Lua

S3 Get Object Metadata, such as ETag

See more Amazon S3 (new) Examples

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

local chilkat = require("chilkat")

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

local rest = chilkat.Rest.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.
local bTls = true
local port = 443
local bAutoReconnect = true
local success = rest:connect("s3-us-west-2.amazonaws.com", port, bTls, bAutoReconnect)

-- Provide AWS credentials.
local authAws = chilkat.AuthAws.new()
authAws.access_key = "AWS_ACCESS_KEY"
authAws.secret_key = "AWS_SECRET_KEY"
authAws.service_name = "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.region = "us-west-2"

success = rest:set_auth_aws(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.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:send_req_no_body("HEAD", "/starfish.jpg")
if not success then
    print(rest.last_error_text)
    return
end

-- Now get the response header.
local statusCode = rest:read_response_header()
if statusCode < 0 then
    print(rest.last_error_text)
    return
end

-- 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.
    print("response status code = " .. statusCode)
    print("response status text = " .. rest.response_status_text)
    print("response header: " .. rest.response_header)
    return
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:
local etag = rest:response_hdr_by_name("ETag")
print("ETag: " .. etag)