.Dd $Mdocdate: December 13 2022 $
.Dt HTTPSERVER 3
.Os Telodendria Project
.Sh NAME
.Nm HttpServer
.Nd Extremely simple HTTP server.
.Sh SYNOPSIS
.In HttpServer.h
.Ft HttpServer *
.Fn HttpServerCreate "unsigned short" "unsigned int" "unsigned int" "HttpHandler *" "void *"
.Ft void
.Fn HttpServerFree "HttpServer *"
.Ft int
.Fn HttpServerStart "HttpServer *"
.Ft void
.Fn HttpServerJoin "HttpServer *"
.Ft void
.Fn HttpServerStop "HttpServer *"
.Ft HashMap *
.Fn HttpRequestHeaders "HttpServerContext *"
.Ft HttpRequestMethod
.Fn HttpRequestMethodGet "HttpServerContext *"
.Ft char *
.Fn HttpRequestPath "HttpServerContext *"
.Ft HashMap *
.Fn HttpRequestParams "HttpServerContext *"
.Ft char *
.Fn HttpResponseHeader "HttpServerContext *" "char *" "char *"
.Ft void
.Fn HttpResponseStatus "HttpServerContext *" HttpStatus"
.Ft FILE *
.Fn HttpStream "HttpServerContext *"
.Ft void
.Fn HttpSendHeaders "HttpServerContext *"
.Sh DESCRIPTION
.Nm
builds on the
.Xr Http 3
API, and provides a very simple, yet very functional API for
creating an HTTP server. It aims at being easy to use and minimal,
yet also efficient. It uses non-blocking I/O, is fully multi-threaded,
very configurable, yet also able to be set up in just two function calls.
.Pp
This API should be familiar to those that have dealt with the HTTP server
libraries of other programming languages, particularly Java. In fact,
much of the terminology used in this code came from Java, and you'll
notice that the way responses are sent and received very closely resemble
the way it's done in Java.
.Pp
An HTTP server itself is created with
.Fn HttpServerCreate ,
which takes the port number to create the server on, the number of threads to
use, the maximum number of connections, a request handler function, and the
arguments to that function, in that order. The request handler function is
of the following type:
.Bd -literal -offset indent
typedef void (HttpHandler) (HttpServerContext *, void *)
.Ed
.Pp
Where the void pointer received is the same pointer that was passed into
.Fn HttpServerCreate
as the last parameter.
.Pp
The returned HttpServer pointer is then managed by
.Fn HttpServerStart ,
.Fn HttpServerStop ,
.Fn HttpServerJoin ,
and
.Fn HttpServerFree .
.Fn HttpServerStart
attempts to start the HTTP server, and returns immediately with the status.
This API is fully threaded and asyncronous, so the caller can continue working
while the HTTP server is running in a separate thread, and managing a pool
of threads to handle responses. Typically at some point after calling
.Fn HttpServerStart ,
the program will have no more work to do, and so it will want to wait for
the HTTP server to finish. This is accomplished with
.Fn HttpServerJoin ,
which joins the HTTP worker thread to the calling thread, making the
calling thread wait until the HTTP server has stopped.
.Pp
The only condition that will cause the HTTP server to stop is when
.Fn HttpServerStop
is invoked. This will typically happen in a signal handler that catches
signals instructing the program to shut down. Only after the server has
been stopped can it be freed with
.Fn HttpServerFree .
Note that calling
.Fn HttpServerFree
while the server is running results in undefined behavior.
.Pp
The remainder of the functions in this API are used inside of the
HTTP handler function passed by the caller of
.Fn HttpServerCreate .
They allow the handler to figure out the context of an HTTP request,
which includes the path that was requested, any parameters, and the
headers used to make the request. They also allow the handler
to respond with a status code, headers, and a body.
.Pp
.Fn HttpRequestHeaders ,
.Fn HttpRequestMethodGet ,
.Fn HttpRequestPath ,
and
.Fn HttpRequestParams
get the information about the request. They should all be passed the
server context pointer that was passed into the handler function.
The data returned by these functions should be treated as read-only,
and should not be freed; their memory is handled outside of the HTTP
server handler function.
.Pp
.Fn HttpResponseHeader
and
.Fn HttpResponseStatus
are used to set response headers, and the response status of the
request, respectively.
.Pp
.Fn HttpStream
returns a stream that is both readable and writable. Reading from
the stream reads the request body that the client sent, if there is
one. Note that the request headers have already been read, so the stream
is correctly positioned at the beginning of the body of the request.
.Fn HttpSendHeaders
must be called before the stream is written to, otherwise a malformed
HTTP response will be sent. An HTTP handler should properly set all
the headers it intends to send, send those headers, and then write the
response  body to the stream. Finally, note that the stream does not
need to be closed by the HTTP handler; in fact, doing so results in
undefined behavior. The stream is managed by the server itself.
.Sh RETURN VALUES
.Pp
.Fn HttpRequestHeaders
and
.Fn HttpRequestParams
return a hash map that can be used to access the request headers and
parameters, if necessary. Note that the request parameters would be
GET parameters, attached to the path that was requested. To get POST
parameters, read the stream returned by
.Fn HttpStream
and pass the contents into
.Fn HttpParamDecode
to get a hash map.
.Pp
.Fn HttpRequestPath
returns a string that represents the path that the client requested. Note
that it is not normalized; it is exactly what the client sent, so it should
be checked for path traversal attacks and other malformed paths that the
client may sent.
.Pp
.Fn HttpResponseHeader
returns the previous value of the given header, or NULL if there was no
previous value.
.Pp
.Fn HttpStream
returns a FILE pointer that can be read and written using the C standard
I/O functions.
.Sh SEE ALSO
.Xr Http 3