Best way to get MD5 of stream and then pass stream to a reader in Node.js

Question

Best way to get MD5 of stream and then pass stream to a reader in Node.js

I'm parsing an email and whenever I hit an attachment, I want to upload the attachment to S3. Whenever an attachment is found I get a stream for the attachment. I want to get the MD5sum of the attachment, then upload it to S3 using the stream again.

Is there anyway to do this without first writing the stream to a file, calculating MD5, then making a readable stream from the file and sending a stream to knox (which would be 3 stream reads)?

parser.on("attachment", function(attachment){
    //Calculate MD5 sum
    var md5sum = '';
    s3client.putStream(attachment.stream, 'blah.jpeg', {
        'md5sum': md5sum
    }, function(err, res) {});
});

node.js
stream
amazon-s3

Answer 1

I think this should work?

var crypt = require("crypto")

function hashFile(attachment){
    var hash = crypt.createHash("md5")
        .update(attachment)
        .digest("base64");


    console.log(hash);
}

hashFile("some attachment blah");

Where the attachment you pass in get's MD5 hashed and return base64 encoded (you could also specify binary, or hex in the digest method)

UPDATE Ok so I looked at that mail parser and notice what it says in the help:

https://github.com/andris9/mailparser#default-behavior

Notice the mention of the checksum property.

Now look at line 283 here: https://github.com/andris9/mailparser/blob/master/lib/mailparser.js

That checksum is the MD5 you want.

So just do attachment.checksum and be done