URI encoding, more accurately known as percent-encoding or URL encoding, is a method used to convert characters into a format that is safely transmitted over the internet within a Uniform Resource Identifier (URI). It ensures that all characters are represented using only the allowed US-ASCII characters within a URI.
Why is URI Encoding Necessary?
Certain characters are reserved or unsafe for use in URIs for various reasons:
- Reserved Characters: These characters have special meanings within the URI syntax (e.g., "/", "?", "#").
- Unsafe Characters: These characters may not be handled correctly by all systems or may be misinterpreted by some browsers or servers (e.g., spaces, "<", ">").
- Non-ASCII Characters: URIs are originally designed to use the US-ASCII character set. Non-ASCII characters (like accented letters or characters from other alphabets) need to be encoded.
How Does URI Encoding Work?
URI encoding replaces unsafe or reserved characters with a "%" followed by the two-digit hexadecimal representation of the character's ASCII value. For example:
- Space: Encoded as
%20 - "&": Encoded as
%26 - "=": Encoded as
%3D
Examples
Let's say you want to include the string "Hello world!" in a URI. Because the space character is not allowed, it needs to be encoded:
- Original String:
Hello world! - Encoded String:
Hello%20world%21
Therefore, the complete URL might look like this:
https://www.example.com/search?q=Hello%20world%21
Characters That Usually Need Encoding
The following characters are commonly encoded in URIs:
"(Double quote):%22#(Hash):%23%(Percent):%25&(Ampersand):%26+(Plus):%2B/(Slash):%2F:(Colon):%3A;(Semicolon):%3B<(Less than):%3C=(Equals):%3D>(Greater than):%3E?(Question mark):%3F@(At sign):%40[(Left square bracket):%5B\(Backslash):%5C](Right square bracket):%5D^(Caret):%5E`(Grave accent):%60{(Left curly brace):%7B|(Vertical bar):%7C}(Right curly brace):%7D~(Tilde):%7E- Space:
%20
Programming Languages and URI Encoding
Most programming languages offer built-in functions or libraries to handle URI encoding and decoding. Examples include:
- JavaScript:
encodeURIComponent()anddecodeURIComponent() - Python:
urllib.parse.quote()andurllib.parse.unquote() - Java:
java.net.URLEncoder.encode()andjava.net.URLDecoder.decode()
URI encoding is essential for ensuring that data is transmitted correctly and consistently across the internet within URLs.
