Lua Requires Chilkat v9.5.0.83+

S3 Resume Download

See more Amazon S3 (new) Examples

Suppose an S3 download of a very large file failed for some reason and you have a partial file on disk. Rather than restart the entire download, you wish to download the remaining portion. This example demonstrates how to finish a previously failed download. 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.
local bTls = true
local port = 443
local bAutoReconnect = true
local success = rest:connect("s3.amazonaws.com", port, bTls, bAutoReconnect)

-- ---------------------------------------------------------------------------
-- Important: For buckets created in regions outside us-east-1,
-- there are three important changes that need to be made.
-- See Working with S3 Buckets in Non-us-east-1 Regions for the details.
-- ---------------------------------------------------------------------------

-- Provide AWS credentials for the REST call.
local authAws = chilkat.AuthAws.new()
authAws.access_key = "AWS_ACCESS_KEY"
authAws.secret_key = "AWS_SECRET_KEY"
authAws.service_name = "s3"
success = rest:set_auth_aws(authAws)

-- Set the bucket name via the HOST header.
-- In this case, the bucket name is "chilkat100".
rest.host = "chilkat100.s3.amazonaws.com"

-- We want to continue downloading a file.
-- The relative local filepath of our previously partially downoaded file is: qa_output/hamlet.xml
-- Let's find out how many bytes are already downloaded.
local fac = chilkat.FileAccess.new()
local localFilepath = "qa_output/hamlet.xml"
-- Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
-- the size of the file as a string, then convert to an integer value.
local sz = fac:file_size(localFilepath)
if sz > 0 then
    print("sz = " .. sz)

    -- If the sz equals 42375 bytes, then we want to add a Range header that looks like this:
    -- Range: bytes=42375-
    local sbRange = chilkat.StringBuilder.new()
    sbRange:append("bytes=")
    sbRange:append_int(sz)
    sbRange:append("-")
    rest:add_header("Range", sbRange:get_as_string())
    print("Added Range: " .. sbRange:get_as_string())
end

-- Send the request to download the remainder of the file.
success = rest:send_req_no_body("GET", "/hamlet.xml")
if not success then
    print(rest.last_error_text)
    return
end

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

print("Response status code = " .. responseStatusCode)

-- We expect a 200 or 206 response status if the file data is coming.
-- Otherwise, we'll get a string response body with an error message(or no response body).
if (responseStatusCode == 200) or (responseStatusCode == 206) then
    local bodyStream = chilkat.Stream.new()

    -- The stream's sink will be a file.
    -- We will append to the file..
    bodyStream.sink_file = localFilepath

    -- Indicate that we wish to append to the output file.
    bodyStream.sink_file_append = true

    -- Read the response body to the stream.  Given that we've
    -- set the stream's sink to a file, it will stream directly
    -- to the file.
    success = rest:read_resp_body_stream(bodyStream, true)
    if not success then
        print(rest.last_error_text)
        return
    end

    print("Successfully downloaded the file.")
else
    local errResponse = rest:read_resp_body_string()
    if not rest.last_method_success then
        print(rest.last_error_text)
    else
        print(errResponse)
    end
end