iOS同步检测网络是否可用

#define kAppleUrlToCheckNetStatus @"http://captive.apple.com/"

- (BOOL)checkNetCanUse {
    
    __block BOOL canUse = NO;
    
    NSString *urlString = kAppleUrlToCheckNetStatus;
    
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    config.timeoutIntervalForRequest = 3;
    
    NSURLSession *session = [NSURLSession sessionWithConfiguration:config];

    //**// 使用信号量实现NSURLSession同步请求**
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
    
    [[session dataTaskWithURL:[NSURL URLWithString:urlString] completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        
        NSString* result = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
        //解析html页面
        NSString *htmlString = [self filterHTML:result];
        //除掉换行符
        NSString *resultString = [htmlString stringByReplacingOccurrencesOfString:@"\n" withString:@""];
        
        if ([resultString isEqualToString:@"SuccessSuccess"]) {
            canUse = YES;
            NSLog(@"手机所连接的网络是可以访问互联网的: %d",canUse);
            
        }else {
            canUse = NO;
            NSLog(@"手机无法访问互联网: %d",canUse);
        }
        
        dispatch_semaphore_signal(semaphore);
    }] resume];
    
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
    
    return canUse;
}

- (NSString *)filterHTML:(NSString *)html {
    
    NSScanner *theScanner;
    NSString *text = nil;
    
    theScanner = [NSScanner scannerWithString:html];
    
    while ([theScanner isAtEnd] == NO) {
        // find start of tag
        [theScanner scanUpToString:@"<" intoString:NULL] ;
        // find end of tag
        [theScanner scanUpToString:@">" intoString:&text] ;
        // replace the found tag with a space
        //(you can filter multi-spaces out later if you wish)
        html = [html stringByReplacingOccurrencesOfString:
                [NSString stringWithFormat:@"%@>", text]
                                               withString:@""];
    }
    return html;
}