网络：NSOutputStream的使用

#import "ViewController.h"@interface ViewController ()<NSURLConnectionDataDelegate>@property (nonatomic, assign) long long fileSize; // 文件总大小@property (nonatomic, assign) long long currentSize; // 当前接收的文件大小@property (nonatomic, strong) NSOutputStream *output; // 文件输出流@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.//    [self serverFileSize];}// 我们在使用别人的软件的时候，点击下载会怎么样？// 提示这个文件是多大，是否下载- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {    [self serverFileSize];}// HEAD用来请求查看文件大小- (void)serverFileSize {    // NSURL    NSString *URLStr =@"http://localhost/01UI基础复习.mp4";    // 百分号转码    URLStr = [URLStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];    NSURL *url = [NSURL URLWithString:URLStr];    // NSURLRequest 获取文件大小，不是使用GET,而是使用HEAD    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];    [request setHTTPMethod:@"HEAD"];    NSURLResponse *response;    // 获取文件大小，是使用同步    [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:NULL];    // 文件总大小//    NSLog(@"%@",response);    self.fileSize = response.expectedContentLength;//    NSLog(@"%lld",fileSize);    // 提示用户文件总大下，是否需要下载    // 下载文件    [self download:url];}- (void)download:(NSURL *)url {    // NSURLRequest 下载文件，从服务器获取的意思 GET    NSURLRequest *request = [NSURLRequest requestWithURL:url];    // 开始下载文件, 知道下载的进度    [NSURLConnection connectionWithRequest:request delegate:self];}#pragma mark - NSURLConnection 代理/** NSFileHandle 选择写入文件的方式初始化，在写入文件之前先把光标移动文件的最后，写完之后关闭 NSOutputStream 初始化的时候选择拼接文件，再打开流，写入数据（多次），关闭流 */// 接收到响应- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {    NSLog(@"接收到响应%@ -- %lld",response,response.expectedContentLength);//    NSHTTPURLResponse *httpResp//    self.fileSize = response.expectedContentLength; // 文件总大小    NSString *path = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"123.mp4"];    self.output = [[NSOutputStream alloc]initToFileAtPath:path append:YES];    // 在写入编辑文件之前，打开文件    [self.output open];}- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {//    NSLog(@"接收到数据 %zd",data.length);    // 如果需要知道进度，首要要知道文件的总大小，还要接收了多少    self.currentSize += data.length;    NSLog(@"%f",(CGFloat)self.currentSize / self.fileSize);    // uunt8_t -> NSData//    [NSData dataWithBytes:<#(nullable const void *)#> length:<#(NSUInteger)#>]    [self.output write:data.bytes maxLength:data.length];}- (void)connectionDidFinishLoading:(NSURLConnection *)connection {    NSLog(@"下载完成了");    // 关闭文件流    [self.output close];}- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {    NSLog(@"出错了");}@end