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diff --git a/web/converse/src/errors.rs b/web/converse/src/errors.rs
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+// Copyright (C) 2018-2021 Vincent Ambo <tazjin@tvl.su>
+//
+// This file is part of Converse.
+//
+// This program is free software: you can redistribute it and/or
+// modify it under the terms of the GNU General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+// General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see
+// <https://www.gnu.org/licenses/>.
+
+//! 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 actix_web;
+use askama;
+use diesel;
+use r2d2;
+use tokio_timer;
+
+pub type Result<T> = result::Result<T, ConverseError>;
+pub type ConverseResult<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 },
+
+    #[fail(display = "error occured during request handling: {}", error)]
+    ActixWeb { error: actix_web::Error },
+
+    #[fail(display = "error occured running timer: {}", error)]
+    Timer { error: tokio_timer::Error },
+
+    #[fail(display = "user {} does not have permission to edit post {}", user, id)]
+    PostEditForbidden { user: i32, id: i32 },
+
+    #[fail(display = "thread {} is closed and can not be responded to", id)]
+    ThreadClosed { id: i32 },
+
+    #[fail(display = "JSON serialisation failed: {}", error)]
+    Serialisation { error: serde_json::Error },
+
+    // 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)]
+    Actix { error: Box<dyn 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<askama::Error> for ConverseError {
+    fn from(error: askama::Error) -> ConverseError {
+        ConverseError::Template {
+            reason: format!("{}", error),
+        }
+    }
+}
+
+impl From<actix::MailboxError> for ConverseError {
+    fn from(error: actix::MailboxError) -> ConverseError {
+        ConverseError::Actix { error: Box::new(error) }
+    }
+}
+
+impl From<actix_web::Error> for ConverseError {
+    fn from(error: actix_web::Error) -> ConverseError {
+        ConverseError::ActixWeb { error }
+    }
+}
+
+impl From<serde_json::Error> for ConverseError {
+    fn from(error: serde_json::Error) -> ConverseError {
+        ConverseError::Serialisation { error }
+    }
+}
+
+impl From<curl::Error> for ConverseError {
+    fn from(error: curl::Error) -> ConverseError {
+        ConverseError::InternalError {
+            reason: format!("error during HTTP request: {}", error),
+        }
+    }
+}
+
+impl From<tokio_timer::Error> for ConverseError {
+    fn from(error: tokio_timer::Error) -> ConverseError {
+        ConverseError::Timer { 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.
+        match *self {
+            ConverseError::ThreadClosed { id } => HttpResponse::SeeOther()
+                .header("Location", format!("/thread/{}#post-reply", id))
+                .finish(),
+            _ => HttpResponse::build(StatusCode::INTERNAL_SERVER_ERROR)
+                .body(format!("An error occured: {}", self))
+        }
+    }
+}