[#2] Create error module

src/error.rs

@@ -0,0 +1,59 @@
+//! Runtime errors for the [`rustpostal`] crate.
+
+use std::error;
+use std::ffi::NulError;
+use std::fmt;
+
+/// An error indicating failure in setting up required `libpostal` resources.
+/// Returned by [`setup`](`LibModules.setup`) method on [`LibModules`].
+#[derive(Debug, Clone)]
+pub struct SetupError;
+
+impl fmt::Display for SetupError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "setup of libpostal resources failed")
+    }
+}
+
+impl error::Error for SetupError {}
+
+/// Error indicating possible runtime failures.
+#[derive(Debug, Clone)]
+pub enum RuntimeError {
+    FailedSetup(SetupError),
+    InvalidAddress(NulError),
+}
+
+impl fmt::Display for RuntimeError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            RuntimeError::FailedSetup(ref err) => err.fmt(f),
+            RuntimeError::InvalidAddress(_) => {
+                write!(f, "input address possibly contains internal null byte")
+            }
+        }
+    }
+}
+
+impl error::Error for RuntimeError {
+    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
+        match *self {
+            RuntimeError::FailedSetup(ref err) => Some(err),
+            RuntimeError::InvalidAddress(ref err) => Some(err),
+        }
+    }
+}
+
+impl From<SetupError> for RuntimeError {
+    /// Create a new [`RuntimeError`] consuming a [`SetupError`].
+    fn from(err: SetupError) -> Self {
+        RuntimeError::FailedSetup(err)
+    }
+}
+
+impl From<NulError> for RuntimeError {
+    /// Create a new [`RuntimeError`] consuming a [`NulError`].
+    fn from(err: NulError) -> Self {
+        RuntimeError::InvalidAddress(err)
+    }
+}

src/lib.rs

@@ -9,9 +9,12 @@ use std::process;
 use self::LibModules::*;
 
 pub mod address;
+pub mod error;
 pub mod expand;
 mod ffi;
 
+use error::SetupError;
+
 /// Library modules to setup and teardown, at the start
 /// and at the end of our program.
 pub enum LibModules {