9.2.2.1. The application/x-www-form-urlencoded encoding

The standard encoding -- application/x-www-form-urlencoded -- converts any spaces in the form values to a plus sign (+), nonalphanumeric characters into a percent sign (%) followed by two hexadecimal digits that are the ASCII code of the character, and the line breaks in multiline form data into %0D%0A.

The standard encoding also includes a name for each field in the form. (A "field" is a discrete element in the form, whose value can be nearly anything from a single number to several lines of text -- the user's address, for example.) If there is more than one value in the field, the values are separated by ampersands.

For example, here's what the browser sends to the server after the user fills out a form with two input fields labeled name and address; the former field has just one line of text, while the latter field has several lines of input:

name=O'Reilly+and+Associates&address=101+Morris+Street%0D%0A
Sebastopol,%0D%0ACA+95472

We've broken the value into two lines for clarity in this book, but in reality, the browser sends the data in an unbroken string. The name field is "O'Reilly and Associates" and the value of the address field, complete with embedded newline characters, is:

101 Morris Street
Sebastopol,
CA 95472

9.2.2.2. The multipart/form-data encoding

After the headers, there is a single blank line followed by the actual value of the field on one or more lines. The section concludes with a repeat of the delimiter line that started the transmission. Another section follows immediately, and the pattern repeats until all of the form parameters have been transmitted. The end of the transmission is indicated by an extra two dashes at the end of the last delimiter line.

As we pointed out earlier, use multipart/form-data encoding only when your form contains a file-selection field. Here's an example of how the transmission of a file-selection field might look:

------------------------------146931364513459
Content-Disposition: form-data; name="thefile"; filename="test"
Content-Type: text/plain
  
First line of the file
...
Last line of the file
------------------------------146931364513459--

9.2.2.3. The text/plain encoding

In this encoding, each element in the form is placed on a single line, with the name and value separated by an equal sign. Returning to our name and address example, the form data would be returned as:

name=O'Reilly and Associates
address=101 Morris Street%0D%0ASebastopol,%0D%0ACA 95472

9.2.4.1. POST or GET?

9.2.4.2. Passing parameters explicitly

x=27&y=33

If the form uses method=GET, the URL used to reference the server-side application looks something like this:

http://www.kumquat.com/cgi-bin/update?x=27&y=33

There is nothing to keep you from creating a conventional <a> tag that invokes the form with any parameter value you desire, like so:

<a href="http://www.kumquat.com/cgi-bin/update?x=19&y=104">

The only hitch is that the ampersand that separates the parameters is also the character-entity insertion character. When placed within the href attribute of the <a> tag, the ampersand will cause the browser to replace the characters following it with a corresponding character entity.

To keep this from happening, you must replace the literal ampersand with its entity equivalent, either &#38; or &amp;. With this substitution, our example of the nonform reference to the server-side application looks like this:

<a href="http://www.kumquat.com/cgi-bin/update?x=19&amp;y=104">