I was pressed for the draft, so let's talk about how long links can be as efficient as short links in the development of mobile terminals

In recent days, , Urged by Bo Ge , Business hours were forced to advance , Just dig into the code warehouse that has been hidden for decades , Found a practical method in the development of long links on mobile terminals many years ago , Long link business code can be as efficient as short link 、 Simple tips , Just deal with it and make a difference .

This article does not address  

TCP

  Make detailed deployment instructions , It won't be about how to use  Socket  Library description 、 Protocol format definition 、 How to transmit is beyond the scope of this article , This paper focuses on how to efficiently and succinctly write a mobile terminal based on  

TCP

  Business code of , Make long link business code as efficient as short link business code .

Let's talk about the basics first ：

Remember the point ：

• Short link ： One  request  Corresponding to one  respones, It must appear in pairs , Yes, there is. , Their relationship is ：R:Q = N:N = 1

• Long link ： Sending and receiving just write data to or read data from the cache , There is no clear  request & respones  The concept of , Their relationship is ：R:Q = M:N

Because of this difference ,

TCP

  Bring link reuse 、 Take the initiative to push 、 Efficient 、 Many advantages, such as speed, also introduce more complexity , One of the problems is based on  

TCP

  Writing business code is cumbersome .

This article will use  iOS  Development as an example , Explain the problem , Students of other languages can achieve the same by themselves .

Short link example

stay App It is very common to make a short link on , adopt  block  Make network requests in the form of , For example, widely used  

AFNetworking

  This is how it is used in the Library ：


NSString *url = @"http://api.xxx.com/method";

[[self shareAFNManager] GET:url parameters:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) { 
 NSLog(@"responseObject-->%@",responseObject);
 UpdateUI()
 } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) { 
 NSLog(@"error-->%@",error);
}];


Here  block  yes  Objective-C  A name in language , It can be interpreted as a function pointer , Because this kind of writing can be in the corresponding  block  Direct business processing in , such as ： to update  UI  etc. , This operation brings a very convenient function to write business , In essence, it is also because the form of short links is satisfied R:Q = N:N = 1 The relationship between

Long link

So it is very troublesome to realize the above functions in long links , except  Socket  Beyond basic functions , Respond to data updates UI You have to deal with network thread switching UI Threads ,UI  Life cycle and data life cycle match , Data notification and many other issues .

stay  handle  perhaps  dispatch  Method implementation , Many students will fall into a trap , Or the implementation is particularly troublesome , Otherwise, the implementation is full of loopholes , In infrequent cases, you may choose  notification  Or a similar simple scheme , Even if this kind of writing, there will be many pits ： Registration of notices 、 management 、 Destruction and so on are all contents that should be handled carefully , This is also the problem that many students cannot write long link business codes .

programme

Now that there's a problem , In line with 「

What is painful is where the need lies

」, Simply sort out according to the idea of short links ：

refine  request & respones, The agreed relationship is ：R:Q = N:N = 1

This is the core issue , As long as this relationship can be abstracted , Then long links can be as convenient as short links , Many students think

TCP

  The problem that the cache module of is difficult to implement will also become very simple .

stay  

TCP

  In the process of protocol customization , Appointment  

message{} & message_reply{}

  Process a network request correspondingly , For example  protobuf  Define a  ping  package

message ping{
 string request_id = 1;
}

message ping_reply{
 string request_id = 1;
}


The protocol is designed according to this Convention  R:Q = N:N = 1  The problem of

request_id

Among them  request_id  Is a relatively 「 SAO 」 The operation of , Introduce a field to solve the big problem perfectly .

Keep in mind the characteristics of short links in the process , Yes, there is. , Come and go （ Don't raise the bar , If there is no network, there will be an error return such as timeout or unlinked network ）.

request_id  from  client  Generate and maintain , Send the request to the server , The server returns this value intact to  client,client  According to this  request_id  Find the original location of the corresponding network request .

For example, call it  SendCore  To realize the network layer , The main structures included are as follows ：


typedef void (^SocketDidReadBlock)(NSError *__nullable error, id __nullable data);

@interface SendCore : NSObject
+ (nullable SendCore *)sharedManager;

- (void) sendEnterChatRoom:(nullable EnterChatRoom *) data completion:(__nullable SocketDidReadBlock)callback;

- (void) CloseSocket;
@end


SocketDidReadBlock  Convention function pointer form , Must meet simple 、 Scalable requirements .

Take the function of entering the chat room as an example :


- (void) sendEnterChatRoom:(nullable EnterChatRoom *) data completion:(__nullable SocketDidReadBlock)callback
{
 if (data == nil ) {
 return;
 }
 
 NSString * blockRequestID =[self createRequestID];
 data.requestId = blockRequestID;
 
 if (callback) {
 [self addRequestIDToMap:blockRequestID block:callback];
 }
 
 [self sendProtocolWithCmd:CmdType_Enter1V1MovieRoom withCmdData:[data data] completion:callback];
}


from  client  Generate a  request_id, And will  callback  Deposit in  block_table in , Solve in the data returned by the server  request_id, And then in  block_table  Find the corresponding function pointer in and execute .


-(void) handerProtocol:(CmdType) protocolID packet:(NSData *) packet
{
 NSError *error = nil;
 id reslutData = nil;
 NSString *requestId = nil;
 switch (protocolID) {
 case CmdType_Enter1V1MovieRoomReply:
 error = nil;
 syncObjInfo =[SyncObjInfo parseFromData:packet error:&error];
 reslutData = syncObjInfo;
 
 requestId = syncObjInfo.requestId;
 didReadBlock = [self getBlockWith:requestId];
 
 break;
 }

 if (didReadBlock) {
 didReadBlock(error, reslutData);
 }

 if (requestId != nil &&
 requestId.length > 0) {
 [self removeRequestIDFormMap:requestId];
 } 
}


Remember to clean up relevant contents and concurrent locks after execution .

Here we are , The main functions have been completed , The effect is as follows ：

 [[SendCore sharedManager] sendEnterChatRoom:room completion:^(NSError * _Nullable error, id _Nullable data) {
 NSLog(@"%@", error);

 if (error == nil) {
 NSLog(@" Successfully entered the chat room ");
 }
}];


In this way, the long link business code is as simple and convenient as the short link business code .

Overtime

There are still some unexpected situations to deal with , The above example only works when the network is normal , For example, timeout. ,

TCP

  No news will come back , So in  SendCore  There are still many things to be done in .

So we go up  addRequestIDToMap  function ：

- (void) addRequestIDToMap:(NSString *) requestID block:(nullable SocketDidReadBlock)callback withTime:(BOOL) timeout{

 if (requestID == nil ||
 requestID.length == 0) {
 return;
 }
 
 if (callback == nil) {
 return;
 }
 
 [self.requestsMapLock lock];
 [self.requestsMap setObject:callback forKey:requestID];
 
 if (timeout) {
 [self.requestsTimeMap setObject:[NSDate date] forKey:requestID];
 }
 
 [self.requestsMapLock unlock];
}


One of them  requestsTimeMap, Recorded  request_id  The time when the request was initiated , With this time , You can handle timeout errors locally

-(void) checkRequestProcessTimeout
{
 NSError * Socket_WAIT_PROCESS_TIMEOUT_SECOND = [NSError errorWithDomain:@"_Socket_WAIT_PROCESS_TIMEOUT_SECOND_" code:408 userInfo:nil];
 
 NSMutableArray * timeoutRequestIDs = [NSMutableArray array];
 NSDate * now = [NSDate date];

 for (NSString * requestID in [self.requestsTimeMap allKeys]) {
 
 if (requestID == nil ||
 [requestID length] <= 0) {
 continue;
 }
 
 NSDate * fireDate = [self.requestsTimeMap objectForKey:requestID];
 NSDate * timeOutTime = [NSDate dateWithTimeInterval:_Socket_WAIT_PROCESS_TIMEOUT_SECOND_ sinceDate:fireDate];
 if ([timeOutTime compare:now] == NSOrderedAscending) {
 [timeoutRequestIDs addObject:requestID];
 }
 }

 for (NSString * requestID in timeoutRequestIDs) {
 if (requestID == nil ||
 [requestID length] <= 0) {
 continue;
 }
 
 SocketDidReadBlock didReadBlock = [self getBlockWith:requestID];
 didReadBlock(Socket_WAIT_PROCESS_TIMEOUT_SECOND, nil);
 [self removeRequestIDFormMap:requestID];
 }
}


By timer , To perform a second  checkRequestProcessTimeout  function , If you find a timeout request, you can adjust it directly  block, And back to  Socket_WAIT_PROCESS_TIMEOUT_SECOND  error .

Through double  table  This problem is well solved in the form of .

cache

Similarly, caching is easier to implement , Reference resources  AFNetworking  Library can realize a set of easy-to-use cache functions .

request_id  Small wonderful use of

request_id  Generated and maintained by the client , Generally, it can be produced in this way ：

- (NSString *)createRequestID {

 NSInteger timeInterval = [NSDate date].timeIntervalSince1970 * 1000000;
 NSString *randomRequestID = [NSString stringWithFormat:@"%ld%d", timeInterval, arc4random() % 100000];

 return randomRequestID;
}


There are some fixed network requests in a certain scenario , Or in order to cooperate with the cache Library , You can define some fixed or specific formats  id.

const USER_INFO_GET_REQUEST_ID = @“04e1c446-b918-40f7-9061-d06b569a9cf0”
@“/ Big function / Small feature /xxx”


request_id  Clever definition of , It will bring unexpected results , Students can play freely .

end

Here we are , All functions are over , From the business code, it is completely impossible to see whether this code is a long link or a short link , The expected purpose has been achieved well , In long link business, business code efficiency is as simple and efficient as short link .

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