Add a backend based on KDE's `kdialog`

6 files changed, 191 insertions, 5 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index edf65a1..c327be9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+# Unreleased
+- Add the `KDialog` backend (contributed by Stephan Sokolow).
+
 # v0.2.1 (2019-06-30)
 - Fix the input and password dialogs for the `zenity` backend (thanks Silvano
   Cortesi for the bug report):
diff --git a/README.md b/README.md
index d2439b0..bd73da3 100644
--- a/README.md
+++ b/README.md
@@ -5,8 +5,9 @@ A Rust library for displaying dialog boxes using various backends.
 [Documentation][]
 
 Currently `dialog-rs` supports input, message, password and question dialogs.
-It can use the `dialog` or `zenity` tools to display the dialog boxes.  If none
-of these tools is available, the dialogs are printed to the standard output.
+It can use the `dialog`, `kdialog`, or `zenity` tools to display the dialog
+boxes.  If none of these tools is available, the dialogs are printed to the
+standard output.
 
 ## Example
 
diff --git a/examples/backend-kdialog.rs b/examples/backend-kdialog.rs
new file mode 100644
index 0000000..5c3fb46
--- /dev/null
+++ b/examples/backend-kdialog.rs
@@ -0,0 +1,18 @@
+// Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+// SPDX-License-Identifier: MIT
+
+use dialog::backends;
+use dialog::DialogBox;
+
+fn main() -> dialog::Result<()> {
+    let mut backend = backends::KDialog::new();
+
+    dialog::Message::new("This is a message.")
+        .title("And this is a title:")
+        .show_with(&backend)?;
+
+    backend.set_icon("error");
+    dialog::Message::new("This is an error message.")
+        .title("Error")
+        .show_with(&backend)
+}
diff --git a/src/backends/kdialog.rs b/src/backends/kdialog.rs
new file mode 100644
index 0000000..153e4c5
--- /dev/null
+++ b/src/backends/kdialog.rs
@@ -0,0 +1,143 @@
+// Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
+// Copyright (C) 2019 Stephan Sokolow <http://www.ssokolow.com/ContactMe>
+// SPDX-License-Identifier: MIT
+
+use std::process;
+
+use crate::{Choice, Error, Input, Message, Password, Question, Result};
+
+/// Subprocess exit codes
+///
+/// Note: `kdialog` doesn't have a fixed correspondence between button labels and status codes.
+/// The following mappings occur:
+///
+/// - Yes/No = `0`/`1`
+/// - Yes/No/Cancel = `0`/`1`/`2`
+/// - OK/Cancel = `0`/`1`
+const OK: i32 = 0;
+const CANCEL: i32 = 1;
+
+/// The `kdialog` backend.
+///
+/// This backend uses the external `kdialog` program to display KDE dialog boxes.
+#[derive(Debug)]
+pub struct KDialog {
+    icon: Option<String>,
+    // TODO: --dontagain
+}
+
+impl KDialog {
+    /// Creates a new `KDialog` instance without configuration.
+    pub fn new() -> KDialog {
+        KDialog { icon: None }
+    }
+
+    /// Sets the icon in the dialog box's titlebar and taskbar button.
+    ///
+    /// The icon can be either a name from the user's configured icon theme, such as `error` or
+    /// `info` or the path to an image to use.
+    ///
+    /// The default image depends on the dialog type.
+    pub fn set_icon(&mut self, icon: impl Into<String>) {
+        self.icon = Some(icon.into());
+    }
+
+    pub(crate) fn is_available() -> bool {
+        super::is_available("kdialog")
+    }
+
+    fn execute(&self, args: Vec<&str>, title: &Option<String>) -> Result<process::Output> {
+        let mut command = process::Command::new("kdialog");
+
+        if let Some(ref icon) = self.icon {
+            command.arg("--icon");
+            command.arg(icon);
+        }
+        if let Some(ref title) = title {
+            command.arg("--title");
+            command.arg(title);
+        }
+
+        command.args(args);
+        command.output().map_err(Error::IoError)
+    }
+}
+
+impl AsRef<KDialog> for KDialog {
+    fn as_ref(&self) -> &Self {
+        self
+    }
+}
+
+fn require_success(status: process::ExitStatus) -> Result<()> {
+    if status.success() {
+        Ok(())
+    } else {
+        if let Some(code) = status.code() {
+            match code {
+                CANCEL => Ok(()),
+                _ => Err(Error::from(("kdialog", status))),
+            }
+        } else {
+            Err(Error::from(("kdialog", status)))
+        }
+    }
+}
+
+fn get_choice(status: process::ExitStatus) -> Result<Choice> {
+    if let Some(code) = status.code() {
+        match code {
+            OK => Ok(Choice::Yes),
+            CANCEL => Ok(Choice::No),
+            _ => Err(Error::from(("kdialog", status))),
+        }
+    } else {
+        Err(Error::from(("kdialog", status)))
+    }
+}
+
+fn get_stdout(output: process::Output) -> Result<Option<String>> {
+    if output.status.success() {
+        String::from_utf8(output.stdout)
+            .map(|s| Some(s.trim_end_matches('\n').to_string()))
+            .map_err(|err| Error::from(err))
+    } else {
+        if let Some(code) = output.status.code() {
+            match code {
+                OK => Ok(None),
+                CANCEL => Ok(None),
+                _ => Err(Error::from(("kdialog", output.status))),
+            }
+        } else {
+            Err(Error::from(("kdialog", output.status)))
+        }
+    }
+}
+
+impl super::Backend for KDialog {
+    fn show_input(&self, input: &Input) -> Result<Option<String>> {
+        let mut args = vec!["--inputbox", &input.text];
+        if let Some(ref default) = input.default {
+            args.push(default);
+        }
+        self.execute(args, &input.title).and_then(get_stdout)
+    }
+
+    fn show_message(&self, message: &Message) -> Result<()> {
+        let args = vec!["--msgbox", &message.text];
+        self.execute(args, &message.title)
+            .and_then(|output| require_success(output.status))
+            .map(|_| ())
+    }
+
+    fn show_password(&self, password: &Password) -> Result<Option<String>> {
+        let args = vec!["--password", &password.text];
+        self.execute(args, &password.title).and_then(get_stdout)
+    }
+
+    fn show_question(&self, question: &Question) -> Result<Choice> {
+        let args = vec!["--yesno", &question.text];
+        self.execute(args, &question.title)
+            .and_then(|output| get_choice(output.status))
+    }
+}
diff --git a/src/backends/mod.rs b/src/backends/mod.rs
index 5ae3cef..d5dac1c 100644
--- a/src/backends/mod.rs
+++ b/src/backends/mod.rs
@@ -2,10 +2,12 @@
 // SPDX-License-Identifier: MIT
 
 mod dialog;
+mod kdialog;
 mod stdio;
 mod zenity;
 
 pub use crate::backends::dialog::Dialog;
+pub use crate::backends::kdialog::KDialog;
 pub use crate::backends::stdio::Stdio;
 pub use crate::backends::zenity::Zenity;
 
@@ -51,6 +53,7 @@ pub(crate) fn is_available(name: &str) -> bool {
 pub(crate) fn from_str(s: &str) -> Option<Box<dyn Backend>> {
     match s.to_lowercase().as_ref() {
         "dialog" => Some(Box::new(Dialog::new())),
+        "kdialog" => Some(Box::new(KDialog::new())),
         "stdio" => Some(Box::new(Stdio::new())),
         "zenity" => Some(Box::new(Zenity::new())),
         _ => None,
diff --git a/src/lib.rs b/src/lib.rs
index f4ac763..61be22b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -15,6 +15,8 @@
 //! These dialog boxes can be displayed using various backends:
 //! - [`Dialog`][]: uses `dialog` to display ncurses-based dialog boxes (requires the external
 //!   `dialog` tool)
+//! - [`KDialog`][]: uses `kdialog` to display Qt-based dialog boxes (requires the external
+//!   `kdialog` tool)
 //! - [`Stdio`][]: prints messages to the standard output and reads user input form standard input
 //!   (intended as a fallback backend)
 //! - [`Zenity`][]: uses `zenity` to display GTK-based dialog boxes (requires the external `zenity`
@@ -72,6 +74,7 @@
 //! [`Message`]: struct.Message.html
 //! [`Password`]: struct.Password.html
 //! [`Question`]: struct.Question.html
+//! [`KDialog`]: backends/struct.KDialog.html
 //! [`Stdio`]: backends/struct.Stdio.html
 //! [`Zenity`]: backends/struct.Zenity.html
 //! [`default_backend`]: fn.default_backend.html
@@ -345,13 +348,16 @@ impl DialogBox for Question {
 /// - If the `DIALOG` environment variable is set to a valid backend name, this backend is used.
 ///   A valid backend name is the name of a struct in the `backends` module implementing the
 ///   `Backend` trait in any case.
-/// - If the `DISPLAY` environment variable is set, the first available backend from this list is
-///   used:
-///   - [`Zenity`][]
+/// - If the `DISPLAY` environment variable is set, the following resolution algorithm is used:
+///   - If the `XDG_CURRENT_DESKTOP` environment variable is set to `KDE`, [`KDialog`][] is used.
+///   - Otherwise, the first available backend from this list is used:
+///     - [`Zenity`][]
+///     - [`KDialog`][]
 /// - If the [`Dialog`][] backend is available, it is used.
 /// - Otherwise, a [`Stdio`][] instance is returned.
 ///
 /// [`Dialog`]: backends/struct.Dialog.html
+/// [`KDialog`]: backends/struct.KDialog.html
 /// [`Stdio`]: backends/struct.Stdio.html
 /// [`Zenity`]: backends/struct.Zenity.html
 pub fn default_backend() -> Box<dyn backends::Backend> {
@@ -363,9 +369,21 @@ pub fn default_backend() -> Box<dyn backends::Backend> {
 
     if let Ok(display) = env::var("DISPLAY") {
         if !display.is_empty() {
+            // Prefer KDialog if the user is logged into a KDE session
+            let kdialog_available = backends::KDialog::is_available();
+            if let Ok(desktop) = env::var("XDG_CURRENT_DESKTOP") {
+                if kdialog_available && desktop == "KDE" {
+                    return Box::new(backends::KDialog::new());
+                }
+            }
+
             if backends::Zenity::is_available() {
                 return Box::new(backends::Zenity::new());
             }
+
+            if kdialog_available {
+                return Box::new(backends::KDialog::new());
+            }
         }
     }