B2 API transaction used to check chunk existence?

When executing a copy command to a storage in B2, for each chunk :d: checks to see if it already exists in the storage, and then copies it.

TRACE BACKBLAZE_CALL [8] URL request 'HEAD https://f001.backblazeb2.com/file/[...]/chunks/90/5915...8083' returned status code 404
INFO SNAPSHOT_COPY Chunk 905915...8083 copied to the destination

The question is: which is the B2 API transaction used for this “check” if the chunk exists?

It uses b2_download_file_by_name with with a header “Range: bytes=0-0”, so it is a class B API call.
See B2 efficiency · Issue #179 · gilbertchen/duplicacy · GitHub