Implementing OSS Multipart Download for Mobile Devices

Technical Points

Best Practices

#import "DownloadService.h"
#import "OSSTestMacros.h"
@implementation DownloadRequest@end@implementation Checkpoint- (instancetype)copyWithZone:(NSZone *)zone {
Checkpoint *other = [[[self class] allocWithZone:zone] init];

other.etag = self.etag;
other.totalExpectedLength = self.totalExpectedLength;

return other;
}
@end
@interface DownloadService()<NSURLSessionTaskDelegate, NSURLSessionDataDelegate>@property (nonatomic, strong) NSURLSession *session; //network session
@property (nonatomic, strong) NSURLSessionDataTask *dataTask; //data request task
@property (nonatomic, copy) DownloadFailureBlock failure; //request failure
@property (nonatomic, copy) DownloadSuccessBlock success; //request success
@property (nonatomic, copy) DownloadProgressBlock progress; //download progress
@property (nonatomic, copy) Checkpoint *checkpoint; //checkpoint
@property (nonatomic, copy) NSString *requestURLString; //the URL of the file for download request
@property (nonatomic, copy) NSString *headURLString; //the URL of the file for head request
@property (nonatomic, copy) NSString *targetPath; //the path of the file
@property (nonatomic, assign) unsigned long long totalReceivedContentLength; //the length of the downloaded content
@property (nonatomic, strong) dispatch_semaphore_t semaphore;
@end@implementation DownloadService- (instancetype)init
{
self = [super init];
if (self) {
NSURLSessionConfiguration *conf = [NSURLSessionConfiguration defaultSessionConfiguration];
conf.timeoutIntervalForRequest = 15;

NSOperationQueue *processQueue = [NSOperationQueue new];
_session = [NSURLSession sessionWithConfiguration:conf delegate:self delegateQueue:processQueue];
_semaphore = dispatch_semaphore_create(0);
_checkpoint = [[Checkpoint alloc] init];
}
return self;
}
+ (instancetype)downloadServiceWithRequest:(DownloadRequest *)request {
DownloadService *service = [[DownloadService alloc] init];
if (service) {
service.failure = request.failure;
service.success = request.success;
service.requestURLString = request.sourceURLString;
service.headURLString = request.headURLString;
service.targetPath = request.downloadFilePath;
service.progress = request.downloadProgress;
if (request.checkpoint) {
service.checkpoint = request.checkpoint;
}
}
return service;
}
/**
* head file information, the etag of the extracted file is compared with the etag saved in the local checkpoint, and the result is returned
*/
- (BOOL)getFileInfo {
__block BOOL resumable = NO;
NSURL *url = [NSURL URLWithString:self.headURLString];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url];
[request setHTTPMethod:@"HEAD"];

NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
if (error) {
cNSLog(@"Failed to obtain file metadata, error : %@", error);
} else {
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
NSString *etag = [httpResponse.allHeaderFields objectForKey:@"Etag"];
if ([self.checkpoint.etag isEqualToString:etag]) {
resumable = YES;
} else {
resumable = NO;
}
}
dispatch_semaphore_signal(self.semaphore);
}];
[task resume];

dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER);
return resumable;
}
/**
* for obtaining the size of the local file
*/
- (unsigned long long)fileSizeAtPath:(NSString *)filePath {
unsigned long long fileSize = 0;
NSFileManager *dfm = [NSFileManager defaultManager];
if ([dfm fileExistsAtPath:filePath]) {
NSError *error = nil;
NSDictionary *attributes = [dfm attributesOfItemAtPath:filePath error:&error];
if (!error && attributes) {
fileSize = attributes.fileSize;
} else if (error) {
NSLog(@"error: %@", error);
}
}
return fileSize;
}
- (void)resume {
NSURL *url = [NSURL URLWithString:self.requestURLString];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url];
[request setHTTPMethod:@"GET"];

BOOL resumable = [self getFileInfo]; // if the resumable is NO, the download cannot be resumed, otherwise go to the resume logic.
if (resumable) {
self.totalReceivedContentLength = [self fileSizeAtPath:self.targetPath];
NSString *requestRange = [NSString stringWithFormat:@"bytes=%llu-", self.totalReceivedContentLength];
[request setValue:requestRange forHTTPHeaderField:@"Range"];
} else {
self.totalReceivedContentLength = 0;
}

if (self.totalReceivedContentLength == 0) {
[[NSFileManager defaultManager] createFileAtPath:self.targetPath contents:nil attributes:nil];
}

self.dataTask = [self.session dataTaskWithRequest:request];
[self.dataTask resume];
}
- (void)pause {
[self.dataTask cancel];
self.dataTask = nil;
}
- (void)cancel {
[self.dataTask cancel];
self.dataTask = nil;
[self removeFileAtPath: self.targetPath];
}
- (void)removeFileAtPath:(NSString *)filePath {
NSError *error = nil;
[[NSFileManager defaultManager] removeItemAtPath:self.targetPath error:&error];
if (error) {
NSLog(@"remove file with error : %@", error);
}
}
#pragma mark - NSURLSessionDataDelegate- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
didCompleteWithError:(nullable NSError *)error {
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)task.response;
if ([httpResponse isKindOfClass:[NSHTTPURLResponse class]]) {
if (httpResponse.statusCode == 200) {
self.checkpoint.etag = [[httpResponse allHeaderFields] objectForKey:@"Etag"];
self.checkpoint.totalExpectedLength = httpResponse.expectedContentLength;
} else if (httpResponse.statusCode == 206) {
self.checkpoint.etag = [[httpResponse allHeaderFields] objectForKey:@"Etag"];
self.checkpoint.totalExpectedLength = self.totalReceivedContentLength + httpResponse.expectedContentLength;
}
}

if (error) {
if (self.failure) {
NSMutableDictionary *userInfo = [NSMutableDictionary dictionaryWithDictionary:error.userInfo];
[userInfo oss_setObject:self.checkpoint forKey:@"checkpoint"];

NSError *tError = [NSError errorWithDomain:error.domain code:error.code userInfo:userInfo];
self.failure(tError);
}
} else if (self.success) {
self.success(@{@"status": @"success"});
}
}
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler
{
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)dataTask.response;
if ([httpResponse isKindOfClass:[NSHTTPURLResponse class]]) {
if (httpResponse.statusCode == 200) {
self.checkpoint.totalExpectedLength = httpResponse.expectedContentLength;
} else if (httpResponse.statusCode == 206) {
self.checkpoint.totalExpectedLength = self.totalReceivedContentLength + httpResponse.expectedContentLength;
}
}

completionHandler(NSURLSessionResponseAllow);
}
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data {

NSFileHandle *fileHandle = [NSFileHandle fileHandleForWritingAtPath:self.targetPath];
[fileHandle seekToEndOfFile];
[fileHandle writeData:data];
[fileHandle closeFile];

self.totalReceivedContentLength += data.length;
if (self.progress) {
self.progress(data.length, self.totalReceivedContentLength, self.checkpoint.totalExpectedLength);
}
}
@end
#import <Foundation/Foundation.h>typedef void(^DownloadProgressBlock)(int64_t bytesReceived, int64_t totalBytesReceived, int64_t totalBytesExpectToReceived);
typedef void(^DownloadFailureBlock)(NSError *error);
typedef void(^DownloadSuccessBlock)(NSDictionary *result);
@interface Checkpoint : NSObject<NSCopying>@property (nonatomic, copy) NSString *etag; // etag value of the resource
@property (nonatomic, assign) unsigned long long totalExpectedLength; //total length of the file
@end@interface DownloadRequest : NSObject@property (nonatomic, copy) NSString *sourceURLString; // the URL for download@property (nonatomic, copy) NSString *headURLString; // the URL for obtaining the file source@property (nonatomic, copy) NSString *downloadFilePath; // the local path of the file@property (nonatomic, copy) DownloadProgressBlock downloadProgress; // download progress@property (nonatomic, copy) DownloadFailureBlock failure; // callback for a download success@property (nonatomic, copy) DownloadSuccessBlock success; // callback for a download failure@property (nonatomic, copy) Checkpoint *checkpoint; // checkpoint for storing the etag of the file@end
@interface DownloadService : NSObject+ (instancetype)downloadServiceWithRequest:(DownloadRequest *)request;/**
* Start the download
*/
- (void)resume;
/**
* Pause the download
*/
- (void)pause;
/**
* Cancel the download
*/
- (void)cancel;
@end
- (void)initDownloadURLs {
OSSPlainTextAKSKPairCredentialProvider *pCredential = [[OSSPlainTextAKSKPairCredentialProvider alloc] initWithPlainTextAccessKey:OSS_ACCESSKEY_ID secretKey:OSS_SECRETKEY_ID];
_mClient = [[OSSClient alloc] initWithEndpoint:OSS_ENDPOINT credentialProvider:pCredential];

// generate the signed URL for the get request
OSSTask *downloadURLTask = [_mClient presignConstrainURLWithBucketName:@"aliyun-dhc-shanghai" withObjectKey:OSS_DOWNLOAD_FILE_NAME withExpirationInterval:1800];
[downloadURLTask waitUntilFinished];
_downloadURLString = downloadURLTask.result;

// generate the signed URL for the head request
OSSTask *headURLTask = [_mClient presignConstrainURLWithBucketName:@"aliyun-dhc-shanghai" withObjectKey:OSS_DOWNLOAD_FILE_NAME httpMethod:@"HEAD" withExpirationInterval:1800 withParameters:nil];
[headURLTask waitUntilFinished];

_headURLString = headURLTask.result;
}
- (IBAction)resumeDownloadClicked:(id)sender {
_downloadRequest = [DownloadRequest new];
_downloadRequest.sourceURLString = _downloadURLString; // set the URL of the resource
_downloadRequest.headURLString = _headURLString;
NSString *documentPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES).firstObject;
_downloadRequest.downloadFilePath = [documentPath stringByAppendingPathComponent:OSS_DOWNLOAD_FILE_NAME]; //set the local storage path of the downloaded file

__weak typeof(self) wSelf = self;
_downloadRequest.downloadProgress = ^(int64_t bytesReceived, int64_t totalBytesReceived, int64_t totalBytesExpectToReceived) {
// totalBytesReceived is the number of bytes that the client currently has cached, and totalBytesExpectToReceived is the total number of bytes that need to be downloaded.
dispatch_async(dispatch_get_main_queue(), ^{
__strong typeof(self) sSelf = wSelf;
CGFloat fProgress = totalBytesReceived * 1.f / totalBytesExpectToReceived;
sSelf.progressLab.text = [NSString stringWithFormat:@"%.2f%%", fProgress * 100];
sSelf.progressBar.progress = fProgress;
});
};
_downloadRequest.failure = ^(NSError *error) {
__strong typeof(self) sSelf = wSelf;
sSelf.checkpoint = error.userInfo[@"checkpoint"];
};
_downloadRequest.success = ^(NSDictionary *result) {
NSLog(@"Download successful");
};
_downloadRequest.checkpoint = self.checkpoint;

NSString *titleText = [[_downloadButton titleLabel] text];
if ([titleText isEqualToString:@"download"]) {
[_downloadButton setTitle:@"pause" forState: UIControlStateNormal];
_downloadService = [DownloadService downloadServiceWithRequest:_downloadRequest];
[_downloadService resume];
} else {
[_downloadButton setTitle:@"download" forState: UIControlStateNormal];
[_downloadService pause];
}
}
- (IBAction)cancelDownloadClicked:(id)sender {
[_downloadButton setTitle:@"download" forState: UIControlStateNormal];
[_downloadService cancel];
}
//1. First use SDK to get the download URL of the object
String signedURLString = ossClient.presignConstrainedObjectURL(bucket, object, expires);
//2. Add the download task mDownloadManager = DownloadManager.getInstance();
mDownloadManager.add(signedURLString, new DownloadListner() {
@Override
public void onFinished() {
Toast.makeText(MainActivity.this, "Download successful", Toast.LENGTH_SHORT).show();
}
@Override
public void onProgress(float progress) {
pb_progress1.setProgress((int) (progress * 100));
tv_progress1.setText(String.format("%.2f", progress * 100) + "%");
}
@Override
public void onPause() {
Toast.makeText(MainActivity.this, "Paused!", Toast.LENGTH_SHORT).show();
}
@Override
public void onCancel() {
tv_progress1.setText("0%");
pb_progress1.setProgress(0);
btn_download1.setText("Download");
Toast.makeText(MainActivity.this, "Download canceled!", Toast.LENGTH_SHORT).show();
}
});

//3. Start the download
mDownloadManager.download(signedURLString);

//4. Pause the download
mDownloadManager.cancel(signedURLString);

//5. Resume the download
mDownloadManager.download(signedURLString);

Improvements

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