amazon web services - How to create folder or key on s3 using AWS SDK for Node.js?

Question

I'm using AWS SDK for Node.js to create a folder or key on s3. I searched on google, but I got nothing. Does anybody know how can I create a folder under my bucket with AWS SDK for Node.js? and how can you check if this folder exists in your bucket already?

if you use console.aws.amazon.com, you can create a folder in your bucket easily. it seems I didn't figure it out how to create it with AWS SDK for Node.js?

Answer 1

S3 is not your typical file system. It's an object store. It has buckets and objects. Buckets are used to store objects, and objects comprise data (basically a file) and metadata (information about the file). When compared to a traditional file system, it's more natural to think of an S3 bucket as a drive rather than as a folder.

You don't need to pre-create a folder structure in an S3 bucket. You can simply put an object with the key cars/ford/focus.png even if cars/ford/ does not exist.

It's valuable to understand what happens at the API level in this case:

• the putObject call will create an object at cars/ford/focus.png but it will not create anything representing the intermediate folder structure of cars/ or cars/ford/.

• the actual folder structure does not exist, but is implied through delimiter=/ when you call listObjects, returning folders in CommonPrefixes and files in Contents.

• you will not be able to test for the ford sub-folder using headObject because cars/ford/ does not actually exist (it is not an object). Instead you have 2 options to see if it (logically) exists:

1. call listObjects with prefix=cars/ford/ and find it in Contents
2. call listObjects with prefix=cars/, delimiter=/ and find it in CommonPrefixes

It is possible to create an S3 object that represents a folder, if you really want to. The AWS S3 console does this, for example. To create myfolder in a bucket named mybucket, you can issue a putObject call with bucket=mybucket, key=myfolder/, and size 0. Note the trailing forward slash.

Here's an example of creating a folder-like object using the awscli:

aws s3api put-object --bucket mybucket --key cars/ --content-length 0

In this case:

• the folder is actually a zero-sized object whose key ends in /. Note that if you leave off the trailing / then you will get a zero-sized object that appears to be a file rather than a folder.

• you are now able to test for the presence of cars/ in mybucket by issuing a headObject call with bucket=mybucket and key=cars/.

Finally, note that your folder delimiter can be anything you like, for example +, because it is simply part of the key and is not actually a folder separator (there are no folders). You can vary your folder delimiter from listObjects call to call if you like.