ipc: Fix a crash in the sexp lexer.

  - Fixes #742.

2 files changed, 10 insertions, 2 deletions

diff --git a/ipc/src/sexp/parse/lexer.rs b/ipc/src/sexp/parse/lexer.rs
index 0a570475..8d091e25 100644
--- a/ipc/src/sexp/parse/lexer.rs
+++ b/ipc/src/sexp/parse/lexer.rs
@@ -121,12 +121,14 @@ impl<'input> Iterator for Lexer<'input> {
                                             *c as char, &input[..offset])))),
                         }
                     }
+
+                    let len = String::from_utf8_lossy(&input);
+                    Some(Err(LexicalError::TruncatedInput(
+                        format!("Expected colon and data after {:?}", len))))
                 },
                 _ => return Some(Err(LexicalError::UnexpectedCharacter(
                     format!("Unexpected character {}", *c as char)))),
             }
-
-            unreachable!()
         })(&self.input)?;
 
         let (l, token) = match len_token {
diff --git a/ipc/src/sexp/parse/mod.rs b/ipc/src/sexp/parse/mod.rs
index 46905fc3..3e3e077e 100644
--- a/ipc/src/sexp/parse/mod.rs
+++ b/ipc/src/sexp/parse/mod.rs
@@ -146,4 +146,10 @@ mod tests {
         assert!(Sexp::from_bytes(
             crate::tests::file("sexp/rsa-signature.sexp")).is_ok());
     }
+
+    /// Demonstrates a crash in the lexer.
+    #[test]
+    fn issue_742() {
+        Sexp::from_bytes(b"7").unwrap_err();
+    }
 }