YYKit源码探究(三) —— NSString分类之Encode and decode(二)

版本记录

版本号 时间
V1.0 2018.03.20

前言

iOS圈内有几个人大家基本都知道,比如说王巍、唐巧,还有YYKit框架的作者现任职于滴滴的郭曜源 - ibireme等。这里有一篇唐巧对他的专访,还有他的 GitHub - Yaoyuan博客,这里贴出来框架YYKit 框架。接下来几篇我们就一起来看一下这个框架。感兴趣的可以看上面写的几篇。
1. YYKit源码探究(一) —— 基本概览
2. YYKit源码探究(二) —— NSString分类之Hash(一)

回顾

上一篇我们分析了NSString分类NSString+YYAdd的Hash部分,这一篇我们就看一下Encode and decode部分。


API接口

下面我们就看一下API接口。

/**
 Returns an NSString for base64 encoded.
 */
- (nullable NSString *)base64EncodedString;

/**
 Returns an NSString from base64 encoded string.
 @param base64Encoding The encoded string.
 */
+ (nullable NSString *)stringWithBase64EncodedString:(NSString *)base64EncodedString;

/**
 URL encode a string in utf-8.
 @return the encoded string.
 */
- (NSString *)stringByURLEncode;

/**
 URL decode a string in utf-8.
 @return the decoded string.
 */
- (NSString *)stringByURLDecode;

/**
 Escape common HTML to Entity.
 Example: "a<b" will be escape to "a&lt;b".
 */
- (NSString *)stringByEscapingHTML;

1. - (nullable NSString *)base64EncodedString;

这个方法的作用就是对给定的字符串进行base64编码。

示例调用

我们先看一下示例调用。

NSString *str = @"abcdefgh";
NSString *base64Str = [str base64EncodedString];
NSLog(@"base64Str = %@", base64Str);
NSLog(@"base64Str length = %ld", base64Str.length);

下面看一下输出结果

2018-03-16 17:51:49.252896+0800 JJWebImage[96399:6379065] base64Str = YWJjZGVmZ2g=
2018-03-16 17:51:49.253034+0800 JJWebImage[96399:6379065] base64Str length = 12

方法实现

下面看一下方法的实现原理。

- (NSString *)base64EncodedString {
    return [[self dataUsingEncoding:NSUTF8StringEncoding] base64EncodedString];
}

然后是进入NSData的分类

- (NSString *)base64EncodedString {
    NSUInteger length = self.length;
    if (length == 0)
        return @"";
    
    NSUInteger out_length = ((length + 2) / 3) * 4;
    uint8_t *output = malloc(((out_length + 2) / 3) * 4);
    if (output == NULL)
        return nil;
    
    const char *input = self.bytes;
    NSInteger i, value;
    for (i = 0; i < length; i += 3) {
        value = 0;
        for (NSInteger j = i; j < i + 3; j++) {
            value <<= 8;
            if (j < length) {
                value |= (0xFF & input[j]);
            }
        }
        NSInteger index = (i / 3) * 4;
        output[index + 0] = base64EncodingTable[(value >> 18) & 0x3F];
        output[index + 1] = base64EncodingTable[(value >> 12) & 0x3F];
        output[index + 2] = ((i + 1) < length)
        ? base64EncodingTable[(value >> 6) & 0x3F]
        : '=';
        output[index + 3] = ((i + 2) < length)
        ? base64EncodingTable[(value >> 0) & 0x3F]
        : '=';
    }
    
    NSString *base64 = [[NSString alloc] initWithBytes:output
                                                length:out_length
                                              encoding:NSASCIIStringEncoding];
    free(output);
    return base64;
}
static const char base64EncodingTable[64]
= "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

2. + (nullable NSString *)stringWithBase64EncodedString:(NSString *)base64EncodedString;

该方法的作用就是对base64加密的字符串进行解密。

示例调用

下面我们就看一下示例调用。

NSString *base64Str = [NSString stringWithBase64EncodedString:@"YWJjZGVmZ2g="];
NSLog(@"base64Str = %@", base64Str);
NSLog(@"base64Str length = %ld", base64Str.length);

下面看一下输出结果

2018-03-16 18:51:54.918780+0800 JJWebImage[96911:6510428] base64Str = abcdefgh
2018-03-16 18:51:54.918904+0800 JJWebImage[96911:6510428] base64Str length = 8

方法实现

下面看一下方法的实现原理。

+ (NSString *)stringWithBase64EncodedString:(NSString *)base64EncodedString {
    NSData *data = [NSData dataWithBase64EncodedString:base64EncodedString];
    return [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
}

上面是调用NSData的类方法,将给定的编码过的字符串进行解密并转化为NSString类型。

+ (NSData *)dataWithBase64EncodedString:(NSString *)base64EncodedString {
    NSInteger length = base64EncodedString.length;
    const char *string = [base64EncodedString cStringUsingEncoding:NSASCIIStringEncoding];
    if (string  == NULL)
        return nil;
    
    while (length > 0 && string[length - 1] == '=')
        length--;
    
    NSInteger outputLength = length * 3 / 4;
    NSMutableData *data = [NSMutableData dataWithLength:outputLength];
    if (data == nil)
        return nil;
    if (length == 0)
        return data;
    
    uint8_t *output = data.mutableBytes;
    NSInteger inputPoint = 0;
    NSInteger outputPoint = 0;
    while (inputPoint < length) {
        char i0 = string[inputPoint++];
        char i1 = string[inputPoint++];
        char i2 = inputPoint < length ? string[inputPoint++] : 'A';
        char i3 = inputPoint < length ? string[inputPoint++] : 'A';
        
        output[outputPoint++] = (base64DecodingTable[i0] << 2)
        | (base64DecodingTable[i1] >> 4);
        if (outputPoint < outputLength) {
            output[outputPoint++] = ((base64DecodingTable[i1] & 0xf) << 4)
            | (base64DecodingTable[i2] >> 2);
        }
        if (outputPoint < outputLength) {
            output[outputPoint++] = ((base64DecodingTable[i2] & 0x3) << 6)
            | base64DecodingTable[i3];
        }
    }
    
    return data;
}

同样用的是下面的解码表

static const short base64DecodingTable[256] = {
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -1, -1, -2,  -1,  -1, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,  -2,  -2, -2, -2,
    -1, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, 62,  -2,  -2, -2, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -2, -2,  -2,  -2, -2, -2,
    -2, 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10,  11,  12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -2,  -2,  -2, -2, -2,
    -2, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,  37,  38, 39, 40,
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -2,  -2,  -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,  -2,  -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,  -2,  -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,  -2,  -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,  -2,  -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,  -2,  -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,  -2,  -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,  -2,  -2, -2, -2,
    -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,  -2,  -2, -2, -2
};

3. - (NSString *)stringByURLEncode

该方法的作用就是对给定的字符串进行URL 的UTF - 8编码。

示例调用

NSString *str = @"http:\\baidu.com?my=我的";
NSString *urlEncodeStr = [str stringByURLEncode];
NSLog(@"urlEncodeStr = %@", urlEncodeStr);
NSLog(@"urlEncodeStr length = %ld", urlEncodeStr.length);

看一下输出结果

2018-03-16 19:03:51.935872+0800 JJWebImage[97043:6603499] urlEncodeStr = http%3A%5Cbaidu.com?my%3D%E6%88%91%E7%9A%84
2018-03-16 19:03:51.936090+0800 JJWebImage[97043:6603499] urlEncodeStr length = 43

方法实现

- (NSString *)stringByURLEncode {
    if ([self respondsToSelector:@selector(stringByAddingPercentEncodingWithAllowedCharacters:)]) {
        /**
         AFNetworking/AFURLRequestSerialization.m
         
         Returns a percent-escaped string following RFC 3986 for a query string key or value.
         RFC 3986 states that the following characters are "reserved" characters.
            - General Delimiters: ":", "#", "[", "]", "@", "?", "/"
            - Sub-Delimiters: "!", "$", "&", "'", "(", ")", "*", "+", ",", ";", "="
         In RFC 3986 - Section 3.4, it states that the "?" and "/" characters should not be escaped to allow
         query strings to include a URL. Therefore, all "reserved" characters with the exception of "?" and "/"
         should be percent-escaped in the query string.
            - parameter string: The string to be percent-escaped.
            - returns: The percent-escaped string.
         */
        static NSString * const kAFCharactersGeneralDelimitersToEncode = @":#[]@"; // does not include "?" or "/" due to RFC 3986 - Section 3.4
        static NSString * const kAFCharactersSubDelimitersToEncode = @"!$&'()*+,;=";
        
        NSMutableCharacterSet * allowedCharacterSet = [[NSCharacterSet URLQueryAllowedCharacterSet] mutableCopy];
        [allowedCharacterSet removeCharactersInString:[kAFCharactersGeneralDelimitersToEncode stringByAppendingString:kAFCharactersSubDelimitersToEncode]];
        static NSUInteger const batchSize = 50;
        
        NSUInteger index = 0;
        NSMutableString *escaped = @"".mutableCopy;
        
        while (index < self.length) {
            NSUInteger length = MIN(self.length - index, batchSize);
            NSRange range = NSMakeRange(index, length);
            // To avoid breaking up character sequences such as 👴🏻👮🏽
            range = [self rangeOfComposedCharacterSequencesForRange:range];
            NSString *substring = [self substringWithRange:range];
            NSString *encoded = [substring stringByAddingPercentEncodingWithAllowedCharacters:allowedCharacterSet];
            [escaped appendString:encoded];
            
            index += range.length;
        }
        return escaped;
    } else {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
        CFStringEncoding cfEncoding = CFStringConvertNSStringEncodingToEncoding(NSUTF8StringEncoding);
        NSString *encoded = (__bridge_transfer NSString *)
        CFURLCreateStringByAddingPercentEscapes(
                                                kCFAllocatorDefault,
                                                (__bridge CFStringRef)self,
                                                NULL,
                                                CFSTR("!#$&'()*+,/:;=?@[]"),
                                                cfEncoding);
        return encoded;
#pragma clang diagnostic pop
    }
}

4. - (NSString *)stringByURLDecode;

该方法的作用就是对给定的字符串进行UTF - 8解码。

示例调用

NSString *str = @"http%3A%5Cbaidu.com?my%3D%E6%88%91%E7%9A%84";
NSString *urlDecodeStr = [str stringByURLDecode];
NSLog(@"urlDecodeStr = %@", urlDecodeStr);
NSLog(@"urlDecodeStr length = %ld", urlDecodeStr.length);

看一下输出结果

2018-03-16 19:08:40.316664+0800 JJWebImage[97127:6649148] urlDecodeStr = http:\baidu.com?my=我的
2018-03-16 19:08:40.316785+0800 JJWebImage[97127:6649148] urlDecodeStr length = 21

方法实现

下面看一下方法的实现原理。

- (NSString *)stringByURLDecode {
    if ([self respondsToSelector:@selector(stringByRemovingPercentEncoding)]) {
        return [self stringByRemovingPercentEncoding];
    } else {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
        CFStringEncoding en = CFStringConvertNSStringEncodingToEncoding(NSUTF8StringEncoding);
        NSString *decoded = [self stringByReplacingOccurrencesOfString:@"+"
                                                            withString:@" "];
        decoded = (__bridge_transfer NSString *)
        CFURLCreateStringByReplacingPercentEscapesUsingEncoding(
                                                                NULL,
                                                                (__bridge CFStringRef)decoded,
                                                                CFSTR(""),
                                                                en);
        return decoded;
#pragma clang diagnostic pop
    }
}

5. - (NSString *)stringByEscapingHTML;

将常见的HTML转义为实体

示例调用

NSString *str = @"a<b";
NSString *escapeStr = [str stringByEscapingHTML];
NSLog(@"escapeStr = %@", escapeStr);
NSLog(@"escapeStr length = %ld", escapeStr.length);

下面看输出结果

2018-03-16 19:14:34.942897+0800 JJWebImage[97214:6700533] urlDecodeStr = a&lt;b
2018-03-16 19:14:34.943013+0800 JJWebImage[97214:6700533] urlDecodeStr length = 6

方法实现

下面看一下方法的实现

- (NSString *)stringByEscapingHTML {
    NSUInteger len = self.length;
    if (!len) return self;
    
    unichar *buf = malloc(sizeof(unichar) * len);
    if (!buf) return self;
    [self getCharacters:buf range:NSMakeRange(0, len)];
    
    NSMutableString *result = [NSMutableString string];
    for (int i = 0; i < len; i++) {
        unichar c = buf[i];
        NSString *esc = nil;
        switch (c) {
            case 34: esc = @"&quot;"; break;
            case 38: esc = @"&amp;"; break;
            case 39: esc = @"&apos;"; break;
            case 60: esc = @"&lt;"; break;
            case 62: esc = @"&gt;"; break;
            default: break;
        }
        if (esc) {
            [result appendString:esc];
        } else {
            CFStringAppendCharacters((CFMutableStringRef)result, &c, 1);
        }
    }
    free(buf);
    return result;
}

后记

本篇继续讲述NSString的分类,主要包括三个方面:base64的编码和解码、URL 的UTF - 8 编码以及将常见的HTML转义为实体。希望大家能喜欢,刚兴趣的可以给个赞和关注,谢谢~~~

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