Merge #693

693: Constification of the wire module r=Dirbaio a=ngc0202

A huge portion of the `wire` module is constifyable, as shown in this commit. Making these `const fn`s, especially the functions set aside in the `field` modules of wire, would be greatly beneficial to me as a consumer of this crate, and I imagine many others. Many of the structs in my own crate's "wire" module for a custom protocol are more constrained versions of the packets and reprs provided by smoltcp. Due to being more constrained, many fields which are variable in the generic reprs are now constant in mine, which then lend themselves to being constants in my crate, however these functions and methods not being marked `const` prevents me from using smoltcp's tools to calculate these values. **Most** of the functions which I marked `const` in this commit are by their very nature/semantics guaranteed to be constifiable anyway, however a handful aren't necessarily, therefore:

**Important note:** While the majority of the functions are marked `const` are very safe to do so, not all of them are guaranteed to be so, and the reviewer of this PR should take caution and feel free to unmark something as const if they're not comfortable making that guarantee in the public API.

Another note: There are various other functions which can't be made `const fn` as written, but could be with minor tweaks. I did not include these tweaks but I think it should be considered as further work for this PR or a potential follow-up PR. Furthermore, plenty outside of `wire` is constifyable as well but I did not include those in the scope of this PR.

Co-authored-by: Nicholas Cyprus <nicholas.cyprus@caci.com>

Author: bors[bot]

.github/workflows/test.yml

@@ -21,7 +21,7 @@ jobs:
         # Failure is permitted on nightly.
         rust:
           - stable
-          - 1.60.0
+          - 1.61.0
           - nightly
 
         features:
@@ -65,7 +65,7 @@ jobs:
         # Failure is permitted on nightly.
         rust:
           - stable
-          - 1.60.0
+          - 1.61.0
           - nightly
 
         features:

Cargo.toml

@@ -2,7 +2,7 @@
 name = "smoltcp"
 version = "0.8.1"
 edition = "2018"
-rust-version = "1.60"
+rust-version = "1.61"
 authors = ["whitequark <whitequark@whitequark.org>"]
 description = "A TCP/IP stack designed for bare-metal, real-time systems without a heap."
 documentation = "https://docs.rs/smoltcp/"

README.md

@@ -11,7 +11,7 @@ include complicated compile-time computations, such as macro or type tricks, eve
 at cost of performance degradation.
 
 _smoltcp_ does not need heap allocation *at all*, is [extensively documented][docs],
-and compiles on stable Rust 1.60 and later.
+and compiles on stable Rust 1.61 and later.
 
 _smoltcp_ achieves [~Gbps of throughput](#examplesbenchmarkrs) when tested against
 the Linux TCP stack in loopback mode.

src/lib.rs

@@ -65,7 +65,7 @@
 //!
 //! # Minimum Supported Rust Version (MSRV)
 //!
-//! This crate is guaranteed to compile on stable Rust 1.60 and up with any valid set of features.
+//! This crate is guaranteed to compile on stable Rust 1.61 and up with any valid set of features.
 //! It *might* compile on older versions but that may change in any new patch release.
 //!
 //! The exception is when using the `defmt` feature, in which case `defmt`'s MSRV applies, which

src/wire/arp.rs

@@ -39,33 +39,33 @@ mod field {
     pub const OPER: Field = 6..8;
 
     #[inline]
-    pub fn SHA(hardware_len: u8, _protocol_len: u8) -> Field {
+    pub const fn SHA(hardware_len: u8, _protocol_len: u8) -> Field {
         let start = OPER.end;
         start..(start + hardware_len as usize)
     }
 
     #[inline]
-    pub fn SPA(hardware_len: u8, protocol_len: u8) -> Field {
+    pub const fn SPA(hardware_len: u8, protocol_len: u8) -> Field {
         let start = SHA(hardware_len, protocol_len).end;
         start..(start + protocol_len as usize)
     }
 
     #[inline]
-    pub fn THA(hardware_len: u8, protocol_len: u8) -> Field {
+    pub const fn THA(hardware_len: u8, protocol_len: u8) -> Field {
         let start = SPA(hardware_len, protocol_len).end;
         start..(start + hardware_len as usize)
     }
 
     #[inline]
-    pub fn TPA(hardware_len: u8, protocol_len: u8) -> Field {
+    pub const fn TPA(hardware_len: u8, protocol_len: u8) -> Field {
         let start = THA(hardware_len, protocol_len).end;
         start..(start + protocol_len as usize)
     }
 }
 
 impl<T: AsRef<[u8]>> Packet<T> {
     /// Imbue a raw octet buffer with ARP packet structure.
-    pub fn new_unchecked(buffer: T) -> Packet<T> {
+    pub const fn new_unchecked(buffer: T) -> Packet<T> {
         Packet { buffer }
     }
 
@@ -289,7 +289,7 @@ impl Repr {
     }
 
     /// Return the length of a packet that will be emitted from this high-level representation.
-    pub fn buffer_len(&self) -> usize {
+    pub const fn buffer_len(&self) -> usize {
         match *self {
             Repr::EthernetIpv4 { .. } => field::TPA(6, 4).end,
         }

src/wire/dhcpv4.rs

@@ -44,7 +44,7 @@ bitflags! {
 }
 
 impl MessageType {
-    fn opcode(&self) -> OpCode {
+    const fn opcode(&self) -> OpCode {
         match *self {
             MessageType::Discover
             | MessageType::Inform
@@ -233,7 +233,7 @@ pub(crate) mod field {
 
 impl<T: AsRef<[u8]>> Packet<T> {
     /// Imbue a raw octet buffer with DHCP packet structure.
-    pub fn new_unchecked(buffer: T) -> Packet<T> {
+    pub const fn new_unchecked(buffer: T) -> Packet<T> {
         Packet { buffer }
     }
 
@@ -1143,7 +1143,7 @@ mod test {
         assert_eq!(packet, DISCOVER_BYTES);
     }
 
-    fn offer_repr() -> Repr<'static> {
+    const fn offer_repr() -> Repr<'static> {
         Repr {
             message_type: MessageType::Offer,
             transaction_id: 0x3d1d,
@@ -1169,7 +1169,7 @@ mod test {
         }
     }
 
-    fn discover_repr() -> Repr<'static> {
+    const fn discover_repr() -> Repr<'static> {
         Repr {
             message_type: MessageType::Discover,
             transaction_id: 0x3d1d,

src/wire/dns.rs

@@ -83,7 +83,7 @@ pub struct Packet<T: AsRef<[u8]>> {
 
 impl<T: AsRef<[u8]>> Packet<T> {
     /// Imbue a raw octet buffer with DNS packet structure.
-    pub fn new_unchecked(buffer: T) -> Packet<T> {
+    pub const fn new_unchecked(buffer: T) -> Packet<T> {
         Packet { buffer }
     }
 
@@ -311,7 +311,7 @@ impl<'a> Question<'a> {
     }
 
     /// Return the length of a packet that will be emitted from this high-level representation.
-    pub fn buffer_len(&self) -> usize {
+    pub const fn buffer_len(&self) -> usize {
         self.name.len() + 4
     }
 
@@ -412,7 +412,7 @@ pub struct Repr<'a> {
 
 impl<'a> Repr<'a> {
     /// Return the length of a packet that will be emitted from this high-level representation.
-    pub fn buffer_len(&self) -> usize {
+    pub const fn buffer_len(&self) -> usize {
         field::HEADER_END + self.question.buffer_len()
     }
 

src/wire/ethernet.rs

@@ -43,7 +43,7 @@ impl Address {
     }
 
     /// Return an Ethernet address as a sequence of octets, in big-endian.
-    pub fn as_bytes(&self) -> &[u8] {
+    pub const fn as_bytes(&self) -> &[u8] {
         &self.0
     }
 
@@ -58,12 +58,12 @@ impl Address {
     }
 
     /// Query whether the "multicast" bit in the OUI is set.
-    pub fn is_multicast(&self) -> bool {
+    pub const fn is_multicast(&self) -> bool {
         self.0[0] & 0x01 != 0
     }
 
     /// Query whether the "locally administered" bit in the OUI is set.
-    pub fn is_local(&self) -> bool {
+    pub const fn is_local(&self) -> bool {
         self.0[0] & 0x02 != 0
     }
 }
@@ -100,7 +100,7 @@ pub const HEADER_LEN: usize = field::PAYLOAD.start;
 
 impl<T: AsRef<[u8]>> Frame<T> {
     /// Imbue a raw octet buffer with Ethernet frame structure.
-    pub fn new_unchecked(buffer: T) -> Frame<T> {
+    pub const fn new_unchecked(buffer: T) -> Frame<T> {
         Frame { buffer }
     }
 
@@ -131,13 +131,13 @@ impl<T: AsRef<[u8]>> Frame<T> {
     }
 
     /// Return the length of a frame header.
-    pub fn header_len() -> usize {
+    pub const fn header_len() -> usize {
         HEADER_LEN
     }
 
     /// Return the length of a buffer required to hold a packet with the payload
     /// of a given length.
-    pub fn buffer_len(payload_len: usize) -> usize {
+    pub const fn buffer_len(payload_len: usize) -> usize {
         HEADER_LEN + payload_len
     }
 
@@ -277,7 +277,7 @@ impl Repr {
     }
 
     /// Return the length of a header that will be emitted from this high-level representation.
-    pub fn buffer_len(&self) -> usize {
+    pub const fn buffer_len(&self) -> usize {
         HEADER_LEN
     }
 

src/wire/icmpv4.rs

@@ -184,7 +184,7 @@ mod field {
 
 impl<T: AsRef<[u8]>> Packet<T> {
     /// Imbue a raw octet buffer with ICMPv4 packet structure.
-    pub fn new_unchecked(buffer: T) -> Packet<T> {
+    pub const fn new_unchecked(buffer: T) -> Packet<T> {
         Packet { buffer }
     }
 
@@ -468,7 +468,7 @@ impl<'a> Repr<'a> {
     }
 
     /// Return the length of a packet that will be emitted from this high-level representation.
-    pub fn buffer_len(&self) -> usize {
+    pub const fn buffer_len(&self) -> usize {
         match self {
             &Repr::EchoRequest { data, .. } | &Repr::EchoReply { data, .. } => {
                 field::ECHO_SEQNO.end + data.len()

src/wire/icmpv6.rs

@@ -55,7 +55,7 @@ impl Message {
     /// is an [NDISC] message type.
     ///
     /// [NDISC]: https://tools.ietf.org/html/rfc4861
-    pub fn is_ndisc(&self) -> bool {
+    pub const fn is_ndisc(&self) -> bool {
         match *self {
             Message::RouterSolicit
             | Message::RouterAdvert
@@ -70,7 +70,7 @@ impl Message {
     /// is an [MLD] message type.
     ///
     /// [MLD]: https://tools.ietf.org/html/rfc3810
-    pub fn is_mld(&self) -> bool {
+    pub const fn is_mld(&self) -> bool {
         match *self {
             Message::MldQuery | Message::MldReport => true,
             _ => false,
@@ -247,7 +247,7 @@ pub(super) mod field {
 
 impl<T: AsRef<[u8]>> Packet<T> {
     /// Imbue a raw octet buffer with ICMPv6 packet structure.
-    pub fn new_unchecked(buffer: T) -> Packet<T> {
+    pub const fn new_unchecked(buffer: T) -> Packet<T> {
         Packet { buffer }
     }
 
@@ -625,7 +625,7 @@ impl<'a> Repr<'a> {
     }
 
     /// Return the length of a packet that will be emitted from this high-level representation.
-    pub fn buffer_len(&self) -> usize {
+    pub const fn buffer_len(&self) -> usize {
         match self {
             &Repr::DstUnreachable { header, data, .. }
             | &Repr::PktTooBig { header, data, .. }