iOS network -04-large file download

Big File Download Considerations

• If you do not dump the downloaded files, it will cause a sharp increase in memory consumption, or even run out of memory resources, causing the program to terminate.
• In the file download process usually occurs midway stop situation, if not to do processing, it is necessary to restart the download, waste traffic.

Solutions for large file downloads

• Process the downloaded files, write the data to disk (usually in a sandbox), and avoid accumulating data in memory (nsurlconnection download), with every bit of data downloaded
  
  • Implementing write Data using the Nsfilehandle class
  • Implementing write Data using the Nsoutputstream class
• When the download task terminates, log the location information at the end of the task so that the next time you start the download

Large file Download (nsurlconnection)

• Breakpoint Download not supported
• Download files using the Nsurlconnection proxy method
• The task of transferring the downloaded file and recording the end location in the proxy method of the callback at different stages of the download task

• To use the Nsfilehandle class to implement the download procedure for writing data ( 完整核心代码 )

  • Set related member properties

  /**所要下载文件的总长度*/@property (nonatomic, assign) NSInteger contentLength;/**已下载文件的总长度*/@property (nonatomic, assign) NSInteger currentLength/**文件句柄，用来实现文件存储*/@property (nonatomic, strong) NSFileHandle *handle;

  • Create, send requests

  // 1. 创建请求路径NSURL *url = [NSURL URLWithString:@"此处为URL字符串"];// 2. 将URL封装成请求NSURLRequest *request = [NSURLRequest requestWithURL:url];// 3. 通过NSURLConnection，并设置代理[NSURLConnection connectionWithRequest:request delegate:self];

  • Comply with Agent protocol Nsurlconnectiondatadelegate, implement proxy method

  /*** The method that is called when the server response is received * /- (void) Connection: (Nsurlconnection *) connection didreceiveresponse: (Nshttpurlresponse *) response{//Get the total length of the file you want to downloadSelf.contentlength = [response.allheaderfields[@"Content-length"] IntegerValue];//Stitching a file path in a sandboxNSString *filepath = [[Nssearchpathfordirectoriesindomains (Nscachesdirectory, Nsuserdomainmask, YES) LastObject] stringbyappendingpathcomponent:@"Minion_15.mp4"];//Create a file of the specified path[[Nsfilemanager Defaultmanager] Createfileatpath:filepath contents:nil Attributes:nil];//Create file handleSelf.handle = [Nsfilehandle filehandleforwritingatpath:filepath];}/*** the method to call when receiving data from the server * /- (void) Connection: (Nsurlconnection *) connection didreceivedata: (NSData *) data{//Navigate to the end of the file and stitch the file data returned by the server to the end of the file each time[Self.handle Seektoendoffile];//through file handle, write file to sandbox[Self.handle Writedata:data];//Stitching The total length of downloaded filesSelf.currentlength + = Data.length;//Calculate Download ProgressCGFloat progress =1.0* SELF.CURRENTLENGTH/SELF.CONTENTLENGTH;}/*** The method that is called when the file is downloaded * /- (void) Connectiondidfinishloading: (nsurlconnection *) connection{//Close the file handle and clear[Self.handle CloseFile]; Self.handle = nil;//Empty downloaded file lengthSelf.currentlength =0;}

• To use the Nsoutputstream class to implement the download procedure for writing data ( 部分代码，其他部分代码同上 )

  • Set Nsoutputstream member properties

  @property (nonatomicstrong) NSOutputStream *stream;

  • Initialize the Nsoutputstream object to open the output stream

  /**接收到服务器响应的时候调用*/- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{    //获取下载数据保存的路径    NSString *cache = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];    NSString *filePath = [cache stringByAppendingPathComponent:response.suggestedFilename];    //利用NSOutputStream往filePath文件中写数据，若append参数为yes，则会写到文件尾部    self.stream = [[NSOutputStream alloc] initToFileAtPath:filePath append:YES];    //打开数据流    [self.stream open];}

  • Write file data

  /**接收到数据的时候调用*/- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{    [self.stream write:[data bytes] maxLength:data.length];}

  • Turn off the output stream

  /**数据下载完毕的时候调用*/- (void)connectionDidFinishLoading:(NSURLConnection *)connection{    [self.stream close];}

Large file Download (nsurlsession)

• Support breakpoint download, automatically record the location of breakpoints when stopping download
• Compliance with Nsurlsessiondownloaddelegate Protocol
• Using nsurlsession to download large files, the downloaded files will be automatically written to the sandbox Temp folder tmp
• After downloading, it is usually necessary to move the downloaded files elsewhere (the data in the TMP folder is deleted periodically), usually in the cache folder

• Detailed download steps

  • Set Download task task as member variable

  @property (nonatomicstrong) NSURLSessionDownloadTask *task;

  • Get Nsurlsession Object

  NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[[NSOperationQueue alloc] init]];

  • Initializing the Download Task task

  self.task = [session downloadTaskWithURL:（此处为下载文件路径URL）];

  • Implementing Proxy methods

  /** Each time the data is written to a temporary file, the method is called once, usually in this method to get the download progress * /- (void) Urlsession: (Nsurlsession *) session Downloadtask: (Nsurlsessiondownloadtask *) downloadtask didwritedata: (int64_t) Byteswritten Totalbyteswritten: (int64_t) Totalbyteswritten totalbytesexpectedtowrite: (int64_t) totalbytesexpectedtowrite{//Calculate Download ProgressCGFloat progress =1.0* Totalbyteswritten/totalbytesexpectedtowrite;}/** The method that is called when the task terminates, usually for a breakpoint download * /- (void) Urlsession: (Nsurlsession *) session Downloadtask: (Nsurlsessiondownloadtask *) Downloadtask Didresumeatoffset: (Int64 _t) Fileoffset expectedtotalbytes: (int64_t) expectedtotalbytes{//fileoffset: The offset when the download task is aborted}/** is called when an error is encountered, the error parameter can only pass client-side errors * /- (void) Urlsession: (Nsurlsession *) session Task: (Nsurlsessiontask *) Task Didcompletewitherror: (Nserror *) error{}/** When the download is complete, you need to cut the file into a folder that can be saved for a long time * /- (void) Urlsession: (Nsurlsession *) session Downloadtask: (Nsurlsessiondownloadtask *) downloadtask Didfinishdownloadingtourl: (Nsurl *) location{//Generate files for long-term saved pathsNSString *file = [[Nssearchpathfordirectoriesindomains (Nscachesdirectory, Nsuserdomainmask, YES) LastObject] StringByAppendingPathComponent:downloadTask.response.suggestedFilename];//Get file handleNsfilemanager *filemanager = [Nsfilemanager Defaultmanager];//Through the file handle, cut the file to the long-term saved path of the file[FileManager moveitematurl:location Tourl:[nsurl fileurlwithpath:file] error:nil];}

  • Operation Task Status

  /**开始/继续下载任务*/[self.task resume];/**暂停下载任务*/[self.task suspend];

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iOS network -04-large file download