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diff --git a/src/ui/terminal/line.h b/src/ui/terminal/line.h
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+// Copyright 2021 Benjamin Barenblat
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+// A terminal driver for single-line UIs.
+
+#ifndef EC_SRC_UI_TERMINAL_LINE_H_
+#define EC_SRC_UI_TERMINAL_LINE_H_
+
+#include <termios.h>
+
+#include <thread>
+
+#include "third_party/abseil/absl/base/thread_annotations.h"
+#include "third_party/abseil/absl/strings/string_view.h"
+#include "third_party/abseil/absl/synchronization/mutex.h"
+
+namespace ec {
+
+// The driver itself.
+//
+// This class is thread-safe, but there are still some sharp edges. See the
+// warning in the constructor documentation about additional steps required to
+// use this class in a multi-threaded program.
+class TerminalLine final {
+ public:
+  // Starts driving the standard input and standard output of the process.
+  //
+  // Multi-threading warning: You must block SIGWINCH in all your program's
+  // threads before constructing an instance of this class. This class detects
+  // failure to block SIGWINCH in the calling thread, but it cannot check all
+  // the threads. It is your responsibility to block SIGWINCH everywhere!
+  // (BlockSigwinch is a convenience function to do this in the current thread.)
+  explicit TerminalLine();
+
+  TerminalLine(const TerminalLine&) = delete;
+  TerminalLine& operator=(const TerminalLine&) = delete;
+
+  ~TerminalLine() noexcept;
+
+  void SetLine(std::string) ABSL_LOCKS_EXCLUDED(mu_);
+  void Refresh() ABSL_LOCKS_EXCLUDED(mu_);
+
+  void SetLineImmediately(std::string text) {
+    SetLine(text);
+    Refresh();
+  }
+
+  char GetChar();
+  char interrupt_char() const noexcept { return current_termios_.c_cc[VINTR]; }
+  char quit_char() const noexcept { return current_termios_.c_cc[VQUIT]; }
+  char suspend_char() const noexcept { return current_termios_.c_cc[VSUSP]; }
+#ifdef VDSUSP
+  char delayed_suspend_char() const noexcept {
+    return current_termios_.c_cc[VDSUSP];
+  }
+#endif
+
+  void Beep() ABSL_LOCKS_EXCLUDED(mu_);
+
+  // Prints the specified message on a new line, and redisplays the original
+  // text on the line after that.
+  void PrintLine(absl::string_view) ABSL_LOCKS_EXCLUDED(mu_);
+
+ private:
+  void EnterRawMode();
+  void ExitRawMode() noexcept;
+
+  void ReportSigwinch() ABSL_LOCKS_EXCLUDED(mu_);
+
+  void WriteRaw(absl::string_view bytes) ABSL_EXCLUSIVE_LOCKS_REQUIRED(mu_);
+
+  termios original_termios_, current_termios_;
+
+  std::thread sigwinch_watcher_;
+
+  absl::Mutex mu_;
+  int columns_ ABSL_GUARDED_BY(mu_);
+  std::string line_ ABSL_GUARDED_BY(mu_);
+};
+
+// Names for control characters.
+constexpr char kControlD = '\x04';
+constexpr char kControlU = '\x15';
+
+// A convenience function to block SIGWINCH in the calling thread.
+void BlockSigwinch();
+
+}  // namespace ec
+
+#endif  // EC_SRC_UI_TERMINAL_LINE_H_