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CGI class in Ruby

By: Jeeva in Ruby Tutorials on 2009年03月03日 [フレーム]

CGI is a large class, providing several categories of methods, many of which are mixed in from other modules. Some of the documentation is in this class, some in the modules CGI::QueryExtension and CGI::HtmlExtension. CGI::Cookie handles cookies.

For queries, CGI provides methods to get at environmental variables, parameters, cookies, and multipart request data. For responses, CGI provides methods for writing output and generating HTML.

Read on for more details. Examples are provided at the bottom.

Queries

The CGI class dynamically mixes in parameter and cookie-parsing functionality, environmental variable access, and support for parsing multipart requests (including uploaded files) from the CGI::QueryExtension module.

Environmental Variables

The standard CGI environmental variables are available as read-only attributes of a CGI object. The following is a list of these variables:

 AUTH_TYPE HTTP_HOST REMOTE_IDENT
 CONTENT_LENGTH HTTP_NEGOTIATE REMOTE_USER
 CONTENT_TYPE HTTP_PRAGMA REQUEST_METHOD
 GATEWAY_INTERFACE HTTP_REFERER SCRIPT_NAME
 HTTP_ACCEPT HTTP_USER_AGENT SERVER_NAME
 HTTP_ACCEPT_CHARSET PATH_INFO SERVER_PORT
 HTTP_ACCEPT_ENCODING PATH_TRANSLATED SERVER_PROTOCOL
 HTTP_ACCEPT_LANGUAGE QUERY_STRING SERVER_SOFTWARE
 HTTP_CACHE_CONTROL REMOTE_ADDR
 HTTP_FROM REMOTE_HOST

For each of these variables, there is a corresponding attribute with the same name, except all lower case and without a preceding HTTP_. content_length and server_port are integers; the rest are strings.

Parameters

The method params() returns a hash of all parameters in the request as name/value-list pairs, where the value-list is an Array of one or more values. The CGI object itself also behaves as a hash of parameter names to values, but only returns a single value (as a String) for each parameter name.

For instance, suppose the request contains the parameter "favourite_colours" with the multiple values "blue" and "green". The following behaviour would occur:

 cgi.params["favourite_colours"] # => ["blue", "green"]
 cgi["favourite_colours"] # => "blue"

If a parameter does not exist, the former method will return an empty array, the latter an empty string. The simplest way to test for existence of a parameter is by the has_key? method.

Cookies

HTTP Cookies are automatically parsed from the request. They are available from the cookies() accessor, which returns a hash from cookie name to CGI::Cookie object.

Multipart requests

If a request's method is POST and its content type is multipart/form-data, then it may contain uploaded files. These are stored by the QueryExtension module in the parameters of the request. The parameter name is the name attribute of the file input field, as usual. However, the value is not a string, but an IO object, either an IOString for small files, or a Tempfile for larger ones. This object also has the additional singleton methods:

local_path(): the path of the uploaded file on the local filesystem

original_filename(): the name of the file on the client computer

content_type(): the content type of the file

Responses

The CGI class provides methods for sending header and content output to the HTTP client, and mixes in methods for programmatic HTML generation from CGI::HtmlExtension and CGI::TagMaker modules. The precise version of HTML to use for HTML generation is specified at object creation time.

Writing output

The simplest way to send output to the HTTP client is using the out() method. This takes the HTTP headers as a hash parameter, and the body content via a block. The headers can be generated as a string using the header() method. The output stream can be written directly to using the print() method.

Generating HTML

Each HTML element has a corresponding method for generating that element as a String. The name of this method is the same as that of the element, all lowercase. The attributes of the element are passed in as a hash, and the body as a no-argument block that evaluates to a String. The HTML generation module knows which elements are always empty, and silently drops any passed-in body. It also knows which elements require matching closing tags and which don't. However, it does not know what attributes are legal for which elements.

There are also some additional HTML generation methods mixed in from the CGI::HtmlExtension module. These include individual methods for the different types of form inputs, and methods for elements that commonly take particular attributes where the attributes can be directly specified as arguments, rather than via a hash.

Examples of use

Get form values

 require "cgi"
 cgi = CGI.new
 value = cgi['field_name'] # <== value string for 'field_name'
 # if not 'field_name' included, then return "".
 fields = cgi.keys # <== array of field names
 # returns true if form has 'field_name'
 cgi.has_key?('field_name')
 cgi.has_key?('field_name')
 cgi.include?('field_name')

CAUTION! cgi['field_name"] returned an Array with the old cgi.rb(included in ruby 1.6)

Get form values as hash

 require "cgi"
 cgi = CGI.new
 params = cgi.params

cgi.params is a hash.

 cgi.params['new_field_name'] = ["value"] # add new param
 cgi.params['field_name'] = ["new_value"] # change value
 cgi.params.delete('field_name') # delete param
 cgi.params.clear # delete all params

Save form values to file

 require "pstore"
 db = PStore.new("query.db")
 db.transaction do
 db["params"] = cgi.params
 end

Restore form values from file

 require "pstore"
 db = PStore.new("query.db")
 db.transaction do
 cgi.params = db["params"]
 end

Get multipart form values

 require "cgi"
 cgi = CGI.new
 value = cgi['field_name'] # <== value string for 'field_name'
 value.read # <== body of value
 value.local_path # <== path to local file of value
 value.original_filename # <== original filename of value
 value.content_type # <== content_type of value

and value has StringIO or Tempfile class methods.

Get cookie values

 require "cgi"
 cgi = CGI.new
 values = cgi.cookies['name'] # <== array of 'name'
 # if not 'name' included, then return [].
 names = cgi.cookies.keys # <== array of cookie names

and cgi.cookies is a hash.

Get cookie objects

 require "cgi"
 cgi = CGI.new
 for name, cookie in cgi.cookies
 cookie.expires = Time.now + 30
 end
 cgi.out("cookie" => cgi.cookies) {"string"}
 cgi.cookies # { "name1" => cookie1, "name2" => cookie2, ... }
 require "cgi"
 cgi = CGI.new
 cgi.cookies['name'].expires = Time.now + 30
 cgi.out("cookie" => cgi.cookies['name']) {"string"}

Print http header and html string to $DEFAULT_OUTPUT ($>)

 require "cgi"
 cgi = CGI.new("html3") # add HTML generation methods
 cgi.out() do
 cgi.html() do
 cgi.head{ cgi.title{"TITLE"} } +
 cgi.body() do
 cgi.form() do
 cgi.textarea("get_text") +
 cgi.br +
 cgi.submit
 end +
 cgi.pre() do
 CGI::escapeHTML(
 "params: " + cgi.params.inspect + "\n" +
 "cookies: " + cgi.cookies.inspect + "\n" +
 ENV.collect() do |key, value|
 key + " --> " + value + "\n"
 end.join("")
 )
 end
 end
 end
 end
 # add HTML generation methods
 CGI.new("html3") # html3.2
 CGI.new("html4") # html4.01 (Strict)
 CGI.new("html4Tr") # html4.01 Transitional
 CGI.new("html4Fr") # html4.01 Frameset

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