URL Loading System Programming Guide-Encoding URL Data(URL数据编码)

来源自：URL Loading System Programming Guide

为了编码URL字符串，可以使用Core Foundatin的CFURLCreateStringByAddingPercentEscapes和CFURLCreateStringByReplacingPercentEscapesUsingEncoding函数。

根据 RFC 3986，在 URL 中的保留的字符如下：

reserved    = gen-delims / sub-delims

gen-delims  = ":" / "/" / "?" / "#" / "[" / "]" / "@"

sub-delims  = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="

因此，为URL正确编码包含在 URL 中UTF 8 字符串，您应该执行以下操作：

CFStringRef originalString = ...

CFStringRef encodedString = CFURLCreateStringByAddingPercentEscapes(
kCFAllocatorDefault,
originalString,
NULL,
CFSTR(":/?#[]@!$&'()*+,;="),
kCFStringEncodingUTF8);

如果你想要解码URL片段，首先必须将URL字符串拆分成其组成部分 （字段和路径部分). If you do not decode it，you will be unable to tell the difference (for example) between an encoded ampersand that was originally part of the contents of a field and a bare ampersand that indicated the end of the field. 。

在将URL分成几部分后，可以解码每个部分，如下所示：

CFStringRef decodedString = CFURLCreateStringByReplacingPercentEscapesUsingEncoding(
kCFAllocatorDefault,
encodedString,
CFSTR(""),
kCFStringEncodingUTF8);

参考：

URL 编码：CFURLCreateStringByAddingPercentEscapes

iOS : How to do proper URL encoding?