s3api head-object does not return proper error for unknown key

[quiver]

This may not be an issue of aws-cli per se, but rather an issue of s3 api in general.

When you execute s3api head-object for unknown key, aws command just returns client error (Unknown), which makes it difficult to track down the problem.
s3 server returns 404 http status for HEAD, but response body is empty.

For comparison, s3api get-object-acl returns A client error (NoSuchKey) for such case and error message is included in xml formatted response body..

Demonstration(removing unrelated parts)

$ aws s3api head-object --bucket my-bucket-name --key unknwon-key  --debug
...
2014-02-22 14:16:49,204 - botocore.vendored.requests.packages.urllib3.connectionpool - DEBUG - "HEAD /data/std.pn HTTP/1.1" 404 0
2014-02-22 14:16:49,205 - botocore.response - DEBUG - Response Headers:
x-amz-id-2: cbPyjTjNGQ0bXHi54ZtkarD9yd2mLFsXZT1afXtlxcVtXpwIbqdhynigPOr+LTnS
server: AmazonS3
transfer-encoding: chunked
x-amz-request-id: E965558DECC7D101
date: Sat, 22 Feb 2014 05:16:25 GMT
content-type: application/xml
2014-02-22 14:16:49,206 - botocore.response - DEBUG - Response Body:

...
2014-02-22 14:16:49,207 - awscli.errorhandler - DEBUG - HTTP Response Code: 404
...
2014-02-22 14:16:49,209 - awscli.clidriver - DEBUG - Exiting with rc 255
A client error (Unknown) occurred when calling the HeadObject operation: Unknown

[messick]

The same useless error happens when the user does not have access to the key in question:

2014-05-15 08:56:32,745 - botocore.vendored.requests.packages.urllib3.connectionpool - DEBUG - "HEAD /whatever.txt HTTP/1.1" 403 0
2014-05-15 08:56:32,746 - botocore.response - DEBUG - Response Headers:
x-amz-id-2: WSuW9Awdc8KiwdoysbWY+3ciyRzdLr543nW1K/pnc1auI27OpOiPC6lLGvUleNB8wofHWHWHrY4=
server: AmazonS3
transfer-encoding: chunked
x-amz-request-id: 6A5B416D7DEC96E7
date: Thu, 15 May 2014 15:56:31 GMT
content-type: application/xml
2014-05-15 08:56:32,746 - botocore.response - DEBUG - Response Body:

2014-05-15 08:56:32,746 - botocore.hooks - DEBUG - Event needs-retry.s3.HeadObject: calling handler <botocore.retryhandler.RetryHandler object at 0x1cb7910>
2014-05-15 08:56:32,746 - botocore.retryhandler - DEBUG - No retry needed.
2014-05-15 08:56:32,747 - botocore.hooks - DEBUG - Event after-call.s3.HeadObject: calling handler <awscli.errorhandler.ErrorHandler object at 0x7fec19b42e50>
2014-05-15 08:56:32,747 - awscli.errorhandler - DEBUG - HTTP Response Code: 403
2014-05-15 08:56:32,747 - awscli.clidriver - DEBUG - Exception caught in main()
....
ClientError: A client error (Unknown) occurred when calling the HeadObject operation: Unknown
2014-05-15 08:56:32,748 - awscli.clidriver - DEBUG - Exiting with rc 255

[jamesls]

This is fixed now in the latest version of the CLI (looks like we forgot to link the fix with this issue):

$ aws s3api head-object --bucket mybucket --key bar.txt

A client error (404) occurred when calling the HeadObject operation: Not Found

The issue here is that this is a HEAD request, which does not contain a response body. In these scenarios we just use the status code message as the error message as shown above.

[pranavgarg]

usually in my case what was happening was there was an extra slash in the front of the key which was causing this issue. Fixing the key name helped overcome this issue