From 164717e19649cf988abfc716687cf675e5a06bf4 Mon Sep 17 00:00:00 2001
From: Nick Mathewson <nickm@torproject.org>
Date: Wed, 10 May 2023 13:07:35 -0400
Subject: [PATCH] linkspec::verbatim: wrapper to give a CircTarget a new set of
 LinkSpecs

---
 crates/tor-linkspec/Cargo.toml      |   3 +-
 crates/tor-linkspec/src/lib.rs      |   2 +
 crates/tor-linkspec/src/verbatim.rs | 109 ++++++++++++++++++++++++++++
 3 files changed, 113 insertions(+), 1 deletion(-)
 create mode 100644 crates/tor-linkspec/src/verbatim.rs

diff --git a/crates/tor-linkspec/Cargo.toml b/crates/tor-linkspec/Cargo.toml
index e6d0ff0d9..8113fc17d 100644
--- a/crates/tor-linkspec/Cargo.toml
+++ b/crates/tor-linkspec/Cargo.toml
@@ -14,9 +14,10 @@ repository = "https://gitlab.torproject.org/tpo/core/arti.git/"
 [features]
 default = []
 full = ["pt-client"]
-experimental = ["decode"]
+experimental = ["decode", "verbatim"]
 pt-client = []
 decode = []
+verbatim = []
 
 [dependencies]
 base64ct = "1.5.1"
diff --git a/crates/tor-linkspec/src/lib.rs b/crates/tor-linkspec/src/lib.rs
index f4b2b0204..8298b0538 100644
--- a/crates/tor-linkspec/src/lib.rs
+++ b/crates/tor-linkspec/src/lib.rs
@@ -45,6 +45,8 @@ mod ls;
 mod owned;
 mod traits;
 mod transport;
+#[cfg(feature = "verbatim")]
+pub mod verbatim;
 
 pub use ids::{
     by_id::{ByRelayIds, ByRelayIdsError},
diff --git a/crates/tor-linkspec/src/verbatim.rs b/crates/tor-linkspec/src/verbatim.rs
new file mode 100644
index 000000000..36e8d9e15
--- /dev/null
+++ b/crates/tor-linkspec/src/verbatim.rs
@@ -0,0 +1,109 @@
+//! Wrappers for using a CircTarget with a verbatim list of
+//! [link specifiers](EncodedLinkSpec).
+
+use crate::{ChanTarget, CircTarget, EncodedLinkSpec, HasAddrs, HasChanMethod, HasRelayIds};
+
+/// A wrapper around an underlying [`CircTarget`] that provides a user-specified
+/// list of [link specifiers](EncodedLinkSpec).
+///
+/// Onion services and their clients use this type of target when telling a
+/// relay to extend a circuit to a target relay (an introduction point or
+/// rendezvous point) chosen by some other party.
+pub struct VerbatimLinkSpecCircTarget<T> {
+    /// The underlying CircTarget
+    target: T,
+    /// The link specifiers to provide.
+    linkspecs: Vec<EncodedLinkSpec>,
+}
+
+impl<T> VerbatimLinkSpecCircTarget<T> {
+    /// Construct a new `VerbatimLinkSpecCircTarget` to wrap an underlying
+    /// `CircTarget` object, and provide it with a new set of encoded link
+    /// specifiers that will be used when telling a relay to extend to this
+    /// node.
+    ///
+    /// Note that nothing here will check that `linkspecs` is sufficient to
+    /// actually connect to the chosen target, or to any target at all. It is
+    /// the caller's responsibility to choose a valid set of link specifiers.
+    pub fn new(target: T, linkspecs: Vec<EncodedLinkSpec>) -> Self {
+        Self { target, linkspecs }
+    }
+}
+
+// Now, the delegation functions.  All of these are simple delegations to
+// self.target, except for `CircTarget::linkspecs` with returns self.linkspecs.
+
+impl<T: HasRelayIds> HasRelayIds for VerbatimLinkSpecCircTarget<T> {
+    fn identity(&self, key_type: crate::RelayIdType) -> Option<crate::RelayIdRef<'_>> {
+        self.target.identity(key_type)
+    }
+}
+impl<T: HasAddrs> HasAddrs for VerbatimLinkSpecCircTarget<T> {
+    fn addrs(&self) -> &[std::net::SocketAddr] {
+        self.target.addrs()
+    }
+}
+impl<T: HasChanMethod> HasChanMethod for VerbatimLinkSpecCircTarget<T> {
+    fn chan_method(&self) -> crate::ChannelMethod {
+        self.target.chan_method()
+    }
+}
+impl<T: ChanTarget> ChanTarget for VerbatimLinkSpecCircTarget<T> {}
+impl<T: CircTarget> CircTarget for VerbatimLinkSpecCircTarget<T> {
+    fn linkspecs(&self) -> tor_bytes::EncodeResult<Vec<EncodedLinkSpec>> {
+        Ok(self.linkspecs.clone())
+    }
+
+    fn ntor_onion_key(&self) -> &tor_llcrypto::pk::curve25519::PublicKey {
+        self.target.ntor_onion_key()
+    }
+
+    fn protovers(&self) -> &tor_protover::Protocols {
+        self.target.protovers()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    // @@ begin test lint list maintained by maint/add_warning @@
+    #![allow(clippy::bool_assert_comparison)]
+    #![allow(clippy::clone_on_copy)]
+    #![allow(clippy::dbg_macro)]
+    #![allow(clippy::print_stderr)]
+    #![allow(clippy::print_stdout)]
+    #![allow(clippy::single_char_pattern)]
+    #![allow(clippy::unwrap_used)]
+    #![allow(clippy::unchecked_duration_subtraction)]
+    //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
+
+    use crate::OwnedCircTarget;
+
+    use super::*;
+    #[test]
+    fn verbatim_linkspecs() {
+        let mut builder = OwnedCircTarget::builder();
+        builder
+            .chan_target()
+            .addrs(vec!["127.0.0.1:11".parse().unwrap()])
+            .ed_identity([42; 32].into())
+            .rsa_identity([45; 20].into());
+        let inner = builder
+            .ntor_onion_key([99; 32].into())
+            .protocols("FlowCtrl=7".parse().unwrap())
+            .build()
+            .unwrap();
+        let weird_linkspecs = vec![EncodedLinkSpec::new(
+            77.into(),
+            b"mysterious whisper".to_vec(),
+        )];
+        let wrapped = VerbatimLinkSpecCircTarget::new(inner.clone(), weird_linkspecs.clone());
+
+        assert_eq!(wrapped.addrs(), inner.addrs());
+        assert!(wrapped.same_relay_ids(&inner));
+        assert_eq!(wrapped.ntor_onion_key(), inner.ntor_onion_key());
+        assert_eq!(wrapped.protovers(), inner.protovers());
+
+        assert_ne!(inner.linkspecs().unwrap(), weird_linkspecs);
+        assert_eq!(wrapped.linkspecs().unwrap(), weird_linkspecs);
+    }
+}