HTTP HEAD 生成方法
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url
cachePolicy:0 timeoutInterval:kTimeout];
request.HTTPMethod = @"HEAD";
[NSURLConnection sendAsynchronousRequest:request queue:self.myQueue
completionHandler:^(NSURLResponse *response, NSData *data, NSError
*connectionError) {
NSLog(@"%@", response);
NSLog(@"---------------");
NSLog(@"%@", data);
}];
运行测试代码可以发现，HEAD方法只是返回资源信息，而不会返回数据体
应用场景：
(1)获取资源Mimetype
(2)获取资源文件大小，用于端点续传或多线程下载
使用代码块来获取资源大小的方法
- (void)fileSizeWithURL:(NSURL *)url completion:(void (^)(long long
contentLength))completion
{
NSMutableURLRequest *request = [NSMutableURLRequest
requestWithURL:url cachePolicy:0 timeoutInterval:kTimeout];
request.HTTPMethod = @"HEAD";
NSURLResponse *response = nil;
[NSURLConnection sendSynchronousRequest:request
returningResponse:&response error:NULL];
completion(response.expectedContentLength);
}
确定每次下载数据包的伪代码实现
- (void)downloadFileWithURL:(NSURL *)url
{
[self fileSizeWithURL:url completion:^(long long
contentLength) {
NSLog(@"文件总大小：%lld",
contentLength);
// 根据大小下载文件
while (contentLength >
kDownloadBytes) {
NSLog(@"每次下载长度：%lld", (long long)kDownloadBytes);
contentLength -= kDownloadBytes;
}
NSLog(@"最后下载字节数：%lld",
contentLength);
}];
}
分段Range代码实现
long long fromBytes = 0;
long long toBytes = 0;
while (contentLength > kDownloadBytes) {
toBytes = fromBytes + kDownloadBytes - 1;
NSString *range = [NSString
stringWithFormat:@"bytes=%lld-%lld", fromBytes, toBytes];
NSLog(@"range %@", range);
fromBytes += kDownloadBytes;
contentLength -= kDownloadBytes;
}
fromBytes = fromBytes + contentLength - 1;
NSString *range = [NSString stringWithFormat:@"bytes=%lld-%lld", fromBytes,
toBytes];
NSLog(@"range %@", range);
分段下载文件
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url
cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:kTimeout];
NSString *range = [NSString stringWithFormat:@"bytes=%lld-%lld", from,
end];
[request setValue:range forHTTPHeaderField:@"Range"];
NSURLResponse *response = nil;
NSData *data = [NSURLConnection sendSynchronousRequest:request
returningResponse:&response error:NULL];
NSLog(@"%@-%@-%ld", range, response, (unsigned long)data.length);
提示：
如果GET包含Range请求头，响应会以状态码206（PartialContent）返回而不是200（OK）
将数据写入文件
// 打开缓存文件
NSFileHandle *fp = [NSFileHandle
fileHandleForWritingAtPath:self.cachePath];
// 如果文件不存在，直接写入数据
if (!fp) {
[data writeToFile:self.cachePath atomically:YES];
} else {
// 移动到文件末尾
[fp seekToEndOfFile];
// 将数据文件追加到文件末尾
[fp writeData:data];
// 关闭文件句柄
[fp closeFile];
}
IOS文件分段下载,码迷,mamicode.com