180 UTL_URL

Using UTL_URL

• Overview

• Exceptions

• Examples

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Overview

A Uniform Resource Locator (URL) is a string that identifies a Web resource, such as a page or a picture. Use a URL to access such resources by way of the HyperText Transfer Protocol (HTTP). For example, the URL for Oracle's Web site is:

http://www.oracle.com

Normally, a URL contains English alphabetic characters, digits, and punctuation symbols. These characters are known as the unreserved characters. Any other characters in URLs, including multibyte characters or binary octet codes, must be escaped to be accurately processed by Web browsers or Web servers. Some punctuation characters, such as dollar sign ($), question mark (?), colon (:), and equals sign (=), are reserved as delimiters in a URL. They are known as the reserved characters. To literally process these characters, instead of treating them as delimiters, they must be escaped.

The unreserved characters are:

• A through Z, a through z, and 0 through 9

• Hyphen (-), underscore (_), period (.), exclamation point (!), tilde (~), asterisk (*), accent ('), left parenthesis ( ( ), right parenthesis ( ) )

The reserved characters are:

• Semi-colon (;) slash (/), question mark (?), colon (:), at sign (@), ampersand (&), equals sign (=), plus sign (+), dollar sign ($), and comma (,)

The UTL_URL package has two functions that provide escape and unescape mechanisms for URL characters. Use the escape function to escape a URL before the URL is used fetch a Web page by way of the UTL_HTTP package. Use the unescape function to unescape an escaped URL before information is extracted from the URL.

For more information, refer to the Request For Comments (RFC) document RFC2396. Note that this URL escape and unescape mechanism is different from the x-www-form-urlencoded encoding mechanism described in the HTML specification:

http://www.w3.org/TR/html

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Exceptions

Table 180-1 lists the exceptions that can be raised when the UTL_URL package API is invoked.

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Examples

You can implement the x-www-form-urlencoded encoding using the UTL_URL.ESCAPE function as follows:

CREATE OR REPLACE FUNCTION form_url_encode (
   data    IN VARCHAR2,
   charset IN VARCHAR2) RETURN VARCHAR2 AS 
BEGIN 
  RETURN utl_url.escape(data, TRUE, charset); -- note use of TRUE
END; 

For decoding data encoded with the form-URL-encode scheme, the following function implements the decording scheme:

CREATE OR REPLACE FUNCTION form_url_decode(
   data    IN VARCHAR2, 
   charset IN VARCHAR2) RETURN VARCHAR2 AS
BEGIN 
  RETURN utl_url.unescape(
     replace(data, '+', ' '), 
     charset); 
END; 

Summary of UTL_URL Subprograms

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ESCAPE Function

This function returns a URL with illegal characters (and optionally reserved characters) escaped using the %2-digit-hex-code format.

Syntax

UTL_URL.ESCAPE (
   url                   IN VARCHAR2 CHARACTER SET ANY_CS,
   escape_reserved_chars IN BOOLEAN  DEFAULT  FALSE,
   url_charset           IN VARCHAR2 DEFAULT  utl_http.body_charset)
 RETURN VARCHAR2;

Parameters

Usage Notes

Use this function to escape URLs that contain illegal characters as defined in the URL specification RFC 2396. The legal characters in URLs are:

• A through Z, a through z, and 0 through 9

• Hyphen (-), underscore (_), period (.), exclamation point (!), tilde (~), asterisk (*), accent ('), left parenthesis ( ( ), right parenthesis ( ) )

The reserved characters consist of:

• Semi-colon (;) slash (/), question mark (?), colon (:), at sign (@), ampersand (&), equals sign (=), plus sign (+), dollar sign ($), and comma (,)

Many of the reserved characters are used as delimiters in the URL. You should escape characters beyond those listed here by using escape_url. Also, to use the reserved characters in the name-value pairs of the query string of a URL, those characters must be escaped separately. An escape_url cannot recognize the need to escape those characters because once inside a URL, those characters become indistinguishable from the actual delimiters. For example, to pass a name-value pair $logon=scott/tiger into the query string of a URL, escape the $ and / separately as %24logon=scott%2Ftiger and use it in the URL.

Normally, you will escape the entire URL, which contains the reserved characters (delimiters) that should not be escaped. For example:

utl_url.escape('http://www.acme.com/a url with space.html')

Returns:

http://foo.com/a%20url%20with%20space.html

In other situations, you may want to send a query string with a value that contains reserved characters. In that case, escape only the value fully (with escape_reserved_chars set to TRUE) and then concatenate it with the rest of the URL. For example:

url := 'http://www.acme.com/search?check=' || utl_url.escape
('Is the use of the "$" sign okay?', TRUE);

This expression escapes the question mark (?), dollar sign ($), and space characters in 'Is the use of the "$" sign okay?' but not the ? after search in the URL that denotes the use of a query string.

The Web server that you intend to fetch Web pages from may use a character set that is different from that of your database. In that case, specify the url_charset as the Web server character set so that the characters that need to be escaped are escaped in the target character set. For example, a user of an EBCDIC database who wants to access an ASCII Web server should escape the URL using US7ASCII so that a space is escaped as %20 (hex code of a space in ASCII) instead of %40 (hex code of a space in EBCDIC).

This function does not validate a URL for the proper URL format.

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UNESCAPE Function

This function unescapes the escape character sequences to its original form in a URL, to convert the %XX escape character sequences to the original characters.

Syntax

UTL_URL.UNESCAPE (
   url            IN VARCHAR2 CHARACTER SET ANY_CS,
   url_charset    IN VARCHAR2 DEFAULT utl_http.body_charset)
                  RETURN VARCHAR2;

Parameters

Usage Notes

The Web server that you receive the URL from may use a character set that is different from that of your database. In that case, specify the url_charset as the Web server character set so that the characters that need to be unescaped are unescaped in the source character set. For example, a user of an EBCDIC database who receives a URL from an ASCII Web server should unescape the URL using US7ASCII so that %20 is unescaped as a space (0x20 is the hex code of a space in ASCII) instead of a ? (because 0x20 is not a valid character in EBCDIC).

This function does not validate a URL for the proper URL format.