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terminal: add a new function to read a single keystroke

Typically, input on the command-line is line-based. It is actually not really easy to get single characters (or better put: keystrokes). We provide two implementations here: - One that handles `/dev/tty` based systems as well as native Windows. The former uses the `tcsetattr()` function to put the terminal into "raw mode", which allows us to read individual keystrokes, one by one. The latter uses `stty.exe` to do the same, falling back to direct Win32 Console access. Thanks to the refactoring leading up to this commit, this is a single function, with the platform-specific details hidden away in conditionally-compiled code blocks. - A fall-back which simply punts and reads back an entire line. Note that the function writes the keystroke into an `strbuf` rather than a `char`, in preparation for reading Escape sequences (e.g. when the user hit an arrow key). This is also required for UTF-8 sequences in case the keystroke corresponds to a non-ASCII letter. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Johannes Schindelin committed Jan 14, 2020 at 18:43 UTC a5e46e6b0101b960c131dd39b50999cc0e69ed2b

2 files changed +58

compat/terminal.c

+55

@@ -60,6 +60,11 @@ static int disable_echo(void)

60 return disable_bits(ECHO);

61 }

63 +static int enable_non_canonical(void)

64 +{

65 + return disable_bits(ICANON | ECHO);

66 +}

67 +

68 #elif defined(GIT_WINDOWS_NATIVE)

70 #define INPUT_PATH "CONIN$"

@@ -151,6 +156,10 @@ static int disable_echo(void)

156 return disable_bits(ENABLE_ECHO_INPUT);

157 }

158

159 +static int enable_non_canonical(void)

160 +{

161 + return disable_bits(ENABLE_ECHO_INPUT | ENABLE_LINE_INPUT | ENABLE_PROCESSED_INPUT);

162 +}

163

164 #endif

165

@@ -198,6 +207,33 @@ char *git_terminal_prompt(const char *prompt, int echo)

207 return buf.buf;

208 }

209

210 +int read_key_without_echo(struct strbuf *buf)

211 +{

212 + static int warning_displayed;

213 + int ch;

214 +

215 + if (warning_displayed || enable_non_canonical() < 0) {

216 + if (!warning_displayed) {

217 + warning("reading single keystrokes not supported on "

218 + "this platform; reading line instead");

219 + warning_displayed = 1;

220 + }

221 +

222 + return strbuf_getline(buf, stdin);

223 + }

224 +

225 + strbuf_reset(buf);

226 + ch = getchar();

227 + if (ch == EOF) {

228 + restore_term();

229 + return EOF;

230 + }

231 +

232 + strbuf_addch(buf, ch);

233 + restore_term();

234 + return 0;

235 +}

236 +

237 #else

238

239 char *git_terminal_prompt(const char *prompt, int echo)

@@ -205,4 +241,23 @@ char *git_terminal_prompt(const char *prompt, int echo)

241 return getpass(prompt);

242 }

243

244 +int read_key_without_echo(struct strbuf *buf)

245 +{

246 + static int warning_displayed;

247 + const char *res;

248 +

249 + if (!warning_displayed) {

250 + warning("reading single keystrokes not supported on this "

251 + "platform; reading line instead");

252 + warning_displayed = 1;

253 + }

254 +

255 + res = getpass("");

256 + strbuf_reset(buf);

257 + if (!res)

258 + return EOF;

259 + strbuf_addstr(buf, res);

260 + return 0;

261 +}

262 +

263 #endif

compat/terminal.h

@@ -3,4 +3,7 @@

4 char *git_terminal_prompt(const char *prompt, int echo);

6 +/* Read a single keystroke, without echoing it to the terminal */

7 +int read_key_without_echo(struct strbuf *buf);

8 +

9 #endif /* COMPAT_TERMINAL_H */