Zstd exposes multiple API flavors which can be used to transform strings into strings. The t type encodes the various ways to pass a string from the OCaml world to ZStd functions.

from_string ?pos ?len s will pass the content of s to Zstd functions. This incurs a copy of the OCaml string when from_string is called.

from_bytes ?pos ?len s will pass the content of s to Zstd functions. This incurs an allocation of a buffer of size len when calling from_bytes, and a copy of the ocaml bytes each time the resulting t is used by a compression / decompression function.

from_bigstring ?pos ?len s will pass the content of s between pos and pos+len to Zstd functions. This does not incur a copy.

from_iobuf iobuf will pass the content of iobuf to Zstd functions. This does not incur a copy.