4 files changed, 75 insertions, 1 deletions
diff --git a/third_party/rust/neqo-common/src/datagram.rs b/third_party/rust/neqo-common/src/datagram.rs
index cc2cb7d113..2f2bb53766 100644
--- a/third_party/rust/neqo-common/src/datagram.rs
+++ b/third_party/rust/neqo-common/src/datagram.rs
@@ -95,6 +95,6 @@ fn fmt_datagram() {
     let d = datagram([0; 1].to_vec());
     assert_eq!(
         &format!("{d:?}"),
-        "Datagram IpTos(Cs0, NotEct) TTL Some(128) [fe80::1]:443->[fe80::1]:443: [1]: 00"
+        "Datagram IpTos(Cs0, Ect0) TTL Some(128) [fe80::1]:443->[fe80::1]:443: [1]: 00"
     );
 }
diff --git a/third_party/rust/neqo-common/src/fuzz.rs b/third_party/rust/neqo-common/src/fuzz.rs
new file mode 100644
index 0000000000..d0a35a49ae
--- /dev/null
+++ b/third_party/rust/neqo-common/src/fuzz.rs
@@ -0,0 +1,43 @@
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::{
+    collections::hash_map::DefaultHasher,
+    fs::File,
+    hash::{Hash, Hasher},
+    io::Write,
+    path::Path,
+};
+
+/// Write a data item `data` for the fuzzing target `target` to the fuzzing corpus. The caller needs
+/// to make sure that `target` is the correct fuzzing target name for the data written.
+///
+/// # Panics
+///
+/// Panics if the corpus directory does not exist or if the corpus item cannot be written.
+pub fn write_item_to_fuzzing_corpus(target: &str, data: &[u8]) {
+    // This bakes in the assumption that we're executing in the root of the neqo workspace.
+    // Unfortunately, `cargo fuzz` doesn't provide a way to learn the location of the corpus
+    // directory.
+    let corpus = Path::new("../fuzz/corpus").join(target);
+    if !corpus.exists() {
+        std::fs::create_dir_all(&corpus).expect("failed to create corpus directory");
+    }
+
+    // Hash the data to get a unique name for the corpus item.
+    let mut hasher = DefaultHasher::new();
+    data.hash(&mut hasher);
+    let item_name = hex::encode(hasher.finish().to_be_bytes());
+    let item_path = corpus.join(item_name);
+    if item_path.exists() {
+        // Don't overwrite existing corpus items.
+        return;
+    }
+
+    // Write the data to the corpus item.
+    let mut file = File::create(item_path).expect("failed to create corpus item");
+    Write::write_all(&mut file, data).expect("failed to write to corpus item");
+}
diff --git a/third_party/rust/neqo-common/src/lib.rs b/third_party/rust/neqo-common/src/lib.rs
index e988c6071d..3a72425e44 100644
--- a/third_party/rust/neqo-common/src/lib.rs
+++ b/third_party/rust/neqo-common/src/lib.rs
@@ -9,6 +9,8 @@
 mod codec;
 mod datagram;
 pub mod event;
+#[cfg(feature = "build-fuzzing-corpus")]
+mod fuzz;
 pub mod header;
 pub mod hrtime;
 mod incrdecoder;
@@ -21,6 +23,8 @@ use std::fmt::Write;
 
 use enum_map::Enum;
 
+#[cfg(feature = "build-fuzzing-corpus")]
+pub use self::fuzz::write_item_to_fuzzing_corpus;
 pub use self::{
     codec::{Decoder, Encoder},
     datagram::Datagram,
diff --git a/third_party/rust/neqo-common/src/tos.rs b/third_party/rust/neqo-common/src/tos.rs
index 533c5447e2..c7e5228dee 100644
--- a/third_party/rust/neqo-common/src/tos.rs
+++ b/third_party/rust/neqo-common/src/tos.rs
@@ -52,6 +52,16 @@ impl From<IpTos> for IpTosEcn {
     }
 }
 
+impl IpTosEcn {
+    #[must_use]
+    pub fn is_ecn_marked(&self) -> bool {
+        match self {
+            IpTosEcn::Ect0 | IpTosEcn::Ect1 | IpTosEcn::Ce => true,
+            IpTosEcn::NotEct => false,
+        }
+    }
+}
+
 /// Diffserv Codepoints, mapped to the upper six bits of the TOS field.
 /// <https://www.iana.org/assignments/dscp-registry/dscp-registry.xhtml>
 #[derive(Copy, Clone, PartialEq, Eq, Enum, Default, Debug)]
@@ -228,6 +238,11 @@ impl IpTos {
     pub fn set_dscp(&mut self, dscp: IpTosDscp) {
         self.0 = u8::from(IpTosEcn::from(*self)) | u8::from(dscp);
     }
+
+    #[must_use]
+    pub fn is_ecn_marked(&self) -> bool {
+        IpTosEcn::from(*self).is_ecn_marked()
+    }
 }
 
 #[cfg(test)]
@@ -346,4 +361,16 @@ mod tests {
         iptos.set_dscp(IpTosDscp::Le);
         assert_eq!(u8::from(iptos), 0b0000_0101);
     }
+
+    #[test]
+    fn iptos_is_ecn_marked() {
+        let iptos: IpTos = (IpTosDscp::Af41, IpTosEcn::Ce).into();
+        assert!(iptos.is_ecn_marked());
+    }
+
+    #[test]
+    fn iptosecn_is_ecn_marked() {
+        assert!(IpTosEcn::Ce.is_ecn_marked());
+        assert!(!IpTosEcn::NotEct.is_ecn_marked());
+    }
 }