iOS-SDK之如何实现分片上传（一）?

下面演示通过分片上传文件的整个流程：

初始化分片上传

1. __block NSString * uploadId = nil;
2. __block NSMutableArray * partInfos = [NSMutableArray new];
4. NSString * uploadToBucket = @"<bucketName>";
5. NSString * uploadObjectkey = @"<objectKey>";
7. OSSInitMultipartUploadRequest * init = [OSSInitMultipartUploadRequest new];
8. init.bucketName = uploadToBucket;
9. init.objectKey = uploadObjectkey;
11. // init.contentType = @"application/octet-stream";
13. OSSTask * initTask = [client multipartUploadInit:init];
15. [initTask waitUntilFinished];
17. if (!initTask.error) {
18.     OSSInitMultipartUploadResult * result = initTask.result;
19.     uploadId = result.uploadId;
20. } else {
21.     NSLog(@"multipart upload failed, error: %@", initTask.error);
22.     return;
23. }

• OSSInitMultipartUploadRequest指定上传文件的所属存储空间Bucket和文件名字。
• multipartUploadInit发挥的结果中包含UploadId，是区分分片上传的唯一标示，后面的操作中会用到。

1. NSString * filePath = [docDir stringByAppendingPathComponent:@"***"];
2. //要上传的文件
3. int chuckCount = *;
4. //分片上传数量
5. uint64_t offset = fileSie/chuckCount;
6. //分片大小
7. for (int i = 1; i <= chuckCount; i++) {
8.     OSSUploadPartRequest * uploadPart = [OSSUploadPartRequest new];
9.     uploadPart.bucketName = uploadToBucket;
10.     uploadPart.objectkey = uploadObjectkey;
11.     uploadPart.uploadId = uploadId;
12.     uploadPart.partNumber = i; // part number start from 1
14.     NSFileHandle* readHandle = [NSFileHandle fileHandleForReadingAtPath:filePath];
15.         [readHandle seekToFileOffset:offset * (i -1)];
17.         NSData* data = [readHandle readDataOfLength:offset];
18.         uploadPart.uploadPartData = data;
20.     OSSTask * uploadPartTask = [client uploadPart:uploadPart];
22.     [uploadPartTask waitUntilFinished];
24.     if (!uploadPartTask.error) {
25.         OSSUploadPartResult * result = uploadPartTask.result;
26.         uint64_t fileSize = [[[NSFileManager defaultManager] attributesOfItemAtPath:uploadPart.uploadPartFileURL.absoluteString error:nil] fileSize];
27.         [partInfos addObject:[OSSPartInfo partInfoWithPartNum:i eTag:result.eTag size:fileSize]];
28.     } else {
29.         NSLog(@"upload part error: %@", uploadPartTask.error);
30.         return;
31.     }
32. }

• 每一个分片上传请求需指定UploadId和PartNum。
• uploadPart要求除最后一个Part外，其他的Part大小都要大于100KB。但是Upload Part接口并不会立即校验上传。Part的大小（因为不知道是否为最后一块）；只有当Complete Multipart Upload的时候才会校验。
• Part号码的范围是1~10000。如果超出这个范围，OSS将返回InvalidArgument的错误码。
• 每次上传part时都要把流定位到此次上传片开头所对应的位置。
• 每次上传part之后，OSS的返回结果会包含一个分片的ETag，值为part数据的MD5值，您需要将它和块编号组合成PartEtag保存，后续完成分片上传需要用到。

1. OSSCompleteMultipartUploadRequest * complete = [OSSCompleteMultipartUploadRequest new];
2. complete.bucketName = uploadToBucket;
3. complete.objectKey = uploadObjectkey;
4. complete.uploadId = uploadId;
5. complete.partInfos = partInfos;
7. OSSTask * completeTask = [client completeMultipartUpload:complete];
9. [[completeTask continueWithBlock:^id(OSSTask *task) {
10.     if (!task.error) {
11.         OSSCompleteMultipartUploadResult * result = task.result;
12.         // ...
13.     } else {
14.         // ...
15.     }
16.     return nil;
17. }] waitUntilFinished];