Object Storage Service:Unduhan yang dapat dilanjutkan (OSS SDK untuk iOS)

Selama proses unduhan, aplikasi menampilkan dialog progres yang menunjukkan persentase unduhan saat ini, bilah progres, serta tombol pause atau cancel untuk unduhan tersebut.

Kode contoh berikut menunjukkan cara melakukan unduhan yang dapat dilanjutkan di iOS:

#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;         // Sesi jaringan.
@property (nonatomic, strong) NSURLSessionDataTask *dataTask;   // Tugas permintaan data.
@property (nonatomic, copy) DownloadFailureBlock failure;    // Dipanggil saat permintaan gagal.
@property (nonatomic, copy) DownloadSuccessBlock success;    // Dipanggil saat permintaan berhasil.
@property (nonatomic, copy) DownloadProgressBlock progress;  // Melacak progres unduhan.
@property (nonatomic, copy) Checkpoint *checkpoint;        // Checkpoint.
@property (nonatomic, copy) NSString *requestURLString;    // URL resource yang akan diunduh.
@property (nonatomic, copy) NSString *headURLString;       // URL untuk permintaan HEAD.
@property (nonatomic, copy) NSString *targetPath;     // Jalur lokal untuk menyimpan file.
@property (nonatomic, assign) unsigned long long totalReceivedContentLength; // Ukuran konten yang telah diterima sejauh ini.
@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;
}
// DownloadRequest adalah inti dari logika unduhan.
+ (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;
}
/**
 * Mendapatkan informasi file menggunakan metode HEAD dan membandingkan ETag file dengan yang ada di checkpoint lokal.
 */
- (BOOL)getFileInfo {
    __block BOOL resumable = NO;
    NSURL *url = [NSURL URLWithString:self.headURLString];
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url];
    [request setHTTPMethod:@"HEAD"];
    // Memproses informasi objek. Misalnya, ETag digunakan untuk pemeriksaan awal pada unduhan yang dapat dilanjutkan, dan content-length digunakan untuk menghitung progres unduhan.
    NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        if (error) {
            NSLog(@"Gagal mendapatkan metadata file. 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;
}
/**
 * Mendapatkan ukuran file lokal.
 */
- (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];    // Nilai kembalian `NO` menunjukkan bahwa kondisi untuk unduhan yang dapat dilanjutkan tidak terpenuhi.
    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(@"hapus file dengan error : %@", error);
    }
}
#pragma mark - NSURLSessionDataDelegate
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
// Menentukan apakah unduhan telah selesai dan melaporkan hasilnya ke layanan tingkat atas.
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);
}
// Menambahkan data yang diterima ke file dan memperbarui progres unduhan.
- (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