@matheusbsbs / matheus-bagliano / commits / d3c2749def

rerere: fix benign off-by-one non-bug and clarify code

rerere_io_putconflict() wants to use a limited fixed-sized buf[] on stack repeatedly to formulate a longer string, but its implementation is doubly confusing: * When it knows that the whole thing fits in buf[], it wants to fill early part of buf[] with conflict marker characters, followed by a LF and a NUL. It miscounts the size of the buffer by 1 and does not use the last byte of buf[]. * When it needs to show only the early part of a long conflict marker string (because the whole thing does not fit in buf[]), it adjusts the number of bytes shown in the current round in a strange-looking way. It makes sure that this round does not emit all bytes and leaves at least one byte to the next round, so that "it all fits" case will pick up the rest and show the terminating LF. While this is correct, one needs to stop and think for a while to realize why it is correct without an explanation. Fix the benign off-by-one, and add comments to explain the strange-looking size adjustment. Signed-off-by: Junio C Hamano <gitster@pobox.com>

Junio C Hamano committed Jul 24, 2015 at 16:01 UTC d3c2749def9563798cea3486f3793ad36d9c1030

1 file changed +8 -1

rerere.c

+8 -1

@@ -125,13 +125,20 @@ static void rerere_io_putconflict(int ch, int size, struct rerere_io *io)

125 char buf[64];

126

127 while (size) {

128 - if (size < sizeof(buf) - 2) {

128 + if (size <= sizeof(buf) - 2) {

129 memset(buf, ch, size);

130 buf[size] = '\n';

131 buf[size + 1] = '\0';

132 size = 0;

133 } else {

134 int sz = sizeof(buf) - 1;

135 +

136 + /*

137 + * Make sure we will not write everything out

138 + * in this round by leaving at least 1 byte

139 + * for the next round, giving the next round

140 + * a chance to add the terminating LF. Yuck.

141 + */

142 if (size <= sz)

143 sz -= (sz - size) + 1;

144 memset(buf, ch, sz);