tor-netdoc: Put the "routerdesc" document type behind a feature.

Nothing in arti currently uses this document type.  Eventually it
will be useful for relays and for bridge clients.

I've left the "SHA1 digest of a router descriptor" type available
unconditinoally, however, since it does get used in a few places.

Part of #125.

crates/tor-netdoc/Cargo.toml

@@ -11,8 +11,15 @@ categories = [ "parser-implementations" ]
 repository="https://gitlab.torproject.org/tpo/core/arti.git/"
 
 [features]
+default = []
+
+# Enable code to build the objects that represent different network documents.
 build_docs = [ "rand" ]
 
+# Enable the "router descriptor" document type, which is needed by relays and
+# bridge clients.
+routerdesc = []
+
 [dependencies]
 tor-llcrypto = { path="../tor-llcrypto", version = "0.0.1"}
 tor-bytes = { path="../tor-bytes", version = "0.0.1"}

crates/tor-netdoc/fuzz/Cargo.toml

@@ -14,6 +14,7 @@ libfuzzer-sys = "0.3"
 
 [dependencies.tor-netdoc]
 path = ".."
+features = [ "routerdesc" ]
 
 # Prevent this from interfering with workspaces
 [workspace]

crates/tor-netdoc/src/doc.rs

@@ -32,4 +32,13 @@
 pub mod authcert;
 pub mod microdesc;
 pub mod netstatus;
+
+#[cfg(any(doc, feature = "routerdesc"))]
 pub mod routerdesc;
+
+#[allow(missing_docs, clippy::missing_docs_in_private_items)]
+#[cfg(not(any(doc, feature = "routerdesc")))]
+pub mod routerdesc {
+    /// The digest of a RouterDesc document, as reported in a NS consensus.
+    pub type RdDigest = [u8; 20];
+}

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

@@ -27,6 +27,11 @@
 //! TODO: There should be accessor functions for some or all of the
 //! fields in RouterDesc.  I'm deferring those until I know what they
 //! should be.
+//!
+//! # Availability
+//!
+//! Most of this module is only available when this crate is built with the
+//! `routerdesc` feature enabled.
 use crate::parse::keyword::Keyword;
 use crate::parse::parser::{Section, SectionRules};
 use crate::parse::tokenize::{ItemResult, NetDocReader};

crates/tor-netdoc/src/lib.rs

@@ -24,6 +24,14 @@
 //! inside directory documents.  Finally, the [`doc`] module defines
 //! the parsers for the documents themselves.
 //!
+//! # Features
+//!
+//! `build_docs`: enable code to construct the objects representing different
+//! network documents.
+//!
+//! `routerdesc`: enable support for the "router descriptor" docment type, which
+//! is needed by bridge clients and relays.
+//!
 //! # Caveat haxxor: limitations and infelicities
 //!
 //! TODO: This crate requires that all of its inputs be valid UTF-8:

crates/tor-netdoc/src/parse/tokenize.rs

@@ -492,6 +492,7 @@ impl<'a, 'b, K: Keyword> MaybeItem<'a, 'b, K> {
     /// If this item is present, parse its argument at position `idx`.
     /// Treat the absence or malformedness of the argument as an error,
     /// but treat the absence of this item as acceptable.
+    #[cfg(any(test, feature = "routerdesc"))]
     pub(crate) fn parse_arg<V: FromStr>(&self, idx: usize) -> Result<Option<V>>
     where
         Error: From<V::Err>,

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

@@ -9,6 +9,7 @@ pub(crate) use b16impl::*;
 pub(crate) use b64impl::*;
 pub(crate) use curve25519impl::*;
 pub(crate) use ed25519impl::*;
+#[cfg(feature = "routerdesc")]
 pub(crate) use edcert::*;
 pub(crate) use fingerprint::*;
 pub(crate) use rsa::*;
@@ -253,6 +254,7 @@ mod rsa {
 }
 
 /// Types for decoding Ed25519 certificates
+#[cfg(feature = "routerdesc")]
 mod edcert {
     use crate::{Error, Pos, Result};
     use tor_cert::{CertType, Ed25519Cert, KeyUnknownCert};

crates/tor-netdoc/src/util.rs

@@ -36,6 +36,7 @@ impl<'a, I: Iterator, F: FnMut(&I::Item) -> bool> PauseAt<'a, I, F> {
         }
     }
     /// Replace the predicate on a PauseAt, returning a new PauseAt.
+    #[cfg(any(test, feature = "routerdesc"))]
     pub(crate) fn new_pred<F2>(self, pred: F2) -> PauseAt<'a, I, F2>
     where
         F2: FnMut(&I::Item) -> bool,

doc/semver_status.md

@@ -22,5 +22,6 @@ We can delete older sections here after we bump the releases.
 tor-client: MODIFIED
 tor-dirclient: MODIFIED
 tor-llcrypto: BREAKING
+tor-netdoc: BREAKING
 tor-persist: BREAKING if `testing` feature is enabled.
 tor-proto: BREAKING