iOS源码补完计划--AFNetworking(四)

作者: kirito_song | 来源:发表于2018-05-23 17:43 被阅读84次

前言
流程图
核心代码
请求头
请求体
- 1、通过Parameters(参数字典)构建的请求体
  - 1、用户自定义block转译
  - 2、AFN默认的转义方式:
    - 将字典转化成字符串并且转译
    - 根据不同情况将参数字符串拼接到URL后、或者放入请求体
- 2、通过文件构建的请求体
  - AFMultipartFormData协议
  - AFHTTPBodyPart
  - AFStreamingMultipartFormData
    - 核心方法（将文件分段拼接）
AFHTTPRequestSerializer
- AFHTTPRequestSerializer.h
- AFHTTPRequestSerializer.m
  - NSInputStream和NSOutputSteam的使用
APIDemo
参考资料

前言

AFNetworking源码第四篇
主要看了看AFURLRequestSerialization的内容
负责网络请求NSMutableURLRequest对象的初始化
以及请求头、请求体、参数、上传文件的自动化配置

几千行代码、很长。但是读下来会受益匪浅

AFN概述:《iOS源码补完计划--AFNetworking 3.1.0源码研读》

流程图

里面的文件实在是太多了、还是先弄个流程图好一些?

AFHTTPRequestSerializer流程图

解释图中几个相关的类:

AFHTTPRequestSerializer
负责请求的生产
AFQueryStringPair
内部有两个属性。分别代表字典的key和value。

@property (readwrite, nonatomic, strong) id field;
@property (readwrite, nonatomic, strong) id value;

在将请求参数拼接进URL或请求体的时候会用到。

AFHTTPBodyPart
请求体单个片段(也就是单个name)
AFStreamingMultipartFormData
用来整合请求体信息、并且整合进request
AFMultipartFormData
负责上传文件拼接的协议、AFStreamingMultipartFormData对象就遵从这个协议。内部将会先转化成AFHTTPBodyPart然后追加给AFStreamingMultipartFormData。
包括追加文件、二进制文件、数据流等等。

核心代码

还是先写一个普通的请求代码:

AFHTTPRequestSerializer * requestSerializer =  [AFHTTPRequestSerializer serializer];
[requestSerializer setValue:@"请求头value1" forHTTPHeaderField:@"请求头key1"];
[requestSerializer setValue:@"请求头value2" forHTTPHeaderField:@"请求头key2"];

NSMutableURLRequest * req = [requestSerializer requestWithMethod:@"POST" URLString:@"http://127.0.0.1:3000/" parameters:@{@"key":@"value"} error:nil];

[[[AFHTTPSessionManager manager] dataTaskWithRequest:req completionHandler:^(NSURLResponse * _Nonnull response, id  _Nullable responseObject, NSError * _Nullable error) {
    
}] resume] ;

AFN内部的操作很直观
1、生成一个_MRequest
2、如果你设置了一些通用属性、则覆盖一下。
3、设置请求头请求体

//通过请求方式、URL、参数字典生成请求
- (NSMutableURLRequest *)requestWithMethod:(NSString *)method
                                 URLString:(NSString *)URLString
                                parameters:(id)parameters
                                     error:(NSError *__autoreleasing *)error
{
    NSParameterAssert(method);
    NSParameterAssert(URLString);

    NSURL *url = [NSURL URLWithString:URLString];

    NSParameterAssert(url);

    NSMutableURLRequest *mutableRequest = [[NSMutableURLRequest alloc] initWithURL:url];
    //设置请求方式
    mutableRequest.HTTPMethod = method;

    //如果某个关键属性被自主设置过、则用新的。不然直接用模板生成的`NSMutableURLRequest`即可
    for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
        if ([self.mutableObservedChangedKeyPaths containsObject:keyPath]) {
            [mutableRequest setValue:[self valueForKeyPath:keyPath] forKey:keyPath];
        }
    }

    //对req进一步设置(拼接URL、请求体、请求头)
    mutableRequest = [[self requestBySerializingRequest:mutableRequest withParameters:parameters error:error] mutableCopy];

    return mutableRequest;
}

//监听集合。蜂窝网络、缓存策略、cookie、管线链接、网络服务类型、超时连接
static NSArray * AFHTTPRequestSerializerObservedKeyPaths() {
    static NSArray *_AFHTTPRequestSerializerObservedKeyPaths = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _AFHTTPRequestSerializerObservedKeyPaths = @[NSStringFromSelector(@selector(allowsCellularAccess)), NSStringFromSelector(@selector(cachePolicy)), NSStringFromSelector(@selector(HTTPShouldHandleCookies)), NSStringFromSelector(@selector(HTTPShouldUsePipelining)), NSStringFromSelector(@selector(networkServiceType)), NSStringFromSelector(@selector(timeoutInterval))];
    });

    return _AFHTTPRequestSerializerObservedKeyPaths;
}

第三步mutableRequest = [[self requestBySerializingRequest:mutableRequest withParameters:parameters error:error] mutableCopy];尤为重要、它完善了整个request的必要信息。

- (NSURLRequest *)requestBySerializingRequest:(NSURLRequest *)request
                               withParameters:(id)parameters
                                        error:(NSError *__autoreleasing *)error
{
    NSParameterAssert(request);

    NSMutableURLRequest *mutableRequest = [request mutableCopy];
    //设置请求头
    [self.HTTPRequestHeaders enumerateKeysAndObjectsUsingBlock:^(id field, id value, BOOL * __unused stop) {
        if (![request valueForHTTPHeaderField:field]) {
            [mutableRequest setValue:value forHTTPHeaderField:field];
        }
    }];

    //根据参数parameters设置查询字段
    NSString *query = nil;
    if (parameters) {
        //看看参数是否需要用户自定义转译
        if (self.queryStringSerialization) {
            NSError *serializationError;
            //调用用户block、获得参数转译的字符串
            query = self.queryStringSerialization(request, parameters, &serializationError);

            if (serializationError) {
                if (error) {
                    *error = serializationError;
                }

                return nil;
            }
        } else {
            //使用AFN的默认转译方式
            switch (self.queryStringSerializationStyle) {
                case AFHTTPRequestQueryStringDefaultStyle:
                    query = AFQueryStringFromParameters(parameters);
                    break;
            }
        }
    }

    //如果请求方式是需要将查询参数拼接到URL后面的(默认包含`GET``HEAD``DELETE`)、则拼接
    if ([self.HTTPMethodsEncodingParametersInURI containsObject:[[request HTTPMethod] uppercaseString]]) {
        if (query && query.length > 0) {
            mutableRequest.URL = [NSURL URLWithString:[[mutableRequest.URL absoluteString] stringByAppendingFormat:mutableRequest.URL.query ? @"&%@" : @"?%@", query]];
        }
    } else {
        //否则、则放入请求体
        // #2864: an empty string is a valid x-www-form-urlencoded payload
        if (!query) {
            query = @"";
        }
        if (![mutableRequest valueForHTTPHeaderField:@"Content-Type"]) {
            [mutableRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
        }
        [mutableRequest setHTTPBody:[query dataUsingEncoding:self.stringEncoding]];
    }

    return mutableRequest;
}

至此一个正常的请求就结束了。
不过、既然是读源码、肯定还需要把每个代码都好好看看。

请求头

请求头可以通过外界设置、保存在字典里。在生成request的时候批量添加设置进去。

/*
    Get方法
 */
- (NSDictionary *)HTTPRequestHeaders {
    //将不可变字典转换成可变字典
    return [NSDictionary dictionaryWithDictionary:self.mutableHTTPRequestHeaders];
}
/*
    设置请求头
 */
- (void)setValue:(NSString *)value
forHTTPHeaderField:(NSString *)field
{
    //对请求头字典进行追加
    [self.mutableHTTPRequestHeaders setValue:value forKey:field];
}

- (NSString *)valueForHTTPHeaderField:(NSString *)field {
    //根据不同的key提取出value
    return [self.mutableHTTPRequestHeaders valueForKey:field];
}

//通过账号密码设置授权请求头
- (void)setAuthorizationHeaderFieldWithUsername:(NSString *)username
                                       password:(NSString *)password
{
    //转化成data
    NSData *basicAuthCredentials = [[NSString stringWithFormat:@"%@:%@", username, password] dataUsingEncoding:NSUTF8StringEncoding];
    //base64编码加密
    NSString *base64AuthCredentials = [basicAuthCredentials base64EncodedStringWithOptions:(NSDataBase64EncodingOptions)0];
    //加入请求头字典
    [self setValue:[NSString stringWithFormat:@"Basic %@", base64AuthCredentials] forHTTPHeaderField:@"Authorization"];
}
//清除授权用请求头
- (void)clearAuthorizationHeader {
    [self.mutableHTTPRequestHeaders removeObjectForKey:@"Authorization"];
}

针对AFN而不是multipart 协议来看、可以讲的没有多少。

请求体

1、通过Parameters(参数字典)构建的请求体

既然提到Parameters、那么就像上面代码里写的一样、所有的Parameters字典、都需要被转义成字符串。

AFN为我们提供了两种转换的方式。

1、用户自定义block转译

没啥说的、参数都给你。自己转译完还给AFN字符串就行

- (void)setQueryStringSerializationWithBlock:(NSString *(^)(NSURLRequest *, id, NSError *__autoreleasing *))block {
    self.queryStringSerialization = block;
}

2、AFN默认的转义方式:

switch (self.queryStringSerializationStyle) {
    case AFHTTPRequestQueryStringDefaultStyle:
        query = AFQueryStringFromParameters(parameters);
        break;
}

虽然是个switch、但是queryStringSerializationStyle默认目前只被提供了一种:

typedef NS_ENUM(NSUInteger, AFHTTPRequestQueryStringSerializationStyle) {
    AFHTTPRequestQueryStringDefaultStyle = 0,
};

但是写成枚举、是为了将来更好的扩展和维护。像这种有可能扩展的地方、是我们值得借鉴的。

将字典转化成字符串并且转译

//将字典参数转化成字符串
NSString * AFQueryStringFromParameters(NSDictionary *parameters) {
    NSMutableArray *mutablePairs = [NSMutableArray array];
    for (AFQueryStringPair *pair in AFQueryStringPairsFromDictionary(parameters)) {
        //将AFQueryStringPair对象转化成key=value的格式并且传递给新的数组
        [mutablePairs addObject:[pair URLEncodedStringValue]];
    }
    //开头添加"&"
    return [mutablePairs componentsJoinedByString:@"&"];
}

//将字典转化成数组{key1[key2]value}
NSArray * AFQueryStringPairsFromDictionary(NSDictionary *dictionary) {
    return AFQueryStringPairsFromKeyAndValue(nil, dictionary);
}

//把key && value 转成数组
NSArray * AFQueryStringPairsFromKeyAndValue(NSString *key, id value) {
    NSMutableArray *mutableQueryStringComponents = [NSMutableArray array];

    //排序 升序
    NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"description" ascending:YES selector:@selector(compare:)];

    if ([value isKindOfClass:[NSDictionary class]]) {
        //参数value为字典
        
        NSDictionary *dictionary = value;
        // Sort dictionary keys to ensure consistent ordering in query string, which is important when deserializing potentially ambiguous sequences, such as an array of dictionaries
        
        /*
            [dictionary.allKeys sortedArrayUsingDescriptors:@[ sortDescriptor ]
            对所有的字典里的nestedKey进行排序
         */
        for (id nestedKey in [dictionary.allKeys sortedArrayUsingDescriptors:@[ sortDescriptor ]]) {
            //获取nestedKey里的value
            id nestedValue = dictionary[nestedKey];
            if (nestedValue) {
                if (key) {
                    //如果指明了key、则为二级字典。用key[nestedKey]进行遍历
                    //比如@{aaa:@{bbb:ccc}};就会被变成aaa[bbb]作为key
                    [mutableQueryStringComponents addObjectsFromArray:AFQueryStringPairsFromKeyAndValue([NSString stringWithFormat:@"%@[%@]", key, nestedKey], nestedValue)];
                }else {
                    //如果没有传入nestedKey、则直接为一级字典。用subkey进行遍历
                    [mutableQueryStringComponents addObjectsFromArray:AFQueryStringPairsFromKeyAndValue(nestedKey, nestedValue)];
                }
//                [mutableQueryStringComponents addObjectsFromArray:AFQueryStringPairsFromKeyAndValue((key ? [NSString stringWithFormat:@"%@[%@]", key, nestedKey] : nestedKey), nestedValue)];
            }
        }
    } else if ([value isKindOfClass:[NSArray class]]) {
        NSArray *array = value;
        for (id nestedValue in array) {
            [mutableQueryStringComponents addObjectsFromArray:AFQueryStringPairsFromKeyAndValue([NSString stringWithFormat:@"%@[]", key], nestedValue)];
        }
    } else if ([value isKindOfClass:[NSSet class]]) {
        NSSet *set = value;
        for (id obj in [set sortedArrayUsingDescriptors:@[ sortDescriptor ]]) {
            [mutableQueryStringComponents addObjectsFromArray:AFQueryStringPairsFromKeyAndValue(key, obj)];
        }
    } else {
        //如果是字符串、则将key、value组合
        //如果是字典的话就会出现key = @"aaaa[bbbb]" value = @"cccc"这种情况、后面会再转化
        [mutableQueryStringComponents addObject:[[AFQueryStringPair alloc] initWithField:key value:value]];
    }

    //返回最终的`AFQueryStringPair`对象数组
    return mutableQueryStringComponents;
}

字典转字符串
NSArray * AFQueryStringPairsFromKeyAndValue(NSString *key, id value)
利用递归的方式对深层次的参数(value是NSDictionary/NSArray/NSSet)进行拆分。
AFQueryStringPair对象

@interface AFQueryStringPair : NSObject
@property (readwrite, nonatomic, strong) id field;
@property (readwrite, nonatomic, strong) id value;

- (instancetype)initWithField:(id)field value:(id)value;

- (NSString *)URLEncodedStringValue;
@end

用来储存每个field(key)对应的value。
比如@{aaa:@{bbb:ccc}};就会被变成aaa[bbb]作为field

转译方法
将每个AFQueryStringPair转译成字符串[pair URLEncodedStringValue]

如果有value则使用key=value、否则直接转译key

- (NSString *)URLEncodedStringValue {
    if (!self.value || [self.value isEqual:[NSNull null]]) {
        return AFPercentEscapedStringFromString([self.field description]);
    } else {
        return [NSString stringWithFormat:@"%@=%@", AFPercentEscapedStringFromString([self.field description]), AFPercentEscapedStringFromString([self.value description])];
    }
}

RFC 3986 规范下需要被保留的字符
":", "#", "[", "]", "@", "?", "/"
"!", "$", "&", "'", "(", ")", "*", "+", ",", ";", "="
在RFC 3986 规范 Section 3.4 下的查询字段、除了"?","/"以外的特殊字符都应该被转义。所以有了以下这个方法:

/**
 对字符串编码
 */
NSString * AFPercentEscapedStringFromString(NSString *string) {
    //":", "#", "[", "]", "@", "?", "/"  除去"?","/"
    static NSString * const kAFCharactersGeneralDelimitersToEncode = @":#[]@"; // does not include "?" or "/" due to RFC 3986 - Section 3.4
    
    //"!", "$", "&", "'", "(", ")", "*", "+", ",", ";", "="
    static NSString * const kAFCharactersSubDelimitersToEncode = @"!$&'()*+,;=";

    
    //将以上两种设置为排除
    NSMutableCharacterSet * allowedCharacterSet = [[NSCharacterSet URLQueryAllowedCharacterSet] mutableCopy];
    /*
        只是[NSCharacterSet URLQueryAllowedCharacterSet]的话以上字符默认是不转译的
        需要移出去。只保留"?"和"/"不转译
    */
    [allowedCharacterSet removeCharactersInString:[kAFCharactersGeneralDelimitersToEncode stringByAppendingString:kAFCharactersSubDelimitersToEncode]];

    // FIXME: https://github.com/AFNetworking/AFNetworking/pull/3028
    // return [string stringByAddingPercentEncodingWithAllowedCharacters:allowedCharacterSet];

    //每次最多转译50个字符
    static NSUInteger const batchSize = 50;

    NSUInteger index = 0;
    NSMutableString *escaped = @"".mutableCopy;

    while (index < string.length) {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wgnu"
        NSUInteger length = MIN(string.length - index, batchSize);
#pragma GCC diagnostic pop
        NSRange range = NSMakeRange(index, length);

        // To avoid breaking up character sequences such as 👴🏻👮🏽
        range = [string rangeOfComposedCharacterSequencesForRange:range];
        
        NSString *substring = [string substringWithRange:range];
        
        NSString *encoded = [substring stringByAddingPercentEncodingWithAllowedCharacters:allowedCharacterSet];
        [escaped appendString:encoded];

        index += range.length;
    }

    return escaped;
}

根据不同情况将参数字符串拼接到URL后、或者放入请求体

//如果请求方式是需要将查询参数拼接到URL后面的(默认包含`GET``HEAD``DELETE`)、则拼接
if ([self.HTTPMethodsEncodingParametersInURI containsObject:[[request HTTPMethod] uppercaseString]]) {
    if (query && query.length > 0) {
        //原url带有参数、则拼接'&'。没参数则拼接'?'
        mutableRequest.URL = [NSURL URLWithString:[[mutableRequest.URL absoluteString] stringByAppendingFormat:mutableRequest.URL.query ? @"&%@" : @"?%@", query]];
    }
} else {
    //否则、则放入请求体
    // #2864: an empty string is a valid x-www-form-urlencoded payload
    if (!query) {
        query = @"";
    }
    if (![mutableRequest valueForHTTPHeaderField:@"Content-Type"]) {
        [mutableRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
    }
    [mutableRequest setHTTPBody:[query dataUsingEncoding:self.stringEncoding]];
}

是否拼接到URL取决于HTTPMethodsEncodingParametersInURI这个属性。
用户可以自定义追加或者删除这个合集的内容。

/**
    需要拼接参数的请求方法、默认包含`GET``HEAD``DELETE`
 */
@property (nonatomic, strong) NSSet <NSString *> *HTTPMethodsEncodingParametersInURI;

2、通过文件构建的请求体

NSMutableURLRequest * request = [[AFHTTPRequestSerializer serializer] multipartFormRequestWithMethod:@"POST" URLString:@"baidu" parameters:parameter constructingBodyWithBlock:^(id<AFMultipartFormData>  _Nonnull formData) {
    
    NSString *documentFolder = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSURL *fileURL = [NSURL fileURLWithPath:[documentFolder stringByAppendingPathComponent:@"1.txt"]];
    [formData appendPartWithFileURL:fileURL name:@"userfile[]" error:NULL];
    NSURL *fileURL1 = [NSURL fileURLWithPath:[documentFolder stringByAppendingPathComponent:@"2.jpg"]];
    [formData appendPartWithFileURL:fileURL1 name:@"userfile[]" fileName:@"aaa.jpg" mimeType:@"image/jpeg" error:NULL];
    
} error:nil];

AFMultipartFormData协议
文件的方式主要通过协议AFMultipartFormData进行、有很多添加方式。

@protocol AFMultipartFormData

- (BOOL)appendPartWithFileURL:(NSURL *)fileURL
                         name:(NSString *)name
                        error:(NSError * _Nullable __autoreleasing *)error;

- (BOOL)appendPartWithFileURL:(NSURL *)fileURL
                         name:(NSString *)name
                     fileName:(NSString *)fileName
                     mimeType:(NSString *)mimeType
                        error:(NSError * _Nullable __autoreleasing *)error;
- (void)appendPartWithInputStream:(nullable NSInputStream *)inputStream
                             name:(NSString *)name
                         fileName:(NSString *)fileName
                           length:(int64_t)length
                         mimeType:(NSString *)mimeType;

- (void)appendPartWithFileData:(NSData *)data
                          name:(NSString *)name
                      fileName:(NSString *)fileName
                      mimeType:(NSString *)mimeType;

- (void)appendPartWithFormData:(NSData *)data
                          name:(NSString *)name;

- (void)appendPartWithHeaders:(nullable NSDictionary <NSString *, NSString *> *)headers
                         body:(NSData *)body;

- (void)throttleBandwidthWithPacketSize:(NSUInteger)numberOfBytes
                                  delay:(NSTimeInterval)delay;

@end

在进行必要的Content-Type生成后、都会流入以下方法：

AFHTTPBodyPart *bodyPart = [[AFHTTPBodyPart alloc] init];
bodyPart.stringEncoding = self.stringEncoding;
bodyPart.headers = headers;
bodyPart.boundary = self.boundary;
bodyPart.bodyContentLength = [body length];
bodyPart.body = body;

[self.bodyStream appendHTTPBodyPart:bodyPart];

将AFHTTPBodyPart实例、追加进self.bodyStream(AFStreamingMultipartFormData实例)

AFHTTPBodyPart

单个请求体文件

@interface AFHTTPBodyPart : NSObject
@property (nonatomic, assign) NSStringEncoding stringEncoding;//编码
@property (nonatomic, strong) NSDictionary *headers;//头信息
@property (nonatomic, copy) NSString *boundary;//边界
@property (nonatomic, strong) id body;//内容
@property (nonatomic, assign) unsigned long long bodyContentLength;//内容大小
@property (nonatomic, strong) NSInputStream *inputStream;//流

@property (nonatomic, assign) BOOL hasInitialBoundary;//是否有初始边界
@property (nonatomic, assign) BOOL hasFinalBoundary;//是否有结束边界

@property (readonly, nonatomic, assign, getter = hasBytesAvailable) BOOL bytesAvailable;//body是否存在
@property (readonly, nonatomic, assign) unsigned long long contentLength;//长度

//读取数据
- (NSInteger)read:(uint8_t *)buffer
        maxLength:(NSUInteger)length;
@end

AFStreamingMultipartFormData

@interface AFStreamingMultipartFormData ()
@property (readwrite, nonatomic, copy) NSMutableURLRequest *request;//请求request
@property (readwrite, nonatomic, assign) NSStringEncoding stringEncoding;//编码
@property (readwrite, nonatomic, copy) NSString *boundary;//边界
@property (readwrite, nonatomic, strong) AFMultipartBodyStream *bodyStream;//body文件整合工具
@end

继承自NSInputStream、因为最后需要将整个实例接入给request.bodyStream。

- (NSMutableURLRequest *)requestByFinalizingMultipartFormData {
    if ([self.bodyStream isEmpty]) {
        //如果body为空、则直接返回request
        return self.request;
    }

    // Reset the initial and final boundaries to ensure correct Content-Length
    [self.bodyStream setInitialAndFinalBoundaries];
    //将请求体接入request
    [self.request setHTTPBodyStream:self.bodyStream];
    //multipart协议请求头
    [self.request setValue:[NSString stringWithFormat:@"multipart/form-data; boundary=%@", self.boundary] forHTTPHeaderField:@"Content-Type"];
    [self.request setValue:[NSString stringWithFormat:@"%llu", [self.bodyStream contentLength]] forHTTPHeaderField:@"Content-Length"];

    return self.request;
}

我们注意到有两个请求头的设置、是multipart协议独有的。
其中、self.bodyStream是我们正在说的AFStreamingMultipartFormData实例。
self.boundary是边界分隔符。
在AFStreamingMultipartFormData初始化时一并初始完成。

@implementation AFStreamingMultipartFormData

- (instancetype)initWithURLRequest:(NSMutableURLRequest *)urlRequest
                    stringEncoding:(NSStringEncoding)encoding
{
    self = [super init];
    if (!self) {
        return nil;
    }

    self.request = urlRequest;
    self.stringEncoding = encoding;
    self.boundary = AFCreateMultipartFormBoundary();
    self.bodyStream = [[AFMultipartBodyStream alloc] initWithStringEncoding:encoding];

    return self;
}

//其中
static NSString * AFCreateMultipartFormBoundary() {
    return [NSString stringWithFormat:@"Boundary+%08X%08X", arc4random(), arc4random()];
}

初次之外、还有三个函数

//如果是开头分隔符的，那么只需在分隔符结尾加一个换行符
static inline NSString * AFMultipartFormInitialBoundary(NSString *boundary) {
    return [NSString stringWithFormat:@"--%@%@", boundary, kAFMultipartFormCRLF];
}
//如果是中间部分分隔符，那么需要分隔符前面和结尾都加换行符
static inline NSString * AFMultipartFormEncapsulationBoundary(NSString *boundary) {
    return [NSString stringWithFormat:@"%@--%@%@", kAFMultipartFormCRLF, boundary, kAFMultipartFormCRLF];
}
//如果是末尾，还得使用--分隔符--作为请求体的结束标志
static inline NSString * AFMultipartFormFinalBoundary(NSString *boundary) {
    return [NSString stringWithFormat:@"%@--%@--%@", kAFMultipartFormCRLF, boundary, kAFMultipartFormCRLF];
}

static inline NSString * AFContentTypeForPathExtension(NSString *extension) {
    NSString *UTI = (__bridge_transfer NSString *)UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, (__bridge CFStringRef)extension, NULL);
    NSString *contentType = (__bridge_transfer NSString *)UTTypeCopyPreferredTagWithClass((__bridge CFStringRef)UTI, kUTTagClassMIMEType);
    if (!contentType) {
        return @"application/octet-stream";
    } else {
        return contentType;
    }
}

服务于第二个请求头[self.bodyStream contentLength]

//计算body大小
- (unsigned long long)contentLength {

    unsigned long long length = 0;
    
    //初始边界  是否有初始边界?初始边界:封装边界(比初始边界多了个开头的\r\n)
    NSData *encapsulationBoundaryData = [([self hasInitialBoundary] ? AFMultipartFormInitialBoundary(self.boundary) : AFMultipartFormEncapsulationBoundary(self.boundary)) dataUsingEncoding:self.stringEncoding];
    length += [encapsulationBoundaryData length];

    //头长度
    NSData *headersData = [[self stringForHeaders] dataUsingEncoding:self.stringEncoding];
    length += [headersData length];

    //内容长度
    length += _bodyContentLength;

    //结束边界 是否有结束边界?结束边界:0
    NSData *closingBoundaryData = ([self hasFinalBoundary] ? [AFMultipartFormFinalBoundary(self.boundary) dataUsingEncoding:self.stringEncoding] : [NSData data]);
    length += [closingBoundaryData length];

    return length;
}

初始化、设置边界、追加body文件、验证有效性

- (instancetype)initWithStringEncoding:(NSStringEncoding)encoding {
    self = [super init];
    if (!self) {
        return nil;
    }

    self.stringEncoding = encoding;
    self.HTTPBodyParts = [NSMutableArray array];
    self.numberOfBytesInPacket = NSIntegerMax;

    return self;
}

//设置初始边界和结束边界
- (void)setInitialAndFinalBoundaries {
    if ([self.HTTPBodyParts count] > 0) {
        for (AFHTTPBodyPart *bodyPart in self.HTTPBodyParts) {
            bodyPart.hasInitialBoundary = NO;
            bodyPart.hasFinalBoundary = NO;
        }

        [[self.HTTPBodyParts firstObject] setHasInitialBoundary:YES];
        [[self.HTTPBodyParts lastObject] setHasFinalBoundary:YES];
    }
}

//追加body文件
- (void)appendHTTPBodyPart:(AFHTTPBodyPart *)bodyPart {
    [self.HTTPBodyParts addObject:bodyPart];
}

//是否为空
- (BOOL)isEmpty {
    return [self.HTTPBodyParts count] == 0;
}

核心方法（将文件分段拼接）

之所以是核心方法、因为这是AFN的一个亮点。

平时在用NSURLRequest上传文件时,一般是两种方法:
1、一个是设置body、但是如果文件稍大的话,将会撑爆内存。
2、另外一种则是创建一个临时文件、将数据拼接进去、然后将文件路径设置为bodyStream、这样就可以分片的上传了。

而AFN这种方式无疑更好、具体来看：

- (NSInteger)read:(uint8_t *)buffer
        maxLength:(NSUInteger)length
{
    if ([self streamStatus] == NSStreamStatusClosed) {
        return 0;
    }
    
    //总大小
    NSInteger totalNumberOfBytesRead = 0;

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wgnu"
    //遍历读取数据
    while ((NSUInteger)totalNumberOfBytesRead < MIN(length, self.numberOfBytesInPacket)) {
        
        //body不存在或者没有可读字节
        if (!self.currentHTTPBodyPart || ![self.currentHTTPBodyPart hasBytesAvailable]) {
            //把下一个body文件赋值给当前body
            if (!(self.currentHTTPBodyPart = [self.HTTPBodyPartEnumerator nextObject])) {
                break;
            }
        } else {
            //存在可读数据
            
            NSUInteger maxLength = MIN(length, self.numberOfBytesInPacket) - (NSUInteger)totalNumberOfBytesRead;
            
            //把当前body读取到buffer中。内部会采用递归的方式将数据分段写入buffer
            NSInteger numberOfBytesRead = [self.currentHTTPBodyPart read:&buffer[totalNumberOfBytesRead] maxLength:maxLength];
            
            if (numberOfBytesRead == -1) {
                self.streamError = self.currentHTTPBodyPart.inputStream.streamError;
                break;
            } else {
                totalNumberOfBytesRead += numberOfBytesRead;

                if (self.delay > 0.0f) {
                    [NSThread sleepForTimeInterval:self.delay];
                }
            }
        }
    }
#pragma clang diagnostic pop

    return totalNumberOfBytesRead;
}

AFHTTPRequestSerializer

其实到这已经没什么特别难得东西了、只剩下一些流程任务

AFHTTPRequestSerializer.h

@interface AFHTTPRequestSerializer : NSObject <AFURLRequestSerialization>

/**
    编码方式。默认`NSUTF8StringEncoding`
 */
@property (nonatomic, assign) NSStringEncoding stringEncoding;

/**
    允许蜂窝网络
 */
@property (nonatomic, assign) BOOL allowsCellularAccess;

/**
    请求的缓存策略
 
     typedef NS_ENUM(NSUInteger, NSURLRequestCachePolicy)
     {
     //默认策略。缓存存在则根据request中Cache-Control字段进行不同操作、否则则请求
     NSURLRequestUseProtocolCachePolicy = 0,
     //每次都请求服务器
     NSURLRequestReloadIgnoringLocalCacheData = 1,
     //忽略本地缓存和中间代理。直接请求原服务器 -- 未实现
     NSURLRequestReloadIgnoringLocalAndRemoteCacheData = 4, // Unimplemented
     //同NSURLRequestReloadIgnoringLocalCacheData
     NSURLRequestReloadIgnoringCacheData = NSURLRequestReloadIgnoringLocalCacheData,
     //有缓存就是用、不管其有效性。即忽略Cache-Control字段、没有就访问源server
     NSURLRequestReturnCacheDataElseLoad = 2,
     //只加载本地数据，不做其他操作，适用于没有网路的情况
     NSURLRequestReturnCacheDataDontLoad = 3,
     //缓存数据必须得到服务器确认才能使用--未实现
     NSURLRequestReloadRevalidatingCacheData = 5, // Unimplemented
 };

 */
@property (nonatomic, assign) NSURLRequestCachePolicy cachePolicy;

/**
    是否使用默认的cookie处理、默认YES
 */
@property (nonatomic, assign) BOOL HTTPShouldHandleCookies;

/**
    管线化传输、默认NO
    正常的HTTP请求都是一个请求对应一个连接、每次TCP链接需要一定的时间。
    管线化:允许一次发送一组请求而不必等到响应。但并不是所有服务器都支持、需要和服务器协商。并且需要提前建立好链接才能使用
 */
@property (nonatomic, assign) BOOL HTTPShouldUsePipelining;

/**
    网络服务类型
     typedef NS_ENUM(NSUInteger, NSURLRequestNetworkServiceType)
     {
     NSURLNetworkServiceTypeDefault = 0, // 普通网络传输，默认使用这个
     NSURLNetworkServiceTypeVoIP = 1,    // 网络语音通信传输，只能在VoIP使用
     NSURLNetworkServiceTypeVideo = 2,   // 影像传输
     NSURLNetworkServiceTypeBackground = 3, // 网络后台传输，优先级不高时可使用。对用户不需要的网络操作可使用
     NSURLNetworkServiceTypeVoice = 4       // 语音传输
     };
 */
@property (nonatomic, assign) NSURLRequestNetworkServiceType networkServiceType;

/**
     超时时间
 */
@property (nonatomic, assign) NSTimeInterval timeoutInterval;

///---------------------------------------
/// @name Configuring HTTP Request Headers
///---------------------------------------

/**
     请求头
 */
@property (readonly, nonatomic, strong) NSDictionary <NSString *, NSString *> *HTTPRequestHeaders;

/**
    初始化一个默认配置的req
 */
+ (instancetype)serializer;

/**
    设置httpheader、如果value为nil、则移除field(key)
 */
- (void)setValue:(nullable NSString *)value
forHTTPHeaderField:(NSString *)field;

/**
    返回field(key)标记的内容
 */
- (nullable NSString *)valueForHTTPHeaderField:(NSString *)field;

/**
    设置请求头中的`Authorization`字段
 */
- (void)setAuthorizationHeaderFieldWithUsername:(NSString *)username
                                       password:(NSString *)password;

/**
    清空请求头
 */
- (void)clearAuthorizationHeader;

///-------------------------------------------------------
/// @name 请求参数配置
///-------------------------------------------------------

/**
    需要拼接参数的请求方法、默认包含`GET``HEAD``DELETE`
 */
@property (nonatomic, strong) NSSet <NSString *> *HTTPMethodsEncodingParametersInURI;

/**
    查询参数的转义样式.(目前只有一种)
 */
- (void)setQueryStringSerializationWithStyle:(AFHTTPRequestQueryStringSerializationStyle)style;

/**
    你也可以自定义参数的转义方式
 */
- (void)setQueryStringSerializationWithBlock:(nullable NSString * (^)(NSURLRequest *request, id parameters, NSError * __autoreleasing *error))block;

///-------------------------------
///   核心方法
///-------------------------------

/**
    如果请求方式为GET`, `HEAD`, or `DELETE时、参数会被拼接到URL中、否则当做body处理
 */
- (NSMutableURLRequest *)requestWithMethod:(NSString *)method
                                 URLString:(NSString *)URLString
                                parameters:(nullable id)parameters
                                     error:(NSError * _Nullable __autoreleasing *)error;

/**
    支持上传数据
 */
- (NSMutableURLRequest *)multipartFormRequestWithMethod:(NSString *)method
                                              URLString:(NSString *)URLString
                                             parameters:(nullable NSDictionary <NSString *, id> *)parameters
                              constructingBodyWithBlock:(nullable void (^)(id <AFMultipartFormData> formData))block
                                                  error:(NSError * _Nullable __autoreleasing *)error;

/**
    这个方法可以把一个带有bodystream请求体的req、转化成不含bodystream的req。
    其中的文件会被转写到fileURL的路径下。
    你可以通过upload直接上传
    NSURLSessionTask中有一个bug，当HTTP body的内容是来自NSStream的时候，request无法发送Content-Length到服务器端，此问题在Amazon S3的Web服务中尤为显著。
 */
- (NSMutableURLRequest *)requestWithMultipartFormRequest:(NSURLRequest *)request
                             writingStreamContentsToFile:(NSURL *)fileURL
                                       completionHandler:(nullable void (^)(NSError * _Nullable error))handler;

@end

AFHTTPRequestSerializer.m

@interface AFHTTPRequestSerializer ()
@property (readwrite, nonatomic, strong) NSMutableSet *mutableObservedChangedKeyPaths;//记录修改过的属性
@property (readwrite, nonatomic, strong) NSMutableDictionary *mutableHTTPRequestHeaders;//请求头字典
@property (readwrite, nonatomic, assign) AFHTTPRequestQueryStringSerializationStyle queryStringSerializationStyle;//参数转义的样式
@property (readwrite, nonatomic, copy) AFQueryStringSerializationBlock queryStringSerialization;//自定义参数转义block
@end

@implementation AFHTTPRequestSerializer

+ (instancetype)serializer {
    return [[self alloc] init];
}

- (instancetype)init {
    self = [super init];
    if (!self) {
        return nil;
    }

    self.stringEncoding = NSUTF8StringEncoding;

    self.mutableHTTPRequestHeaders = [NSMutableDictionary dictionary];

    // Accept-Language HTTP Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4
    /**
     *  传递可接受的语言，q代表对语言的喜好程度，默认是取出前5个的数据，不足5个，取实际的个数
     */
    NSMutableArray *acceptLanguagesComponents = [NSMutableArray array];
    [[NSLocale preferredLanguages] enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        float q = 1.0f - (idx * 0.1f);
        [acceptLanguagesComponents addObject:[NSString stringWithFormat:@"%@;q=%0.1g", obj, q]];
        *stop = q <= 0.5f;
    }];
    //放到请求头里
    [self setValue:[acceptLanguagesComponents componentsJoinedByString:@", "] forHTTPHeaderField:@"Accept-Language"];

    //获取用户信息
    NSString *userAgent = nil;
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wgnu"
#if TARGET_OS_IOS
    // User-Agent Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.43
    userAgent = [NSString stringWithFormat:@"%@/%@ (%@; iOS %@; Scale/%0.2f)", [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleExecutableKey] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleIdentifierKey], [[NSBundle mainBundle] infoDictionary][@"CFBundleShortVersionString"] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleVersionKey], [[UIDevice currentDevice] model], [[UIDevice currentDevice] systemVersion], [[UIScreen mainScreen] scale]];
#elif TARGET_OS_WATCH
    // User-Agent Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.43
    userAgent = [NSString stringWithFormat:@"%@/%@ (%@; watchOS %@; Scale/%0.2f)", [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleExecutableKey] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleIdentifierKey], [[NSBundle mainBundle] infoDictionary][@"CFBundleShortVersionString"] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleVersionKey], [[WKInterfaceDevice currentDevice] model], [[WKInterfaceDevice currentDevice] systemVersion], [[WKInterfaceDevice currentDevice] screenScale]];
#elif defined(__MAC_OS_X_VERSION_MIN_REQUIRED)
    userAgent = [NSString stringWithFormat:@"%@/%@ (Mac OS X %@)", [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleExecutableKey] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleIdentifierKey], [[NSBundle mainBundle] infoDictionary][@"CFBundleShortVersionString"] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleVersionKey], [[NSProcessInfo processInfo] operatingSystemVersionString]];
#endif
#pragma clang diagnostic pop
    if (userAgent) {
        if (![userAgent canBeConvertedToEncoding:NSASCIIStringEncoding]) {
            NSMutableString *mutableUserAgent = [userAgent mutableCopy];
            if (CFStringTransform((__bridge CFMutableStringRef)(mutableUserAgent), NULL, (__bridge CFStringRef)@"Any-Latin; Latin-ASCII; [:^ASCII:] Remove", false)) {
                userAgent = mutableUserAgent;
            }
        }
        //将用户信息写入请求头
        [self setValue:userAgent forHTTPHeaderField:@"User-Agent"];
    }

    // HTTP Method Definitions; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html
    self.HTTPMethodsEncodingParametersInURI = [NSSet setWithObjects:@"GET", @"HEAD", @"DELETE", nil];

    self.mutableObservedChangedKeyPaths = [NSMutableSet set];
    //批量添加监听
    for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
        if ([self respondsToSelector:NSSelectorFromString(keyPath)]) {
            [self addObserver:self forKeyPath:keyPath options:NSKeyValueObservingOptionNew context:AFHTTPRequestSerializerObserverContext];
        }
    }

    return self;
}

- (void)dealloc {
    //移除监听
    for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
        if ([self respondsToSelector:NSSelectorFromString(keyPath)]) {
            [self removeObserver:self forKeyPath:keyPath context:AFHTTPRequestSerializerObserverContext];
        }
    }
}

#pragma mark -

// Workarounds for crashing behavior using Key-Value Observing with XCTest
// See https://github.com/AFNetworking/AFNetworking/issues/2523

- (void)setAllowsCellularAccess:(BOOL)allowsCellularAccess {
    [self willChangeValueForKey:NSStringFromSelector(@selector(allowsCellularAccess))];
    _allowsCellularAccess = allowsCellularAccess;
    [self didChangeValueForKey:NSStringFromSelector(@selector(allowsCellularAccess))];
}

- (void)setCachePolicy:(NSURLRequestCachePolicy)cachePolicy {
    [self willChangeValueForKey:NSStringFromSelector(@selector(cachePolicy))];
    _cachePolicy = cachePolicy;
    [self didChangeValueForKey:NSStringFromSelector(@selector(cachePolicy))];
}

- (void)setHTTPShouldHandleCookies:(BOOL)HTTPShouldHandleCookies {
    [self willChangeValueForKey:NSStringFromSelector(@selector(HTTPShouldHandleCookies))];
    _HTTPShouldHandleCookies = HTTPShouldHandleCookies;
    [self didChangeValueForKey:NSStringFromSelector(@selector(HTTPShouldHandleCookies))];
}

- (void)setHTTPShouldUsePipelining:(BOOL)HTTPShouldUsePipelining {
    [self willChangeValueForKey:NSStringFromSelector(@selector(HTTPShouldUsePipelining))];
    _HTTPShouldUsePipelining = HTTPShouldUsePipelining;
    [self didChangeValueForKey:NSStringFromSelector(@selector(HTTPShouldUsePipelining))];
}

- (void)setNetworkServiceType:(NSURLRequestNetworkServiceType)networkServiceType {
    [self willChangeValueForKey:NSStringFromSelector(@selector(networkServiceType))];
    _networkServiceType = networkServiceType;
    [self didChangeValueForKey:NSStringFromSelector(@selector(networkServiceType))];
}

- (void)setTimeoutInterval:(NSTimeInterval)timeoutInterval {
    [self willChangeValueForKey:NSStringFromSelector(@selector(timeoutInterval))];
    _timeoutInterval = timeoutInterval;
    [self didChangeValueForKey:NSStringFromSelector(@selector(timeoutInterval))];
}

#pragma mark -

/*
    对请求头进行操作
 */
- (NSDictionary *)HTTPRequestHeaders {
    //将不可变字典转换成可变字典
    return [NSDictionary dictionaryWithDictionary:self.mutableHTTPRequestHeaders];
}

- (void)setValue:(NSString *)value
forHTTPHeaderField:(NSString *)field
{
    //对请求头字典进行追加
    [self.mutableHTTPRequestHeaders setValue:value forKey:field];
}

- (NSString *)valueForHTTPHeaderField:(NSString *)field {
    //根据不同的key提取出value
    return [self.mutableHTTPRequestHeaders valueForKey:field];
}

//通过账号密码设置授权请求头
- (void)setAuthorizationHeaderFieldWithUsername:(NSString *)username
                                       password:(NSString *)password
{
    //转化成data
    NSData *basicAuthCredentials = [[NSString stringWithFormat:@"%@:%@", username, password] dataUsingEncoding:NSUTF8StringEncoding];
    //base64编码加密
    NSString *base64AuthCredentials = [basicAuthCredentials base64EncodedStringWithOptions:(NSDataBase64EncodingOptions)0];
    //加入请求头字典
    [self setValue:[NSString stringWithFormat:@"Basic %@", base64AuthCredentials] forHTTPHeaderField:@"Authorization"];
}

//清除授权用请求头
- (void)clearAuthorizationHeader {
    [self.mutableHTTPRequestHeaders removeObjectForKey:@"Authorization"];
}

#pragma mark -
//设置查询参数的编码方式
- (void)setQueryStringSerializationWithStyle:(AFHTTPRequestQueryStringSerializationStyle)style {
    self.queryStringSerializationStyle = style;
    self.queryStringSerialization = nil;
}

//设置查询参数自定义编码的block
- (void)setQueryStringSerializationWithBlock:(NSString *(^)(NSURLRequest *, id, NSError *__autoreleasing *))block {
    self.queryStringSerialization = block;
}

#pragma mark -

//通过请求方式、URL、参数字典生成请求
- (NSMutableURLRequest *)requestWithMethod:(NSString *)method
                                 URLString:(NSString *)URLString
                                parameters:(id)parameters
                                     error:(NSError *__autoreleasing *)error
{
    NSParameterAssert(method);
    NSParameterAssert(URLString);

    NSURL *url = [NSURL URLWithString:URLString];

    NSParameterAssert(url);

    NSMutableURLRequest *mutableRequest = [[NSMutableURLRequest alloc] initWithURL:url];
    //设置请求方式
    mutableRequest.HTTPMethod = method;

    //如果某个关键属性被自主设置过、则用新的。不然直接用模板生成的`NSMutableURLRequest`即可
    for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
        if ([self.mutableObservedChangedKeyPaths containsObject:keyPath]) {
            [mutableRequest setValue:[self valueForKeyPath:keyPath] forKey:keyPath];
        }
    }

    //对req进一步设置(拼接URL、请求体、请求头)
    mutableRequest = [[self requestBySerializingRequest:mutableRequest withParameters:parameters error:error] mutableCopy];

    return mutableRequest;
}

/*
    数据上传专用处理
    不允许GET&&HEAD方法
    参数将会拼接到formdata中以表单的形式上传
 */
- (NSMutableURLRequest *)multipartFormRequestWithMethod:(NSString *)method
                                              URLString:(NSString *)URLString
                                             parameters:(NSDictionary *)parameters
                              constructingBodyWithBlock:(void (^)(id <AFMultipartFormData> formData))block
                                                  error:(NSError *__autoreleasing *)error
{
    NSParameterAssert(method);
    NSParameterAssert(![method isEqualToString:@"GET"] && ![method isEqualToString:@"HEAD"]);

    //生成req
    NSMutableURLRequest *mutableRequest = [self requestWithMethod:method URLString:URLString parameters:nil error:error];

    // 创建一个`AFStreamingMultipartFormData`实例，用来处理数据。
    __block AFStreamingMultipartFormData *formData = [[AFStreamingMultipartFormData alloc] initWithURLRequest:mutableRequest stringEncoding:NSUTF8StringEncoding];

    if (parameters) {
        //遍历参数字典(转化成的数组)
        for (AFQueryStringPair *pair in AFQueryStringPairsFromDictionary(parameters)) {
            NSData *data = nil;
            if ([pair.value isKindOfClass:[NSData class]]) {
                data = pair.value;
            } else if ([pair.value isEqual:[NSNull null]]) {
                data = [NSData data];
            } else {
                data = [[pair.value description] dataUsingEncoding:self.stringEncoding];
            }

            if (data) {
                //将每个参数拼接到`AFStreamingMultipartFormData`对象中
                [formData appendPartWithFormData:data name:[pair.field description]];
            }
        }
    }

    if (block) {
        block(formData);
    }
    //将请求体数据接入请求、并且返回处理完成的req
    return [formData requestByFinalizingMultipartFormData];
}

//将请求体中的文件、剥离出来
- (NSMutableURLRequest *)requestWithMultipartFormRequest:(NSURLRequest *)request
                             writingStreamContentsToFile:(NSURL *)fileURL
                                       completionHandler:(void (^)(NSError *error))handler
{
    //是否有HTTPBodyStream
    NSParameterAssert(request.HTTPBodyStream);
    //是否是个文件
    NSParameterAssert([fileURL isFileURL]);

    //获取写入对象
    NSInputStream *inputStream = request.HTTPBodyStream;
   // 使用outputStream将HTTPBodyStream的内容写入到路径为fileURL的文件中
    NSOutputStream *outputStream = [[NSOutputStream alloc] initWithURL:fileURL append:NO];
    __block NSError *error = nil;

    //异步写入
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        //开启读写工具
        [inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
        [outputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

        [inputStream open];
        [outputStream open];

        
        //读取数据 `hasBytesAvailable`代表是否有可用字节
        while ([inputStream hasBytesAvailable] && [outputStream hasSpaceAvailable]) {
            uint8_t buffer[1024];
            //将数据读取到buffer、每次最大读取1024
            NSInteger bytesRead = [inputStream read:buffer maxLength:1024];
            if (inputStream.streamError || bytesRead < 0) {
                error = inputStream.streamError;
                break;
            }
            
            //将buffer写入
            NSInteger bytesWritten = [outputStream write:buffer maxLength:(NSUInteger)bytesRead];
            if (outputStream.streamError || bytesWritten < 0) {
                error = outputStream.streamError;
                break;
            }
            
            //如果读取与写入都为0、代表转写结束
            if (bytesRead == 0 && bytesWritten == 0) {
                break;
            }
        }

        [outputStream close];
        [inputStream close];

        if (handler) {
            dispatch_async(dispatch_get_main_queue(), ^{
                handler(error);
            });
        }
    });

    NSMutableURLRequest *mutableRequest = [request mutableCopy];
    mutableRequest.HTTPBodyStream = nil;

    return mutableRequest;
}

#pragma mark - AFURLRequestSerialization

- (NSURLRequest *)requestBySerializingRequest:(NSURLRequest *)request
                               withParameters:(id)parameters
                                        error:(NSError *__autoreleasing *)error
{
    NSParameterAssert(request);

    NSMutableURLRequest *mutableRequest = [request mutableCopy];
    //设置请求头
    [self.HTTPRequestHeaders enumerateKeysAndObjectsUsingBlock:^(id field, id value, BOOL * __unused stop) {
        if (![request valueForHTTPHeaderField:field]) {
            [mutableRequest setValue:value forHTTPHeaderField:field];
        }
    }];

    //根据参数parameters设置查询字段
    NSString *query = nil;
    if (parameters) {
        //看看参数是否需要用户自定义转译
        if (self.queryStringSerialization) {
            NSError *serializationError;
            //调用用户block、获得参数转译的字符串
            query = self.queryStringSerialization(request, parameters, &serializationError);

            if (serializationError) {
                if (error) {
                    *error = serializationError;
                }

                return nil;
            }
        } else {
            //使用AFN的默认转译方式
            switch (self.queryStringSerializationStyle) {
                case AFHTTPRequestQueryStringDefaultStyle:
                    query = AFQueryStringFromParameters(parameters);
                    break;
            }
        }
    }

    //如果请求方式是需要将查询参数拼接到URL后面的(默认包含`GET``HEAD``DELETE`)、则拼接
    if ([self.HTTPMethodsEncodingParametersInURI containsObject:[[request HTTPMethod] uppercaseString]]) {
        if (query && query.length > 0) {
            //原url带有参数、则拼接'&'。没参数则拼接'?'
            mutableRequest.URL = [NSURL URLWithString:[[mutableRequest.URL absoluteString] stringByAppendingFormat:mutableRequest.URL.query ? @"&%@" : @"?%@", query]];
        }
    } else {
        //否则、则放入请求体
        // #2864: an empty string is a valid x-www-form-urlencoded payload
        if (!query) {
            query = @"";
        }
        if (![mutableRequest valueForHTTPHeaderField:@"Content-Type"]) {
            [mutableRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
        }
        [mutableRequest setHTTPBody:[query dataUsingEncoding:self.stringEncoding]];
    }

    return mutableRequest;
}

#pragma mark - NSKeyValueObserving
//可以决定是否发送KVO通知
+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key {
    if ([AFHTTPRequestSerializerObservedKeyPaths() containsObject:key]) {
        return NO;
    }

    return [super automaticallyNotifiesObserversForKey:key];
}


- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(__unused id)object
                        change:(NSDictionary *)change
                       context:(void *)context
{
    if (context == AFHTTPRequestSerializerObserverContext) {
        if ([change[NSKeyValueChangeNewKey] isEqual:[NSNull null]]) {
            //如果没有新值、则清空所属监听
            [self.mutableObservedChangedKeyPaths removeObject:keyPath];
        } else {
            [self.mutableObservedChangedKeyPaths addObject:keyPath];
        }
    }
}

#pragma mark - NSSecureCoding

+ (BOOL)supportsSecureCoding {
    return YES;
}

- (instancetype)initWithCoder:(NSCoder *)decoder {
    self = [self init];
    if (!self) {
        return nil;
    }

    self.mutableHTTPRequestHeaders = [[decoder decodeObjectOfClass:[NSDictionary class] forKey:NSStringFromSelector(@selector(mutableHTTPRequestHeaders))] mutableCopy];
    self.queryStringSerializationStyle = (AFHTTPRequestQueryStringSerializationStyle)[[decoder decodeObjectOfClass:[NSNumber class] forKey:NSStringFromSelector(@selector(queryStringSerializationStyle))] unsignedIntegerValue];

    return self;
}

- (void)encodeWithCoder:(NSCoder *)coder {
    [coder encodeObject:self.mutableHTTPRequestHeaders forKey:NSStringFromSelector(@selector(mutableHTTPRequestHeaders))];
    [coder encodeInteger:self.queryStringSerializationStyle forKey:NSStringFromSelector(@selector(queryStringSerializationStyle))];
}

#pragma mark - NSCopying

- (instancetype)copyWithZone:(NSZone *)zone {
    AFHTTPRequestSerializer *serializer = [[[self class] allocWithZone:zone] init];
    serializer.mutableHTTPRequestHeaders = [self.mutableHTTPRequestHeaders mutableCopyWithZone:zone];
    serializer.queryStringSerializationStyle = self.queryStringSerializationStyle;
    serializer.queryStringSerialization = self.queryStringSerialization;

    return serializer;
}

@end

#pragma mark - 请求体

//请求体拼接
static NSString * AFCreateMultipartFormBoundary() {
    return [NSString stringWithFormat:@"Boundary+%08X%08X", arc4random(), arc4random()];
}

static NSString * const kAFMultipartFormCRLF = @"\r\n";

static inline NSString * AFMultipartFormInitialBoundary(NSString *boundary) {
    return [NSString stringWithFormat:@"--%@%@", boundary, kAFMultipartFormCRLF];
}

static inline NSString * AFMultipartFormEncapsulationBoundary(NSString *boundary) {
    return [NSString stringWithFormat:@"%@--%@%@", kAFMultipartFormCRLF, boundary, kAFMultipartFormCRLF];
}

static inline NSString * AFMultipartFormFinalBoundary(NSString *boundary) {
    return [NSString stringWithFormat:@"%@--%@--%@", kAFMultipartFormCRLF, boundary, kAFMultipartFormCRLF];
}

static inline NSString * AFContentTypeForPathExtension(NSString *extension) {
    NSString *UTI = (__bridge_transfer NSString *)UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, (__bridge CFStringRef)extension, NULL);
    NSString *contentType = (__bridge_transfer NSString *)UTTypeCopyPreferredTagWithClass((__bridge CFStringRef)UTI, kUTTagClassMIMEType);
    if (!contentType) {
        return @"application/octet-stream";
    } else {
        return contentType;
    }
}

NSUInteger const kAFUploadStream3GSuggestedPacketSize = 1024 * 16;
NSTimeInterval const kAFUploadStream3GSuggestedDelay = 0.2;


/**
    单个请求体文件
 */
@interface AFHTTPBodyPart : NSObject
@property (nonatomic, assign) NSStringEncoding stringEncoding;//编码
@property (nonatomic, strong) NSDictionary *headers;//请求头
@property (nonatomic, copy) NSString *boundary;//边界
@property (nonatomic, strong) id body;//内容
@property (nonatomic, assign) unsigned long long bodyContentLength;//内容大小
@property (nonatomic, strong) NSInputStream *inputStream;//流

@property (nonatomic, assign) BOOL hasInitialBoundary;//是否有初始边界
@property (nonatomic, assign) BOOL hasFinalBoundary;//是否有结束边界

@property (readonly, nonatomic, assign, getter = hasBytesAvailable) BOOL bytesAvailable;//body是否存在
@property (readonly, nonatomic, assign) unsigned long long contentLength;//长度

//读取数据
- (NSInteger)read:(uint8_t *)buffer
        maxLength:(NSUInteger)length;
@end

//body文件整合工具
@interface AFMultipartBodyStream : NSInputStream <NSStreamDelegate>
@property (nonatomic, assign) NSUInteger numberOfBytesInPacket;//包大小
@property (nonatomic, assign) NSTimeInterval delay;//延迟
@property (nonatomic, strong) NSInputStream *inputStream;//输入流
@property (readonly, nonatomic, assign) unsigned long long contentLength;//内容大小
@property (readonly, nonatomic, assign, getter = isEmpty) BOOL empty;//是否为空

//初始化以及编码方式
- (instancetype)initWithStringEncoding:(NSStringEncoding)encoding;
//设置请求体数据片段的初始边界和结束边界
- (void)setInitialAndFinalBoundaries;
//追加请求体数据
- (void)appendHTTPBodyPart:(AFHTTPBodyPart *)bodyPart;
@end

#pragma mark -

//数据和request连接器
@interface AFStreamingMultipartFormData ()
@property (readwrite, nonatomic, copy) NSMutableURLRequest *request;//请求request
@property (readwrite, nonatomic, assign) NSStringEncoding stringEncoding;//编码
@property (readwrite, nonatomic, copy) NSString *boundary;//边界
@property (readwrite, nonatomic, strong) AFMultipartBodyStream *bodyStream;//body文件整合工具
@end

@implementation AFStreamingMultipartFormData

- (instancetype)initWithURLRequest:(NSMutableURLRequest *)urlRequest
                    stringEncoding:(NSStringEncoding)encoding
{
    self = [super init];
    if (!self) {
        return nil;
    }

    self.request = urlRequest;
    self.stringEncoding = encoding;
    self.boundary = AFCreateMultipartFormBoundary();
    self.bodyStream = [[AFMultipartBodyStream alloc] initWithStringEncoding:encoding];

    return self;
}

- (BOOL)appendPartWithFileURL:(NSURL *)fileURL
                         name:(NSString *)name
                        error:(NSError * __autoreleasing *)error
{
    NSParameterAssert(fileURL);
    NSParameterAssert(name);

    //https://www.baidu.com/abc.html     结果就是abc.html
    NSString *fileName = [fileURL lastPathComponent];
    //文件类型
    NSString *mimeType = AFContentTypeForPathExtension([fileURL pathExtension]);

    return [self appendPartWithFileURL:fileURL name:name fileName:fileName mimeType:mimeType error:error];
}

#pragma mark - 将文件添加进请求体
- (BOOL)appendPartWithFileURL:(NSURL *)fileURL
                         name:(NSString *)name
                     fileName:(NSString *)fileName
                     mimeType:(NSString *)mimeType
                        error:(NSError * __autoreleasing *)error
{
    NSParameterAssert(fileURL);
    NSParameterAssert(name);
    NSParameterAssert(fileName);
    NSParameterAssert(mimeType);

    if (![fileURL isFileURL]) {
        NSDictionary *userInfo = @{NSLocalizedFailureReasonErrorKey: NSLocalizedStringFromTable(@"Expected URL to be a file URL", @"AFNetworking", nil)};
        if (error) {
            *error = [[NSError alloc] initWithDomain:AFURLRequestSerializationErrorDomain code:NSURLErrorBadURL userInfo:userInfo];
        }

        return NO;
    } else if ([fileURL checkResourceIsReachableAndReturnError:error] == NO) {
        NSDictionary *userInfo = @{NSLocalizedFailureReasonErrorKey: NSLocalizedStringFromTable(@"File URL not reachable.", @"AFNetworking", nil)};
        if (error) {
            *error = [[NSError alloc] initWithDomain:AFURLRequestSerializationErrorDomain code:NSURLErrorBadURL userInfo:userInfo];
        }

        return NO;
    }

    //获取文件属性
    NSDictionary *fileAttributes = [[NSFileManager defaultManager] attributesOfItemAtPath:[fileURL path] error:error];
    if (!fileAttributes) {
        return NO;
    }

    NSMutableDictionary *mutableHeaders = [NSMutableDictionary dictionary];
    //请求头
    [mutableHeaders setValue:[NSString stringWithFormat:@"form-data; name=\"%@\"; filename=\"%@\"", name, fileName] forKey:@"Content-Disposition"];
    [mutableHeaders setValue:mimeType forKey:@"Content-Type"];

    //创建请求体模型、加入bodyStream准备处理
    AFHTTPBodyPart *bodyPart = [[AFHTTPBodyPart alloc] init];
    bodyPart.stringEncoding = self.stringEncoding;
    bodyPart.headers = mutableHeaders;
    bodyPart.boundary = self.boundary;
    bodyPart.body = fileURL;
    bodyPart.bodyContentLength = [fileAttributes[NSFileSize] unsignedLongLongValue];
    [self.bodyStream appendHTTPBodyPart:bodyPart];

    return YES;
}

#pragma mark - 将数据流添加进请求体
- (void)appendPartWithInputStream:(NSInputStream *)inputStream
                             name:(NSString *)name
                         fileName:(NSString *)fileName
                           length:(int64_t)length
                         mimeType:(NSString *)mimeType
{
    NSParameterAssert(name);
    NSParameterAssert(fileName);
    NSParameterAssert(mimeType);

    NSMutableDictionary *mutableHeaders = [NSMutableDictionary dictionary];
    [mutableHeaders setValue:[NSString stringWithFormat:@"form-data; name=\"%@\"; filename=\"%@\"", name, fileName] forKey:@"Content-Disposition"];
    [mutableHeaders setValue:mimeType forKey:@"Content-Type"];

    AFHTTPBodyPart *bodyPart = [[AFHTTPBodyPart alloc] init];
    bodyPart.stringEncoding = self.stringEncoding;
    bodyPart.headers = mutableHeaders;
    bodyPart.boundary = self.boundary;
    bodyPart.body = inputStream;

    bodyPart.bodyContentLength = (unsigned long long)length;

    [self.bodyStream appendHTTPBodyPart:bodyPart];
}

#pragma mark - 通过二进制文件设置请求体
- (void)appendPartWithFileData:(NSData *)data
                          name:(NSString *)name
                      fileName:(NSString *)fileName
                      mimeType:(NSString *)mimeType
{
    NSParameterAssert(name);
    NSParameterAssert(fileName);
    NSParameterAssert(mimeType);

    NSMutableDictionary *mutableHeaders = [NSMutableDictionary dictionary];
    [mutableHeaders setValue:[NSString stringWithFormat:@"form-data; name=\"%@\"; filename=\"%@\"", name, fileName] forKey:@"Content-Disposition"];
    [mutableHeaders setValue:mimeType forKey:@"Content-Type"];

    [self appendPartWithHeaders:mutableHeaders body:data];
}


- (void)appendPartWithFormData:(NSData *)data
                          name:(NSString *)name
{
    NSParameterAssert(name);

    NSMutableDictionary *mutableHeaders = [NSMutableDictionary dictionary];
    [mutableHeaders setValue:[NSString stringWithFormat:@"form-data; name=\"%@\"", name] forKey:@"Content-Disposition"];

    [self appendPartWithHeaders:mutableHeaders body:data];
}

- (void)appendPartWithHeaders:(NSDictionary *)headers
                         body:(NSData *)body
{
    NSParameterAssert(body);

    AFHTTPBodyPart *bodyPart = [[AFHTTPBodyPart alloc] init];
    bodyPart.stringEncoding = self.stringEncoding;
    bodyPart.headers = headers;
    bodyPart.boundary = self.boundary;
    bodyPart.bodyContentLength = [body length];
    bodyPart.body = body;

    [self.bodyStream appendHTTPBodyPart:bodyPart];
}


- (void)throttleBandwidthWithPacketSize:(NSUInteger)numberOfBytes
                                  delay:(NSTimeInterval)delay
{
    self.bodyStream.numberOfBytesInPacket = numberOfBytes;
    self.bodyStream.delay = delay;
}

#pragma mark - 将请求体数据接入请求
- (NSMutableURLRequest *)requestByFinalizingMultipartFormData {
    if ([self.bodyStream isEmpty]) {
        //如果body为空、则直接返回request
        return self.request;
    }

    // Reset the initial and final boundaries to ensure correct Content-Length
    [self.bodyStream setInitialAndFinalBoundaries];
    //将请求体接入request
    [self.request setHTTPBodyStream:self.bodyStream];
    
    [self.request setValue:[NSString stringWithFormat:@"multipart/form-data; boundary=%@", self.boundary] forHTTPHeaderField:@"Content-Type"];
    [self.request setValue:[NSString stringWithFormat:@"%llu", [self.bodyStream contentLength]] forHTTPHeaderField:@"Content-Length"];

    return self.request;
}

@end

NSInputStream和NSOutputSteam的使用

AFN的这个方法可以将请求体中的文件、剥离出来。具体怎么剥离呢？
就是将NSInputStream对象的内容转写到NSOutputSteam
和之前AFStreamingMultipartFormData的转写方法相比、少了很多判断、是最干净的案例了。

- (NSMutableURLRequest *)requestWithMultipartFormRequest:(NSURLRequest *)request
                             writingStreamContentsToFile:(NSURL *)fileURL
                                       completionHandler:(void (^)(NSError *error))handler
{
    //是否有HTTPBodyStream
    NSParameterAssert(request.HTTPBodyStream);
    //是否是个文件
    NSParameterAssert([fileURL isFileURL]);

    //获取写入对象
    NSInputStream *inputStream = request.HTTPBodyStream;
   // 使用outputStream将HTTPBodyStream的内容写入到路径为fileURL的文件中
    NSOutputStream *outputStream = [[NSOutputStream alloc] initWithURL:fileURL append:NO];
    __block NSError *error = nil;

    //异步写入
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        //开启读写工具
        [inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
        [outputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

        [inputStream open];
        [outputStream open];

        
        //读取数据 `hasBytesAvailable`代表是否有可用字节
        while ([inputStream hasBytesAvailable] && [outputStream hasSpaceAvailable]) {
            uint8_t buffer[1024];
            //将数据读取到buffer、每次最大读取1024
            NSInteger bytesRead = [inputStream read:buffer maxLength:1024];
            if (inputStream.streamError || bytesRead < 0) {
                error = inputStream.streamError;
                break;
            }
            
            //将buffer写入
            NSInteger bytesWritten = [outputStream write:buffer maxLength:(NSUInteger)bytesRead];
            if (outputStream.streamError || bytesWritten < 0) {
                error = outputStream.streamError;
                break;
            }
            
            //如果读取与写入都为0、代表转写结束
            if (bytesRead == 0 && bytesWritten == 0) {
                break;
            }
        }

        [outputStream close];
        [inputStream close];

        if (handler) {
            dispatch_async(dispatch_get_main_queue(), ^{
                handler(error);
            });
        }
    });

    NSMutableURLRequest *mutableRequest = [request mutableCopy];
    mutableRequest.HTTPBodyStream = nil;

    return mutableRequest;
}

当然、这个HttpBodySteam必须是通过AFN生成的AFMultipartBodyStream实例
才会执行这个代理方法

- (NSInteger)read:(uint8_t *)buffer
        maxLength:(NSUInteger)length
{
    if ([self streamStatus] == NSStreamStatusClosed) {
        return 0;
    }
    
    //总大小
    NSInteger totalNumberOfBytesRead = 0;

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wgnu"
    //遍历读取数据
    while ((NSUInteger)totalNumberOfBytesRead < MIN(length, self.numberOfBytesInPacket)) {
        
        //body不存在或者没有可读字节
        if (!self.currentHTTPBodyPart || ![self.currentHTTPBodyPart hasBytesAvailable]) {
            //把下一个body文件赋值给当前body
            if (!(self.currentHTTPBodyPart = [self.HTTPBodyPartEnumerator nextObject])) {
                break;
            }
        } else {
            //存在可读数据
            
            NSUInteger maxLength = MIN(length, self.numberOfBytesInPacket) - (NSUInteger)totalNumberOfBytesRead;
            
            //把当前body读取到buffer中。内部会采用递归的方式将数据分段写入buffer
            NSInteger numberOfBytesRead = [self.currentHTTPBodyPart read:&buffer[totalNumberOfBytesRead] maxLength:maxLength];
            
            if (numberOfBytesRead == -1) {
                self.streamError = self.currentHTTPBodyPart.inputStream.streamError;
                break;
            } else {
                totalNumberOfBytesRead += numberOfBytesRead;

                if (self.delay > 0.0f) {
                    [NSThread sleepForTimeInterval:self.delay];
                }
            }
        }
    }
#pragma clang diagnostic pop

    return totalNumberOfBytesRead;
}

APIDemo

说实话两个文件加起来两千多行、每行都想顾及到我自己都不知道怎么写...但是把很多代码都进行了注释、有兴趣可以自取:

GitHub

参考资料

AFNetworking源码 - Multipart协议，AFURLRequestSerialization和AFURLResponseSerialization
iOS开发笔记之基于键值的观察者模式(KVO)
AFNetworking 3.0 源码解读（三）之 AFURLRequestSerialization
HTTP请求报文（请求行、请求头、请求体）
HTTP协议之multipart/form-data请求分析

iOS源码补完计划--AFNetworking(四)

目录

前言

AFN概述:《iOS源码补完计划--AFNetworking 3.1.0源码研读》

流程图

核心代码

请求头

请求体

1、通过`Parameters`(参数字典)构建的请求体

将字典转化成字符串并且转译

根据不同情况将参数字符串拼接到URL后、或者放入请求体

2、通过文件构建的请求体

AFStreamingMultipartFormData

核心方法（将文件分段拼接）

AFHTTPRequestSerializer

AFHTTPRequestSerializer.h

AFHTTPRequestSerializer.m

NSInputStream和NSOutputSteam的使用

APIDemo

GitHub

参考资料

相关文章

网友评论

延伸阅读

深度阅读

栏目导航

热点阅读

技术干货

IOS

程序员

iOS网络

iOS源码补完计划--AFNetworking(四)

目录

前言

AFN概述:《iOS源码补完计划--AFNetworking 3.1.0源码研读》

流程图

核心代码

请求头

请求体

1、通过Parameters(参数字典)构建的请求体

将字典转化成字符串并且转译

根据不同情况将参数字符串拼接到URL后、或者放入请求体

2、通过文件构建的请求体

AFStreamingMultipartFormData

核心方法（将文件分段拼接）

AFHTTPRequestSerializer

AFHTTPRequestSerializer.h

AFHTTPRequestSerializer.m

NSInputStream和NSOutputSteam的使用

APIDemo

GitHub

参考资料

相关文章

网友评论

延伸阅读

深度阅读

栏目导航

热点阅读

技术干货

IOS

程序员

iOS网络

1、通过`Parameters`(参数字典)构建的请求体