1 files changed, 43 insertions, 0 deletions
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");
+}