More informative errors (#543)

Before this change, errors from other libraries (eg `serde::de::Error`)
were converted to a context error where the context was named after the library
(eg `ErrorKind::Serde`). This change replaces these contexts with meaningful
descriptions of the actual operation going on (eg `InvalidModuleName(String)`).

The `From<other_library::Error> for this_crate::Error` impls have also been
removed, since the generic error kinds these impls relied on no longer exist,
and to ensure that new error kind contexts are added in the future
as necessary.

edgelet/dps/src/error.rs

@@ -3,41 +3,43 @@
 use std::fmt;
 use std::fmt::Display;
 
-use base64::DecodeError;
 use failure::{Backtrace, Context, Fail};
-use serde_json::Error as SerdeError;
-use tokio::timer::Error as TimerError;
 
-use edgelet_core::Error as CoreError;
 use edgelet_http::{Error as HttpError, ErrorKind as HttpErrorKind};
 
 #[derive(Debug)]
 pub struct Error {
     inner: Context<ErrorKind>,
 }
 
-#[derive(Debug, Fail)]
+#[derive(Clone, Copy, Debug, Fail)]
 pub enum ErrorKind {
-    #[fail(display = "Core error")]
-    Core,
-    #[fail(display = "Http error")]
-    Http,
-    #[fail(display = "Serde error")]
-    Serde,
-    #[fail(display = "DPS returned an empty response when a value was expected")]
-    Unexpected,
-    #[fail(display = "Invalid Tpm token")]
+    #[fail(display = "Could not get device registration result")]
+    GetDeviceRegistrationResult,
+
+    #[fail(display = "Could not get operation ID")]
+    GetOperationId,
+
+    #[fail(display = "Could not get operation status")]
+    GetOperationStatus,
+
+    #[fail(display = "Could not get token")]
+    GetToken,
+
+    #[fail(display = "Could not get TPM challenge key")]
+    GetTpmChallengeKey,
+
+    #[fail(display = "Could not get TPM challenge key because the TPM token is invalid")]
     InvalidTpmToken,
-    #[fail(display = "Assignment failed")]
-    AssignmentFailed,
-    #[fail(display = "Timer error")]
-    TimerError,
-    #[fail(display = "DPS operation not assigned")]
-    NotAssigned,
-    #[fail(display = "Error during keystore operation")]
-    Keystore,
-    #[fail(display = "Decode error")]
-    Decode,
+
+    #[fail(display = "DPS registration succeeded but returned an empty response")]
+    RegisterWithAuthUnexpectedlySucceeded,
+
+    #[fail(display = "DPS registration failed")]
+    RegisterWithAuthUnexpectedlyFailed,
+
+    #[fail(display = "DPS registration failed because the DPS operation is not assigned")]
+    RegisterWithAuthUnexpectedlyFailedOperationNotAssigned,
 }
 
 impl Fail for Error {
@@ -76,48 +78,8 @@ impl From<Context<ErrorKind>> for Error {
     }
 }
 
-impl From<CoreError> for Error {
-    fn from(error: CoreError) -> Self {
-        Error {
-            inner: error.context(ErrorKind::Core),
-        }
-    }
-}
-
-impl From<HttpError> for Error {
-    fn from(error: HttpError) -> Self {
-        Error {
-            inner: error.context(ErrorKind::Http),
-        }
-    }
-}
-
-impl From<SerdeError> for Error {
-    fn from(error: SerdeError) -> Self {
-        Error {
-            inner: error.context(ErrorKind::Serde),
-        }
-    }
-}
-
 impl From<Error> for HttpError {
     fn from(err: Error) -> Self {
         HttpError::from(err.context(HttpErrorKind::TokenSource))
     }
 }
-
-impl From<TimerError> for Error {
-    fn from(error: TimerError) -> Self {
-        Error {
-            inner: error.context(ErrorKind::TimerError),
-        }
-    }
-}
-
-impl From<DecodeError> for Error {
-    fn from(error: DecodeError) -> Self {
-        Error {
-            inner: error.context(ErrorKind::Decode),
-        }
-    }
-}