AFNetworking源码分析 (3)--AFURLReque

作者: Arnold134777 | 来源:发表于2017-06-17 22:15 被阅读104次

系列文章：

[AFNetWorking源码分析 (1)--AFHTTPSessionManager] (http://www.jianshu.com/p/bbfa827d699e)

[AFNetWorking源码分析 (2)--NSURLSessionDownloadTask] (http://www.jianshu.com/p/db275fd86640)

上文中我们分析了AF中关于网络下载，NSURLSessionDownloadTask的分析。
本章将开始分析Serialization中的一个核心类请求数据封装类--AFURLRequestSerialization。

1.初始化requestSerializer

参考例子沿用(1)中的例子：

AFHTTPSessionManager *session = [AFHTTPSessionManager manager];
session.responseSerializer.acceptableContentTypes = [NSSet setWithObjects:@"text/html",@"application/json", @"text/json" ,@"text/javascript", nil];
session.responseSerializer = [AFHTTPResponseSerializer serializer];
[session GET:@"https://www.baidu.com"
  parameters:nil
    progress:nil
     success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
         NSLog(@"请求成功");
     } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
          NSLog(@"请求失败");
     }];

查看manager的调用栈我们在AFHTTPSessionManager的如下接口完成对全局
requestSerializer的初始化。

- (instancetype)initWithBaseURL:(NSURL *)url
           sessionConfiguration:(NSURLSessionConfiguration *)configuration
{
    ...
    self.requestSerializer = [AFHTTPRequestSerializer serializer];
    ...

    return self;
}

1.1 [AFHTTPRequestSerializer serializer]

// 1.指定数据的编码格式
self.stringEncoding = NSUTF8StringEncoding;

// 2.请求的头部信息字典
self.mutableHTTPRequestHeaders = [NSMutableDictionary dictionary];

// 3.设置头部中请求的自然语言列表
// Accept-Language HTTP Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4
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;
}];
[self setValue:[acceptLanguagesComponents componentsJoinedByString:@", "] forHTTPHeaderField:@"Accept-Language"];

// 4.设置请求的UA
NSString *userAgent = nil;
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]];
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;
        }
    }
    [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];

// 5.kvo的方式监听allowsCellularAccess，cachePolicy，HTTPShouldHandleCookies，HTTPShouldUsePipelining，networkServiceType，timeoutInterval的属性的变化
self.mutableObservedChangedKeyPaths = [NSMutableSet set];
for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
    if ([self respondsToSelector:NSSelectorFromString(keyPath)]) {
        [self addObserver:self forKeyPath:keyPath options:NSKeyValueObservingOptionNew context:AFHTTPRequestSerializerObserverContext];
    }
}

举例当外部更改cachePolicy的值时，依次执行如下方法：

 // 1.必须调用willChangeValueForKey与didChangeValueForKey自己触发observeValueForKeyPath的调用，因为代码段2
- (void)setCachePolicy:(NSURLRequestCachePolicy)cachePolicy {
    [self willChangeValueForKey:NSStringFromSelector(@selector(cachePolicy))];
    _cachePolicy = cachePolicy;
    [self didChangeValueForKey:NSStringFromSelector(@selector(cachePolicy))];
}

// 2.可以指定属性变化时observeValueForKeyPath是否自动执行，很显然这里监听的几个属性都是需要手动触发，这也就解释了1中的问题
+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key {
    if ([AFHTTPRequestSerializerObservedKeyPaths() containsObject:key]) {
        return NO;
    }

    return [super automaticallyNotifiesObserversForKey:key];
}

// 3.监听上述kvo监听的几个属性值的变化，操作全局的变化的属性集合
- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(__unused id)object
                        change:(NSDictionary *)change
                       context:(void *)context
{
    if (context == AFHTTPRequestSerializerObserverContext) {
        if ([change[NSKeyValueChangeNewKey] isEqual:[NSNull null]]) {
            [self.mutableObservedChangedKeyPaths removeObject:keyPath];
        } else {
            [self.mutableObservedChangedKeyPaths addObject:keyPath];
        }
    }
}

2.根据requestSerializer初始化request

初始化request的代码如下：

NSError *serializationError = nil;
NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];

下面我们来具体分析具体的处理逻辑。

2.1 requestWithMethod:URLString:parameters:error:

// 1.初始化request的实例
NSMutableURLRequest *mutableRequest = [[NSMutableURLRequest alloc] initWithURL:url];
mutableRequest.HTTPMethod = method;

// 2.将requestSerializer 中的存储的请求策略的属性值赋值给re  quest
for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
    if ([self.mutableObservedChangedKeyPaths containsObject:keyPath]) {
        [mutableRequest setValue:[self valueForKeyPath:keyPath] forKey:keyPath];
    }
}

mutableRequest = [[self requestBySerializingRequest:mutableRequest withParameters:parameters error:error] mutableCopy];

2.2 requestBySerializingRequest:withParameters:error:

该接口是AFURLRequestSerialization 协议定义的接口，该协议同时实现NSObject,NSSecureCoding, NSCopying 三个协议用于实现基本的Object行为，安全编码，拷贝功能。下面我们会依次分析实现这个协议的三个类：AFHTTPRequestSerializer,AFJSONRequestSerializer,AFPropertyListRequestSerializer

2.2.1 AFHTTPRequestSerializer

- (NSURLRequest *)requestBySerializingRequest:(NSURLRequest *)request
                               withParameters:(id)parameters
                                        error:(NSError *__autoreleasing *)error
{
    NSParameterAssert(request);
    
    // 1.遍历外部设置的httpRequestHeaders然后依次设置到mutableRequest中
    NSMutableURLRequest *mutableRequest = [request mutableCopy];

    [self.HTTPRequestHeaders enumerateKeysAndObjectsUsingBlock:^(id field, id value, BOOL * __unused stop) {
        if (![request valueForHTTPHeaderField:field]) {
            [mutableRequest setValue:value forHTTPHeaderField:field];
        }
    }];

   // 2.处理请求的参数
    NSString *query = nil;
    if (parameters) {
        // 2.1 如果外部自己实现参数的处理则直接获取外部处理数据
        if (self.queryStringSerialization) {
            NSError *serializationError;
            query = self.queryStringSerialization(request, parameters, &serializationError);

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

                return nil;
            }
        } else {
            // 2.2 否则走默认的实现方式，这里递归的方式实现（下面会具体分析）
            switch (self.queryStringSerializationStyle) {
                case AFHTTPRequestQueryStringDefaultStyle:
                    query = AFQueryStringFromParameters(parameters);
                    break;
            }
        }
    }

    // 3.将parameters处理后的数据拼接到URL中还是设置到httpBody中，默认的`GET`, `HEAD`,`DELETE`是拼接到URL中,`POST`,`PUT`是设置到httpBody中
    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 {
        // #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;
}

2.2.1.1 AFQueryStringFromParameters(NSDictionary *parameters)

源码注释很清楚，此处只写出核心思想：

核心函数：AFQueryStringPairsFromKeyAndValue

核心思想：递归的方式实现，针对NSDictionary,NSArray,NSSet 三种数据遍历处理，然后针对每个内部元素递归处理。

Model：AFQueryStringPair是临时存储key与value的实例类，其中有一个核心的函数AFPercentEscapedStringFromString

2.2.1.2 AFPercentEscapedStringFromString(NSString *string)

NSString * AFPercentEscapedStringFromString(NSString *string) {

    // 1.将部分分隔符与保留字排除在允许不编码的字符集内
    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]];

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

    // 2.处理多字节字符的问题，我们平常书写的字符, 并不全部都是用唯一的一个16位字符来表示, 而是有一部分用两个16位字符来表示（表情字符）
    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);
        // 2.1 分段处理一个个完整的字符，然后再次拼接
        // 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;
}

2.2.2 AFJSONRequestSerializer,AFPropertyListRequestSerializer

都是AFHTTPRequestSerializer的派生类，一般针对POST,PUT的网络请求，对请求的字典参数分别使用NSJSONSerialization，NSPropertyListSerialization 序列化。

/**
 `AFJSONRequestSerializer` is a subclass of `AFHTTPRequestSerializer` that encodes parameters as JSON using `NSJSONSerialization`, setting the `Content-Type` of the encoded request to `application/json`.
 */
@interface AFJSONRequestSerializer : AFHTTPRequestSerializer

/**
 `AFPropertyListRequestSerializer` is a subclass of `AFHTTPRequestSerializer` that encodes parameters as JSON using `NSPropertyListSerializer`, setting the `Content-Type` of the encoded request to `application/x-plist`.
 */
@interface AFPropertyListRequestSerializer : AFHTTPRequestSerializer

2.3 multipartFormRequestWithMethod:URLString:parameters:constructingBodyWithBlock:error:

我们先看看接口注释：

Creates an `NSMutableURLRequest` object with the specified HTTP method and URLString, and constructs a `multipart/form-data` 
HTTP body, using the specified parameters and multipart form data block。
Multipart form requests are automatically streamed, reading files directly from disk along with in-memory data in a single HTTP body. The resulting `NSMutableURLRequest` object has an `HTTPBodyStream` property, so refrain from setting `HTTPBodyStream` or `HTTPBody` on this request object, as it will clear out the multipart form body stream.

显而易见这里是上传数据的接口。

2.3.1 图片上传的例子

首先利用ImageServer,搭建一个本地的图片服务器供iOS上传接口测试使用。下面是iOS具体上传的例子：

- (void)uploadImage{
    self.session = [AFHTTPSessionManager manager];
    _session.responseSerializer = [AFJSONResponseSerializer serializer];
    _session.responseSerializer.acceptableContentTypes = nil;
    NSString *path = [[NSBundle mainBundle] pathForResource:@"github_1"
                                           ofType:@"jpeg"];
    NSData *data = [NSData dataWithContentsOfFile:path];
    NSString *url = @"http://192.168.2.12:8888/";
    NSMutableURLRequest *request = [_session.requestSerializer
                                    multipartFormRequestWithMethod:@"POST"
                                    URLString:url
                                    parameters:nil
                                    constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
                                        [formData appendPartWithFileData:data
                                                                    name:@"file"
                                                                fileName:@"github_1.jpeg"
                                                                mimeType:@"application/octet-stream"];
                                    }
                                    
                                    error:nil];
    request.timeoutInterval = 10;
    
    NSURLSessionUploadTask *uploadTask = [_session uploadTaskWithRequest:request fromData:nil progress:nil completionHandler:^(NSURLResponse * _Nonnull response, id  _Nullable responseObject, NSError * _Nullable error) {
        if (error == nil) {
            NSLog(@"文件上传成功");
        } else {
            NSLog(@"文件上传失败 -> %@",error);
        }
    }];
    [uploadTask resume];
}

2.3.2 具体的实现分析

我们先使用Charles抓包看一下请求的格式：

POST / HTTP/1.1
Host    127.0.0.1:8989
Content-Type    multipart/form-data; boundary=Boundary+0544FD8CDFD7A4C1
Connection  keep-alive
Accept  */*
User-Agent  InterView/1.0 (iPhone; iOS 10.0; Scale/2.00)
Accept-Language en;q=1, zh-Hans-US;q=0.9
Content-Length  11027
Accept-Encoding gzip, deflate


--Boundary+0544FD8CDFD7A4C1
Content-Disposition: form-data; name="file"; filename="github_1.jpeg"
Content-Type: application/octet-stream

// 二进制数据

--Boundary+0544FD8CDFD7A4C1--

Content-Type必须是这样的Content-Type: multipart/form-data; boundary=${bound}，类似0544FD8CDFD7A4C1是随机数生成的。

每一部分以$--{bound}开始，以--{bound}--结束。

下面我们针对代码具体分析。

2.3.2.1 AFHTTPRequestSerializer multipartFormRequestWithMethod:URLString:parameters:constructingBodyWithBlock:error:

// 1.初始化一个待提交的multipart的实例
__block AFStreamingMultipartFormData *formData = [[AFStreamingMultipartFormData alloc] initWithURLRequest:mutableRequest stringEncoding:NSUTF8StringEncoding];

// 2.针对请求的参数依次拼接到请求的formData中
if (parameters) {
    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) {
            [formData appendPartWithFormData:data name:[pair.field description]];
        }
    }
}

// 3.外部如果需要对提交的表单做操作可以实现该block,完成自定义的操作
if (block) {
    block(formData);
}

// 4.将整理的表单数据配置到请求的实例中
return [formData requestByFinalizingMultipartFormData];

2.3.2.2 AFStreamingMultipartFormData initWithURLRequest:stringEncoding:

self.request = urlRequest;
self.stringEncoding = encoding;

// 1.这里说明了是随机数字的16进制字符拼接(见下接口实现)
self.boundary = AFCreateMultipartFormBoundary();

// 2.初始化数据流的实例，后续会设置到请求request中
self.bodyStream = [[AFMultipartBodyStream alloc] initWithStringEncoding:encoding];


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

2.3.2.3 AFStreamingMultipartFormData requestByFinalizingMultipartFormData

- (NSMutableURLRequest *)requestByFinalizingMultipartFormData {
    if ([self.bodyStream isEmpty]) {
        return self.request;
    }

    // 1.对bodyStream中的HTTPBodyParts集合中的每一个AFHTTPBodyPart做hasInitialBoundary，hasFinalBoundary的标识，以便区分设置2.2.2开始部分请求数据。
    
    [self.bodyStream setInitialAndFinalBoundaries];
    
    // 2.将数据流绑定到请求的request实例中
    // 官方描述：The input stream should be unopened and the receiver will take over as the stream’s delegate
    [self.request setHTTPBodyStream:self.bodyStream];

    // 3.设置请求的头信息
    [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;
}

2.3.2.4 read:maxLength:

当[self.request setHTTPBodyStream:self.bodyStream];设置后，请求任务开始执行，下面的方法就会被回调：

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

    NSInteger totalNumberOfBytesRead = 0;
    
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wgnu"

    // 1.遍历的方式读取么一个AFHTTPBodyPart中的数据
    while ((NSUInteger)totalNumberOfBytesRead < MIN(length, self.numberOfBytesInPacket)) {
        if (!self.currentHTTPBodyPart || ![self.currentHTTPBodyPart hasBytesAvailable]) {
            // 2.读取到最后一个为nil时跳出循环
            if (!(self.currentHTTPBodyPart = [self.HTTPBodyPartEnumerator nextObject])) {
                break;
            }
        } else {
           // 3.读取当前的AFHTTPBodyPart中的收
            NSUInteger maxLength = MIN(length, self.numberOfBytesInPacket) - (NSUInteger)totalNumberOfBytesRead;
            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;
}

2.3.2.5 AFHTTPBodyPart read:maxLength:

// 四个状态的改变，表示依次解析顶部分割标识，headers数据,二进制数据bodyData,底部分割标识
- (NSInteger)read:(uint8_t *)buffer
        maxLength:(NSUInteger)length
{
    NSInteger totalNumberOfBytesRead = 0;

    if (_phase == AFEncapsulationBoundaryPhase) {
       
    }

    if (_phase == AFHeaderPhase) {
    
    }

    if (_phase == AFBodyPhase) {
        
    }

    if (_phase == AFFinalBoundaryPhase) {
       
    }

    return totalNumberOfBytesRead;
}

- (NSInteger)readData:(NSData *)data
           intoBuffer:(uint8_t *)buffer
            maxLength:(NSUInteger)length
{
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wgnu"
    NSRange range = NSMakeRange((NSUInteger)_phaseReadOffset, MIN([data length] - ((NSUInteger)_phaseReadOffset), length));
    [data getBytes:buffer range:range];
#pragma clang diagnostic pop

    _phaseReadOffset += range.length;
    
    // 1.当_phaseReadOffset < [data length] 标识数据已经读取完毕
    if (((NSUInteger)_phaseReadOffset) >= [data length]) {
        // 2.存在有数据未读取完成，继续改变状态读取相应的信息
        [self transitionToNextPhase];
    }

    return (NSInteger)range.length;
}