为Amazon S3生成具有最大内容长度的预签名PUT URL

Question

I'm trying to generate a pre-signed URL a client can use to upload an image to a specific S3 bucket. I've succesfully generated requests to GET files, like so:

GeneratePresignedUrlRequest urlRequest = new GeneratePresignedUrlRequest(bucket, filename);
urlRequest.setMethod(method);
urlRequest.setExpiration(expiration);

where expiration and method are Date and HttpMethod objects respectively.

Now I'm trying to create a URL to allow users to PUT a file, but I can't figure out how to set the maximum content-length. I did find information on POST policies , but I'd prefer to use PUT here - I'd also like to avoid constructing the JSON, though that doesn't seem possible.

Lastly, an alternative answer could be some way to pass an image upload from the API Gateway to Lambda so I can upload it from Lambda to S3 after validating file type and size (which isn't ideal).

Answer 1

While I haven't managed to limit the file size on upload, I ended up creating a Lambda function that is activated on upload to a temporary bucket. The function has a signature like the below

public static void checkUpload(S3EventNotification event) {

(this is notable because all the guides I found online refer to a S3Event class that doesn't seem to exist anymore)

The function pulls the file's metadata (not the file itself, as that potentially counts as a large download) and checks the file size. If it's acceptable, it downloads the file then uploads it to the destination bucket. If not, it simply deletes the file.

This is far from ideal, as uploads failing to meet the criteria will seem to work but then simply never show up (as S3 will issue a 200 status code on upload without caring what Lambda's response is).

This is effectively a workaround rather than a solution, so I won't be accepting this answer.