fix: put file corruption with chunked transfer

When on linux with O_TMPFILE support, we issue and fallocate for
the expected object size ax an optimization for the underlying
filesystem to allocate the full file all ate once. With the chunked
transfer encoding, the final object size is recoded in the
X-Amz-Decoded-Content-Length instead of the standard ContentLength
which includes the chunk encoding in the payload.

We were incorrectly using the content length to fallocate the
file which would cause the filesystem to pad out any unwritten
length to this size with 0s.

The fix here is to make sure we pass the X-Amz-Decoded-Content-Length
as the object size to the backend for all PUTs.

Fixes #753

s3api/controllers/base.go

@@ -1544,11 +1544,19 @@ func (c S3ApiController) PutActions(ctx *fiber.Ctx) error {
 	granWrite := ctx.Get("X-Amz-Grant-Write")
 	grantWriteACP := ctx.Get("X-Amz-Grant-Write-Acp")
 
-	// Other headers
+	// Content Length
 	contentLengthStr := ctx.Get("Content-Length")
 	if contentLengthStr == "" {
 		contentLengthStr = "0"
 	}
+	// Use decoded content length if available because the
+	// middleware will decode the chunked transfer encoding
+	decodedLength := ctx.Get("X-Amz-Decoded-Content-Length")
+	if decodedLength != "" {
+		contentLengthStr = decodedLength
+	}
+
+	// Other headers
 	bucketOwner := ctx.Get("X-Amz-Expected-Bucket-Owner")
 	storageClass := ctx.Get("X-Amz-Storage-Class")