Tweak implementation and documentation.

Enables applications to read piped data while maintaining interactive
keyboard input by redirecting stdin to /dev/tty when explicitly enabled.

.gitignore

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

README.md

@@ -378,6 +378,8 @@ 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)
 
+
+
 ## Build using CMake
 
 It is **highly** recommended to use CMake FetchContent to depend on FTXUI so you may specify which commit you would like to depend on.

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

@@ -43,10 +43,11 @@ class ScreenInteractive : public Screen {
   static ScreenInteractive TerminalOutput();
 
   // Destructor.
-  ~ScreenInteractive();
+  ~ScreenInteractive() override;
 
   // Options. Must be called before Loop().
   void TrackMouse(bool enable = true);
+  void HandlePipedInput(bool enable = true);
 
   // Return the currently active screen, nullptr if none.
   static ScreenInteractive* Active();
@@ -100,6 +101,8 @@ class ScreenInteractive : public Screen {
   void Draw(Component component);
   void ResetCursorPosition();
 
+  void InstallPipedInputHandling();
+
   void Signal(int signal);
 
   void FetchTerminalEvents();
@@ -117,6 +120,7 @@ class ScreenInteractive : public Screen {
                     int dimx,
                     int dimy,
                     bool use_alternative_screen);
+
   const Dimension dimension_;
   const bool use_alternative_screen_;
 
@@ -141,6 +145,9 @@ class ScreenInteractive : public Screen {
   bool force_handle_ctrl_c_ = true;
   bool force_handle_ctrl_z_ = true;
 
+  // Piped input handling state (POSIX only)
+  bool handle_piped_input_ = true;
+
   // The style of the cursor to restore on exit.
   int cursor_reset_shape_ = 1;
 

src/ftxui/component/screen_interactive.cpp

@@ -372,6 +372,18 @@ void ScreenInteractive::TrackMouse(bool enable) {
   track_mouse_ = enable;
 }
 
+/// @brief Enable or disable automatic piped input handling.
+/// 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. Default is true.
+/// @note This must be called before Loop().
+/// @note This feature is enabled by default.
+/// @note This feature is only available on POSIX systems (Linux/macOS).
+void ScreenInteractive::HandlePipedInput(bool enable) {
+  handle_piped_input_ = enable;
+}
+
 /// @brief Add a task to the main loop.
 /// It will be executed later, after every other scheduled tasks.
 void ScreenInteractive::Post(Task task) {
@@ -658,11 +670,55 @@ void ScreenInteractive::Install() {
   // ensure it is fully applied:
   Flush();
 
+  // Redirect the true terminal to stdin, so that we can read keyboard input
+  // directly from stdin, even if the input is piped from a file or another
+  // process.
+  //
+  // TODO: Instead of redirecting stdin, we could define the file descriptor to
+  // read from, and use it in the TerminalInputParser.
+  InstallPipedInputHandling();
+
   quit_ = false;
 
   PostAnimationTask();
 }
 
+void ScreenInteractive::InstallPipedInputHandling() {
+#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 redirect it.
+  if (isatty(STDIN_FILENO)) {
+    return;
+  }
+
+  // Save the current stdin so we can restore it later.
+  int original_fd = dup(STDIN_FILENO);
+  if (original_fd < 0) {
+    return;
+  }
+
+  // Redirect stdin to the controlling terminal for keyboard input.
+  if (std::freopen("/dev/tty", "r", stdin) == nullptr) {
+    // Failed to open /dev/tty (containers, headless systems, etc.)
+    // Clean up and continue without redirection
+    close(original_fd);
+    return;
+  }
+
+  // Restore the original stdin file descriptor on exit.
+  on_exit_functions.emplace([=] {
+    dup2(original_fd, STDIN_FILENO);
+    close(original_fd);
+  });
+#endif
+}
+
 // private
 void ScreenInteractive::Uninstall() {
   ExitNow();

src/ftxui/component/screen_interactive_piped_input_test.cpp

@@ -0,0 +1,220 @@
+// Copyright 2025 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+#include <gtest/gtest.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <cstdio>
+#include <sys/stat.h>
+
+#include "ftxui/component/component.hpp"
+#include "ftxui/component/screen_interactive.hpp"
+#include "ftxui/dom/elements.hpp"
+
+#if !defined(_WIN32) && !defined(__EMSCRIPTEN__)
+
+namespace ftxui {
+
+namespace {
+
+// Test fixture for piped input functionality
+class PipedInputTest : public ::testing::Test {
+ protected:
+  void SetUp() override {
+    // Save original stdin for restoration
+    original_stdin_ = dup(STDIN_FILENO);
+  }
+
+  void TearDown() override {
+    // Restore original stdin
+    if (original_stdin_ >= 0) {
+      dup2(original_stdin_, STDIN_FILENO);
+      close(original_stdin_);
+    }
+  }
+
+  // Create a pipe and redirect stdin to read from it
+  void SetupPipedStdin() {
+    if (pipe(pipe_fds_) == 0) {
+      dup2(pipe_fds_[0], STDIN_FILENO);
+      close(pipe_fds_[0]);
+      // Keep write end open for writing test data
+      piped_stdin_setup_ = true;
+    }
+  }
+
+  // Write test data to the piped stdin
+  void WriteToPipedStdin(const std::string& data) {
+    if (piped_stdin_setup_) {
+      write(pipe_fds_[1], data.c_str(), data.length());
+      close(pipe_fds_[1]); // Close write end to signal EOF
+    }
+  }
+
+  // Check if /dev/tty is available (not available in some CI environments)
+  bool IsTtyAvailable() {
+    struct stat st;
+    return stat("/dev/tty", &st) == 0;
+  }
+
+ private:
+  int original_stdin_ = -1;
+  int pipe_fds_[2] = {-1, -1};
+  bool piped_stdin_setup_ = false;
+};
+
+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 redirect stdin since HandlePipedInput is on by default
+  screen.Install();
+
+  // Stdin should be the tty
+  EXPECT_TRUE(isatty(STDIN_FILENO));
+
+  screen.Uninstall();
+}
+
+TEST_F(PipedInputTest, ExplicitlyDisabled) {
+  // Test that explicitly disabling works
+  auto screen = ScreenInteractive::TerminalOutput();
+  screen.HandlePipedInput(false);
+  auto component = Renderer([] { return text("test"); });
+
+  SetupPipedStdin();
+  WriteToPipedStdin("test data\n");
+
+  screen.Install();
+  
+  // Stdin should still be the pipe since feature is disabled
+  EXPECT_FALSE(isatty(STDIN_FILENO));
+  
+  screen.Uninstall();
+}
+
+TEST_F(PipedInputTest, ExplicitlyEnabled) {
+  if (!IsTtyAvailable()) {
+    GTEST_SKIP() << "/dev/tty not available in this environment";
+  }
+
+  auto screen = ScreenInteractive::TerminalOutput();
+  screen.HandlePipedInput(true); // Explicitly enable
+  auto component = Renderer([] { return text("test"); });
+
+  SetupPipedStdin();
+  WriteToPipedStdin("test data\n");
+
+  // Before install: stdin should be piped
+  EXPECT_FALSE(isatty(STDIN_FILENO));
+
+  screen.Install();
+  
+  // After install with piped input handling: stdin should be redirected to tty
+  EXPECT_TRUE(isatty(STDIN_FILENO));
+  
+  screen.Uninstall();
+  
+  // After uninstall: stdin should be restored to original state
+  // Note: This will be the pipe we set up, so it should be non-tty
+  EXPECT_FALSE(isatty(STDIN_FILENO));
+}
+
+TEST_F(PipedInputTest, NormalStdinUnchanged) {
+  // Test that normal stdin (not piped) is not affected
+  auto screen = ScreenInteractive::TerminalOutput();
+  auto component = Renderer([] { return text("test"); });
+
+  // Don't setup piped stdin - use normal stdin
+  bool original_isatty = isatty(STDIN_FILENO);
+
+  screen.Install();
+  
+  // Stdin should remain unchanged
+  EXPECT_EQ(original_isatty, isatty(STDIN_FILENO));
+  
+  screen.Uninstall();
+  
+  // Stdin should still be unchanged
+  EXPECT_EQ(original_isatty, isatty(STDIN_FILENO));
+}
+
+TEST_F(PipedInputTest, MultipleInstallUninstallCycles) {
+  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");
+
+  // First cycle
+  screen.Install();
+  EXPECT_TRUE(isatty(STDIN_FILENO));
+  screen.Uninstall();
+  EXPECT_FALSE(isatty(STDIN_FILENO));
+
+  // Second cycle should work the same
+  screen.Install();
+  EXPECT_TRUE(isatty(STDIN_FILENO));
+  screen.Uninstall();
+  EXPECT_FALSE(isatty(STDIN_FILENO));
+}
+
+TEST_F(PipedInputTest, HandlePipedInputMethodBehavior) {
+  auto screen = ScreenInteractive::TerminalOutput();
+  
+  // Test method can be called multiple times
+  screen.HandlePipedInput(true);
+  screen.HandlePipedInput(false);
+  screen.HandlePipedInput(true);
+  
+  // Should be enabled after last call
+  SetupPipedStdin();
+  WriteToPipedStdin("test data\n");
+
+  if (IsTtyAvailable()) {
+    screen.Install();
+    EXPECT_TRUE(isatty(STDIN_FILENO));
+    screen.Uninstall();
+  }
+}
+
+// Test the graceful fallback when /dev/tty is not available
+// This test simulates environments like containers where /dev/tty might not exist
+TEST_F(PipedInputTest, GracefulFallbackWhenTtyUnavailable) {
+  auto screen = ScreenInteractive::TerminalOutput();
+  auto component = Renderer([] { return text("test"); });
+
+  SetupPipedStdin();
+  WriteToPipedStdin("test data\n");
+
+  // This test doesn't directly mock /dev/tty unavailability since that's hard to do
+  // in a unit test environment, but the code path handles freopen() failure gracefully
+  screen.Install();
+  
+  // The behavior depends on whether /dev/tty is available
+  // If available, stdin gets redirected; if not, it remains piped
+  // Both behaviors are correct
+  
+  screen.Uninstall();
+  
+  // After uninstall, stdin should be restored
+  EXPECT_FALSE(isatty(STDIN_FILENO)); // Should still be our test pipe
+}
+
+}  // namespace
+
+}  // namespace ftxui
+
+#endif  // !defined(_WIN32) && !defined(__EMSCRIPTEN__)