序言
在上一篇文章文章中，簡單介紹了GCDAsyncSocket的使用，socket創(chuàng)建、連接、發(fā)送消息、接收消息、關(guān)閉socket、粘包分包、以及心跳包機制。并且立下了一個flag，所以在這篇文章，將帶來GCDAsyncSocket的源碼分析，看看在GCDAsyncSocket中是如何運用原生代碼并封裝起來的，在簡單實現(xiàn)的原生代碼基礎(chǔ)上，他又做了什么樣的操作。
我們還是按照創(chuàng)建socket、連接socket、發(fā)送消息、接收消息、關(guān)閉socket的順序，一步一步深入了解GCDAsyncSocket。
1. GCDAsyncSocket初始化
在開始之前，GCDAsyncSocket.m中聲明了許許多多的成員變量，先看看都是啥。
@implementation GCDAsyncSocket
{
//flags，當前正在做操作的標識符
uint32_t flags;
uint16_t config;
//代理
__weak id<GCDAsyncSocketDelegate> delegate;
//代理回調(diào)的queue
dispatch_queue_t delegateQueue;
//本地IPV4Socket
int socket4FD;
//本地IPV6Socket
int socket6FD;
//unix域的套接字 // 進程通訊 locahost VS 127.0.0.1
int socketUN;
//unix域 服務(wù)端 url
NSURL *socketUrl;
//狀態(tài)Index
int stateIndex;
//本機的IPV4地址 --- 地址host interface
NSData * connectInterface4;
//本機的IPV6地址
NSData * connectInterface6;
//本機unix域地址
NSData * connectInterfaceUN;
//這個類的對Socket的操作都在這個queue中，串行
dispatch_queue_t socketQueue;
// 源 ---> mergdata get_data buffer tls ssl CFStream
// data
dispatch_source_t accept4Source;
dispatch_source_t accept6Source;
dispatch_source_t acceptUNSource;
//連接timer,GCD定時器 重連
dispatch_source_t connectTimer;
dispatch_source_t readSource;
dispatch_source_t writeSource;
dispatch_source_t readTimer;
dispatch_source_t writeTimer;
//讀寫數(shù)據(jù)包數(shù)組 類似queue，最大限制為5個包 - FIFO
NSMutableArray *readQueue;
NSMutableArray *writeQueue;
//當前正在讀寫數(shù)據(jù)包
GCDAsyncReadPacket *currentRead;
GCDAsyncWritePacket *currentWrite;
//當前socket未獲取完的數(shù)據(jù)大小
unsigned long socketFDBytesAvailable;
//全局公用的提前緩沖區(qū)
GCDAsyncSocketPreBuffer *preBuffer;
#if TARGET_OS_IPHONE
CFStreamClientContext streamContext;
//讀的數(shù)據(jù)流 ---- c
CFReadStreamRef readStream;
//寫的數(shù)據(jù)流
CFWriteStreamRef writeStream;
#endif
//SSL上下文，用來做SSL認證
SSLContextRef sslContext;
//全局公用的SSL的提前緩沖區(qū)
GCDAsyncSocketPreBuffer *sslPreBuffer;
size_t sslWriteCachedLength;
//記錄SSL讀取數(shù)據(jù)錯誤
OSStatus sslErrCode;
//記錄SSL握手的錯誤
OSStatus lastSSLHandshakeError;
//socket隊列的標識key -- key - queue
void *IsOnSocketQueueOrTargetQueueKey;
id userData;
//連接備選服務(wù)端地址的延時 （另一個IPV4或IPV6）
NSTimeInterval alternateAddressDelay;
}
創(chuàng)建函數(shù)
self.socket = [[GCDAsyncSocket alloc] initWithDelegate:self delegateQueue:dispatch_get_global_queue(0, 0)];
這個init方法最終將會來到，在這個方法里，socketQueue傳值為NULL，所以后面如果有sq的部分可以先行跳過，等梳理完了，再去看看這個sq具體都干了啥。
- (id)initWithDelegate:(id)aDelegate delegateQueue:(dispatch_queue_t)dq socketQueue:(dispatch_queue_t)sq
{
if((self = [super init]))
{
delegate = aDelegate;
delegateQueue = dq;
//這個宏是在sdk6.0之后才有的,如果是之前的,則OS_OBJECT_USE_OBJC為0，!0即執(zhí)行if語句
//對6.0的適配，如果是6.0以下，則去retain release，6.0之后ARC也管理了GCD
//作者很細
#if !OS_OBJECT_USE_OBJC
if (dq) dispatch_retain(dq);
#endif
//創(chuàng)建socket，先都置為 -1 , 代表socket默認創(chuàng)建失敗
//本機的ipv4
socket4FD = SOCKET_NULL;
//ipv6
socket6FD = SOCKET_NULL;
//應(yīng)該是UnixSocket
socketUN = SOCKET_NULL;
//url
socketUrl = nil;
//狀態(tài)
stateIndex = 0;
//這里并沒有sq，可以選擇跳過
if (sq)
{
//如果scoketQueue是global的,則報錯。斷言必須要一個非并行queue。
NSAssert(sq != dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0),
@"The given socketQueue parameter must not be a concurrent queue.");
NSAssert(sq != dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0),
@"The given socketQueue parameter must not be a concurrent queue.");
NSAssert(sq != dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
@"The given socketQueue parameter must not be a concurrent queue.");
//拿到scoketQueue
socketQueue = sq;
//iOS6之下retain
#if !OS_OBJECT_USE_OBJC
dispatch_retain(sq);
#endif
}
else
{
//沒有的話創(chuàng)建一個socketQueue， 名字為：GCDAsyncSocket,NULL = 串行
socketQueue = dispatch_queue_create([GCDAsyncSocketQueueName UTF8String], NULL);
}
//比如原來為 0X123 -> NULL 變成 0X222->0X123->NULL
//自己的指針等于自己原來的指針，成二級指針了 看了注釋是為了以后省略&,讓代碼更可讀？
//這里不懂作者的用意，繼續(xù)往下看
IsOnSocketQueueOrTargetQueueKey = &IsOnSocketQueueOrTargetQueueKey;
void *nonNullUnusedPointer = (__bridge void *)self;
//dispatch_queue_set_specific給當前隊里加一個標識 dispatch_get_specific當前線程取出這個標識，判斷是不是在這個隊列
dispatch_queue_set_specific(socketQueue, IsOnSocketQueueOrTargetQueueKey, nonNullUnusedPointer, NULL);
//讀的數(shù)組
readQueue = [[NSMutableArray alloc] initWithCapacity:5];
currentRead = nil;
//寫的數(shù)組
writeQueue = [[NSMutableArray alloc] initWithCapacity:5];
currentWrite = nil;
//緩沖區(qū) 設(shè)置大小為 4kb
preBuffer = [[GCDAsyncSocketPreBuffer alloc] initWithCapacity:(1024 * 4)];
#pragma mark alternateAddressDelay??
//交替地址延時？？ wtf 應(yīng)該是用來給備用地址的
alternateAddressDelay = 0.3;
}
return self;
}
看完這段代碼...懵逼。只是一些初始化操作。本來還以為create()會在這里面呢，很無奈啊，哎，先不管了，繼續(xù)往下看吧。
2. GCDAsyncSocket Connect
外層調(diào)用
[self.socket connectToHost:@"127.0.0.1" onPort:8090 withTimeout:-1 error:&error];
底層最終會來到這里，每個方法都好長啊 - - 。這里的inInterface傳入的是nil，所以，跟上面那個方法的sq一樣，如果有遇到可以選擇跳過。
- (BOOL)connectToHost:(NSString *)inHost
onPort:(uint16_t)port
viaInterface:(NSString *)inInterface
withTimeout:(NSTimeInterval)timeout
error:(NSError **)errPtr
{
//LogObjc(LOG_FLAG_VERBOSE, @"%@: %@", THIS_FILE, THIS_METHOD) -- 跟蹤當前行為
LogTrace();
//拿到host ,copy防止值被修改
NSString *host = [inHost copy];
//interface？接口？先不管 反正是nil
NSString *interface = [inInterface copy];
//聲明兩個__block的臨時變量
__block BOOL result = NO;
//error信息
__block NSError *preConnectErr = nil;
//gcdBlock ,都包裹在自動釋放池中 :
// 1: 大量臨時變量 connect : 重連
// 2: 自定義線程管理 : nsoperation
// 3: 非UI 命令 工具
dispatch_block_t block = ^{ @autoreleasepool {
// Check for problems with host parameter
// 翻譯：檢查host參數(shù) 是否存在問題
if ([host length] == 0)
{
NSString *msg = @"Invalid host parameter (nil or \"\"). Should be a domain name or IP address string.";
preConnectErr = [self badParamError:msg];
// 其實就是return,大牛的代碼真是充滿逼格 - ret
// 里面有注釋，有想法的可以自己去看看，大概意思就是
// 可以讓這個return能更快的被read，后面還有很多地方被調(diào)用到
return_from_block;
}
//一個前置的檢查,如果沒通過返回，這q個檢查里，如果interface有值，則會將本機的IPV4 IPV6的 address設(shè)置上。
// 參數(shù) : 指針 操作同一片內(nèi)存空間
// 因為interface 是nil，所以不會執(zhí)行return
if (![self preConnectWithInterface:interface error:&preConnectErr])
{
return_from_block;
}
// We've made it past all the checks.我們已經(jīng)檢查了所有參數(shù)
// It's time to start the connection process.是時候開始連接了
//flags 做或等運算。 flags標識為開始Socket連接
flags |= kSocketStarted;
//又是一個{}? 只是為了標記么？
LogVerbose(@"Dispatching DNS lookup...");
//很可能給我們的服務(wù)端的參數(shù)是一個可變字符串
//所以我們需要copy，在Block里同步的執(zhí)行
//這種基于Block的異步查找，不需要擔(dān)心它被改變
//copy，防止改變
NSString *hostCpy = [host copy];
//拿到狀態(tài) 初始化的時候 stateIndex = 0
int aStateIndex = stateIndex;
__weak GCDAsyncSocket *weakSelf = self;
//獲取全局并發(fā)Queue
dispatch_queue_t globalConcurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
//異步執(zhí)行，這里的autoreleasepool 跟上面的一樣，可以往上翻
dispatch_async(globalConcurrentQueue, ^{ @autoreleasepool {
//忽視循環(huán)引用，牛逼
#pragma clang diagnostic push
#pragma clang diagnostic warning "-Wimplicit-retain-self"
//查找錯誤
NSError *lookupErr = nil;
//server地址數(shù)組（包含IPV4 IPV6的地址 sockaddr_in6、sockaddr_in類型）
NSMutableArray *addresses = [[self class] lookupHost:hostCpy port:port error:&lookupErr];
//strongSelf
__strong GCDAsyncSocket *strongSelf = weakSelf;
//完整Block安全形態(tài)，在加個if
if (strongSelf == nil) return_from_block;
//如果有錯
if (lookupErr)
{
//用cocketQueue
dispatch_async(strongSelf->socketQueue, ^{ @autoreleasepool {
//一些錯誤處理，清空一些數(shù)據(jù)等等
[strongSelf lookup:aStateIndex didFail:lookupErr];
}});
}
//正常
else
{
NSData *address4 = nil;
NSData *address6 = nil;
//遍歷地址數(shù)組
for (NSData *address in addresses)
{
//判斷address4為空，且address為IPV4
if (!address4 && [[self class] isIPv4Address:address])
{
address4 = address;
}
//判斷address6為空，且address為IPV6
else if (!address6 && [[self class] isIPv6Address:address])
{
address6 = address;
}
}
//異步去發(fā)起
dispatch_async(strongSelf->socketQueue, ^{ @autoreleasepool {
// 方法名大概是說，address4 address6 兩個地址都成功獲取到了。
[strongSelf lookup:aStateIndex didSucceedWithAddress4:address4 address6:address6];
}});
}
#pragma clang diagnostic pop
}});
//開啟連接超時
[self startConnectTimeout:timeout];
result = YES;
}};
//在socketQueue中執(zhí)行這個Block
if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
block();
//否則同步的調(diào)起這個queue去執(zhí)行
else
dispatch_sync(socketQueue, block);
//如果有錯誤，賦值錯誤
if (errPtr) *errPtr = preConnectErr;
//把連接是否成功的result返回
return result;
}
這個connect跟想的也不太一樣，并沒有熟悉的connect()，有毒。但是！還知道這個方法里都干了啥呢。
[strongSelf lookup:aStateIndex didSucceedWithAddress4:address4 address6:address6];
一探究竟！
- (void)lookup:(int)aStateIndex didSucceedWithAddress4:(NSData *)address4 address6:(NSData *)address6
{
LogTrace();
NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
//至少有一個server地址
NSAssert(address4 || address6, @"Expected at least one valid address");
//如果狀態(tài)不一致，說明斷開連接
if (aStateIndex != stateIndex)
{
LogInfo(@"Ignoring lookupDidSucceed, already disconnected");
// The connect operation has been cancelled.
// That is, socket was disconnected, or connection has already timed out.
return;
}
// Check for problems
//分開判斷。
BOOL isIPv4Disabled = (config & kIPv4Disabled) ? YES : NO;
BOOL isIPv6Disabled = (config & kIPv6Disabled) ? YES : NO;
if (isIPv4Disabled && (address6 == nil))
{
NSString *msg = @"IPv4 has been disabled and DNS lookup found no IPv6 address.";
[self closeWithError:[self otherError:msg]];
return;
}
if (isIPv6Disabled && (address4 == nil))
{
NSString *msg = @"IPv6 has been disabled and DNS lookup found no IPv4 address.";
[self closeWithError:[self otherError:msg]];
return;
}
// Start the normal connection process
NSError *err = nil;
//調(diào)用連接方法，如果失敗，則錯誤返回
if (![self connectWithAddress4:address4 address6:address6 error:&err])
{
[self closeWithError:err];
}
}
咦，好像有點苗頭，看作者悄咪咪的都干了些啥。
if (![self connectWithAddress4:address4 address6:address6 error:&err])
繼續(xù)點進去看看
- (BOOL)connectWithAddress4:(NSData *)address4 address6:(NSData *)address6 error:(NSError **)errPtr
{
LogTrace();
NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
//輸出了兩個地址的信息
LogVerbose(@"IPv4: %@:%hu", [[self class] hostFromAddress:address4], [[self class] portFromAddress:address4]);
LogVerbose(@"IPv6: %@:%hu", [[self class] hostFromAddress:address6], [[self class] portFromAddress:address6]);
//判斷是否傾向于IPV6
BOOL preferIPv6 = (config & kPreferIPv6) ? YES : NO;
// Create and bind the sockets
//如果有IPV4地址
if (address4)
{
LogVerbose(@"Creating IPv4 socket");
// 咦？這不是創(chuàng)建嗎，瞧瞧我發(fā)現(xiàn)了啥。
socket4FD = [self createSocket:AF_INET connectInterface:connectInterface4 errPtr:errPtr];
}
//如果有IPV6地址，同上
if (address6)
{
LogVerbose(@"Creating IPv6 socket");
socket6FD = [self createSocket:AF_INET6 connectInterface:connectInterface6 errPtr:errPtr];
}
//如果都為空，直接返回
if (socket4FD == SOCKET_NULL && socket6FD == SOCKET_NULL)
{
return NO;
}
//主選socketFD,備選alternateSocketFD
int socketFD, alternateSocketFD;
//主選地址和備選地址
NSData *address, *alternateAddress;
//IPV6
if ((preferIPv6 && socket6FD) || socket4FD == SOCKET_NULL)
{
socketFD = socket6FD;
alternateSocketFD = socket4FD;
address = address6;
alternateAddress = address4;
}
//主選IPV4
else
{
socketFD = socket4FD;
alternateSocketFD = socket6FD;
address = address4;
alternateAddress = address6;
}
//拿到當前狀態(tài)
int aStateIndex = stateIndex;
// 我去，這不是連接嗎？都悄咪咪的把創(chuàng)建跟連接放在這個方法里了，糟老頭子壞得很。
[self connectSocket:socketFD address:address stateIndex:aStateIndex];
//如果有備選地址
if (alternateAddress)
{
//延遲去連接備選的地址
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(alternateAddressDelay * NSEC_PER_SEC)), socketQueue, ^{
[self connectSocket:alternateSocketFD address:alternateAddress stateIndex:aStateIndex];
});
}
return YES;
}
作者是真的皮啊，把這么重要的方法，放在一個if里面？騷還是你騷啊。
總算是找到創(chuàng)建跟連接了，說什么也要點進去看看吧。
先看創(chuàng)建
//創(chuàng)建Socket
- (int)createSocket:(int)family connectInterface:(NSData *)connectInterface errPtr:(NSError **)errPtr
{
// 注意
// 這個connectInterface 創(chuàng)建socketFD4跟6時，分別是傳入了connectInterface4與connectInterface6
// 這兩個值，在preConnectWithInterface時，如果interface不為空，就會賦值，但是interface一直是nil,所以
// connectInterface4與connectInterface6 都是nil
// 創(chuàng)建socket,用的SOCK_STREAM TCP流
// 總算是看到了熟悉的東西
int socketFD = socket(family, SOCK_STREAM, 0);
//如果創(chuàng)建失敗 SOCKET_NULL = -1
if (socketFD == SOCKET_NULL)
{
if (errPtr)
*errPtr = [self errnoErrorWithReason:@"Error in socket() function"];
return socketFD;
}
//和connectInterface綁定，由于connectInterface 是nil 所以這個方法會放回YES,
//所以不會走進去
if (![self bindSocket:socketFD toInterface:connectInterface error:errPtr])
{
//綁定失敗，直接關(guān)閉返回
[self closeSocket:socketFD];
return SOCKET_NULL;
}
// Prevent SIGPIPE signals
//防止終止進程的信號？
int nosigpipe = 1;
//SO_NOSIGPIPE是為了避免網(wǎng)絡(luò)錯誤，而導(dǎo)致進程退出。用這個來避免系統(tǒng)發(fā)送signal
//setsockopt()函數(shù)，用于任意類型、任意狀態(tài)套接口的設(shè)置選項值。百度百科有詳解
setsockopt(socketFD, SOL_SOCKET, SO_NOSIGPIPE, &nosigpipe, sizeof(nosigpipe));
return socketFD;
}
再來就是連接socket
- (void)connectSocket:(int)socketFD address:(NSData *)address stateIndex:(int)aStateIndex
{
//已連接，關(guān)閉連接返回
if (self.isConnected)
{
[self closeSocket:socketFD];
return;
}
// Start the connection process in a background queue
//開始連接過程，在后臺queue中
__weak GCDAsyncSocket *weakSelf = self;
//獲取到全局Queue
dispatch_queue_t globalConcurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
//新線程
dispatch_async(globalConcurrentQueue, ^{
#pragma clang diagnostic push
#pragma clang diagnostic warning "-Wimplicit-retain-self"
//調(diào)用connect方法，該函數(shù)阻塞線程，所以要異步新線程
//客戶端向特定網(wǎng)絡(luò)地址的服務(wù)器發(fā)送連接請求，連接成功返回0，失敗返回 -1。
int result = connect(socketFD, (const struct sockaddr *)[address bytes], (socklen_t)[address length]);
//老樣子，安全判斷
__strong GCDAsyncSocket *strongSelf = weakSelf;
if (strongSelf == nil) return_from_block;
//在socketQueue中，開辟線程
dispatch_async(strongSelf->socketQueue, ^{ @autoreleasepool {
//如果狀態(tài)為已經(jīng)連接，關(guān)閉連接返回
if (strongSelf.isConnected)
{
[strongSelf closeSocket:socketFD];
// 又是這個裝逼寫法
return_from_block;
}
//說明連接成功
if (result == 0)
{
//關(guān)閉掉另一個沒用的socket
[self closeUnusedSocket:socketFD];
//調(diào)用didConnect，生成stream，改變狀態(tài)等等！
[strongSelf didConnect:aStateIndex];
}
//連接失敗
else
{
//關(guān)閉當前socket
[strongSelf closeSocket:socketFD];
// If there are no more sockets trying to connect, we inform the error to the delegate
//返回連接錯誤的error
if (strongSelf.socket4FD == SOCKET_NULL && strongSelf.socket6FD == SOCKET_NULL)
{
NSError *error = [strongSelf errnoErrorWithReason:@"Error in connect() function"];
[strongSelf didNotConnect:aStateIndex error:error];
}
}
}});
#pragma clang diagnostic pop
});
//輸出正在連接中
LogVerbose(@"Connecting...");
}
至此，我們就看到了socket的創(chuàng)建跟連接的實現(xiàn)原理，接下來說讀寫操作。
由于篇幅問題這里另起一篇文章看這里
