Merge a6612eda35 into 346f751527

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

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.
 - Fix vertical `ftxui::Slider`. The "up" key was previously decreasing the

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/receiver.hpp

@@ -4,7 +4,6 @@
 #ifndef FTXUI_COMPONENT_RECEIVER_HPP_
 #define FTXUI_COMPONENT_RECEIVER_HPP_
 
-#include <ftxui/util/warn_windows_macro.hpp>
 #include <algorithm>           // for copy, max
 #include <atomic>              // for atomic, __atomic_base
 #include <condition_variable>  // for condition_variable
@@ -12,6 +11,7 @@
 #include <mutex>               // for mutex, unique_lock
 #include <queue>               // for queue
 #include <utility>             // for move
+#include "ftxui/util/warn_windows_macro.hpp"
 
 namespace ftxui {
 

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 +145,11 @@ 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;
+  // 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;
 

include/ftxui/util/warn_windows_macro.hpp

@@ -2,8 +2,8 @@
 // Use of this source code is governed by the MIT license that can be found in
 // the LICENSE file.
 
-#ifndef FTXUI_UTIL_WARN_WINDOWS_MACRO_H_
-#define FTXUI_UTIL_WARN_WINDOWS_MACRO_H_
+#ifndef FTXUI_UTIL_WARN_WINDOWS_MACRO_HPP_
+#define FTXUI_UTIL_WARN_WINDOWS_MACRO_HPP_
 
 #ifdef min
 #error \
@@ -15,4 +15,4 @@
     "The macro 'max' is defined, which conflicts with the standard C++ library and FTXUI. This is often caused by including <windows.h>. To fix this, add '#define NOMINMAX' before including <windows.h>, or pass '/DNOMINMAX' as a compiler flag."
 #endif
 
-#endif  // FTXUI_UTIL_WARN_WINDOWS_MACRO_H_
+#endif  // FTXUI_UTIL_WARN_WINDOWS_MACRO_HPP_

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
@@ -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) {
@@ -527,6 +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(); });
@@ -592,9 +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
@@ -622,7 +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
 
@@ -663,6 +678,37 @@ void ScreenInteractive::Install() {
   PostAnimationTask();
 }
 
+void ScreenInteractive::InstallPipedInputHandling() {
+  tty_fd_ = STDIN_FILENO;
+#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(STDIN_FILENO)) {
+    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_ = STDIN_FILENO;  // 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();
@@ -1096,7 +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 =
@@ -1108,7 +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

@@ -0,0 +1,222 @@
+// 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 <fcntl.h>
+#include <gtest/gtest.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <cstdio>
+
+#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__)