CODEWITHSUNDEEP
uploadnsurlconnectionmultipartform-data
Advaith
Advaith

Reputation: 1117

NSURLConnection uploading large files

I need to upload large files like video from my iphone. Basically I need to read data as chunks and upload each chunk. My upload is multipart upload. How to achieve this using NSURLConnection?

Thanks in advance!

Upvotes: 0

Views: 1067

Answers (1)

CouchDeveloper
CouchDeveloper

Reputation: 19106

You likely use a "Form-based File Upload over HTML". This is a specialized form of a multipart/form-data POST request.
See Form-based File Upload in HTML and many other sources in the web.

When dealing with large files, you need to strive to keep your memory footprint acceptable low. Thus, the input source for the request data should be a NSInputStream which precisely avoids this problem. You create an instance of NSInputStream with a class factory method where you specify the file you want to upload. When setting up the NSMutableURLRequest you set the input stream via setHTTPBodyStream.

At any rate, use NSURLConnection in asynchronous mode implementing the delegates. You will need to keep a reference of the connection object in order to be able to cancel it, if this is required.

Every multipart shall have a Content-Type - especially the file part - and every part should have a Content-Length, unless chunked transfer encoding is used.

You may want to explicitly set the Content-Length header of the file part with the correct length. Otherwise, if NSURLConnection cannot determine the content length itself - and this is the true when you set an input stream - then NSURLConnection uses chunked transfer encoding. Depending on the content type a few servers may have difficulties processing either chunked transfer encoded bodies or very large bodies.

Since there is a high chance for mobile devices to loose their connection in the field during a upload request, you should also consider to utilize "HTTP range headers". Both, server and client need to support this. See "14.35 Range" RFC 2616, and various other sources regarding "resumable file upload".

There is no system framework that helps you setting up the multipart body and calculating the correct content length for the whole message. Doing this yourself without third party library support is quite error prone and cumbersome, but doable.

Upvotes: 1

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