Return unknown error when none is returned by last_error

Fixes #60

2 files changed, 6 insertions, 1 deletions

diff --git a/src/error.rs b/src/error.rs
index 7019aa9..e402010 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -44,6 +44,11 @@ impl Error {
         Error::new(raw::LIBSSH2_ERROR_CHANNEL_EOF_SENT, "end of file")
     }
 
+    /// Generate an error for unknown failure
+    pub fn unknown() -> Error {
+        Error::new(libc::c_int::min_value(), "no other error listed")
+    }
+
     /// Construct an error from an error code from libssh2
     pub fn from_errno(code: libc::c_int) -> Error {
         let msg = match code {
diff --git a/src/util.rs b/src/util.rs
index 1955431..31637dc 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -20,7 +20,7 @@ pub trait SessionBinding<'sess>: Sized {
     unsafe fn from_raw_opt(sess: &'sess Session, raw: *mut Self::Raw)
                            -> Result<Self, Error> {
         if raw.is_null() {
-            Err(Error::last_error(sess).unwrap())
+            Err(Error::last_error(sess).unwrap_or_else(Error::unknown))
         } else {
             Ok(SessionBinding::from_raw(sess, raw))
         }