+ 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.
+
+ 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 server
+ 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.
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