tests(fuzz): Add parse_duration fuzzing target

Add a fuzzing target for parsing into a Duration.

fuzz/Cargo.toml

@@ -35,3 +35,10 @@ path = "fuzzers/parse_date.rs"
 test = false
 doc = false
 bench = false
+
+[[bin]]
+name = "parse_duration"
+path = "fuzzers/parse_duration.rs"
+test = false
+doc = false
+bench = false

fuzz/fuzzers/parse_duration.rs

@@ -0,0 +1,31 @@
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| test_parse_duration(data));
+
+pub fn test_parse_duration(data: &[u8]) {
+    use std::str::from_utf8;
+    use std::str::FromStr;
+
+    // input must be text
+    let Ok(original_text) = from_utf8(data) else {
+        return;
+    };
+
+    // parse input as a duration
+    let Ok(duration) = prost_types::Duration::from_str(original_text) else {
+        if original_text.ends_with("s") {
+            assert!(
+                original_text.parse::<f64>().is_err(),
+                "prost failed to parse duration, but it seems to be a valid number: {}",
+                original_text
+            );
+        }
+        return;
+    };
+
+    // roundtrip to and from string
+    let roundtrip_text = format!("{duration}");
+    assert_eq!(Ok(&duration), roundtrip_text.parse().as_ref());
+}