Struct Mss

pub struct Mss(/* private fields */);

Maximum segment size, that is the maximum TCP payload one segment can carry.

Mss also acts as a witness that the contained value is >= Mss::MIN.

Implementations

impl Mss

pub const MIN: Mss

The minimum MSS allowed by TCP.

Although enforcing a minimum MSS is outside the recommendations of any RFC, it is a common practice on other platforms and has multiple benefits:

1. Ensures there is enough space to transmit TCP Options & IP Options. See RFC 6691 section 2, which clarifies that The TCP MSS OPTION […] SHOULD NOT be decreased to account for any possible IP or TCP options; conversely, the sender MUST reduce the TCP data length to account for any IP or TCP options that it is including in the packets that it sends.
2. Protects against DOS attacks in which the attacker initiates TCP connections with an intentionally small MSS to incur additional packet processing overhead on the victim. See
   • FreeBSD: https://www.cve.org/CVERecord?id=CVE-2004-0002
   • Linux: https://www.cve.org/CVERecord?id=CVE-2019-11479

Here, the value 216 is inspired by FreeBSD. It’s large enough to satisfy points 1 & 2 from above, while remaining small enough to support all link-layer technologies on the open Internet.

pub const DEFAULT_IPV4: Mss

Per RFC 9293 Section 3.7.1: If an MSS Option is not received at connection setup, TCP implementations MUST assume a default send MSS of 536 (576 - 40) for IPv4.

pub const DEFAULT_IPV6: Mss

Per RFC 9293 Section 3.7.1: If an MSS Option is not received at connection setup, TCP implementations MUST assume a default send MSS of […] 1220 (1280 - 60) for IPv6 (MUST-15).

pub const fn new(mss: u16) -> Option<Self>

Creates Mss, provided the given value satisfies the requirements.

pub fn from_mms(mms: Mms) -> Option<Self>

Creates MSS from the maximum message size of the IP layer.

pub const fn default<I: Ip>() -> Self

Create a new Mss with the IP-version default value, as defined by RFC 9293.

pub const fn get(&self) -> u16

Gets the numeric value of the MSS.

Trait Implementations

impl Clone for Mss

fn clone(&self) -> Mss

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Mss

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl From<Mss> for u32

fn from(Mss: Mss) -> Self

Converts to this type from the input type.

impl From<Mss> for usize

fn from(Mss: Mss) -> Self

Converts to this type from the input type.

impl Ord for Mss

fn cmp(&self, other: &Mss) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for Mss

fn eq(&self, other: &Mss) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for Mss

fn partial_cmp(&self, other: &Mss) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Copy for Mss

impl Eq for Mss

impl StructuralPartialEq for Mss