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 PATH_INFO or, if that is not present, the SCRIPT_NAME variable, as sent from the web server. That value is appended to the value of the DOCUMENT_ROOT or the 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 specified file is not present or an unhandled failure occurs while processing the request, Lasso will look for a file named error.lasso at the original file’s directory path. If an error.lasso file is not found, 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, 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 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 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 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 Content-Type. Both multipart/form-data and 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 web_request object makes header data available through the following methods. All header names and values are treated as strings.

type web_request
web_request->headers() → trait_forEach

The 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 header method returns the first header pair matching the name parameter, otherwise returns “void” if the header is not found. The 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 “0” or “false” is returned for other non-existent value types.

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.

web_request->param(name::string, joiner=?)

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”. The methods that accept a name parameter return the first matching argument’s string value. If no argument matches, a “void” value is returned.

The params method presents both argument sources as a single queriable 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, the resulting argument values are returned in a staticarray. If a string value is passed, 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 no 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.


Returns the respective arguments in a format similar to how they were received. In the case of 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 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 web_request methods. The web_request object provides methods to directly access the pre-parsed cookie data.

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 a 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 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 the server:

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

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 the 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.


Returns an array in which each element 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:

The name of the “file” input type. (In our example, “photo”)
The MIME content type of the file.
The original name of the uploaded file.
The path to which the file was temporarily uploaded.
The size of the file in bytes.

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

[with file_info in web_request->fileUploads do {^]

The preceding example produces HTML like this:


The following example moves 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 do just that.

To track files, you first need an input named “_lasso_upload_tracker_id” with a unique value in your form. 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, the status of that process can be checked in another thread. This is done by passing the unique ID to the upload_tracker->check method of the 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.


<!DOCTYPE html>
   <title>Upload A Photo</title>
   <script type="text/javascript">
      function trackProgress(id) {
            "/progress.lasso?id=" + id,
   [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]">
         <legend>Upload a Photo</legend>
         <input type="file" name="photo">
         <input type="submit"


[local(info) = upload_tracker->check(web_request->param('id'))]
<!DOCTYPE html>
[if(#info->first > 0 and #info->first != #info->second)]
   <meta http-equiv="refresh" content="1">
[if(#info->first > 0 and #info->second > 0)]
<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))

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 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 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. (See the File System 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 include file content.

type web_response

Locates and runs the file specified by the path. The includeLibrary and includeLibraryOnce member methods run the file but do not insert the result into the response. The includeOnce and includeLibraryOnce member methods will only include the file if it has not already been included during the course of that request.

These will fail if the specified file does not exist.

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.

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. Returns the list of currently executing file names as an object that can be iterated or used in a query expression.


Locates the file and returns 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 web_response bound methods:


Includes the file specified by the path in the same manner as the web_response->include and web_response->includeLibrary methods.

Writing Response Headers

The 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.

web_response->headers() → trait_ForEach

Returns existing outgoing headers. The first method finds the first occurrence of the specified 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.


Permits 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 requires 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 requiers 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 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, SSL secure flag, and HttpOnly 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.

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

Sets the specified cookie. Any duplicate cookie would be replaced. The first parameter must be the cookie name=value pair. If used, the -domain and -path keyword parameters must have string values. Setting -secure causes the cookie to only be sent over HTTPS connections, and -httponly blocks client-side scripts from accessing the cookie.

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 specifies the absolute date at which the cookie will expire. A duration specifies the time that the cookie should expire based on the time at which the cookie is being set. An integer or string specifies the number of minutes until the cookie expires. Any other object type is appended directly to the outgoing cookie header string.

Changed in version 9.3.1: Added -httponly flag.

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 programatically inspecting and setting 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, such as when displaying an error message.


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.


For complex HTTP sessions, this allows for sending the HTTP response body in multiple chunks. Each time it is called, it sends the current contents of the response in 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 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 Content-Type header adjusted accordingly. The method web_response->rawContent can 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 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 web_response object provides the 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.

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 replaces all existing headers with new MIME-Version, Content-Type, Content-Disposition and Content-Length headers.

The first parameter (“data”) can be any object that supports 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 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:

  • -type (string) – Specifies the value for the Content-Type header. If this is not specified and -skipProbe is not set to “false”, 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 application/octet-stream content type.
  • -disposition (string) – Sets the value for the Content-Disposition header, defaulting to “attachment”. The other possible value is “inline”.
  • -charset (string) – If given, this string will be appended to the Content-Type header as a “;charset=” component.
  • -skipProbe (boolean) – Defaults to “false”. If set to “true”, no content type probe will occur.
  • -noAbort (boolean) – Defaults to “false”. This means that sendFile will abort by default after the data is delivered to the client. Set this parameter to “true” in order to prevent the abort.
  • -chunkSize (integer) – 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.
  • -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 byte stream for the current chunk as well as an integer indicating the overall size of the bytes being sent.

If the sendFile method succeeds and does not abort, no value is returned.


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:

web_response->setStatus(code::integer, msg::string)
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 web_request and 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.


Installs code to be invoked at the beginning of each request. The code will have access to the web_request and 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 web_request and web_response within it.


Sets 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.