Uploading big file using Objective-C API V2 very SLOW...

// My code can be summarized as follows:

// sorry for the indentation, it seems the code indentation is gone.

const NSUInteger DB_CHUNK_SIZE = 5*1024*1024;

DropboxClient *client = [DropboxClientsManager authorizedClient];

// create dropboxObj to pass parameters
TGDropboxObject *dropboxObj = [[TGDropboxObject alloc] init];
dropboxObj.progressBlock = progress;
dropboxObj.completionBlock = completion;
dropboxObj.fileSize = [self getFileSize:localPath fromInternal:fromInternal];
dropboxObj.chunkSize = DB_CHUNK_SIZE;
dropboxObj.curTotalBytes = 0;
dropboxObj.srcPath = localPath;
dropboxObj.dstPath = remotePath;
dropboxObj.fromInternal = fromInternal;
if (fromInternal) {
dropboxObj.fileHandle = [NSFileHandle fileHandleForReadingAtPath:localPath];
}
// skip……

NSData *data = [self readDataOfLength:dropboxObj.chunkSize fromObj:dropboxObj];// read one chunk of data

DBUploadTask<DBFILESUploadSessionStartResult *, DBNilObject *> *uploadTask;

uploadTask = [client.filesRoutes uploadSessionStartData:data];
[uploadTask response:^(DBFILESUploadSessionStartResult * _Nullable result, DBNilObject * _Nullable obj, DBRequestError * _Nullable requestError) {

if (result) { // success for the first chunk
dropboxObj.sessionId = result.sessionId;

DBFILESUploadSessionCursor *cursor = [[DBFILESUploadSessionCursor alloc] initWithSessionId:result.sessionId offset:[NSNumber numberWithUnsignedLongLong:[self getOffsetFromObj:dropboxObj]]];

[self uploadNextFromObj:dropboxObj cursor:cursor];// do upload for subsequent chunks
}
else { // failure
[self closeFileFromObj:dropboxObj];

// skip…

dropboxObj.completionBlock(nil, error);
}
}];

// progress block for uploadTask
[uploadTask progress:^(int64_t bytesWritten, int64_t totalBytesWritten, int64_t totalBytesExpectedToWrite) {
dropboxObj.curTotalBytes += bytesWritten;
CGFloat progress = (CGFloat)dropboxObj.curTotalBytes / (CGFloat)dropboxObj.fileSize;
NSLog(@"start: bytesWritten = %lld progress = %.4f", bytesWritten, progress);
dropboxObj.progressBlock(progress);
}];

// The method for uploading subsequent chunks:

//-------------------------------------------------------
- (void)uploadNextFromObj:(TGDropboxObject *)dropboxObj cursor:(DBFILESUploadSessionCursor *)cursor {

DropboxClient *client = [DropboxClientsManager authorizedClient];
NSData *const chunk = [self readDataOfLength:dropboxObj.chunkSize fromObj:dropboxObj];
const BOOL isLastChunk = chunk.length < dropboxObj.chunkSize;

if (isLastChunk == NO) {
DBUploadTask<DBNilObject *, DBFILESUploadSessionLookupError *> *continueTask;

continueTask = [client.filesRoutes uploadSessionAppendV2Data:cursor inputData:chunk];
[continueTask response:^(DBNilObject * _Nullable obj, DBFILESUploadSessionLookupError * _Nullable lookupError, DBRequestError * _Nullable requestError) {

if (lookupError == nil) { // success
DBFILESUploadSessionCursor *cursor = [[DBFILESUploadSessionCursor alloc] initWithSessionId:dropboxObj.sessionId offset:[NSNumber numberWithUnsignedLongLong:[self getOffsetFromObj:dropboxObj]]];

[self uploadNextFromObj:dropboxObj cursor:cursor];

} else { // failure
[self closeFileFromObj:dropboxObj];

// skip…

dropboxObj.completionBlock(nil, error);
}
}];

// progress block for continueTask
[continueTask progress:^(int64_t bytesWritten, int64_t totalBytesWritten, int64_t totalBytesExpectedToWrite) {
dropboxObj.curTotalBytes += bytesWritten;
CGFloat progress = (CGFloat)dropboxObj.curTotalBytes / (CGFloat)dropboxObj.fileSize;
NSLog(@"continue: bytesWritten = %lld progress = %.4f", bytesWritten, progress);
dropboxObj.progressBlock(progress);
}];
}
else { // last chunk
DBUploadTask<DBFILESFileMetadata *, DBFILESUploadSessionFinishError *> *finishTask;
DBFILESCommitInfo *info = [[DBFILESCommitInfo alloc] initWithPath:dropboxObj.dstPath];

finishTask = [client.filesRoutes uploadSessionFinishData:cursor commit:info inputData:chunk];
[finishTask response:^(DBFILESFileMetadata * _Nullable metaData, DBFILESUploadSessionFinishError * _Nullable finishError, DBRequestError * _Nullable requestError) {
DLog(@"metaData: %@", metaData);
[self closeFileFromObj:dropboxObj];

// skip…

dropboxObj.completionBlock(metaData, error);
}];
[finishTask progress:^(int64_t bytesWritten, int64_t totalBytesWritten, int64_t totalBytesExpectedToWrite) {
dropboxObj.curTotalBytes += bytesWritten;
CGFloat progress = (CGFloat)dropboxObj.curTotalBytes / (CGFloat)dropboxObj.fileSize;
NSLog(@"finish: bytesWritten = %lld progress = %.4f", bytesWritten, progress);
dropboxObj.progressBlock(progress);
}];
}
}

// If there is anything unclear, just tell me, I can provide further infomation.