Add cross-platform masked input utility with tests

src/tests/test_seed_prompt.py

@@ -0,0 +1,30 @@
+import types
+from utils import seed_prompt
+
+
+def test_masked_input_posix_backspace(monkeypatch, capsys):
+    seq = iter(["a", "b", "\x7f", "c", "\n"])
+    monkeypatch.setattr(seed_prompt.sys.stdin, "read", lambda n=1: next(seq))
+    monkeypatch.setattr(seed_prompt.sys.stdin, "fileno", lambda: 0)
+    monkeypatch.setattr(seed_prompt.termios, "tcgetattr", lambda fd: None)
+    monkeypatch.setattr(seed_prompt.termios, "tcsetattr", lambda fd, *_: None)
+    monkeypatch.setattr(seed_prompt.tty, "setraw", lambda fd: None)
+
+    result = seed_prompt.masked_input("Enter: ")
+    assert result == "ac"
+    out = capsys.readouterr().out
+    assert out.startswith("Enter: ")
+    assert out.count("*") == 3
+
+
+def test_masked_input_windows_space(monkeypatch, capsys):
+    seq = iter(["x", "y", " ", "z", "\r"])
+    fake_msvcrt = types.SimpleNamespace(getwch=lambda: next(seq))
+    monkeypatch.setattr(seed_prompt, "msvcrt", fake_msvcrt)
+    monkeypatch.setattr(seed_prompt.sys, "platform", "win32", raising=False)
+
+    result = seed_prompt.masked_input("Password: ")
+    assert result == "xy z"
+    out = capsys.readouterr().out
+    assert out.startswith("Password: ")
+    assert out.count("*") == 4

src/utils/__init__.py

@@ -25,6 +25,7 @@ try:
         update_checksum_file,
     )
     from .password_prompt import prompt_for_password
+    from .seed_prompt import masked_input
     from .input_utils import timed_input
     from .memory_protection import InMemorySecret
     from .clipboard import copy_to_clipboard
@@ -58,6 +59,7 @@ __all__ = [
     "exclusive_lock",
     "shared_lock",
     "prompt_for_password",
+    "masked_input",
     "timed_input",
     "InMemorySecret",
     "copy_to_clipboard",

src/utils/seed_prompt.py

@@ -0,0 +1,73 @@
+import os
+import sys
+
+try:
+    import msvcrt  # type: ignore
+except ImportError:  # pragma: no cover - Windows only
+    msvcrt = None  # type: ignore
+
+try:
+    import termios
+    import tty
+except ImportError:  # pragma: no cover - POSIX only
+    termios = None  # type: ignore
+    tty = None  # type: ignore
+
+
+def _masked_input_windows(prompt: str) -> str:
+    """Windows implementation using ``msvcrt``."""
+    if msvcrt is None:  # pragma: no cover - should not happen
+        return input(prompt)
+
+    sys.stdout.write(prompt)
+    sys.stdout.flush()
+    buffer: list[str] = []
+    while True:
+        ch = msvcrt.getwch()
+        if ch in ("\r", "\n"):
+            sys.stdout.write("\n")
+            return "".join(buffer)
+        if ch in ("\b", "\x7f"):
+            if buffer:
+                buffer.pop()
+                sys.stdout.write("\b \b")
+        else:
+            buffer.append(ch)
+            sys.stdout.write("*")
+        sys.stdout.flush()
+
+
+def _masked_input_posix(prompt: str) -> str:
+    """POSIX implementation using ``termios`` and ``tty``."""
+    if termios is None or tty is None:  # pragma: no cover - should not happen
+        return input(prompt)
+
+    fd = sys.stdin.fileno()
+    old_settings = termios.tcgetattr(fd)
+    sys.stdout.write(prompt)
+    sys.stdout.flush()
+    buffer: list[str] = []
+    try:
+        tty.setraw(fd)
+        while True:
+            ch = sys.stdin.read(1)
+            if ch in ("\r", "\n"):
+                sys.stdout.write("\n")
+                return "".join(buffer)
+            if ch in ("\x7f", "\b"):
+                if buffer:
+                    buffer.pop()
+                    sys.stdout.write("\b \b")
+            else:
+                buffer.append(ch)
+                sys.stdout.write("*")
+            sys.stdout.flush()
+    finally:
+        termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
+
+
+def masked_input(prompt: str) -> str:
+    """Return input from the user while masking typed characters."""
+    if sys.platform == "win32":
+        return _masked_input_windows(prompt)
+    return _masked_input_posix(prompt)