.. _requests-responses:

**************************
Web Requests and Responses
**************************

Lasso Server receives requests from whichever HTTP server it is connected to.
Each request consists of the headers and body data as sent by the requesting
user agent, as well as data from the HTTP server such as the local web server
root directory and other metadata. The request data is parsed and made available
for the code that is run to handle the request. Handling a request entails
creating the resulting headers and body data for the reply. This data is sent to
the web server, which is then sent to the connected user agent. The request is
complete after the response data is sent.

The code that is chosen to handle a request is based on the path in the
:envvar:`PATH_INFO` or, if that is not present, the :envvar:`SCRIPT_NAME`
variable, as sent from the web server. That value is appended to the value of
the :envvar:`DOCUMENT_ROOT` or the :envvar:`LASSOSERVER_DOCUMENT_ROOT` variable
and the resulting file path is used as the response. That response may be a
script file located on the local file system or it may address a component of a
LassoApp. Either way, the file is compiled if necessary and executed.

If the indicated file is not present or an unhandled failure occurs while
processing the request, then Lasso will look for a file named
:file:`error.lasso` at the original file's directory path. If an
:file:`error.lasso` file is not found, then Lasso will look up one directory
level for the error file, and so on, until the web file root directory is
reached or the error file is found. If no error file is found to handle the
situation, then a standard error message and stack trace is printed.

Finally, Lasso provides a means for running code before or after a request. This
enables interception of the standard request processing flow at either point.
This can be useful when using virtual URLs and serving dynamic, database-driven
content or when rewriting outgoing response data.


Web Requests
============

Lasso Server makes web request data available through a :type:`web_request`
object. An instance of this object is created for each request before processing
begins. The request handling code can obtain its request object instance by
calling the `web_request` method.

The :type:`web_request` object has the following purposes:

-  Making available all variables sent by the web server
-  Including all client header information
-  Making available all data sent by the web client
-  Including tokenized GET arguments
-  Including processed POST body data

A :type:`web_request` object will process the incoming data to make access to
the various components of a web request more convenient. For example, all HTTP
cookies are found and separated made available through the
`web_request->cookies` or `web_request->cookie(name)` methods. Standard HTTP
headers are made available through accessors such as `web_request->requestURI`
or `web_request->httpHost`.

The incoming GET arguments are tokenized and can be retrieved by name or
iterated over in their entirety. The request's POST body is processed depending
on the incoming :mailheader:`Content-Type`. Both :mimetype:`multipart/form-data`
and :mimetype:`application/x-www-form-urlencoded` content types are
automatically handled. This includes the processing of file uploads, the results
of which are made available through the `web_request->fileUploads` method,
described below.


Reading Request Headers
-----------------------

The incoming HTTP request headers are pre-processed by the web server and then
further processed by Lasso. All header names are normalized to uppercase by the
web server and prepended with ``HTTP_`` and all dashes (``-``) replaced with
underscores (``_``). Once received by Lasso, any leading ``HTTP_`` prepended by
the web server to each variable is stripped. All underscores (``_``) are then
converted to dashes (``-``).

The :type:`web_request` object makes header data available through the following
methods. All header names and values are treated as strings.

.. type:: web_request

.. member:: web_request->headers()::trait_forEach
.. member:: web_request->header(name::string)
.. member:: web_request->rawHeader(name::string)

   The `~web_request->headers` method returns all of the headers as an object
   that can be iterated or used in a query expression. Each header element is
   presented as a pair object containing the header name and value as the pair's
   first and second elements, respectively. The `~web_request->header` method
   returns the first header pair, which matches the name parameter. It returns
   "void" if the header is not found. The `~web_request->rawHeader` method works
   the same, but fetches the raw unnormalized header name/value as sent by the
   web server.

The next set of methods is presented in a table matching the method name to its
corresponding raw web request variable name. For headers that return a string
value, an empty string is returned if the header has no value or is not present.
A zero or "false" is returned for other non-existent value types.

.. tabularcolumns:: lll

.. _requests-responses-variable-methods:

.. table:: Web Request Variable Methods

   =================================== ==================== ====================
   Web Request Method                  Web Request Variable Return Type
   =================================== ==================== ====================
   ``web_request->contentLength``      CONTENT_LENGTH       integer
   ``web_request->contentType``        CONTENT_TYPE         string
   ``web_request->gatewayInterface``   GATEWAY_INTERFACE    string
   ``web_request->httpAccept``         HTTP_ACCEPT          string
   ``web_request->httpAcceptEncoding`` HTTP_ACCEPT_ENCODING string
   ``web_request->httpAcceptLanguage`` HTTP_ACCEPT_LANGUAGE string
   ``web_request->httpCacheControl``   HTTP_CACHE_CONTROL   string
   ``web_request->httpConnection``     HTTP_CONNECTION      string
   ``web_request->httpCookie``         HTTP_COOKIE          string
   ``web_request->httpHost``           HTTP_HOST            string
   ``web_request->httpReferer``        HTTP_REFERER         string
   ``web_request->httpReferrer``       HTTP_REFERER         string
   ``web_request->httpUserAgent``      HTTP_USER_AGENT      string
   ``web_request->isHttps``            HTTPS                boolean
   ``web_request->path``               PATH                 string
   ``web_request->pathInfo``           SCRIPT_NAME          string
   ``web_request->pathTranslated``     PATH_TRANSLATED      string
   ``web_request->remoteAddr``         REMOTE_ADDR          string
   ``web_request->remotePort``         REMOTE_PORT          integer
   ``web_request->requestMethod``      REQUEST_METHOD       string
   ``web_request->requestURI``         REQUEST_URI          string
   ``web_request->scriptFilename``     SCRIPT_FILENAME      string
   ``web_request->scriptName``         SCRIPT_NAME          string
   ``web_request->scriptURI``          SCRIPT_URI           string
   ``web_request->scriptURL``          SCRIPT_URL           string
   ``web_request->serverAddr``         SERVER_ADDR          string
   ``web_request->serverAdmin``        SERVER_ADMIN         string
   ``web_request->serverName``         SERVER_NAME          string
   ``web_request->serverPort``         SERVER_PORT          integer
   ``web_request->serverProtocol``     SERVER_PROTOCOL      string
   ``web_request->serverSignature``    SERVER_SIGNATURE     string
   ``web_request->serverSoftware``     SERVER_SOFTWARE      string
   =================================== ==================== ====================


Reading GET and POST Arguments
------------------------------

Lasso automatically tokenizes GET arguments and processes the POST body into a
series of name/value pairs according to the sent content type. These two sets of
pairs can be retrieved separately or treated as a single series of elements.
File uploads are not included in the POST arguments, but are made available
through the `web_request->fileUploads` method.

The value for any GET or POST argument is always a bytes object. The name is
always a string.

.. member: web_request->param(name::string)
.. member:: web_request->param(name::string, joiner= ?)
.. member:: web_request->params()
.. member:: web_request->queryParam(name::string)
.. member:: web_request->queryParams()
.. member:: web_request->postParam(name::string)
.. member:: web_request->postParams()

   This set of methods refers to the GET arguments as the "query" params and any
   POST arguments as the "post" params. Both sets together are just the
   "params". For the methods that accept a name parameter, they return the first
   matching argument's string value. If no argument matches, then a "void" value
   is returned.

   The `~web_request->params` method presents both argument sources as a single
   queriable :type:`tie` object with the POST arguments occurring first. The
   `param(name::string, joiner)` method presents an interface for accessing
   arguments that occur more than once. The ``joiner`` parameter is used to
   determine the result of the method. If "void" is passed, then the resulting
   argument values are returned in a staticarray. If a string value is passed,
   then the argument values are joined with that string in between each value.
   The result of passing any other object type will depend on the behavior of
   its ``+`` operator.

   The methods that accept zero parameters return all of the GET, POST, or both
   argument pairs as an object which may be iterated over or used in a query
   expression.

.. member:: web_request->queryString()
.. member:: web_request->postString()

   These methods return the respective arguments in a format similar to how they
   were received. In the case of `~web_request->queryString` the GET arguments
   are returned verbatim. The POST string is created by concatenating each POST
   argument together with "&" in between each name/value, each of which are
   separated by "=". This will vary from the exact given POST only in the case of
   :mimetype:`multipart/form-data` input.


Reading Cookies
---------------

Cookie values are sent as HTTP header fields. As such, they can be read and
parsed from the various header-related :type:`web_request` methods. The
:type:`web_request` object provides methods to directly access the pre-parsed
cookie data.

.. member:: web_request->cookie(named::string)
.. member:: web_request->cookies()::trait_forEach

   The first method searches for the named cookie and returns its value if
   found. If the cookie is not found then "void" is returned. The second method
   returns all the cookies as an object, which can be iterated over or used in a
   query expression. The cookie elements are presented as pair objects
   containing the cookie names and values as the pairs' first and second
   members.


Uploading Files
---------------

Lasso can process and manage files uploaded to your web server by visitors to
your website. To allow visitors to upload files to your web server, use an HTML
``<form>`` tag along with an ``<input>`` tag for each file being uploaded. The
form tag must have an "enctype" attribute of :mimetype:`multipart/form-data`,
and the "input" tags for file uploads need to have a "type" attribute of "file".
The following HTML code could be used to upload a single file to your server::

   <form action="upload_file.lasso" method="post" enctype="multipart/form-data">
      <fieldset>
         <legend>Upload a Photo</legend>
         <input type="file" name="photo">
         <input type="submit" name="submit" value="Upload">
      </fieldset>
   </form>

The "file" input tells the browser to show controls for selecting a file to be
uploaded to the web server. Once a user selects the file and then clicks
"Upload", the form will upload the data to your web server and the files can be
processed by "upload_file.lasso", the Lasso file specified as the action of the
form submission.

Uploaded files processed by Lasso are initially stored in a temporary location.
If you do nothing with them, they will be deleted. If you wish to keep them, you
should move them to a different directory. To inspect and process these uploaded
files use the `web_request->fileUploads` method.

.. member:: web_request->fileUploads()

   This method returns an array, each element of which holds information about
   an uploaded file. The size of this array will be equal to the number of files
   uploaded. Each element of the array is a staticarray of pairs that houses the
   following information about the files:

   fieldname
      The name of the "file" input type. (In our example, "photo")
   contenttype
      The MIME content type of the file.
   filename
      The original name of the uploaded file.
   tmpfilename
      The path to which the file was temporarily uploaded.
   filesize
      The size of the file in bytes.

The following example code will loop through all uploaded files and display this
information::

   <dl>
   [with file_info in web_request->fileUploads do {^]
      <dt>[#file_info->find('filename')->first->second]</dt>
      <dd>
         <ul>
            <li>[#file_info->find('tmpfilename')->first->second]</li>
            <li>[#file_info->find('contenttype')->first->second]</li>
            <li>[#file_info->find('filesize')->first->second]</li>
            <li>[#file_info->find('fieldname')->first->second]</li>
         </ul>
      </dd>
   [^}]
   </dl>

The preceding example produces HTML like this::

   <dl>
      <dt>MyAvatar.jpg</dt>
      <dd>
         <ul>
            <li>//tmp/lassoqM9SFY37921967.uld</li>
            <li>image/jpeg</li>
            <li>851191</li>
            <li>photo</li>
         </ul>
      </dd>
   </dl>

The following example will move uploaded files out of their temporary location
and into the "/assets/img/avatars/" directory in the web root, overwriting any
existing files with the same name::

   local(path) = '/assets/img/avatars/'
   with upload in web_request->fileUploads
   do file(#upload->find('tmpfilename')->first->second)
         ->moveTo(#path + #upload->find('filename')->first->second, true)


Monitoring Uploads
^^^^^^^^^^^^^^^^^^

If you expect the uploads to take a lot of time, either due to uploading many
files or a few large ones, you may want to provide feedback to your visitors
that the browser and server are working on the uploads. Lasso comes with a
method that will allow you to do just that.

To track files, you first need an input named "_lasso_upload_tracker_id"
with a unique value in your form. You can use `lasso_uniqueid` to generate a
UUID which is essentially guaranteed to be unique each time you call it. With
that in place, while the thread that processes the form submission is working on
uploading the files, you can check the status of that process in another thread.
This is done by passing the unique ID to the `upload_tracker->check` method of
the :thread:`upload_tracker` thread object. That method returns a staticarray
whose first element is the amount of data uploaded, the second is the total size
of all the files being uploaded, and the third is the name of the current file
being uploaded.

The following basic example has a form set up properly in "index.lasso". When
the submit button is pressed it opens another window to display "progress.lasso"
before submitting the form. This page calls `upload_tracker->check` with the
unique ID that gets passed to it. It also uses ``<meta http-equiv="refresh"
content="1">`` to refresh itself every second. The result is that we get a
progress bar that is updated every second.

.. rubric:: index.lasso

::

   <!DOCTYPE html>
   <html>
   <head>
      <title>Upload A Photo</title>
      <script type="text/javascript">
         function trackProgress(id) {
            window.open(
               "/progress.lasso?id=" + id,
               null,
               "height=100,width=400,location=no,menubar=no,resizable=yes,scrollbars=yes,title=yes"
            );
         }
      </script>
   </head>
   <body>
      [local(id) = lasso_uniqueid]
      <form action="upload_file.lasso" method="post" enctype="multipart/form-data">
         <input type="hidden"
            name="_lasso_upload_tracker_id" value="[#id]">
         <fieldset>
            <legend>Upload a Photo</legend>
            <input type="file" name="photo">
            <input type="submit"
               value="Upload"
               onclick="trackProgress('[#id->encodeUrl]')">
         </fieldset>
      </form>
   </body>
   </html>

.. rubric:: progress.lasso

::

   [local(info) = upload_tracker->check(web_request->param('id'))]
   <!DOCTYPE html>
   <html>
   <head>
   [if(#info->first > 0 and #info->first != #info->second)]
      <meta http-equiv="refresh" content="1">
   [/if]
   </head>
   <body>
   [if(#info->first > 0 and #info->second > 0)]
   [#info->last]
   <div style="background-color: white;border: 1px solid black;width:380px;height: 20px;">
      <div style="background-color: black;height: 20px;width: [
         380 * (decimal(#info->first) / decimal(#info->second))
      ]px;"></div>
   </div>
   [/if]
   </body>
   </html>


Web Responses
=============

Sending a response to a web request is a simple as having "The Words" in the
targeted "\*.lasso" text file. Files requested through a web request are assumed
to begin as plain text. Lasso code can be inserted into the file between any of
the following delimiters: ``[ ... ]``, ``<?lasso ... ?>``, or ``<?= ... ?>``.

Because supporting the ``[ ... ]`` delimiters can be problematic for embedding
with other technologies (i.e., JavaScript and CSS), they can be disabled for the
remainder of the file by having the literal ``[no_square_brackets]`` as the
first line.

Any code between the delimiters will have the results of the expressions within
its body converted to string objects and included in the response output string.
Code between auto-collecting captures is included as well. For example, values
produced by code between ``inline(...) ... /inline`` or
``inline(...) => {^ ... ^}`` would be included in the output. Such code is free
to call any methods or types to formulate the response data.

The request is completed when the initial code has run to the end, when the
`abort` method is called, or when an unhandled failure occurs. Outgoing data is
buffered for as long as possible, but can be forced out at any point using the
`web_response->sendChunk` method. Calling `abort` (either `web_response->abort`
or the unbound method; both have the same behavior) will complete the request by
halting all processing and sending the existing response data as-is.

The :type:`web_response` object automatically routes requests for LassoApps.
Request paths that begin with "/lasso9/" are reserved for LassoApp usage and
will be routed there. Lasso Server ignores physical file paths beginning with
"/lasso9/" during the processing of a web request.


Including Files
---------------

It is often useful to split up large template files into smaller reusable
components. For example, a header or footer could be split out and reused on all
pages. The :type:`web_response` object provides a variety of methods for
including other source code files. Files included in this way behave just as a
file accessed directly would. That is, they begin executing as plain text and
any Lasso code must be included between delimiters.

The path to an include file can be full or relative. Complete paths from the
file system root are accepted as well. Consult the :ref:`files` chapter for more
details on how file paths are treated in Lasso. Components of LassoApps can be
included as well by beginning the path with "/lasso9/", then the app name and
then the path to the component.

Any of the following methods can be used to include file content.

.. type:: web_response

.. member:: web_response->include(path::string)
.. member:: web_response->includeOnce(path::string)
.. member:: web_response->includeLibrary(path::string)
.. member:: web_response->includeLibraryOnce(path::string)

   These methods locate and run the file indicated by the path. The
   `~web_response->includeLibrary` and `~web_response->includeLibraryOnce`
   member methods run the file but do not insert the result into the response.
   The `~web_response->includeOnce` and `~web_response->includeLibraryOnce`
   member methods will only include the file if it has not already been included
   during the course of that request.

   These methods will fail if the indicated file does not exist.

.. member:: web_response->includeBytes(path::string)::bytes

   Locates the file and includes the raw file data as bytes. The method will
   fail if the file does not exist.

.. member:: web_response->includes()::trait_forEach

   Lasso keeps track of web files that are being executed. As execution of a
   file begins, the file's name is pushed onto an internally kept stack. As a
   file's execution ends, that name is popped from the stack. This method
   provides access to that stack. This method returns the list of currently
   executing file names as an object that can be iterated or used in a query
   expression.

.. member:: web_response->getInclude(path::string)

   Locates the file and will return an object that can be invoked to execute the
   file. The method will fail if the file does not exist.

For compatibility and simplicity, Lasso supports the following unbound methods
which function in the same manner as the :type:`web_response` bound methods:

.. method:: include(path::string)
.. method:: library(path::string)

   These methods include the file indicated by the path in the same manner as
   the `web_response->include` and `web_response->includeLibrary` methods.


Writing Response Headers
------------------------

The :type:`web_response` object provides methods for setting the outgoing
response's HTTP headers. When a request is begun, a few default HTTP headers are
established. The request handler code can add, modify, or remove these headers
as needed. Headers can be set or removed freely during a request; however, once
any data has been sent then headers can no longer be effectively manipulated.

Note that the HTTP status code and message are not HTTP headers and so are not
manipulated through these methods.

.. member:: web_response->header(name::path)
.. member:: web_response->headers()::trait_ForEach

   These methods return existing outgoing headers. The first method finds the
   first occurrence of the indicated header and returns its value. The second
   method returns all the current headers as an object that can be iterated over
   or used in a query expression. Each element is a pair object containing the
   header name/value in the pair's first/second.

.. member:: web_response->setHeaders(headers::trait_forEach)
.. member:: web_response->replaceHeader(header::pair)
.. member:: web_response->addHeader(header::pair)

   These methods permit headers to be set or replaced. The first method sets all
   the headers for the response. These headers should be given as a series of
   pairs containing the header names/values. The second method accepts a header
   name/value pair and replaces matching header with the new value. If the
   existing header isn't found, the new header is simply added. The third method
   accepts a new header name/value pair and adds it to the list of outgoing
   headers. This method does not check for duplicate headers.


Setting Cookies
---------------

Outgoing cookies are added to the response HTTP headers by the
:type:`web_response` object. It provides a method for setting a cookie and a
method for enumerating all cookies being set.

Setting a cookie requires specifying a name and a value and optionally a domain,
expiration, path, and SSL secure flag. These values are supplied as parameters
when setting a cookie. Cookie headers are not created until the request
processing is completed and the response is to be sent to the client.

.. member:: web_response->setCookie(nv::pair, \
      -domain= ?, \
      -expires= ?, \
      -path= ?, \
      -secure= false)

   Sets the indicated cookie. Any duplicate cookie would be replaced. The first
   parameter must be the cookie :samp:`{name}={value}` pair. If used, the
   ``-domain`` and ``-path`` keyword parameters must have string values.

   The ``-expires`` parameter can be either a date object, a duration object, an
   integer, a string, or any object that will produce a suitable value when
   converted into a string. A date indicates the absolute date at which the
   cookie will expire. A duration indicates the time that the cookie should
   expire based on the time at which the cookie is being set. An integer
   indicates the number of minutes until the cookie expires. Any other object
   type is appended directly to the outgoing cookie header string.

.. member:: web_response->cookies()::trait_forEach

   Returns a list of all the cookies set for this response. The individual
   cookies are represented by map objects containing keys for 'name', 'value',
   'domain', 'expiration', 'path' and 'secure'. Manipulating a cookie value in
   the list will alter its resulting cookie header.


Setting the Response Body
-------------------------

Lasso allows you to programatically inspect and set the contents of the response
body. This can be useful for code that needs to clear any data that has been
already added to the response body and insert something completely different
(e.g. display an error message).

.. member:: web_response->rawContent
.. member:: web_response->rawContent=(text)

   The first method returns the current contents of the response body. Note that
   any plain text or auto-collected data in the currently executing code file
   will not be part of the body until the code file finishes processing. The
   second method allows for setting the contents of the response body to the
   value specified by the ``text`` parameter.

.. member:: web_response->sendChunk()

   This method is used in complex HTTP sessions, and allows for sending the HTTP
   response body in multiple chunks. Each time it is called, it sends the
   current contents of the response in `~web_response->rawContent` and then
   clears it for building the next chunk. If the headers for the response have
   not yet been sent, it will first send them before sending the first chunk.


Sending Response Data
---------------------

By default, the result of a request will have a :mimetype:`text/html` content
type with a UTF-8 character set and the body data will be generated from a Lasso
string object that always consists of Unicode character data. In order to output
binary data, the bytes need to be set directly and the response's
:mailheader:`Content-Type` header adjusted accordingly. The method
`web_response->rawContent` can be used to get or set the outgoing content data.

It is advised to call `web_response->abort` soon after setting binary response
data or at least to ensure that no stray character data is inadvertently added
into the outgoing data buffer as it will corrupt the output.

When manually setting the raw content, the :mailheader:`Content-Type` header
should usually be adjusted to accommodate the change. Use the
`web_response->replaceHeader` method to replace the existing header with the
new value.

The :type:`web_response` object provides the `~web_response->sendFile` method
which packages together many of the steps required to send binary data to the
client to be viewed either inline or downloaded as an attachment.

.. member:: web_response->sendFile(data::trait_each_sub, name= null, \
      -type= null, \
      -disposition= 'attachment', \
      -charset= '', \
      -skipProbe= false, \
      -noAbort= false, \
      -chunkSize= fcgi_bodyChunkSize, \
      -monitor= null)

   Sets the raw content and headers for the response. It then optionally aborts,
   ending the request and delivering the data to the client. This method
   replaces all existing headers with new :mailheader:`MIME-Version`,
   :mailheader:`Content-Type`, :mailheader:`Content-Disposition` and
   :mailheader:`Content-Length` headers.

   The first parameter ("data") can be any object that supports
   :trait:`trait_each_sub`. This includes objects such as string, bytes, and
   file. The second parameter ("name") is optional, but if given it will trigger
   the addition of a "filename=" element to the
   :mailheader:`Content-Disposition` header. This controls the file name that
   the user agent will use to save a downloaded file.

   The subsequent keyword parameters control the following:

   :param string -type:
      Indicates the value for the :mailheader:`Content-Type` header. If this is
      not specified and ``-skipProbe`` is not set to "false", then the incoming
      data will be lightly probed to determine what type of data it is. The
      following data types are automatically recognized: GIF, PDF, PNG, JPEG.
      Unrecognized data types are set to have the
      :mimetype:`application/octet-stream` content type.
   :param string -disposition:
      Indicates the value for the :mailheader:`Content-Disposition` header. This
      value defaults to "attachment". The other possible value is "inline".
   :param string -charset:
      If given, this string will be appended to the :mailheader:`Content-Type`
      header as a "|semi| charset=" component.
   :param boolean -skipProbe:
      Defaults to "false". If set to "true", no content type probe will occur.
   :param boolean -noAbort:
      Defaults to "false". This means that `~web_response->sendFile` will abort
      by default after the data is delivered to the client. Set this parameter
      to "true" in order to prevent the abort.
   :param integer -chunkSize:
      Sets the size of the buffer with which the data is read and sent to the
      client. This mainly has a benefit when sending physical file data as it
      controls the memory usage. This value defaults to "65535", the result of
      the `fcgi_bodyChunkSize` method.
   :param -monitor:
      An object can be given to monitor the send process. Whatever object is
      given here will have its invoke method called for each chunk sent. The
      invoke will be passed the bytes object for the current chunk as well as an
      integer indicating the overall size of the bytes being sent.

   If the `~web_response->sendFile` method succeeds and does not abort, no value
   is returned.

.. |semi| unicode:: 0x3B
   :trim:

.. method:: web_response->abort()

   Stops Lasso from sending any further data. Same as calling `abort`.


HTTP Response Status
--------------------

The HTTP response status line consists of a numeric code and a short textual
message. When a request is first started it is given a "200 OK" status line. If
a file is requested that does not exist, Lasso will respond with a "404 Not
Found" status. An unhandled failure will generate a "500 Unhandled Failure"
status.

The status can be set or reset multiple times. Its value is not used until the
request data is sent to the client. However, once any data has been sent then
the status can no longer effectively be set.

The following methods get or set the HTTP response status:

.. member:: web_response->setStatus(code::integer, msg::string)
.. member:: web_response->getStatus()::pair

   The first method sets the HTTP status code and message. The second returns
   the status as a pair containing the code/message as the pair's first/second.


At Begin and End
================

Lasso permits arbitrary code to be run immediately before and immediately after
a request with full access to the :type:`web_request` and :type:`web_response`
objects. Code run before a request can manipulate the request data that will be
used by the request handler code. Code run after a request can manipulate the
outgoing headers and content body, doing tasks such as rewriting HTML links or
compressing data for efficiency.

Code to be run after a request completes is added during the request itself
through the `web_response->addAtEnd` method. Since code to be run before a
request must be added outside of any request, the `define_atBegin` method is
used. These methods are described below.

.. method:: define_atBegin(code)

   Installs code to be invoked at the beginning of each request. The code will
   have access to the :type:`web_request` and :type:`web_response` objects that
   will be available during the request's duration. At-begin code can set
   response headers and data and complete the request if it chooses, thus fully
   intercepting the normal request URI file request and processing routines.
   This is the recommended route for applications wanting to provide virtual
   URLs. Once an at-begin is in place it cannot be removed. Multiple at-begins
   are supported and are run in the order in which they are installed. (The
   easiest way to install an at-begin is to place it in the instance's
   "LassoStartup" directory.)

   The object installed as the at-begin code is copied to each request's thread
   each time. This means that a capture's local variables or any object's data
   members are deeply copied each time. The most efficient steps would be to
   define a method as the at-begin handler and then pass a reference to that
   method as the at-begin code. For example, passing ``\foo`` to
   `define_atBegin` would pass the ``foo`` method to `define_atBegin`. It would
   be invoked for each request and use the :type:`web_request` and
   :type:`web_response` within it.

.. method:: define_atEnd(code)
.. member:: web_response->addAtEnd(code)

   These methods set the parameter to be run at the request's end. (The
   `define_atEnd` method just calls `web_response->addAtEnd`.) At-end code is
   normally run before data is sent to the client, but this may not be the case
   if data has been manually pushed using the `web_response->sendChunk` method.
   At-begins are executed before the session link rewriter is run. Multiple
   at-ends are supported and each are run in the order in which they were
   installed.

   At-ends are added on a per-request basis, as opposed to at-begins which are
   added globally. At-end code is not copied in any way. A capture passed to
   this method will be detached.