feat(errors): Introduce error module with custom error type

Introduces an error type using the failure crate. This type has
foreign error links established to various errors that can occur
within Converse.

4 files changed, 83 insertions, 2 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 7b84193ebe77..50fdc3ba985f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -251,6 +251,7 @@ dependencies = [
  "chrono 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "diesel 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "env_logger 0.5.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "failure 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures 0.1.21 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "r2d2 0.8.2 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/Cargo.toml b/Cargo.toml
index 76dccad89b00..9bcfafac4f14 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -15,3 +15,4 @@ futures = "*"
 tera = "0.11"
 serde = "1.0"
 serde_derive = "1.0"
+failure = "*"
diff --git a/src/errors.rs b/src/errors.rs
new file mode 100644
index 000000000000..3cbda5f4e55d
--- /dev/null
+++ b/src/errors.rs
@@ -0,0 +1,75 @@
+//! This module defines custom error types using the `failure`-crate.
+//! Links to foreign error types (such as database connection errors)
+//! are established in a similar way as was tradition in
+//! `error_chain`, albeit manually.
+
+use std::result;
+use actix_web::{ResponseError, HttpResponse};
+use actix_web::http::StatusCode;
+
+// Modules with foreign errors:
+use actix;
+use diesel;
+use r2d2;
+use tera;
+
+pub type Result<T> = result::Result<T, ConverseError>;
+
+#[derive(Debug, Fail)]
+pub enum ConverseError {
+    #[fail(display = "an internal Converse error occured: {}", reason)]
+    InternalError { reason: String },
+
+    #[fail(display = "a database error occured: {}", error)]
+    Database { error: diesel::result::Error },
+
+    #[fail(display = "a database connection pool error occured: {}", error)]
+    ConnectionPool { error: r2d2::Error },
+
+    #[fail(display = "a template rendering error occured: {}", reason)]
+    Template { reason: String },
+
+    // This variant is used as a catch-all for wrapping
+    // actix-web-compatible response errors, such as the errors it
+    // throws itself.
+    #[fail(display = "Actix response error: {}", error)]
+    ActixWeb { error: Box<ResponseError> },
+}
+
+// Establish conversion links to foreign errors:
+
+impl From<diesel::result::Error> for ConverseError {
+    fn from(error: diesel::result::Error) -> ConverseError {
+        ConverseError::Database { error }
+    }
+}
+
+impl From<r2d2::Error> for ConverseError {
+    fn from(error: r2d2::Error) -> ConverseError {
+        ConverseError::ConnectionPool { error }
+    }
+}
+
+impl From<tera::Error> for ConverseError {
+    fn from(error: tera::Error) -> ConverseError {
+        ConverseError::Template {
+            reason: format!("{}", error),
+        }
+    }
+}
+
+impl From<actix::MailboxError> for ConverseError {
+    fn from(error: actix::MailboxError) -> ConverseError {
+        ConverseError::ActixWeb { error: Box::new(error) }
+    }
+}
+
+// Support conversion of error type into HTTP error responses:
+
+impl ResponseError for ConverseError {
+    fn error_response(&self) -> HttpResponse {
+        // Everything is mapped to internal server errors for now.
+        HttpResponse::build(StatusCode::INTERNAL_SERVER_ERROR)
+            .body(format!("An error occured: {}", self))
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index 8ce4e1082e4e..767d45891c3b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -10,6 +10,9 @@ extern crate tera;
 #[macro_use]
 extern crate serde_derive;
 
+#[macro_use]
+extern crate failure;
+
 extern crate chrono;
 extern crate actix;
 extern crate actix_web;
@@ -18,10 +21,11 @@ extern crate r2d2;
 extern crate futures;
 extern crate serde;
 
-pub mod schema;
-pub mod models;
 pub mod db;
+pub mod errors;
 pub mod handlers;
+pub mod models;
+pub mod schema;
 
 use actix::prelude::*;
 use actix_web::*;