation) is implemented in less than 1,000 lines of C code (and most are considerably smaller than that), allowing them to be easily studied and understood. * Security -- Since each program runs in a process of its own, it can be assigned proper permissions. Most noteworthy of all, the userplex program ensures that serving of user home directories only happens by code that is actually logged in as the user in question; and the htparser program, being the only program which speaks directly with the clients, can run perfectly well as a non-user (like nobody) and be chroot'ed into an empty directory. * Persistence -- Though Ashd is a multi-process program, it is not in the same sense as e.g. Apache. Each request handler continues to run indefinitely and does not spawn multiple copies of itself, meaning that all process state persists between requests – session data can be kept in memory, connections to back-end services can be kept open, and so on. * Clean modularity -- With only a rather basic understanding of HTTP and the internal Ashd protocol, it is quite easy to write new request handlers to extend the server's functionality; and one can do that even without needing root privileges on the system. Getting Started To get Ashd installed and running quickly, please follow the instructions in the `INSTALL' file. Architecture Overview Though the server as a whole is called `Ashd', there is no actual program by that name. The `htparser' program of Ashd implements a minimal HTTP server. It speaks HTTP (1.0 and 1.1) with clients, but it does not know anything about actually handling the requests it receives. Rather, having started a handler program as specified on the command-line, it packages the requests up and passes them to that handler program. That handler program may choose to only look at part of the URL and pass the request on to other handler programs based on what it sees. In that way, the handler programs form a tree-like structure, corresponding roughly to the URL space of the server. In order to do that, the packaged request which is passed between the handler programs contains the part of the URL which remains to be parsed, referred to as the `rest string' or the `point' (in deference to Emacs parlance). For a technical description of the architecture, see the ashd(7) manpage, available in the `doc' directory of this source tree. The Cast As an introduction to the various programs that compose Ashd, here is a listing of the more important programs. All of them have manpages, so please see those for further details. * htparser -- The `actual' HTTP server. htparser is the program that listens to TCP connections and speaks HTTP with the clients. * dirplex -- dirplex is the program used for serving files from actual directories, in a manner akin to how most other HTTP servers work. In order to do that, dirplex maps URLs into existing physical files, and then performs various kinds of pattern-matching against the names of those physical files to determine the handler to call to actually serve them. * patplex -- Performs pattern matching against logical request parameters such as the rest string, URL or various headers to determine a program to pass the request to. As such, patplex can be used to implement such things as virtual directories or virtual hosts. * sendfile -- A simple handler program for sending literal file contents, normally called by dirplex for serving ordinary files. It handles caching using the Last-Modified and related headers. It also handles MIME-type detection if a specific MIME-type was not specified. * callcgi -- Translates an Ashd request into a CGI environment, and runs either the requested file directly as a CGI script, or an external CGI handler. Thus, it can be used to serve, for example, PHP pages. * userplex -- Handles `user directories', to use Apache parlance; you may know them otherwise as /~user/ URLs. When a request is made for the directory of a specific user, it makes sure that the request handler runs as the user in question.