Add opt-in piped input support for POSIX systems

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

src/ftxui/component/screen_interactive_piped_input_test.cpp

@@ -0,0 +1,219 @@
+// 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, DefaultBehaviorNoChange) {
+  // Test that HandlePipedInput is disabled by default
+  auto screen = ScreenInteractive::TerminalOutput();
+  auto component = Renderer([] { return text("test"); });
+
+  SetupPipedStdin();
+  WriteToPipedStdin("test data\n");
+
+  // Install should not redirect stdin since HandlePipedInput not called
+  screen.Install();
+  
+  // Stdin should still be the pipe (isatty should return false)
+  EXPECT_FALSE(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, PipedInputDetectionAndRedirection) {
+  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();
+  screen.HandlePipedInput(true);
+  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();
+  screen.HandlePipedInput(true);
+  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();
+  screen.HandlePipedInput(true);
+  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__)