Change Content-Disposition of existing S3 object - amazon-web-services

Question

In S3 REST API I am adding metadata to an existing object by using the PUT (Copy) command and copying a key to the same location with 'x-amz-metadata-directive' = 'REPLACE'
What I want to do is change the download file name by setting:
Content-Disposition: attachment; filename=foo.bar;
This sets the metadata correctly but when I download the file it still uses the key name instead of 'foo.bar'
I use a software tool S3 Browser to view the metadata and it looks correct (apart from 'Content-Disposition' being all lower case as that's was S3 ask me to sign)
Then using S3 Browser I just pressed, then save without changing anything and now it works???
What am I missing how come setting a metadata 'Content-Disposition: attachment; filename=foo.bar;' from my web app does not work but does work from S3 Browser?

Answer 1

Edited for clarity:
Content-Disposition must be set explicitly and not included as x-amz-meta-Content-Disposition. All metadata header names must start with "x-amz-meta-" and be all lowercase.
Thanks to #Eyal for clarifying.
Original:
>SOLVED:
>
>The Doco at http://docs.amazonwebservices.com/AmazonS3/latest/dev/index.html?RESTAuthentication.html
>
>seems to be wrong it says:
>
>Notice how the 'x-amz-' headers are sorted, white-space trimmed, converted tolowercase, and multiple headers with the same name have been joined using a comma toseparate values.
>
>Note how only the Content-Type and Content-MD5HTTPentity headers appear in the StringToSign .The otherContent-* entity headers do not.
However Content-Disposition must be set specifically and not included as : x-amz-meta-Content-Disposition
>
>It now works fine.

Answer 2

here: this uses the cli to set the content-disposition header on all files in a path inside a bucket (and also sets them as public):
aws s3 ls s3://mybucket/brand_img/ios/|awk {'print $4'} > objects.txt
while read line; do aws s3api copy-object --bucket mybucket \
--copy-source /mybucket/brand_img/ios/$line --key brand_img/ios/$line \
--metadata-directive REPLACE --metadata Content-Disposition=$line --acl public-read; done < objects.txt