Fix stdin references.

Refactored the POSIX piped input handling to avoid redirecting stdin.
Instead, it now directly opens and reads from /dev/tty for keyboard input
when stdin is piped, allowing applications to process piped data while
still receiving interactive keyboard events.

This addresses the TODO comment in ScreenInteractive::InstallPipedInputHandling().

.gitignore

@@ -44,6 +44,7 @@ out/
 !doc/**/*.html
 !doc/**/*.xml
 !doc/**/*.md
+!doc/*.md
 
 # examples directory:
 !examples/**/*.cpp

BUILD.bazel

@@ -169,13 +169,15 @@ ftxui_cc_library(
         "src/ftxui/component/util.cpp",
         "src/ftxui/component/window.cpp",
 
-
         # Private header from ftxui:dom.
         "src/ftxui/dom/node_decorator.hpp",
 
         # Private header from ftxui:screen.
         "src/ftxui/screen/string_internal.hpp",
         "src/ftxui/screen/util.hpp",
+
+        # Private header.
+        "include/ftxui/util/warn_windows_macro.hpp",
     ],
     hdrs = [
         "include/ftxui/component/animation.hpp",

CHANGELOG.md

@@ -27,6 +27,12 @@ Next
 - Remove dependency on 'pthread'.
 
 ### Component
+- Feature: POSIX Piped Input Handling.
+  - Allows FTXUI applications to read data from stdin (when piped) while still receiving keyboard input from the terminal.
+  - Enabled by default.
+  - Can be disabled using `ScreenInteractive::HandlePipedInput(false)`.
+  - Only available on Linux and macOS.
+  Thanks @HarryPehkonen for PR #1094.
 - Fix ScreenInteractive::FixedSize screen stomps on the preceding terminal
   output. Thanks @zozowell in #1064.
 

README.md

@@ -378,21 +378,7 @@ Several games using the FTXUI have been made during the Game Jam:
 - [smoothlife](https://github.com/cpp-best-practices/game_jam/blob/main/Jam1_April_2022/smoothlife.md)
 - [Consu](https://github.com/cpp-best-practices/game_jam/blob/main/Jam1_April_2022/consu.md)
 
-## Advanced Usage
 
-### Piped Input Support
-
-If your application reads from stdin (piped data) and also needs interactive keyboard input:
-
-```cpp
-auto screen = ScreenInteractive::Fullscreen();
-screen.HandlePipedInput(true);  // Enable before Loop()
-screen.Loop(component);
-```
-
-This allows commands like `cat data.txt | your_app` to work with full keyboard interaction.
-
-**Note:** This feature is only available on POSIX systems (Linux/macOS). On Windows, the method call is a no-op.
 
 ## Build using CMake
 

doc/posix_pipe.md

@@ -0,0 +1,58 @@
+# POSIX Piped Input in FTXUI
+
+> [!WARNING]
+> This feature works only on Linux and macOS. It is not supported on
+> Windows and WebAssembly.
+
+## What is a POSIX Pipe?
+
+A POSIX pipe is a way for two separate programs to communicate. One program sends its output directly as input to another program. Think of it like a one-way tube for data.
+
+**Example:**
+
+Imagine you want to list files and then filter them interactively.
+
+- `ls`: Lists files.
+- `interactive_grep`: An FTXUI application that filters text and lets you type.
+
+You can connect them with a pipe (`|`):
+
+```bash
+ls -l | interactive_grep
+```
+
+Here's what happens:
+1. `ls -l` lists files with details.
+2. The `|` sends this list directly to `interactive_grep`.
+3. `interactive_grep` receives the list and displays it. Because it's an FTXUI app, you can then type to filter the list, even though it received initial data from `ls`.
+
+## How FTXUI Handles Piped Input
+
+Now that you understand what a POSIX pipe is, let's look at how FTXUI uses them.
+
+FTXUI lets your application read data from other programs (like from a pipe) while still allowing you to use your keyboard for interaction. This is useful for interactive command-line tools that process data.
+
+Normally, FTXUI applications receive all input from `stdin`. However, when FTXUI detects that `stdin` is connected to the output of a pipe (meaning data is being piped into your application), it automatically switches to reading interactive keyboard input from `/dev/tty`. This ensures that your application can still receive user input even while processing piped data.
+
+This feature is **turned on by default**.
+
+If your FTXUI application needs to read piped data and also respond to keyboard input, you typically don't need to do anything special:
+
+```cpp
+auto screen = ScreenInteractive::Fullscreen();
+// screen.HandlePipedInput(true); // This is enabled by default
+screen.Loop(component);
+```
+
+
+## Turning Off Piped Input
+
+If you don't need this feature, or if it conflicts with your custom input handling, you can turn it off.
+
+To disable it, call `HandlePipedInput(false)` before starting your application's main loop:
+
+```cpp
+auto screen = ScreenInteractive::Fullscreen();
+screen.HandlePipedInput(false); // Turn off piped input handling
+screen.Loop(component);
+```

include/ftxui/component/screen_interactive.hpp

@@ -43,7 +43,7 @@ class ScreenInteractive : public Screen {
   static ScreenInteractive TerminalOutput();
 
   // Destructor.
-  ~ScreenInteractive();
+  ~ScreenInteractive() override;
 
   // Options. Must be called before Loop().
   void TrackMouse(bool enable = true);
@@ -101,6 +101,8 @@ class ScreenInteractive : public Screen {
   void Draw(Component component);
   void ResetCursorPosition();
 
+  void InstallPipedInputHandling();
+
   void Signal(int signal);
 
   void FetchTerminalEvents();
@@ -118,6 +120,7 @@ class ScreenInteractive : public Screen {
                     int dimx,
                     int dimy,
                     bool use_alternative_screen);
+
   const Dimension dimension_;
   const bool use_alternative_screen_;
 
@@ -142,12 +145,10 @@ class ScreenInteractive : public Screen {
   bool force_handle_ctrl_c_ = true;
   bool force_handle_ctrl_z_ = true;
 
-#if !defined(_WIN32) && !defined(__EMSCRIPTEN__)
   // Piped input handling state (POSIX only)
-  bool handle_piped_input_ = false;
-  bool stdin_was_redirected_ = false;
-  int original_stdin_fd_ = -1;
-#endif
+  bool handle_piped_input_ = true;
+  // File descriptor for /dev/tty, used for piped input handling.
+  int tty_fd_ = -1;
 
   // The style of the cursor to restore on exit.
   int cursor_reset_shape_ = 1;

src/ftxui/component/screen_interactive.cpp

@@ -112,13 +112,13 @@ void ftxui_on_resize(int columns, int rows) {
 
 #else  // POSIX (Linux & Mac)
 
-int CheckStdinReady() {
+int CheckStdinReady(int fd) {
   timeval tv = {0, 0};  // NOLINT
   fd_set fds;
   FD_ZERO(&fds);                                          // NOLINT
-  FD_SET(STDIN_FILENO, &fds);                             // NOLINT
-  select(STDIN_FILENO + 1, &fds, nullptr, nullptr, &tv);  // NOLINT
-  return FD_ISSET(STDIN_FILENO, &fds);                    // NOLINT
+  FD_SET(fd, &fds);                             // NOLINT
+  select(fd + 1, &fds, nullptr, nullptr, &tv);  // NOLINT
+  return FD_ISSET(fd, &fds);                    // NOLINT
 }
 
 #endif
@@ -373,22 +373,16 @@ void ScreenInteractive::TrackMouse(bool enable) {
 }
 
 /// @brief Enable or disable automatic piped input handling.
-/// When enabled, FTXUI will detect piped input and redirect stdin to /dev/tty
+/// When enabled, FTXUI will detect piped input and redirect stdin from /dev/tty
 /// for keyboard input, allowing applications to read piped data while still
 /// receiving interactive keyboard events.
-/// @param enable Whether to enable piped input handling
+/// @param enable Whether to enable piped input handling. Default is true.
 /// @note This must be called before Loop().
-/// @note This feature is disabled by default for backward compatibility.
+/// @note This feature is enabled by default.
 /// @note This feature is only available on POSIX systems (Linux/macOS).
-#if !defined(_WIN32) && !defined(__EMSCRIPTEN__)
 void ScreenInteractive::HandlePipedInput(bool enable) {
   handle_piped_input_ = enable;
 }
-#else
-void ScreenInteractive::HandlePipedInput(bool /*enable*/) {
-  // This feature is not supported on this platform.
-}
-#endif
 
 /// @brief Add a task to the main loop.
 /// It will be executed later, after every other scheduled tasks.
@@ -545,6 +539,8 @@ void ScreenInteractive::Install() {
   // https://github.com/ArthurSonzogni/FTXUI/issues/846
   Flush();
 
+  InstallPipedInputHandling();
+
   // After uninstalling the new configuration, flush it to the terminal to
   // ensure it is fully applied:
   on_exit_functions.emplace([] { Flush(); });
@@ -610,9 +606,10 @@ void ScreenInteractive::Install() {
   }
 
   struct termios terminal;  // NOLINT
-  tcgetattr(STDIN_FILENO, &terminal);
-  on_exit_functions.emplace(
-      [=] { tcsetattr(STDIN_FILENO, TCSANOW, &terminal); });
+  tcgetattr(tty_fd_, &terminal);
+  on_exit_functions.emplace([terminal = terminal, tty_fd_ = tty_fd_] {
+    tcsetattr(tty_fd_, TCSANOW, &terminal);
+  });
 
   // Enabling raw terminal input mode
   terminal.c_iflag &= ~IGNBRK;  // Disable ignoring break condition
@@ -640,7 +637,7 @@ void ScreenInteractive::Install() {
                              // read.
   terminal.c_cc[VTIME] = 0;  // Timeout in deciseconds for non-canonical read.
 
-  tcsetattr(STDIN_FILENO, TCSANOW, &terminal);
+  tcsetattr(tty_fd_, TCSANOW, &terminal);
 
 #endif
 
@@ -676,47 +673,45 @@ void ScreenInteractive::Install() {
   // ensure it is fully applied:
   Flush();
 
-#if !defined(_WIN32) && !defined(__EMSCRIPTEN__)
-  // Handle piped input redirection if explicitly enabled by the application.
-  // This allows applications to read data from stdin while still receiving
-  // keyboard input from the terminal for interactive use.
-  if (handle_piped_input_ && !stdin_was_redirected_ && !isatty(STDIN_FILENO)) {
-    // Save the current stdin so we can restore it later
-    original_stdin_fd_ = dup(STDIN_FILENO);
-    if (original_stdin_fd_ >= 0) {
-      // Redirect stdin to the controlling terminal for keyboard input
-      if (freopen("/dev/tty", "r", stdin) != nullptr) {
-        stdin_was_redirected_ = true;
-      } else {
-        // Failed to open /dev/tty (containers, headless systems, etc.)
-        // Clean up and continue without redirection
-        close(original_stdin_fd_);
-        original_stdin_fd_ = -1;
-      }
-    }
-    // If dup() failed, we silently continue without redirection
-  }
-#endif
-
   quit_ = false;
 
   PostAnimationTask();
 }
 
+void ScreenInteractive::InstallPipedInputHandling() {
+  tty_fd_ = fileno(stdin);  // NOLINT
+#if !defined(_WIN32) && !defined(__EMSCRIPTEN__)
+  // Handle piped input redirection if explicitly enabled by the application.
+  // This allows applications to read data from stdin while still receiving
+  // keyboard input from the terminal for interactive use.
+  if (!handle_piped_input_) {
+    return;
+  }
+
+  // If stdin is a terminal, we don't need to open /dev/tty.
+  if (isatty(fileno(stdin))) {
+    return;
+  }
+
+  // Open /dev/tty for keyboard input.
+  tty_fd_ = open("/dev/tty", O_RDONLY);
+  if (tty_fd_ < 0) {
+    // Failed to open /dev/tty (containers, headless systems, etc.)
+    tty_fd_ = fileno(stdin);  // Fallback to stdin.
+    return;
+  }
+
+  // Close the /dev/tty file descriptor on exit.
+  on_exit_functions.emplace([this] {
+    close(tty_fd_);
+    tty_fd_ = -1;
+  });
+#endif
+}
+
 // private
 void ScreenInteractive::Uninstall() {
   ExitNow();
-  
-#if !defined(_WIN32) && !defined(__EMSCRIPTEN__)
-  // Restore stdin to its original state if we redirected it
-  if (stdin_was_redirected_ && original_stdin_fd_ >= 0) {
-    dup2(original_stdin_fd_, STDIN_FILENO);
-    close(original_stdin_fd_);
-    original_stdin_fd_ = -1;
-    stdin_was_redirected_ = false;
-  }
-#endif
-  
   OnExit();
 }
 
@@ -1147,7 +1142,7 @@ void ScreenInteractive::FetchTerminalEvents() {
     internal_->terminal_input_parser.Add(out[i]);
   }
 #else  // POSIX (Linux & Mac)
-  if (!CheckStdinReady()) {
+  if (!CheckStdinReady(tty_fd_)) {
     const auto timeout =
         std::chrono::steady_clock::now() - internal_->last_char_time;
     const size_t timeout_ms =
@@ -1159,7 +1154,7 @@ void ScreenInteractive::FetchTerminalEvents() {
 
   // Read chars from the terminal.
   std::array<char, 128> out{};
-  size_t l = read(fileno(stdin), out.data(), out.size());
+  size_t l = read(tty_fd_, out.data(), out.size());
 
   // Convert the chars to events.
   for (size_t i = 0; i < l; ++i) {

src/ftxui/component/screen_interactive_piped_input_test.cpp

@@ -63,19 +63,23 @@ class PipedInputTest : public ::testing::Test {
   bool piped_stdin_setup_ = false;
 };
 
-TEST_F(PipedInputTest, DefaultBehaviorNoChange) {
-  // Test that HandlePipedInput is disabled by default
+TEST_F(PipedInputTest, DefaultBehaviorEnabled) {
+  // Test that HandlePipedInput is enabled by default
+  if (!IsTtyAvailable()) {
+    GTEST_SKIP() << "/dev/tty not available in this environment";
+  }
+
   auto screen = ScreenInteractive::TerminalOutput();
   auto component = Renderer([] { return text("test"); });
 
   SetupPipedStdin();
   WriteToPipedStdin("test data\n");
 
-  // Install should not redirect stdin since HandlePipedInput not called
+  // Install should redirect stdin since HandlePipedInput is on by default
   screen.Install();
 
-  // Stdin should still be the pipe (isatty should return false)
-  EXPECT_FALSE(isatty(STDIN_FILENO));
+  // Stdin should be the tty
+  EXPECT_TRUE(isatty(STDIN_FILENO));
 
   screen.Uninstall();
 }
@@ -97,7 +101,7 @@ TEST_F(PipedInputTest, ExplicitlyDisabled) {
   screen.Uninstall();
 }
 
-TEST_F(PipedInputTest, PipedInputDetectionAndRedirection) {
+TEST_F(PipedInputTest, ExplicitlyEnabled) {
   if (!IsTtyAvailable()) {
     GTEST_SKIP() << "/dev/tty not available in this environment";
   }
@@ -127,7 +131,6 @@ TEST_F(PipedInputTest, PipedInputDetectionAndRedirection) {
 TEST_F(PipedInputTest, NormalStdinUnchanged) {
   // Test that normal stdin (not piped) is not affected
   auto screen = ScreenInteractive::TerminalOutput();
-  screen.HandlePipedInput(true);
   auto component = Renderer([] { return text("test"); });
 
   // Don't setup piped stdin - use normal stdin
@@ -150,7 +153,6 @@ TEST_F(PipedInputTest, MultipleInstallUninstallCycles) {
   }
 
   auto screen = ScreenInteractive::TerminalOutput();
-  screen.HandlePipedInput(true);
   auto component = Renderer([] { return text("test"); });
 
   SetupPipedStdin();
@@ -192,7 +194,6 @@ TEST_F(PipedInputTest, HandlePipedInputMethodBehavior) {
 // This test simulates environments like containers where /dev/tty might not exist
 TEST_F(PipedInputTest, GracefulFallbackWhenTtyUnavailable) {
   auto screen = ScreenInteractive::TerminalOutput();
-  screen.HandlePipedInput(true);
   auto component = Renderer([] { return text("test"); });
 
   SetupPipedStdin();