(Tcl) S3 Get Object Metadata, such as ETag

Demonstrates how to get an S3 object's metadata using a HEAD request.

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load ./chilkat.dll

# This example requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

set rest [new_CkRest]

# Connect to the Amazon AWS REST server in the desired region.
# In this case we connect to S3 in the "us-west-2" region.
set bTls 1
set port 443
set bAutoReconnect 1
set success [CkRest_Connect $rest "s3-us-west-2.amazonaws.com" $port $bTls $bAutoReconnect]

# Provide AWS credentials.
set authAws [new_CkAuthAws]

CkAuthAws_put_AccessKey $authAws "AWS_ACCESS_KEY"
CkAuthAws_put_SecretKey $authAws "AWS_SECRET_KEY"
CkAuthAws_put_ServiceName $authAws "s3"

# This particular bucket is in the Oregon region, as opposed to the US Standard,
# therefore the Region must be set appropriately.
# Also note that we connected to "s3-us-west-2.amazonaws.com".
CkAuthAws_put_Region $authAws "us-west-2"

set success [CkRest_SetAuthAws $rest $authAws]

# Note: The above REST connection and setup of the AWS credentials
# can be done once.  After connecting, any number of REST calls can be made.
# The "auto reconnect" property passed to rest.Connect indicates that if
# the connection is lost, a REST method call will automatically reconnect
# if needed.
# --------------------------------------------------------------------------

# Set the bucket name via the HOST header.
# In this case, the bucket name is "chilkat.ocean".
# Note that the Host header should use "bucketName.s3.amazonaws.com", not "bucketName.s3-us-west-2.amazonaws.com"
CkRest_put_Host $rest "chilkat.ocean.s3.amazonaws.com"

# Our object is "starfish.jpg".
# Get the metadata.
# Since we are sending a HEAD request, we shouldn't use any of the Full* methods.
# Instead, send the request, then just read the response header.
set success [CkRest_SendReqNoBody $rest "HEAD" "/starfish.jpg"]
if {$success != 1} then {
    puts [CkRest_lastErrorText $rest]
    delete_CkRest $rest
    delete_CkAuthAws $authAws
    exit
}

# Now get the response header.
set statusCode [CkRest_ReadResponseHeader $rest]
if {$statusCode < 0} then {
    puts [CkRest_lastErrorText $rest]
    delete_CkRest $rest
    delete_CkAuthAws $authAws
    exit
}

# When successful, the S3 Storage service will respond with a 200 response code,
# with an XML body.  
if {$statusCode != 200} then {
    # Examine the request/response to see what happened.
    puts "response status code = $statusCode"
    puts "response status text = [CkRest_responseStatusText $rest]"
    puts "response header: [CkRest_responseHeader $rest]"
    delete_CkRest $rest
    delete_CkAuthAws $authAws
    exit
}

# The response header contains information about the S3 object.
# For example:

# 	HTTP/1.1 200 OK
# 	x-amz-id-2: GrV/hrB2EUkBlWc0h3JDdmVIrYDXfPC7CGvo/qSVRmYRPwilAOry8+4r2YWl4xJfa1HRYXrP808=
# 	x-amz-request-id: 4BDC6D6AEA0BDEF3
# 	Date: Mon, 13 May 2019 22:03:13 GMT
# 	Last-Modified: Mon, 10 Nov 2014 16:10:23 GMT
# 	ETag: "2e9c59dbf2662367dc97dfdda85da048"
# 	Accept-Ranges: bytes
# 	Content-Type: image/jpg
# 	Content-Length: 6229
# 	Server: AmazonS3

# Get the ETag response header value:
set etag [CkRest_responseHdrByName $rest "ETag"]
puts "ETag: $etag"

delete_CkRest $rest
delete_CkAuthAws $authAws