Struct Alpn

#[repr(transparent)]
pub struct Alpn(pub Vec<String>);

RFC 9460 SVCB and HTTPS Resource Records, Nov 2023

7.1.  "alpn" and "no-default-alpn"

  The "alpn" and "no-default-alpn" SvcParamKeys together indicate the
  set of Application-Layer Protocol Negotiation (ALPN) protocol
  identifiers [ALPN] and associated transport protocols supported by
  this service endpoint (the "SVCB ALPN set").

  As with Alt-Svc [AltSvc], each ALPN protocol identifier is used to
  identify the application protocol and associated suite of protocols
  supported by the endpoint (the "protocol suite").  The presence of an
  ALPN protocol identifier in the SVCB ALPN set indicates that this
  service endpoint, described by TargetName and the other parameters
  (e.g., "port"), offers service with the protocol suite associated
  with this ALPN identifier.

  Clients filter the set of ALPN identifiers to match the protocol
  suites they support, and this informs the underlying transport
  protocol used (such as QUIC over UDP or TLS over TCP).  ALPN protocol
  identifiers that do not uniquely identify a protocol suite (e.g., an
  Identification Sequence that can be used with both TLS and DTLS) are
  not compatible with this SvcParamKey and MUST NOT be included in the
  SVCB ALPN set.

7.1.1.  Representation

  ALPNs are identified by their registered "Identification Sequence"
  (alpn-id), which is a sequence of 1-255 octets.

  alpn-id = 1*255OCTET

  For "alpn", the presentation value SHALL be a comma-separated list
  (Appendix A.1) of one or more alpn-ids.  Zone-file implementations
  MAY disallow the "," and "\" characters in ALPN IDs instead of
  implementing the value-list escaping procedure, relying on the opaque
  key format (e.g., key1=\002h2) in the event that these characters are
  needed.

  The wire-format value for "alpn" consists of at least one alpn-id
  prefixed by its length as a single octet, and these length-value
  pairs are concatenated to form the SvcParamValue.  These pairs MUST
  exactly fill the SvcParamValue; otherwise, the SvcParamValue is
  malformed.

  For "no-default-alpn", the presentation and wire-format values MUST
  be empty.  When "no-default-alpn" is specified in an RR, "alpn" must
  also be specified in order for the RR to be "self-consistent"
  (Section 2.4.3).

  Each scheme that uses this SvcParamKey defines a "default set" of
  ALPN IDs that are supported by nearly all clients and servers; this
  set MAY be empty.  To determine the SVCB ALPN set, the client starts
  with the list of alpn-ids from the "alpn" SvcParamKey, and it adds
  the default set unless the "no-default-alpn" SvcParamKey is present.

7.1.2.  Use

  To establish a connection to the endpoint, clients MUST

  1.  Let SVCB-ALPN-Intersection be the set of protocols in the SVCB
      ALPN set that the client supports.

  2.  Let Intersection-Transports be the set of transports (e.g., TLS,
      DTLS, QUIC) implied by the protocols in SVCB-ALPN-Intersection.

  3.  For each transport in Intersection-Transports, construct a
      ProtocolNameList containing the Identification Sequences of all
      the client's supported ALPN protocols for that transport, without
      regard to the SVCB ALPN set.

  For example, if the SVCB ALPN set is ["http/1.1", "h3"] and the
  client supports HTTP/1.1, HTTP/2, and HTTP/3, the client could
  attempt to connect using TLS over TCP with a ProtocolNameList of
  ["http/1.1", "h2"] and could also attempt a connection using QUIC
  with a ProtocolNameList of ["h3"].

  Once the client has constructed a ClientHello, protocol negotiation
  in that handshake proceeds as specified in [ALPN], without regard to
  the SVCB ALPN set.

  Clients MAY implement a fallback procedure, using a less-preferred
  transport if more-preferred transports fail to connect.  This
  fallback behavior is vulnerable to manipulation by a network attacker
  who blocks the more-preferred transports, but it may be necessary for
  compatibility with existing networks.

  With this procedure in place, an attacker who can modify DNS and
  network traffic can prevent a successful transport connection but
  cannot otherwise interfere with ALPN protocol selection.  This
  procedure also ensures that each ProtocolNameList includes at least
  one protocol from the SVCB ALPN set.

  Clients SHOULD NOT attempt connection to a service endpoint whose
  SVCB ALPN set does not contain any supported protocols.

  To ensure consistency of behavior, clients MAY reject the entire SVCB
  RRset and fall back to basic connection establishment if all of the
  compatible RRs indicate "no-default-alpn", even if connection could
  have succeeded using a non-default ALPN protocol.

  Zone operators SHOULD ensure that at least one RR in each RRset
  supports the default transports.  This enables compatibility with the
  greatest number of clients.

Tuple Fields

0: Vec<String>

Trait Implementations

impl<'r> BinDecodable<'r> for Alpn

fn read(decoder: &mut BinDecoder<'r>) -> Result<Alpn, ProtoError>

This expects the decoder to be limited to only this field, i.e. the end of input for the decoder is the end of input for the fields

  The wire format value for "alpn" consists of at least one alpn-id
  prefixed by its length as a single octet, and these length-value
  pairs are concatenated to form the SvcParamValue.  These pairs MUST
  exactly fill the SvcParamValue; otherwise, the SvcParamValue is
  malformed.

fn from_bytes(bytes: &'r [u8]) -> Result<Self, ProtoError>

Returns the object in binary form

impl BinEncodable for Alpn

fn emit(&self, encoder: &mut BinEncoder<'_>) -> Result<(), ProtoError>

The wire format value for “alpn” consists of at least one alpn-id prefixed by its length as a single octet, and these length-value pairs are concatenated to form the SvcParamValue. These pairs MUST exactly fill the SvcParamValue; otherwise, the SvcParamValue is malformed.

fn to_bytes(&self) -> Result<Vec<u8>, ProtoError>

Returns the object in binary form

impl Clone for Alpn

fn clone(&self) -> Alpn

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Alpn

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

Formats the value using the given formatter.

impl Display for Alpn

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

The presentation value SHALL be a comma-separated list (Appendix A.1) of one or more “alpn-id“s.

impl Hash for Alpn

fn hash<__H>(&self, state: &mut __H)

where __H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Alpn

fn eq(&self, other: &Alpn) -> 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 Eq for Alpn

impl StructuralPartialEq for Alpn