Enum ClientHelloExtension

pub enum ClientHelloExtension {
    ServerName(Option<Host>),
    SupportedGroups(Vec<SupportedGroup>),
    ECPointFormats(Vec<ECPointFormat>),
    SignatureAlgorithms(Vec<SignatureScheme>),
    ApplicationLayerProtocolNegotiation(Vec<ApplicationProtocol>),
    SupportedVersions(Vec<ProtocolVersion>),
    Opaque {
        id: ExtensionId,
        data: Vec<u8>,
    },
}

Extensions that can be set in a ClientHello message by a TLS client.

While its name may infer that an extension is by definition optional, you would be wrong to think so. These extensions are also used to fill historical gaps in the TLS specifications and as a consequence there are a couple of extensions that are pretty much in any ClientHello message.

Most of the defined variants of this enum are examples of such “required” extensions. Extensions like ClientHelloExtension::ApplicationLayerProtocolNegotiation are not required but due to benefits it offers it also is pretty much always present, as it helps save application negotiation roundtrips;

Variants

ServerName(Option<Host>)

name of the server the client intends to connect to

TLS does not provide a mechanism for a client to tell a server the name of the server it is contacting. It may be desirable for clients to provide this information to facilitate secure connections to servers that host multiple ‘virtual’ servers at a single underlying network address.

In order to provide any of the server names, clients MAY include an extension of type “server_name” in the (extended) client hello.

Reference

• https://www.iana.org/go/rfc6066
• https://www.iana.org/go/rfc9261

SupportedGroups(Vec<SupportedGroup>)

indicates which elliptic curves the client supports

This extension is required… despite being an extension.

Renamed from EllipticCurves, which some material might still reference it as.

Reference

• https://www.iana.org/go/rfc8422
• https://www.iana.org/go/rfc7919

ECPointFormats(Vec<ECPointFormat>)

indicates the set of point formats that the client can parse

For this extension, the opaque extension_data field contains ECPointFormatList.

Reference

• https://www.iana.org/go/rfc8422

SignatureAlgorithms(Vec<SignatureScheme>)

Algorithms supported by the client for signing certificates.

Reference

• https://www.iana.org/go/rfc8446

ApplicationLayerProtocolNegotiation(Vec<ApplicationProtocol>)

Application Layer Protocol Negotiation, often referred to as ALPN.

Used to indicate the application layer protocols the client supports, e.g. h2 or h3. Allowing the server to immediately serve content using one of the supported protocols avoiding otherwise wasteful upgrade roundtrips.

Reference

• https://www.iana.org/go/rfc7301

SupportedVersions(Vec<ProtocolVersion>)

used by the client to indicate which versions of TLS it supports

Reference

• https://www.iana.org/go/rfc8446

Opaque

Any extension not supported by Rama, as it is still to be done or considered out of scope.

Fields

id: ExtensionId

extension id

data: Vec<u8>

extension data

Implementations

impl ClientHelloExtension

pub fn id(&self) -> ExtensionId

returns the ExtensionId which identifies this ClientHelloExtension.

Trait Implementations

impl Clone for ClientHelloExtension

fn clone(&self) -> ClientHelloExtension

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for ClientHelloExtension

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

Formats the value using the given formatter.