What's wrong with my code to upload a file to AWS S3 using a pre-signed URL?

Question

I want to upload a file from an iOS App to an AWS S3 bucket using a pre-signed URL. The URL is correct because it works with curl on the command line.

curl -v -k --upload-file FILENAME "https://MYBUCKET.amazonaws.com:443/KEYNAME?Signature=...&Expires=1391691489&AWSAccessKeyId=..."

With the following Objective-C code ...

- (void)upload:(NSString *)url fileData:(NSData *)fileData
{
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setURL:[NSURL URLWithString:url]];
    [request setHTTPMethod:@"PUT"];
    [request setHTTPBody:fileData];
    [request setValue:[NSString stringWithFormat:@"%d", [fileData length]] forHTTPHeaderField:@"Content-Length"];
    [request setValue:@"audio/mpeg" forHTTPHeaderField:@"Content-Type"];
    [request setValue:@"public-read" forHTTPHeaderField:@"x-amz-acl"];
    [request setValue:@"iPhone-OS/6.0 fr_FR NE" forHTTPHeaderField:@"User-Agent"];

    _connection = [NSURLConnection connectionWithRequest:request delegate:self];
    [_connection start];
}

... I get this error:

Error Domain=NSURLErrorDomain Code=-1001 "The request timed out." UserInfo=0x9c49560 {NSErrorFailingURLStringKey=https://MYBUCKET.s3.amazonaws.com:443/KEYNAME?Signature=...&Expires=1391703958&AWSAccessKeyId=..., NSErrorFailingURLKey=https://MYBUCKET.amazonaws.com:443/KEYNAME?Signature=...&Expires=1391703958&AWSAccessKeyId=..., NSLocalizedDescription=The request timed out., NSUnderlyingError=0x9c48c80 "The request timed out."}

I used WireShark to see if there is any traffic and there is a lot of traffic.

I have no idea what's wrong with my code. It seems the file transfer does not terminate correctly.

How big is the file and roughly how long would it take to transfer? — David Snabel-Caunt, Feb 06 '14 at 16:52
It's 5.5 MB. Using curl it take a few seconds to upload. I already tried to set the timeout to 120 seconds. But I still get a request time out. — Jan Deinhard, Feb 06 '14 at 16:54

Jan Deinhard · Accepted Answer · 2014-02-16T09:09:04.483

I solved this myself. The Content-Type header was the culprit. In total despair I tested my code with a very small text file and got 403 as the HTTP status code from S3. No timeout. Such progress. I also got a very informative error message:

<?xml version="1.0" encoding="UTF-8"?>
<Error>
    <Code>SignatureDoesNotMatch</Code><Message>The request signature we calculated does not match the signature you provided. Check your key and signing method.</Message><StringToSignBytes>...</StringToSignBytes><RequestId>...</RequestId><HostId>...</HostId><SignatureProvided>...</SignatureProvided>
    <StringToSign>PUT

    text/plain
    1391784394
    KEYNAME</StringToSign>
    <AWSAccessKeyId>...</AWSAccessKeyId>
</Error>

Obviously the content type string (text/plain in this case) is expected in the string-to-sign if it is provided as an HTTP header from the client. Don't ask me why this causes a timeout with large (5.5MB?) files. I hope this will save someone else a few hours of life time.

The easiest fix is to just remove the line

[request setValue:@"..." forHTTPHeaderField:@"Content-Type"];

If you know the content type when you create the pre-signed URL you can of course add the string to the string-to-sign then.

Do you have solution to GET object, I am having issue of "AccessDenied". I am struggling for the same. — Mrug, Mar 05 '15 at 13:05

What's wrong with my code to upload a file to AWS S3 using a pre-signed URL?

1 Answers1