Module IPv4.Writer

Efficient IPv4 payload composition.

A t value represents a payload to be sent in an IPv4 packet. Three constructors are provided depending on whether the data is already in memory as a string, as multiple strings, or should be written directly into the outgoing buffer. The writer handles fragmentation transparently when the payload exceeds the path MTU.

type ipv4 = t
type t
val of_string : ipv4 -> string -> t

of_string ipv4 str creates a writer that sends str as the payload.

val of_strings : ipv4 -> string list -> t

of_strings ipv4 strs creates a writer that sends the concatenation of strs as the payload. This avoids copying the strings into a single buffer.

val into : ipv4 -> len:int -> (Bstr.t -> unit) -> t

into ipv4 ~len fn creates a writer that fills the payload by calling fn buf, where buf is a buffer of size len positioned after the IPv4 header. This is the zero-copy path for upper-layer protocols (like UDP's UDP.sendfn) that can write directly into the outgoing frame.