feat: constant for handling missing password

src/read.rs

@@ -489,11 +489,7 @@ impl<R: Read + io::Seek> ZipArchive<R> {
         let data = &mut self.files[file_number];
 
         match (password, data.encrypted) {
-            (None, true) => {
+            (None, true) => return Err(ZipError::UnsupportedArchive(ZipError::PASSWORD_REQUIRED)),
-                return Err(ZipError::UnsupportedArchive(
-                    "Password required to decrypt file",
-                ))
-            }
             (Some(_), false) => password = None, //Password supplied, but none needed! Discard.
             _ => {}
         }

src/result.rs

@@ -32,6 +32,21 @@ pub enum ZipError {
     FileNotFound,
 }
 
+impl ZipError {
+    /// The text used as an error when a password is required and not supplied
+    ///
+    /// ```rust,no_run
+    /// # use zip::result::ZipError;
+    /// # let mut archive = zip::ZipArchive::new(std::io::Cursor::new(&[])).unwrap();
+    /// match archive.by_index(1) {
+    ///     Err(ZipError::UnsupportedArchive(ZipError::PASSWORD_REQUIRED)) => eprintln!("a password is needed to unzip this file"),
+    ///     _ => (),
+    /// }
+    /// # ()
+    /// ```
+    pub const PASSWORD_REQUIRED: &'static str = "Password required to decrypt file";
+}
+
 impl From<ZipError> for io::Error {
     fn from(err: ZipError) -> io::Error {
         io::Error::new(io::ErrorKind::Other, err)

tests/zip_crypto.rs

@@ -47,9 +47,9 @@ fn encrypted_file() {
         // No password
         let file = archive.by_index(0);
         match file {
-            Err(zip::result::ZipError::UnsupportedArchive("Password required to decrypt file")) => {
+            Err(zip::result::ZipError::UnsupportedArchive(
-                ()
+                zip::result::ZipError::PASSWORD_REQUIRED,
-            }
+            )) => (),
             Err(_) => panic!(
                 "Expected PasswordRequired error when opening encrypted file without password"
             ),