Multer S3 with stream transforms

Streaming multer storage engine for AWS S3.

This project is mostly an integration piece for existing code samples from Multer's storage engine documentation with s3fs as the substitution piece for file system. Existing solutions I found required buffering the multipart uploads into the actual filesystem which is difficult to scale.

Installation

npm install --save multer-s3-v3

Usage

var aws = require("aws-sdk");
var express = require("express");
var multer = require("multer");
var multerS3 = require("multer-s3-v3");

var app = express();
var s3 = new aws.S3({
  /* ... */
});

var upload = multer({
  storage: multerS3({
    s3: s3,
    bucket: "some-bucket",
    metadata: function(req, file, cb) {
      cb(null, { fieldName: file.fieldname });
    },
    key: function(req, file, cb) {
      cb(null, Date.now().toString());
    },
    throwMimeTypeConflictErrorIf: (contentType, mimeType, _file) => ![mimeType, 'application/octet-stream'].includes(contentType)
  })
});

app.post("/upload", upload.array("photos", 3), function(req, res, next) {
  res.send("Successfully uploaded " + req.files.length + " files!");
});

File information

Each file contains the following information exposed by multer-s3:

Key	Description	Note
size	Size of the file in bytes
bucket	The bucket used to store the file	S3Storage
key	The name of the file	S3Storage
acl	Access control for the file	S3Storage
contentType	The mimetype used to upload the file	S3Storage
metadata	The metadata object to be sent to S3	S3Storage
location	The S3 url to access the file	S3Storage
etag	The etagof the uploaded file in S3	S3Storage
contentDisposition	The contentDisposition used to upload the file	S3Storage
storageClass	The storageClass to be used for the uploaded file in S3	S3Storage
versionId	The versionId is an optional param returned by S3 for versioned buckets.	S3Storage

Setting ACL

ACL values can be set by passing an optional acl parameter into the multerS3 object.

var upload = multer({
  storage: multerS3({
    s3: s3,
    bucket: "some-bucket",
    acl: "public-read",
    key: function(req, file, cb) {
      cb(null, Date.now().toString());
    }
  })
});

Available options for canned ACL.

ACL Option	Permissions added to ACL
private	Owner gets FULL_CONTROL. No one else has access rights (default).
public-read	Owner gets FULL_CONTROL. The AllUsers group gets READ access.
public-read-write	Owner gets FULL_CONTROL. The AllUsers group gets READ and WRITE access. Granting this on a bucket is generally not recommended.
aws-exec-read	Owner gets FULL_CONTROL. Amazon EC2 gets READ access to GET an Amazon Machine Image (AMI) bundle from Amazon S3.
authenticated-read	Owner gets FULL_CONTROL. The AuthenticatedUsers group gets READ access.
bucket-owner-read	Object owner gets FULL_CONTROL. Bucket owner gets READ access. If you specify this canned ACL when creating a bucket, Amazon S3 ignores it.
bucket-owner-full-control	Both the object owner and the bucket owner get FULL_CONTROL over the object. If you specify this canned ACL when creating a bucket, Amazon S3 ignores it.
log-delivery-write	The LogDelivery group gets WRITE and READ_ACP permissions on the bucket. For more information on logs.

Setting Metadata

The metadata option is a callback that accepts the request and file, and returns a metadata object to be saved to S3.

Here is an example that stores all fields in the request body as metadata, and uses an id param as the key:

var opts = {
  s3: s3,
  bucket: config.originalsBucket,
  metadata: function(req, file, cb) {
    cb(null, Object.assign({}, req.body));
  },
  key: function(req, file, cb) {
    cb(null, req.params.id + ".jpg");
  }
};

Setting Cache-Control header

The optional cacheControl option sets the Cache-Control HTTP header that will be sent if you're serving the files directly from S3. You can pass either a string or a function that returns a string.

Here is an example that will tell browsers and CDNs to cache the file for one year:

var upload = multer({
  storage: multerS3({
    s3: s3,
    bucket: "some-bucket",
    cacheControl: "max-age=31536000",
    key: function(req, file, cb) {
      cb(null, Date.now().toString());
    }
  })
});

Setting Custom Content-Type

The optional contentType option can be used to set Content/mime type of the file. By default the content type is set to application/octet-stream. If you want multer-s3 to automatically find the content-type of the file, use the multerS3.AUTO_CONTENT_TYPE constant. Here is an example that will detect the content type of the file being uploaded.

var upload = multer({
  storage: multerS3({
    s3: s3,
    bucket: "some-bucket",
    contentType: multerS3.AUTO_CONTENT_TYPE,
    key: function(req, file, cb) {
      cb(null, Date.now().toString());
    }
  })
});

You may also use a function as the contentType, which should be of the form function(req, file, cb).

Setting StorageClass

storageClass values can be set by passing an optional storageClass parameter into the multerS3 object.

var upload = multer({
  storage: multerS3({
    s3: s3,
    bucket: "some-bucket",
    acl: "public-read",
    storageClass: "REDUCED_REDUNDANCY",
    key: function(req, file, cb) {
      cb(null, Date.now().toString());
    }
  })
});

Setting Content-Disposition

The optional contentDisposition option can be used to set the Content-Disposition header for the uploaded file. By default, the contentDisposition isn't forwarded. As an example below, using the value attachment forces the browser to download the uploaded file instead of trying to open it.

var upload = multer({
  storage: multerS3({
    s3: s3,
    bucket: "some-bucket",
    acl: "public-read",
    contentDisposition: "attachment",
    key: function(req, file, cb) {
      cb(null, Date.now().toString());
    }
  })
});

Using Server-Side Encryption

An overview of S3's server-side encryption can be found in the S3 Docs; be advised that customer-managed keys (SSE-C) is not implemented at this time.

You may use the S3 server-side encryption functionality via the optional serverSideEncryption and sseKmsKeyId parameters. Full documentation of these parameters in relation to the S3 API can be found here and here.

serverSideEncryption has two valid values: 'AES256' and 'aws:kms'. 'AES256' utilizes the S3-managed key system, while 'aws:kms' utilizes the AWS KMS system and accepts the optional sseKmsKeyId parameter to specify the key ID of the key you wish to use. Leaving sseKmsKeyId blank when 'aws:kms' is specified will use the default KMS key. Note: You must instantiate the S3 instance with signatureVersion: 'v4' in order to use KMS-managed keys [Docs], and the specified key must be in the same AWS region as the S3 bucket used.

var upload = multer({
  storage: multerS3({
    s3: s3,
    bucket: "some-bucket",
    acl: "authenticated-read",
    contentDisposition: "attachment",
    serverSideEncryption: "AES256",
    key: function(req, file, cb) {
      cb(null, Date.now().toString());
    }
  })
});

Using transforms

The transforms option is a function or object with field.

Here is an example with simple transform as function:

var sharp = require("sharp");

var opts = {
  s3: s3,
  bucket: config.originalsBucket,
  transforms: () =>
    sharp()
      .resize(1920, 1080)
      .max()
      .withoutEnlargement()
      .jpeg({
        progressive: true,
        quality: 80
      }),
  metadata: function(req, file, cb) {
    cb(null, Object.assign({}, req.body));
  },
  key: function(req, file, cb) {
    cb(null, req.params.id + ".jpg");
  }
};

And here is exemple with field specific transform:

var sharp = require("sharp");

var opts = {
  s3: s3,
  bucket: config.originalsBucket,
  transforms: {
    avatar: () =>
      sharp()
        .resize(1920, 1080)
        .max()
        .withoutEnlargement()
        .jpeg({
          progressive: true,
          quality: 80
        })
  },
  metadata: function(req, file, cb) {
    cb(null, Object.assign({}, req.body));
  },
  key: function(req, file, cb) {
    cb(null, req.params.id + ".jpg");
  }
};

Other Options

throwMimeTypeConflictErrorIf: (resolvedContentType, clientSpecifiedMimeType, file) => boolean

If provided, this will be called to determine when to throw an exception (instead of uploading). It receives the following parameters:

1. detected contentType as reported by package file-type
2. the mime-type encoded in the multi-part form data for a given file
3. the file object itself

Testing

The tests mock all access to S3 and can be run completely offline.

npm test