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.\" Copyright (c) 2001-2002 Packet Design, LLC.
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.\" Author: Archie Cobbs <archie@freebsd.org>
.\"
.\" $Id: http_servlet.3,v 1.1.1.1 2012/02/21 23:25:53 misho Exp $
.\"
.Dd April 22, 2002
.Dt HTTP_SERVLET 3
.Os
.Sh NAME
.Nm http_servlet
.Nd HTTP response generation API
.Sh LIBRARY
PDEL Library (libpdel, \-lpdel)
.Sh SYNOPSIS
.In sys/types.h
.In stdio.h
.In netinet/in.h
.In openssl/ssl.h
.In pdel/http/http_defs.h
.In pdel/http/http_server.h
.In pdel/http/http_servlet.h
.Sh DESCRIPTION
The
.Nm http_servlet
API provides an interface for user code to generate HTTP responses
for the
.Xr http_server 3
HTTP server.
.Pp
The PDEL library comes with these predefined servlets:
.Pp
.Bl -dash -compact -offset 3n
.It
HTTP basic authentication:
.Xr http_servlet_basicauth 3
.It
HTTP secure cookie authentication:
.Xr http_servlet_cookieauth 3
.It
HTTP redirect servlet:
.Xr http_servlet_redirect 3
.It
File servlet:
.Xr http_servlet_file 3
.It
.Xr tmpl 3
template servlet:
.Xr http_servlet_tmpl 3
.It
XML servlet:
.Xr http_servlet_xml 3
.It
XML-RPC servlet:
.Xr http_servlet_xmlrpc 3
.El
.Pp
Servlets are registered by first constructing the servlet object
and then invoking
.Fn http_server_register_servlet .
A servlet is represented by a
.Li "struct http_servlet" :
.Pp
.Bd -literal -offset 3n
typedef int  http_servlet_run_t(struct http_servlet *servlet,
               struct http_request *req, struct http_response *resp);
typedef void http_servlet_destroy_t(struct http_servlet *servlet);

struct http_servlet {
    void                     *arg;         /* servlet cookie */
    struct http_servlet_hook *hook;        /* server info */
    http_servlet_run_t       *run;         /* execute method */
    http_servlet_destroy_t   *destroy;     /* destructor */
};
.Ed
.Pp
The
.Va arg
fields is private to the servlet itself and is ignored by the server.
.Pp
The
.Va hook
is an
.Xr http_server 3
private pointer that should be initialized to
.Dv NULL
when the servlet is constructed.
This pointer is set to a non-
.Dv NULL
value when the servlet is registered with a server.
The servlet itself should not dereference or modify this field.
.Pp
.Fn run
executes the servlet for a single request/response pair.
Each response is handled by the server in a separate thread,
and several request/response pairs may exist at the same time for
the same servlet object; i.e., servlets are multi-threaded.
Synchronization is the responsibility of the servlet.
The thread executing the servlet may be canceled at any
cancellation point, e.g., if the requesting user-agent closes the connection
before the response has been sent.
This means that the servlet code may need to register thread cleanup hooks
to avoid leaking memory or other resources.
.Pp
.Fn destroy
will be called when the servlet is being
unregistered and destroyed (servlets can be registered only once;
unregistering a servlet destroys it).
It should free any resources allocated when the servlet was constructed.
The
.Xr http_server 3
code guarantees that when
.Fn destroy
is invoked, there will be no instances of the
.Fn run
method currently executing.
.Sh RETURN VALUES
If successful,
.Fn run
should return 1 to indicate that the response is complete, or 0 to
indicate that the servlet did not generate a response and execution
should continue with the next-best matching servlet.
Zero return values are used by servlets that only generate a response
conditionally, e.g., authorization servlets.
.Pp
On failure
.Fn run
should -1 and set
.Va errno .
In this case (typically due to a system error), if a response has not
yet been sent, a generic "500 Internal Server Error" response will be
automatically generated with the error string from
.Xr strerror 3 .
.Sh SEE ALSO
.Xr http_client 3 ,
.Xr http_request 3 ,
.Xr http_response 3 ,
.Xr http_server 3 ,
.Xr http_servlet_basicauth 3 ,
.Xr http_servlet_cookieauth 3 ,
.Xr http_servlet_file 3 ,
.Xr http_servlet_redirect 3 ,
.Xr http_servlet_tmpl 3 ,
.Xr http_servlet_xml 3 ,
.Xr http_servlet_xmlrpc 3 ,
.Xr libpdel 3
.Rs
.%A R. Fielding
.%A J. Gettys
.%A J. Mogul
.%A H. Frystyk
.%A L. Masinter
.%A P. Leach
.%A T. Berners-Lee
.%T "Hypertext Transfer Protocol -- HTTP/1.1"
.%O RFC 2616
.Re
.Sh HISTORY
The PDEL library was developed at Packet Design, LLC.
.Dv "http://www.packetdesign.com/"
.Sh AUTHORS
.An Archie Cobbs Aq archie@freebsd.org