5373fbcd1
Denis Vlasenko
2008-10-14
Subject
vi: add comments to Rob's algorithm of reading and matching ESC sequences (nice work btw!)
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editors/vi.c+33 -23
| @@ -2243,60 +2243,70 @@ static char readit(void) // read (maybe cursor) key from stdin | |
| fflush(stdout); | |
| - | // If no data, block waiting for input. |
| n = chars_to_parse; | |
| - | while (!n) { |
| + | if (n == 0) { |
| + | // If no data, block waiting for input. |
| n = safe_read(0, readbuffer, 1); | |
| if (n <= 0) { | |
| + | error: |
| place_cursor(rows - 1, 0, FALSE); // go to bottom of screen | |
| clear_to_eol(); // erase to end of line | |
| cookmode(); // terminal to "cooked" | |
| bb_error_msg_and_die("can't read user input"); | |
| } | |
| - | // Returning NUL from this routine would be bad. |
| - | if (*readbuffer) break; |
| } | |
| // Grab character to return from buffer | |
| - | c = *readbuffer; |
| + | c = readbuffer[0]; |
| + | // Returning NUL from this routine would be bad. |
| + | if (c == '\0') |
| + | c = ' '; |
| n--; | |
| - | if (n) memmove(readbuffer, readbuffer+1, n); |
| + | if (n) memmove(readbuffer, readbuffer + 1, n); |
| // If it's an escape sequence, loop through known matches. | |
| if (c == 27) { | |
| const struct esc_cmds *eindex; | |
| - | for (eindex = esccmds; eindex < esccmds+ARRAY_SIZE(esccmds); eindex++) { |
| - | int i=0, cnt = strnlen(eindex->seq, 4); |
| + | for (eindex = esccmds; eindex < esccmds + ARRAY_SIZE(esccmds); eindex++) { |
| + | // n - position in seq to read |
| + | int i = 0; // position in seq to compare |
| + | int cnt = strnlen(eindex->seq, 4); |
| // Loop through chars in this sequence. | |
| for (;;) { | |
| - | |
| - | // If we've matched this escape sequence so far but need more |
| - | // chars, read another as long as it wouldn't block. (Note that |
| - | // escape sequences come in as a unit, so if we would block |
| - | // it's not really an escape sequence.) |
| + | // We've matched this escape sequence up to [i-1] |
| if (n <= i) { | |
| + | // Need more chars, read another one if it wouldn't block. |
| + | // (Note that escape sequences come in as a unit, |
| + | // so if we would block it's not really an escape sequence.) |
| struct pollfd pfd; | |
| pfd.fd = 0; | |
| pfd.events = POLLIN; | |
| - | if (0 < safe_poll(&pfd, 1, 300) |
| - | && 0 < safe_read(0, readbuffer + n, 1)) |
| - | n++; |
| - | |
| - | // Since the array is sorted from shortest to longest, if |
| - | // we needed more data we can't match anything later, so |
| - | // break out of both loops. |
| - | else goto loop_out; |
| + | // TODO: what is a good timeout here? why? |
| + | if (safe_poll(&pfd, 1, /*timeout:*/ 0)) { |
| + | if (safe_read(0, readbuffer + n, 1) <= 0) |
| + | goto error; |
| + | n++; |
| + | } else { |
| + | // No more data! |
| + | // Array is sorted from shortest to longest, |
| + | // we can't match anything later in array, |
| + | // break out of both loops. |
| + | goto loop_out; |
| + | } |
| } | |
| - | if (readbuffer[i] != eindex->seq[i]) break; |
| - | if (++i == cnt) { |
| + | if (readbuffer[i] != eindex->seq[i]) |
| + | break; // try next seq |
| + | if (++i == cnt) { // entire seq matched |
| c = eindex->val; | |
| n = 0; | |
| goto loop_out; | |
| } | |
| } | |
| } | |
| + | // We did not find matching sequence, it was a bare ESC. |
| + | // We possibly read and stored more input in readbuffer by now. |
| } | |
| loop_out: | |