fix bug where get_named() could panic on non-existent fields

Author: dwrensha

capnp/src/schema.rs

@@ -60,21 +60,19 @@ impl StructSchema {
         let fields = self.get_fields()?;
         let mut lower: usize = 0;
         let mut upper: usize = self.raw.generic.members_by_name.len();
-        let mut mid: usize = (lower + upper) / 2;
-        let mut candidate_index = self.raw.generic.members_by_name[mid];
-        let mut candidate_name = fields.get(candidate_index).get_proto().get_name()?;
 
         while lower < upper {
+            let mid: usize = (lower + upper) / 2;
+            let candidate_index = self.raw.generic.members_by_name[mid];
+            let candidate_name = fields.get(candidate_index).get_proto().get_name()?;
+
             use core::cmp::Ordering;
             match (&name).partial_cmp(&candidate_name) {
                 Some(Ordering::Equal) => return Ok(Some(fields.get(candidate_index))),
                 Some(Ordering::Greater) => lower = mid + 1,
                 Some(Ordering::Less) => upper = mid,
                 None => unreachable!(),
             }
-            mid = (lower + upper) / 2;
-            candidate_index = self.raw.generic.members_by_name[mid];
-            candidate_name = fields.get(candidate_index).get_proto().get_name()?;
         }
         Ok(None)
     }

capnpc/test/dynamic.rs

@@ -391,3 +391,17 @@ fn test_stringify_list_list() {
     let stringified = format!("{:?}", root.into_reader());
     assert_eq!(stringified, "[[1111, 2222, 3333], [123456]]");
 }
+
+#[test]
+fn test_get_named_missing() {
+    let mut builder = message::Builder::new_default();
+    let root: test_all_types::Builder<'_> = builder.init_root();
+    let root: dynamic_value::Builder<'_> = root.into();
+    let mut root: dynamic_struct::Builder<'_> = root.downcast();
+    test_util::dynamic_init_test_message(root.reborrow());
+    let root = root.into_reader();
+    // try a bunch of fields that don't exist
+    assert!(root.get_named("AAAAAAA").is_err());
+    assert!(root.get_named("abcdef").is_err());
+    assert!(root.get_named("zzzzzzz").is_err());
+}