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URL encoding, officially known as percent-encoding, is a method to encode arbitrary data in a uniform resource identifier (URI) using only the US-ASCII characters legal within a URI. Although it is known as URL encoding , it is also used more generally within the main Uniform Resource Identifier (URI) set, which includes both Uniform Resource ...
Percent-encoding of reserved characters in URLs and query strings can significantly increase their length, and while Apache HTTP Server can handle up to 4,000 characters in a URL, [5] Microsoft Internet Explorer is limited to 2,048 characters in any URL. [6]
For example, this is the source of the special handling of plus sign, '+' within browser URL percent encoding (which today, with the deprecation of indexed search, is all but redundant with %20). Also some web servers supporting CGI (e.g., Apache ) will process the query string into command line arguments if it does not contain an equals sign ...
The following normalizations are described in RFC 3986 [1] to result in equivalent URIs: . Converting percent-encoded triplets to uppercase. The hexadecimal digits within a percent-encoding triplet of the URI (e.g., %3a versus %3A) are case-insensitive and therefore should be normalized to use uppercase letters for the digits A-F. [2] Example:
A percent-encoding of an identifying data octet is a sequence of three characters, consisting of the character % followed by the two hexadecimal digits representing that octet's numeric value. [ 13 ] : §2.1
Even though PHP's urlencode() automatically percent-encodes them, these characters do not get URL-encoded by wfUrlencode(). The ":" symbol is a partial exception – it is not encoded anywhere except for IIS 7.0.
Other octets must be percent-encoded. If the data is Base64-encoded, then the data part may contain only valid Base64 characters. [ 7 ] Note that Base64-encoded data: URIs use the standard Base64 character set (with ' + ' and ' / ' as characters 62 and 63) rather than the so-called " URL-safe Base64 " character set.
An "encoding sniffing algorithm" is defined in the specification to determine the character encoding of the document based on multiple sources of input, including: Explicit user instruction; An explicit meta tag within the first 1024 bytes of the document; A byte order mark (BOM) within the first three bytes of the document