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

Hello,

recently our app updates the Dropbox related code from API V1 to API V2. Usually we need to transfer files to Dropbox, it is OK for small files, but for video files of size about 1.5 GB the progress is very slow, and often the upload is stopped due to request timeout.... 

We use the following API calls:

1. Start the upload

[client.filesRoutes uploadSessionStartData:data];

2. Repeatedly upload new chunk of data

[client.filesRoutes uploadSessionAppendV2Data:cursor inputData:chunk];

3. Finish upload for the last chunk

[client.filesRoutes uploadSessionFinishData:cursor commit:info inputData:chunk];

And the log messages are as follows:

2017-01-20 14:25:11.336692 MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0000

2017-01-20 14:25:11.343177MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0000

2017-01-20 14:25:11.349521MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0001

2017-01-20 14:25:11.353344MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0001

// Skip...

2017-01-20 14:25:55.059215MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0003

2017-01-20 14:25:55.070222MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0003

2017-01-20 14:26:17.700571MyApp[19184:6471639] start: bytesWritten = 65536 progress = 0.0003

2017-01-20 14:26:17.704239MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0003

2017-01-20 14:26:34.987083MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0004

2017-01-20 14:26:34.992280MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0004

2017-01-20 14:26:35.005880MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0004

// No data downloaded for about 23 sec

2017-01-20 14:26:58.848907MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0004

2017-01-20 14:26:58.855699MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0004

2017-01-20 14:26:58.871372MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0005

2017-01-20 14:26:58.873328MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0005

2017-01-20 14:27:15.431969MyApp[19184:6471639] start: bytesWritten = 65536 progress = 0.0005

2017-01-20 14:27:15.436307MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0006

2017-01-20 14:27:44.313052MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0006

2017-01-20 14:27:44.318937MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0006

2017-01-20 14:27:44.323024MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0006

2017-01-20 14:27:44.327415MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0006

2017-01-20 14:28:10.012220MyApp[19184:6471639] start: bytesWritten = 65536 progress = 0.0007

2017-01-20 14:28:10.015194 MyApp[19184:6471639] start: bytesWritten = 32768 progress = 0.0007

// Skip...

2017-01-20 14:59:18.994143 MyApp[19184:6471639] __70-[....]_block_invoke [Line 92] start: requestError = DropboxClientError[{

    NSError = "Error Domain=NSURLErrorDomain Code=-1001 \"\U8981\U6c42\U903e\U6642\U3002\" UserInfo={NSUnderlyingError=0x17025bb70 {Error Domain=kCFErrorDomainCFNetwork Code=-1001 \"(null)\" UserInfo={_kCFStreamErrorCodeKey=-2102, _kCFStreamErrorDomainKey=4}}, NSErrorFailingURLStringKey=https://api-content.dropbox.com/2/files/upload_session/start, NSErrorFailingURLKey=https://api-content.dropbox.com/2/files/upload_session/start, _kCFStreamErrorDomainKey=4, _kCFStreamErrorCodeKey=-2102, NSLocalizedDescription=\U8981\U6c42\U903e\U6642\U3002}";

}];

2017-01-20 14:59:18.994833 MyApp[19184:6471639] __74-[...]_block_invoke_2 [Line 428] Failed To Upload /Horrible.Bosses.2011.DVDRip.XVID.AC3.HQ.Hive-CM8.avi

Error = DBRequestErrorClient

2017-01-20 14:59:18.995478 MyApp[19184:6475977] [] __tcp_connection_write_eof_block_invoke Write close callback received error: [89] Operation canceled

It can be seen from the log messages that the time the data arrived is not very smooth, and finally the operation is canceld.

My questions:

Is it pure network traffic problem?(Our network is relatively fast.)

Or is there something in API V2's upload API that causes the upload so slow?

Thanks for your attention.

Best regards,

Logan