netdoc: add a new type for Nicknames

Relay nicknames are always between 1 and 19 characters long, and
they're always ASCII: That means that storing them in a [u8;19] will
always be possible, and always use less resources than storing them
in a String.

Fortunately, the tinystr crate already helps us with this kind of
thing.

Cargo.lock

@@ -994,6 +994,17 @@ dependencies = [
  "winapi 0.3.9",
 ]
 
+[[package]]
+name = "displaydoc"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3bf95dc3f046b9da4f2d51833c0d3547d8564ef6910f5c1ed130306a75b92886"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "downcast-rs"
 version = "1.2.0"
@@ -3142,6 +3153,15 @@ version = "0.2.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "42657b1a6f4d817cda8e7a0ace261fe0cc946cf3a80314390b22cc61ae080792"
 
+[[package]]
+name = "tinystr"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0949a998f5fdb6b70a86deb1c8b8e2119f981f59b1b050344dbd3c40d8894c59"
+dependencies = [
+ "displaydoc",
+]
+
 [[package]]
 name = "tinyvec"
 version = "1.6.0"
@@ -3651,6 +3671,7 @@ dependencies = [
  "signature",
  "thiserror",
  "time",
+ "tinystr",
  "tor-bytes",
  "tor-cert",
  "tor-checkable",

crates/tor-netdoc/Cargo.toml

@@ -60,6 +60,7 @@ once_cell = "1"
 phf = { version = "0.10.0", features = ["macros"] }
 serde = "1.0.103"
 signature = "1"
+tinystr = "0.5"
 thiserror = "1"
 visible = { version = "0.0.1", optional = true }
 visibility = { version = "0.0.1", optional = true }

crates/tor-netdoc/src/doc/netstatus/rs.rs

@@ -39,7 +39,7 @@ struct GenericRouterStatus<D> {
     ///
     /// Nicknames can be used for convenience purpose, but no more:
     /// there is no mechanism to enforce their uniqueness.
-    nickname: String,
+    nickname: Nickname,
     /// Fingerprint of the old-style RSA identity for this relay.
     identity: RsaIdentity,
     /// A list of address:port values where this relay can be reached.
@@ -115,8 +115,8 @@ macro_rules! implement_accessors {
                 &self.rs.protos
             }
             /// Return the nickname of this routerstatus.
-            pub fn nickname(&self) -> &String {
-                &self.rs.nickname
+            pub fn nickname(&self) -> &str {
+                self.rs.nickname.as_str()
             }
             /// Return the relay flags of this routerstatus.
             pub fn flags(&self) -> &RelayFlags {
@@ -177,7 +177,7 @@ where
         use NetstatusKwd::*;
         // R line
         let r_item = sec.required(RS_R)?;
-        let nickname = r_item.required_arg(0)?.to_string();
+        let nickname = r_item.required_arg(0)?.parse()?;
         let ident = r_item.required_arg(1)?.parse::<B64>()?;
         let identity = RsaIdentity::from_bytes(ident.as_bytes()).ok_or_else(|| {
             EK::BadArgument

crates/tor-netdoc/src/doc/netstatus/rs/build.rs

@@ -118,7 +118,7 @@ impl<D: Clone> RouterStatusBuilder<D> {
     }
     /// Try to build a GenericRouterStatus from this builder.
     fn finish(&self) -> Result<GenericRouterStatus<D>> {
-        let nickname = self.nickname.clone().unwrap_or_else(|| "Unnamed".into());
+        let nickname = self.nickname.as_deref().unwrap_or("Unnamed").parse()?;
         let identity = self
             .identity
             .ok_or(Error::CannotBuild("Missing RSA identity"))?;

crates/tor-netdoc/src/doc/routerdesc.rs

@@ -100,7 +100,7 @@ pub struct RouterDesc {
     /// Human-readable nickname for this relay.
     ///
     /// This is not secure, and not guaranteed to be unique.
-    nickname: String,
+    nickname: Nickname,
     /// IPv4 address for this relay.
     ipv4addr: Option<net::Ipv4Addr>,
     /// IPv4 ORPort for this relay.
@@ -481,10 +481,7 @@ impl RouterDesc {
         let (nickname, ipv4addr, orport, dirport) = {
             let rtrline = header.required(ROUTER)?;
             (
-                // Unwrap should be safe because above `required` should return
-                // an `Error::MissingToken` if `ROUTER` is not `Ok`
-                #[allow(clippy::unwrap_used)]
-                rtrline.arg(0).unwrap().to_string(),
+                rtrline.parse_arg::<Nickname>(0)?,
                 Some(rtrline.parse_arg::<net::Ipv4Addr>(1)?),
                 rtrline.parse_arg(2)?,
                 // Skipping socksport.
@@ -815,7 +812,7 @@ mod test {
             .check_signature()?
             .dangerously_assume_timely();
 
-        assert_eq!(rd.nickname, "idun2");
+        assert_eq!(rd.nickname.as_str(), "idun2");
         assert_eq!(rd.orport, 9001);
         assert_eq!(rd.dirport, 0);
 

crates/tor-netdoc/src/types.rs

@@ -7,3 +7,6 @@ pub mod family;
 pub(crate) mod misc;
 pub mod policy;
 pub mod version;
+
+#[cfg(feature = "dangerous-expose-struct-fields")]
+pub use misc::Nickname;

crates/tor-netdoc/src/types/misc.rs

@@ -15,6 +15,11 @@ pub(crate) use fingerprint::*;
 pub(crate) use rsa::*;
 pub(crate) use timeimpl::*;
 
+#[cfg(feature = "dangerous-expose-struct-fields")]
+pub use nickname::Nickname;
+#[cfg(not(feature = "dangerous-expose-struct-fields"))]
+pub(crate) use nickname::Nickname;
+
 /// Describes a value that van be decoded from a bunch of bytes.
 ///
 /// Used for decoding the objects between BEGIN and END tags.
@@ -390,6 +395,61 @@ mod fingerprint {
     }
 }
 
+/// A type for relay nicknames
+mod nickname {
+    use crate::{Error, ParseErrorKind as EK, Pos, Result};
+    use tinystr::TinyAsciiStr;
+
+    /// This is a strange limit, but it comes from Tor.
+    const MAX_NICKNAME_LEN: usize = 19;
+
+    /// The nickname for a Tor relay.
+    ///
+    /// These nicknames are legacy mechanism that's occasionally useful in
+    /// debugging. They should *never* be used to uniquely identify relays;
+    /// nothing prevents two relays from having the same nickname.
+    ///
+    /// Nicknames are required to be ASCII, alphanumeric, and between 1 and 19
+    /// characters inclusive.
+    #[cfg_attr(feature = "dangerous-expose-struct-fields", visibility::make(pub))]
+    #[derive(Clone, Debug)]
+
+    pub(crate) struct Nickname(tinystr::TinyAsciiStr<MAX_NICKNAME_LEN>);
+
+    impl Nickname {
+        /// Return a view of this nickname as a string slice.
+        pub(crate) fn as_str(&self) -> &str {
+            self.0.as_str()
+        }
+    }
+
+    impl std::fmt::Display for Nickname {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            self.as_str().fmt(f)
+        }
+    }
+
+    impl std::str::FromStr for Nickname {
+        type Err = Error;
+
+        fn from_str(s: &str) -> Result<Self> {
+            let tiny = TinyAsciiStr::from_str(s).map_err(|_| {
+                EK::BadArgument
+                    .at_pos(Pos::at(s))
+                    .with_msg("Invalid nickname")
+            })?;
+
+            if tiny.is_ascii_alphanumeric() && !tiny.is_empty() {
+                Ok(Nickname(tiny))
+            } else {
+                Err(EK::BadArgument
+                    .at_pos(Pos::at(s))
+                    .with_msg("Invalid nickname"))
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 mod test {
     #![allow(clippy::unwrap_used)]
@@ -519,4 +579,28 @@ mod test {
         assert!("ffffffffff".parse::<Fingerprint>().is_err());
         Ok(())
     }
+
+    #[test]
+    fn nickname() -> Result<()> {
+        let n: Nickname = "Foo".parse()?;
+        assert_eq!(n.as_str(), "Foo");
+        assert_eq!(n.to_string(), "Foo");
+
+        let word = "Untr1gonometr1cally";
+        assert_eq!(word.len(), 19);
+        let long: Nickname = word.parse()?;
+        assert_eq!(long.as_str(), word);
+
+        let too_long = "abcdefghijklmnopqrstuvwxyz";
+        let not_ascii = "Eyjafjallajökull";
+        let too_short = "";
+        let other_invalid = "contains space";
+        assert!(not_ascii.len() <= 19);
+        assert!(too_long.parse::<Nickname>().is_err());
+        assert!(not_ascii.parse::<Nickname>().is_err());
+        assert!(too_short.parse::<Nickname>().is_err());
+        assert!(other_invalid.parse::<Nickname>().is_err());
+
+        Ok(())
+    }
 }

doc/semver_status.md

@@ -31,6 +31,11 @@ MODIFIED: New APIs for CachedDir, Error.
 
 BREAKING: Added new cache_trust element to DirMgrConfig.
 
+### tor-netdoc
+
+BREAKING: Routerstatus::nickname() now returns &str, not &String.
+
 ### tor-persist
 
 +BREAKING: Replaced from_path with from_path_and_mistrust
+