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It appears there may be a misunderstanding about how Amazon S3 handles SHA-256 checksums for presigned URLs. When using presigned URLs for S3 uploads, you typically don't need to calculate and include the SHA-256 hash of the content in the x-amz-content-sha256
header.
For presigned URLs, the x-amz-content-sha256
header is usually set to UNSIGNED-PAYLOAD
by default. This is why your upload works when you use UNSIGNED-PAYLOAD
instead of the calculated hash.
If you want to include a checksum for data integrity verification, S3 supports several checksum algorithms, including SHA-256. However, for this purpose, you would use a different header: x-amz-checksum-sha256
.
To use the SHA-256 checksum with S3, you need to:
- Calculate the SHA-256 hash of your content.
- Base64 encode the resulting hash.
- Include this Base64 encoded hash in the
x-amz-checksum-sha256
header.
Here's how you could modify your code to produce the correct format:
private async getSHA256ChecksumFromBlob(imageBlob: Blob): Promise<string> { const arrayBuffer = await imageBlob.arrayBuffer(); const hashBuffer = await crypto.subtle.digest("SHA-256", arrayBuffer); const hashArray = Array.from(new Uint8Array(hashBuffer)); const hashBase64 = btoa(String.fromCharCode.apply(null, hashArray)); return hashBase64; }
This function will return a Base64 encoded SHA-256 hash that you can use with the x-amz-checksum-sha256
header when uploading to S3.
Remember, when using presigned URLs, you typically don't need to include the content hash in the signature calculation. The presigned URL already contains the necessary signature. You would only include the x-amz-checksum-sha256
header if you want S3 to perform an additional integrity check on the uploaded data.
If you're still encountering issues, make sure that your backend is correctly generating the presigned URL and that you're including all the necessary headers in your upload request. You may also want to check if your S3 bucket or the specific operation requires any special configurations for checksums.
Sources
Introducing default data integrity protections for new objects in Amazon S3 | AWS News Blog
Amazon S3 Security Features - Amazon Web Services
S3 SHA256 Checksum for Presigned URL in File Upload | AWS re:Post
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