Expose static descriptions for parser errors

src/lib.rs

@@ -117,8 +117,17 @@ pub enum Error {
 }
 
 impl Error {
+    /// Returns the error's description as a static string.
+    ///
+    /// This is the same message produced by the [`Display`](fmt::Display)
+    /// implementation, without allocating a string.
+    ///
+    /// ```
+    /// let description: &'static str = httparse::Error::HeaderName.description_str();
+    /// assert_eq!(description, "invalid header name");
+    /// ```
     #[inline]
-    fn description_str(&self) -> &'static str {
+    pub fn description_str(&self) -> &'static str {
         match *self {
             Error::HeaderName => "invalid header name",
             Error::HeaderValue => "invalid header value",

tests/error_description.rs

@@ -0,0 +1,29 @@
+use httparse::{Error, Request, EMPTY_HEADER};
+
+#[test]
+fn error_descriptions_are_static_and_match_display() {
+    for error in [
+        Error::HeaderName,
+        Error::HeaderValue,
+        Error::NewLine,
+        Error::Status,
+        Error::Token,
+        Error::TooManyHeaders,
+        Error::Version,
+    ] {
+        let description: &'static str = error.description_str();
+        assert_eq!(description, error.to_string());
+    }
+}
+
+#[test]
+fn parsed_error_description_outlives_the_error() {
+    let description: &'static str = {
+        let mut headers = [EMPTY_HEADER; 1];
+        let error = Request::new(&mut headers)
+            .parse(b"GET / HTTP/1.1\r\ninvalid header: value\r\n\r\n")
+            .unwrap_err();
+        error.description_str()
+    };
+    assert_eq!(description, "invalid header name");
+}