Check file size on S3 without downloading?

Node.js example:

const AWS = require('aws-sdk');
const s3 = new AWS.S3();

function sizeOf(key, bucket) {
    return s3.headObject({ Key: key, Bucket: bucket })
        .promise()
        .then(res => res.ContentLength);
}


// A test
sizeOf('ahihi.mp4', 'output').then(size => console.log(size));

Doc is here.

This is a solution for whoever is using Java and the S3 java library provided by Amazon. If you are using com.amazonaws.services.s3.AmazonS3 you can use a GetObjectMetadataRequest request which allows you to query the object length.

The libraries you have to use are:

<!-- https://mvnrepository.com/artifact/com.amazonaws/aws-java-sdk-s3 -->
<dependency>
    <groupId>com.amazonaws</groupId>
    <artifactId>aws-java-sdk-s3</artifactId>
    <version>1.11.511</version>
</dependency>

Imports:

import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3ClientBuilder;
import com.amazonaws.services.s3.model.*;

And the code you need to get the content length:

GetObjectMetadataRequest metadataRequest = new GetObjectMetadataRequest(bucketName, fileName);
final ObjectMetadata objectMetadata = s3Client.getObjectMetadata(metadataRequest);
long contentLength = objectMetadata.getContentLength();

Before you can execute the code above, you will need to build the S3 client. Here is some example code for that:

AWSCredentials credentials = new BasicAWSCredentials(
            accessKey,
            secretKey
);
s3Client = AmazonS3ClientBuilder.standard()
            .withRegion(clientRegion)
            .withCredentials(new AWSStaticCredentialsProvider(credentials))
            .build();

You can simply use the s3 ls command:

aws s3 ls s3://mybucket --recursive --human-readable --summarize

Outputs

2013-09-02 21:37:53   10 Bytes a.txt
2013-09-02 21:37:53  2.9 MiB foo.zip
2013-09-02 21:32:57   23 Bytes foo/bar/.baz/a
2013-09-02 21:32:58   41 Bytes foo/bar/.baz/b
2013-09-02 21:32:57  281 Bytes foo/bar/.baz/c
2013-09-02 21:32:57   73 Bytes foo/bar/.baz/d
2013-09-02 21:32:57  452 Bytes foo/bar/.baz/e
2013-09-02 21:32:57  896 Bytes foo/bar/.baz/hooks/bar
2013-09-02 21:32:57  189 Bytes foo/bar/.baz/hooks/foo
2013-09-02 21:32:57  398 Bytes z.txt

Total Objects: 10
   Total Size: 2.9 MiB

Reference: https://docs.aws.amazon.com/cli/latest/reference/s3/ls.html

Send an HTTP HEAD request to the object. A HEAD request will retrieve the same HTTP headers as a GET request, but it will not retrieve the body of the object (saving you bandwidth). You can then parse out the Content-Length header value from the HTTP response headers.