iOS GCDAsyncSocket原始碼分析(一)
阿新 • • 發佈:2019-12-25
序言
在上一篇文章文章中,簡單介紹了GCDAsyncSocket的使用,socket建立、連線、傳送訊息、接收訊息、關閉socket、粘包分包、以及心跳包機制。並且立下了一個flag,所以在這篇文章,將帶來GCDAsyncSocket的原始碼分析,看看在GCDAsyncSocket中是如何運用原生程式碼並封裝起來的,在簡單實現的原生程式碼基礎上,他又做了什麼樣的操作。
我們還是按照建立socket、連線socket、傳送訊息、接收訊息、關閉socket的順序,一步一步深入瞭解GCDAsyncSocket。
1. GCDAsyncSocket初始化
在開始之前,GCDAsyncSocket.m中聲明瞭許許多多的成員變數,先看看都是啥。
@implementation GCDAsyncSocket
{
//flags,當前正在做操作的識別符號
uint32_t flags;
uint16_t config;
//代理
__weak id<GCDAsyncSocketDelegate> delegate;
//代理回撥的queue
dispatch_queue_t delegateQueue;
//本地IPV4Socket
int socket4FD;
//本地IPV6Socket
int socket6FD;
//unix域的套接字 // 程序通訊 locahost VS 127.0.0.1
int socketUN;
//unix域 服務端 url
NSURL *socketUrl;
//狀態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,序列
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;
//連線timer,GCD定時器 重連
dispatch_source_t connectTimer;
dispatch_source_t read Source;
dispatch_source_t writeSource;
dispatch_source_t readTimer;
dispatch_source_t writeTimer;
//讀寫資料包陣列 類似queue,最大限制為5個包 - FIFO
NSMutableArray *readQueue;
NSMutableArray *writeQueue;
//當前正在讀寫資料包
GCDAsyncReadPacket *currentRead;
GCDAsyncWritePacket *currentWrite;
//當前socket未獲取完的資料大小
unsigned long socketFDBytesAvailable;
//全域性公用的提前緩衝區
GCDAsyncSocketPreBuffer *preBuffer;
#if TARGET_OS_IPHONE
CFStreamClientContext streamContext;
//讀的資料流 ---- c
CFReadStreamRef readStream;
//寫的資料流
CFWriteStreamRef writeStream;
#endif
//SSL上下文,用來做SSL認證
SSLContextRef sslContext;
//全域性公用的SSL的提前緩衝區
GCDAsyncSocketPreBuffer *sslPreBuffer;
size_t sslWriteCachedLength;
//記錄SSL讀取資料錯誤
OSStatus sslErrCode;
//記錄SSL握手的錯誤
OSStatus lastSSLHandshakeError;
//socket佇列的標識key -- key - queue
void *IsOnSocketQueueOrTargetQueueKey;
id userData;
//連線備選服務端地址的延時 (另一個IPV4或IPV6)
NSTimeInterval alternateAddressDelay;
}
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建立函式
self.socket = [[GCDAsyncSocket alloc] initWithDelegate:self delegateQueue:dispatch_get_global_queue(0,0)];
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這個init方法最終將會來到,在這個方法裡,socketQueue傳值為NULL,所以後面如果有sq的部分可以先行跳過,等梳理完了,再去看看這個sq具體都幹了啥。
- (id)initWithDelegate:(id)aDelegate delegateQueue:(dispatch_queue_t)dq socketQueue:(dispatch_queue_t)sq
{
if((self = [super init]))
{
delegate = aDelegate;
delegateQueue = dq;
//這個巨集是在sdk6.0之後才有的,如果是之前的,則OS_OBJECT_USE_OBJC為0,!0即執行if語句
//對6.0的適配,如果是6.0以下,則去retain release,6.0之後ARC也管理了GCD
//作者很細
#if !OS_OBJECT_USE_OBJC
if (dq) dispatch_retain(dq);
#endif
//建立socket,先都置為 -1,代表socket預設建立失敗
//本機的ipv4
socket4FD = SOCKET_NULL;
//ipv6
socket6FD = SOCKET_NULL;
//應該是UnixSocket
socketUN = SOCKET_NULL;
//url
socketUrl = nil;
//狀態
stateIndex = 0;
//這裡並沒有sq,可以選擇跳過
if (sq)
{
//如果scoketQueue是global的,則報錯。斷言必須要一個非並行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,@"The given socketQueue parameter must not be a concurrent queue.");
NSAssert(sq != dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,@"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
{
//沒有的話建立一個socketQueue, 名字為:GCDAsyncSocket,NULL = 序列
socketQueue = dispatch_queue_create([GCDAsyncSocketQueueName UTF8String],NULL);
}
//比如原來為 0X123 -> NULL 變成 0X222->0X123->NULL
//自己的指標等於自己原來的指標,成二級指標了 看了註釋是為了以後省略&,讓程式碼更可讀?
//這裡不懂作者的用意,繼續往下看
IsOnSocketQueueOrTargetQueueKey = &IsOnSocketQueueOrTargetQueueKey;
void *nonNullUnusedPointer = (__bridge void *)self;
//dispatch_queue_set_specific給當前隊里加一個標識 dispatch_get_specific當前執行緒取出這個標識,判斷是不是在這個佇列
dispatch_queue_set_specific(socketQueue,IsOnSocketQueueOrTargetQueueKey,nonNullUnusedPointer,NULL);
//讀的陣列
readQueue = [[NSMutableArray alloc] initWithCapacity:5];
currentRead = nil;
//寫的陣列
writeQueue = [[NSMutableArray alloc] initWithCapacity:5];
currentWrite = nil;
//緩衝區 設定大小為 4kb
preBuffer = [[GCDAsyncSocketPreBuffer alloc] initWithCapacity:(1024 * 4)];
#pragma mark alternateAddressDelay??
//交替地址延時?? wtf 應該是用來給備用地址的
alternateAddressDelay = 0.3;
}
return self;
}
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看完這段程式碼...懵逼。只是一些初始化操作。本來還以為create()
會在這裡面呢,很無奈啊,哎,先不管了,繼續往下看吧。
2. GCDAsyncSocket Connect
外層呼叫
[self.socket connectToHost:@"127.0.0.1" onPort:8090 withTimeout:-1 error:&error];
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底層最終會來到這裡,每個方法都好長啊 - - 。這裡的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?介面?先不管 反正是nil
NSString *interface = [inInterface copy];
//宣告兩個__block的臨時變數
__block BOOL result = NO;
//error資訊
__block NSError *preConnectErr = nil;
//gcdBlock,都包裹在自動釋放池中 :
// 1: 大量臨時變數 connect : 重連
// 2: 自定義執行緒管理 : nsoperation
// 3: 非UI 命令 工具
dispatch_block_t block = ^{ @autoreleasepool {
// Check for problems with host parameter
// 翻譯:檢查host引數 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,大牛的程式碼真是充滿逼格 - ret
// 裡面有註釋,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,後面還有很多地方被呼叫到
return_from_block;
}
//一個前置的檢查,如果沒通過返回,這q個檢查裡,如果interface有值,則會將本機的IPV4 IPV6的 address設定上。
// 引數 : 指標 操作同一片記憶體空間
// 因為interface 是nil,所以不會執行return
if (![self preConnectWithInterface:interface error:&preConnectErr])
{
return_from_block;
}
// We've made it past all the checks.我們已經檢查了所有引數
// It's time to start the connection process.是時候開始連線了
//flags 做或等運算。 flags標識為開始Socket連線
flags |= kSocketStarted;
//又是一個{}? 只是為了標記麼?
LogVerbose(@"Dispatching DNS lookup...");
//很可能給我們的服務端的引數是一個可變字串
//所以我們需要copy,在Block裡同步的執行
//這種基於Block的非同步查詢,不需要擔心它被改變
//copy,防止改變
NSString *hostCpy = [host copy];
//拿到狀態 初始化的時候 stateIndex = 0
int aStateIndex = stateIndex;
__weak GCDAsyncSocket *weakSelf = self;
//獲取全域性併發Queue
dispatch_queue_t globalConcurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);
//非同步執行,這裡的autoreleasepool 跟上面的一樣,可以往上翻
dispatch_async(globalConcurrentQueue,^{ @autoreleasepool {
//忽視迴圈引用,牛逼
#pragma clang diagnostic push
#pragma clang diagnostic warning "-Wimplicit-retain-self"
//查詢錯誤
NSError *lookupErr = nil;
//server地址陣列(包含IPV4 IPV6的地址 sockaddr_in6、sockaddr_in型別)
NSMutableArray *addresses = [[self class] lookupHost:hostCpy port:port error:&lookupErr];
//strongSelf
__strong GCDAsyncSocket *strongSelf = weakSelf;
//完整Block安全形態,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,清空一些資料等等
[strongSelf lookup:aStateIndex didFail:lookupErr];
}});
}
//正常
else
{
NSData *address4 = nil;
NSData *address6 = nil;
//遍歷地址陣列
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;
}
}
//非同步去發起
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
}});
//開啟連線超時
[self startConnectTimeout:timeout];
result = YES;
}};
//在socketQueue中執行這個Block
if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
block();
//否則同步的調起這個queue去執行
else
dispatch_sync(socketQueue,block);
//如果有錯誤,賦值錯誤
if (errPtr) *errPtr = preConnectErr;
//把連線是否成功的result返回
return result;
}
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這個connect跟想的也不太一樣,並沒有熟悉的connect()
,有毒。但是!還知道這個方法裡都幹了啥呢。
[strongSelf lookup:aStateIndex didSucceedWithAddress4:address4 address6:address6];
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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");
//如果狀態不一致,說明斷開連線
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;
//呼叫連線方法,如果失敗,則錯誤返回
if (![self connectWithAddress4:address4 address6:address6 error:&err])
{
[self closeWithError:err];
}
}
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咦,好像有點苗頭,看作者悄咪咪的都幹了些啥。
if (![self connectWithAddress4:address4 address6:address6 error:&err])
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繼續點進去看看
- (BOOL)connectWithAddress4:(NSData *)address4 address6:(NSData *)address6 error:(NSError **)errPtr
{
LogTrace();
NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey),@"Must be dispatched on socketQueue");
//輸出了兩個地址的資訊
LogVerbose(@"IPv4: %@:%hu",[[self class] hostFromAddress:address4],[[self class] portFromAddress:address4]);
LogVerbose(@"IPv6: %@:%hu",[[self class] hostFromAddress:address6],[[self class] portFromAddress:address6]);
//判斷是否傾向於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?這不是建立嗎,瞧瞧我發現了啥。
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
int aStateIndex = stateIndex;
// 我去,這不是連線嗎?都悄咪咪的把建立跟連線放在這個方法裡了,糟老頭子壞得很。
[self connectSocket:socketFD address:address stateIndex:aStateIndex];
//如果有備選地址
if (alternateAddress)
{
//延遲去連線備選的地址
dispatch_after(dispatch_time(DISPATCH_TIME_NOW,(int64_t)(alternateAddressDelay * NSEC_PER_SEC)),socketQueue,^{
[self connectSocket:alternateSocketFD address:alternateAddress stateIndex:aStateIndex];
});
}
return YES;
}
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作者是真的皮啊,把這麼重要的方法,放在一個if裡面?騷還是你騷啊。 總算是找到建立跟連線了,說什麼也要點進去看看吧。 先看建立
//建立Socket
- (int)createSocket:(int)family connectInterface:(NSData *)connectInterface errPtr:(NSError **)errPtr
{
// 注意
// 這個connectInterface 建立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
// 建立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);
//如果建立失敗 SOCKET_NULL = -1
if (socketFD == SOCKET_NULL)
{
if (errPtr)
*errPtr = [self errnoErrorWithReason:@"Error in socket() function"];
return socketFD;
}
//和connectInterface繫結,由於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])
{
//繫結失敗,直接關閉返回
[self closeSocket:socketFD];
return SOCKET_NULL;
}
// Prevent SIGPIPE signals
//防止終止程序的訊號?
int nosigpipe = 1;
//SO_NOSIGPIPE是為了避免網路錯誤,而導致程序退出。用這個來避免系統傳送signal
//setsockopt()函式,用於任意型別、任意狀態套介面的設定選項值。百度百科有詳解
setsockopt(socketFD,SOL_SOCKET,SO_NOSIGPIPE,&nosigpipe,sizeof(nosigpipe));
return socketFD;
}
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再來就是連線socket
- (void)connectSocket:(int)socketFD address:(NSData *)address stateIndex:(int)aStateIndex
{
//已連線,關閉連線返回
if (self.isConnected)
{
[self closeSocket:socketFD];
return;
}
// Start the connection process in a background queue
//開始連線過程,在後臺queue中
__weak GCDAsyncSocket *weakSelf = self;
//獲取到全域性Queue
dispatch_queue_t globalConcurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);
//新執行緒
dispatch_async(globalConcurrentQueue,^{
#pragma clang diagnostic push
#pragma clang diagnostic warning "-Wimplicit-retain-self"
//呼叫connect方法,該函式阻塞執行緒,所以要非同步新執行緒
//客戶端向特定網路地址的伺服器傳送連線請求,連線成功返回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,開闢執行緒
dispatch_async(strongSelf->socketQueue,^{ @autoreleasepool {
//如果狀態為已經連線,關閉連線返回
if (strongSelf.isConnected)
{
[strongSelf closeSocket:socketFD];
// 又是這個裝逼寫法
return_from_block;
}
//說明連線成功
if (result == 0)
{
//關閉掉另一個沒用的socket
[self closeUnusedSocket:socketFD];
//呼叫didConnect,生成stream,改變狀態等等!
[strongSelf didConnect:aStateIndex];
}
//連線失敗
else
{
//關閉當前socket
[strongSelf closeSocket:socketFD];
// If there are no more sockets trying to connect,we inform the error to the delegate
//返回連線錯誤的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
});
//輸出正在連線中
LogVerbose(@"Connecting...");
}
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至此,我們就看到了socket的建立跟連線的實現原理,接下來說讀寫操作。 由於篇幅問題這裡另起一篇文章看這裡