(Ruby) S3 Get Object Metadata, such as ETag

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

Chilkat Ruby Downloads install from rubygems.org gem install chilkat or download... Ruby Library for Windows, MacOS, Linux, Alpine Linux

require 'chilkat'

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

rest = Chilkat::CkRest.new()

# Connect to the Amazon AWS REST server in the desired region.
# In this case we connect to S3 in the "us-west-2" region.
bTls = true
port = 443
bAutoReconnect = true
success = rest.Connect("s3-us-west-2.amazonaws.com",port,bTls,bAutoReconnect)

# Provide AWS credentials.
authAws = Chilkat::CkAuthAws.new()
authAws.put_AccessKey("AWS_ACCESS_KEY")
authAws.put_SecretKey("AWS_SECRET_KEY")
authAws.put_ServiceName("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".
authAws.put_Region("us-west-2")

success = rest.SetAuthAws(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"
rest.put_Host("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.
success = rest.SendReqNoBody("HEAD","/starfish.jpg")
if (success != true)
    print rest.lastErrorText() + "\n";
    exit
end

# Now get the response header.
statusCode = rest.ReadResponseHeader()
if (statusCode < 0)
    print rest.lastErrorText() + "\n";
    exit
end

# When successful, the S3 Storage service will respond with a 200 response code,
# with an XML body.  
if (statusCode != 200)
    # Examine the request/response to see what happened.
    print "response status code = " + statusCode.to_s() + "\n";
    print "response status text = " + rest.responseStatusText() + "\n";
    print "response header: " + rest.responseHeader() + "\n";
    exit
end

# 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:
etag = rest.responseHdrByName("ETag")
print "ETag: " + etag + "\n";