ifMatch

Uploads the object only if the ETag (entity tag) value provided during the WRITE operation matches the ETag of the object in S3. If the ETag values do not match, the operation returns a 412 Precondition Failed error.

If a conflicting operation occurs during the upload S3 returns a 409 ConditionalRequestConflict response. On a 409 failure you should fetch the object's ETag and retry the upload.

Expects the ETag value as a string.

For more information about conditional requests, see RFC 7232, or Conditional requests in the Amazon S3 User Guide.