Is terminal a tty and reverted feature from 0.17 which introduced a bug. (#405)

CHANGELOG.md

@@ -1,3 +1,7 @@
+# Version 0.17.1
+- Reverted bug in 0.17.0: "Make terminal size function fallback to `STDOUT_FILENO` if `/dev/tty` is missing.".
+- Support for querying whether the current instance is a TTY.
+
 # Version 0.17
 - Impl Display for MoveToColumn, MoveToNextLine, MoveToPreviousLine
 - Make unix event reader always use `/dev/tty`.

README.md

@@ -35,6 +35,7 @@ see [Tested Terminals](#tested-terminals) for more info).
 - Detailed documentation
 - Few dependencies
 - Full control over writing and flushing output buffer
+- Is tty
 - Cursor 
     - Move the cursor N times (up, down, left, right)
     - Move to previous / next line
@@ -139,7 +140,7 @@ To optional feature flags.
 
 ```toml
 [dependencies.crossterm]
-version = "0.14"
+version = "0.17"
 features = ["event-stream"] 
 ```
 

examples/README.md

@@ -16,7 +16,8 @@ The examples are compatible with the latest release.
 | :------- | :------- | :------- |
 | `examples/interactive-test` | interactive, walk trough, demo | cursor, style, event
 | `event-*`| event reading demos | (async) event reading
-| `stderr` | crossterm over stderr demo, | raw mode, alternate screen, custom output
+| `stderr` | crossterm over stderr demo | raw mode, alternate screen, custom output
+| `is_tty` | Is this instance a tty ? | tty |
 
 ## Run examples
 

examples/is_tty.rs

@@ -0,0 +1,10 @@
+use crossterm::tty::IsTty;
+use std::io::stdin;
+
+pub fn main() {
+    if stdin().is_tty() {
+        println!("Is TTY");
+    } else {
+        println!("Is not TTY");
+    }
+}

src/event/sys/unix/file_descriptor.rs

@@ -65,14 +65,18 @@ impl Drop for FileDesc {
 
 /// Creates a file descriptor pointing to the standard input or `/dev/tty`.
 pub fn tty_fd() -> Result<FileDesc> {
-    let (fd, close_on_drop) = (
+    let (fd, close_on_drop) = if unsafe { libc::isatty(libc::STDIN_FILENO) == 1 } {
+        (libc::STDIN_FILENO, false)
+    } else {
+        (
             fs::OpenOptions::new()
                 .read(true)
                 .write(true)
                 .open("/dev/tty")?
                 .into_raw_fd(),
             true,
-    );
+        )
+    };
 
     Ok(FileDesc::new(fd, close_on_drop))
 }

src/lib.rs

@@ -242,6 +242,9 @@ pub mod style;
 /// A module to work with the terminal.
 pub mod terminal;
 
+/// A module to query if the current instance is a tty.
+pub mod tty;
+
 mod ansi;
 #[cfg(windows)]
 pub(crate) mod ansi_support;

src/tty.rs

@@ -0,0 +1,38 @@
+//! Making it a little more convenient and safe to query whether
+//! something is a terminal teletype or not.
+//! This module defines the IsTty trait and the is_tty method to
+//! return true if the item represents a terminal.
+
+#[cfg(unix)]
+use std::os::unix::io::AsRawFd;
+#[cfg(windows)]
+use std::os::windows::io::AsRawHandle;
+#[cfg(windows)]
+use winapi::um::consoleapi::GetConsoleMode;
+
+/// Adds the `is_tty` method to types that might represent a terminal
+pub trait IsTty {
+    /// Returns true when an instance is a terminal teletype, otherwise false.
+    fn is_tty(&self) -> bool;
+}
+
+/// On unix, the `isatty()` function returns true if a file
+/// descriptor is a terminal.
+#[cfg(unix)]
+impl<S: AsRawFd> IsTty for S {
+    fn is_tty(&self) -> bool {
+        let fd = self.as_raw_fd();
+        unsafe { libc::isatty(fd) == 1 }
+    }
+}
+
+/// On windows, `GetConsoleMode` will return true if we are in a terminal.
+/// Otherwise false.
+#[cfg(windows)]
+impl<S: AsRawHandle> IsTty for S {
+    fn is_tty(&self) -> bool {
+        let mut mode = 0;
+        let ok = unsafe { GetConsoleMode(self.as_raw_handle() as *mut _, &mut mode) };
+        ok == 1
+    }
+}