iOS development-Implementation of large file download and breakpoint download ideas

 @property (nonatomic,strong) NSFileHandle *writeHandle;
@property (nonatomic,assign) long long totalLength; 

// Create a request  NSURL *url = [NSURL URLWithString:@""];
  NSURLRequest *request = [NSURLRequest requestWithURL:url];
  // Use NSURLConnection to initiate an asynchronous request  [NSURLConnection connectionWithRequest:request delegate:self]; 

/** Call the following proxy method when receiving the server's response
   1. Create an empty file
   2. Use a handle object to associate this empty file with the purpose of making it easier to write data behind an empty file
 */
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(nonnull NSURLResponse *)response
{
  // Create file path  NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)lastObject];
  NSString *filePath = [caches stringByAppendingPathComponent:@""];
  
  // Create an empty file into the sandbox  NSFileManager *mgr = [NSFileManager defaultManager];
  [mgr createFileAtPath:filePath contents:nil attributes:nil];
  
  // Create a file handle for writing data   = [NSFileHandle fileHandleForWritingAtPath:filePath];
  
  // Get the total size of the file   = ;
}

/** Call the following proxy method when receiving file data returned by the server
   Use the handle object to add data to the end of the file
  */
- (void)connection:(NSURLConnection *)connection didReceiveData:(nonnull NSData *)data
{
  // Move to the end of the file  [ seekToEndOfFile];
  
  // Write data to the sandbox  [ writeData:data];
}

/**
   Close the handle object when all data is received
  */
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
  // Close the file and clear it  [ closeFile];
   = nil;
} 

NSURLSession *session = [NSURLSession sharedSession];
  NSURL *url = [NSURL URLWithString:@""];
  // Can be used to download large files, and the data will be stored in the tmp folder in the sandbox  NSURLSessionDownloadTask *task = [session downloadTaskWithURL:url completionHandler:^(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {
    // location: the path to store temporary files (downloaded files)    
    // Create storage file path    NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)lastObject];
    //: The file name recommended is generally the same as the file name on the server side    NSString *file = [caches stringByAppendingPathComponent:];
    
    /**Cut or copy temporary files to the Caches folder
      AtPath: file path before clipping
      toPath: the file path after clipping
      */
    NSFileManager *mgr = [NSFileManager defaultManager];
    [mgr moveItemAtPath: toPath:file error:nil];
  }];
  [task resume]; 

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
  // Create a download task and set up a proxy  NSURLSessionConfiguration *cfg = [NSURLSessionConfiguration defaultSessionConfiguration];
  NSURLSession *session = [NSURLSession sessionWithConfiguration:cfg delegate:self delegateQueue:[NSOperationQueue mainQueue]];
  
  NSURL *url = [NSURL URLWithString:@""];
  NSURLSessionDownloadTask *task = [session downloadTaskWithURL:url];
  [task resume];
}

#pragma mark - 
/**
   Called after downloading
   Parameters: lication The path of the temporary file (downloaded file)
  */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location{
  // Create storage file path  NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)lastObject];
  //: The file name recommended is generally the same as the file name on the server side  NSString *file = [caches stringByAppendingPathComponent:];
  
  /**Cut or copy temporary files to the Caches folder
    AtPath: file path before clipping
    toPath: the file path after clipping
    */
  NSFileManager *mgr = [NSFileManager defaultManager];
  [mgr moveItemAtPath: toPath:file error:nil];
}

/**
   It will be called whenever a part is downloaded (may be called multiple times)
   parameter:
     bytesWritten How many downloads did this call
     totalBytesWritten How long has the accumulated written into the sandbox?
     totalBytesExpectedToWrite file size
  */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
   didWriteData:(int64_t)bytesWritten
 totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{
  // Here you can do some operations such as displaying progress}

/**
   Used when restoring download
  */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
 didResumeAtOffset:(int64_t)fileOffset
expectedTotalBytes:(int64_t)expectedTotalBytes
{
  // Used for breakpoint continuous transmission} 

@property (nonatomic,assign) long long currentLength;
@property (nonatomic,strong) NSURLConnection *conn; 

  // Record breakpoints and accumulate file length   += ; 

- (IBAction)download:(UIButton *)sender {
  
   = !;
  
  if () { // Continue (start) download    NSURL *url = [NSURL URLWithString:@""];
    // ****The key point is to use NSMutableURLRequest to set the request header Range    NSMutableURLRequest *mRequest = [NSMutableURLRequest requestWithURL:url];
    
    NSString *range = [NSString stringWithFormat:@"bytes=%lld-",];
    [mRequest setValue:range forHTTPHeaderField:@"Range"];
    
    // download     = [NSURLConnection connectionWithRequest:mRequest delegate:self];
  }else{
    [ cancel];
     = nil;
  }
} 

 if () return; 

 @property (nonatomic,strong) NSURLSession *session;
@property (nonatomic,strong) NSData *resumeData; //Includes the start location of the continued download and the downloaded URL@property (nonatomic,strong) NSURLSessionDownloadTask *task; 

// Lazy loading session- (NSURLSession *)session
{
  if (!_session) {
    NSURLSessionConfiguration *cfg = [NSURLSessionConfiguration defaultSessionConfiguration];
     = [NSURLSession sessionWithConfiguration:cfg delegate:self delegateQueue:[NSOperationQueue mainQueue]];
  }
  return _session;
}

- (IBAction)download:(UIButton *)sender {
  
   = !;
  if ( == nil) { // Start (continue) Download    if () { // Recover the data originally      [self resume];
    }else{
      [self start]; // Start without data    }
  }else{ // pause    [self pause];
  }
}

// Start from scratch- (void)start{
  NSURL *url = [NSURL URLWithString:@""];
   = [ downloadTaskWithURL:url];
  [ resume];
}

// pause- (void)pause{
  __weak typeof(self) vc = self;
  [ cancelByProducingResumeData:^(NSData * _Nullable resumeData) {
    //resumeData: contains the start location for continuing to download and the downloaded URL     = resumeData;
     = nil;
  }];
}

// recover- (void)resume{
  // Pass in the data returned from the last pause of download and reply to the download   = [ downloadTaskWithResumeData:];
  // Start the task  [ resume];
  // Clear   = nil;
}

#pragma mark - NSURLSessionDownloadDelegate
/**
   Called after downloading
   Parameters: lication The path of the temporary file (downloaded file)
  */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location{
  // Create storage file path  NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)lastObject];
  //: The file name recommended is generally the same as the file name on the server side  NSString *file = [caches stringByAppendingPathComponent:];
  
  /**Cut or copy temporary files to the Caches folder
    AtPath: file path before clipping
    toPath: the file path after clipping
    */
  NSFileManager *mgr = [NSFileManager defaultManager];
  [mgr moveItemAtPath: toPath:file error:nil];
}

/**
   It will be called whenever a part is downloaded (may be called multiple times)
   parameter:
     bytesWritten How many downloads did this call
     totalBytesWritten How long has the accumulated written into the sandbox?
     totalBytesExpectedToWrite file size
  */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
   didWriteData:(int64_t)bytesWritten
 totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{
  // Here you can do some operations such as displaying progress}

/**
   Used when restoring download
  */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
 didResumeAtOffset:(int64_t)fileOffset
expectedTotalBytes:(int64_t)expectedTotalBytes
{
}