通过回形针向S3提供Content-MD5标头

Question

I'm using Paperclip to upload files directly to s3 for my rails web app. I'm currently trying to exploit the md5 check integrated in amazon s3 to verify that the upload was carried on successfully. Paperclip offers a s3_headers hash that you can populate with whatever fields you need. Content-Type is automatically filled. Content-MD5 needs to be Base64 encoded so I provide it this way:

:s3_headers => {:content_md5 => Base64.strict_encode64(md5sum)},

I use strict_encode64 because encode64 adds an unnecessary trailing \\n. With this setup I always receive an InvalidDigest error from aws-sdk, even though paperclip correctly shows the calculated header. I also tried to use plain, unencoded md5sum, with similar results.

Answer 1

If md5sum is a string of hex digits, like the std output from the Linux application md5sum , try this:

:s3_headers => {:content_md5 => [[md5sum].pack("H*")].pack("m0") }

For example, from the rails console:

> md5sum = "7d592a3129ab6a867cf6e2eb60f9ef83"
> [[md5sum].pack("H*")].pack("m0")
 => "fVkqMSmraoZ89uLrYPnvgw=="

Answer 2

Take the md5 of your source, convert each (character couple) from string to hex (2 bytes become 1 byte); then base64 encode and you will be fine.