Lambda FunctionZip doesn't support a stream object

[rclark]

According to the documentation http://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/Lambda.html#uploadFunction-property

FunctionZip: new Buffer('...') || 'STRING_VALUE' || streamObject, /* required */

This works fine as long as I provide a buffer object, but if I provide a stream (via fs.createReadStream), I get the following error:

TypeError: Not a string or buffer
        at Hash.update (crypto.js:240:17)
        at Object.util.crypto.hash (/home/travis/build/mapbox/streambot/node_modules/aws-sdk/lib/util.js:507:24)
        at Object.sha256 (/home/travis/build/mapbox/streambot/node_modules/aws-sdk/lib/util.js:461:26)
        at V4.hash [as hexEncodedHash] (/home/travis/build/mapbox/streambot/node_modules/aws-sdk/lib/signers/v4.js:172:28)
        at V4.hexEncodedBodyHash (/home/travis/build/mapbox/streambot/node_modules/aws-sdk/lib/signers/v4.js:181:19)
        at V4.canonicalString (/home/travis/build/mapbox/streambot/node_modules/aws-sdk/lib/signers/v4.js:126:21)
        at V4.stringToSign (/home/travis/build/mapbox/streambot/node_modules/aws-sdk/lib/signers/v4.js:113:41)
        at V4.signature (/home/travis/build/mapbox/streambot/node_modules/aws-sdk/lib/signers/v4.js:105:43)
        at V4.authorization (/home/travis/build/mapbox/streambot/node_modules/aws-sdk/lib/signers/v4.js:82:36)
        at V4.addAuthorization (/home/travis/build/mapbox/streambot/node_modules/aws-sdk/lib/signers/v4.js:35:12)

[lsegal]

The logic S3 uses to sign payloads should probably be moved directly into the V4 signer so all services can make use of this logic.

A temporary workaround would be to do the following:

var lambda = new AWS.Lambda();
var params = { ... };
lambda.uploadFunction(params).
    on('build', AWS.S3.prototype.computeSha256).
    send(function(data, err) {
  console.log(data, err);
});

Let me know if that works for you. Note that it uses a private API, so it should just be a workaround, not permanent code.

Note also that stream support will still only work with rewindable/seekable streams (namely file objects), as we must be able to seek the stream to compute a checksum of the body prior to sending.

[rclark]

In my situation today using a buffer is totally reasonable (although #551 can be a problem with larger buffers), but thanks for the workaround. You suspect this logic will move into the v4 signer relatively soon?

[lsegal]

@rclark yea this should be a fairly easy refactor. I'm just not near my dev machine right now, but it should get looked at this week.

[lsegal]

/cc @AdityaManohar

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