into_cstruct ~pseudoheader ~payload t buf attempts to assemble a UDP header in buf with t.src_port and t.dst_port set, along with the correct length and checksum. It does not write pseudoheader or payload into the buffer, but requires them to calculate the correct checksum.

make_cstruct ~pseudoheader ~payload t allocates, fills, and and returns a buffer representing the UDP header corresponding to t. make_cstruct will allocate 8 bytes for the UDP header. payload and pseudoheader are not directly represented in the output, and are required for correct computation of the UDP checksum only. The checksum will be properly set to reflect the pseudoheader, header, and payload.