Function secp256k1::ffi::secp256k1_ec_pubkey_serialize

pub unsafe fn secp256k1_ec_pubkey_serialize(
    cx: *const Context,
    output: *mut c_uchar,
    out_len: *mut size_t,
    pk: *const PublicKey,
    compressed: c_uint
) -> c_int

Serialize PublicKey back to 33/65 byte pubkey