color: add color_set helper for copying raw colors

To set up default colors, we sometimes strcpy() from the
default string literals into our color buffers. This isn't a
bug (assuming the destination is COLOR_MAXLEN bytes), but
makes it harder to audit the code for problematic strcpy
calls.

Let's introduce a color_set which copies under the
assumption that there are COLOR_MAXLEN bytes in the
destination (of course you can call it on a smaller buffer,
so this isn't providing a huge amount of safety, but it's
more convenient than calling xsnprintf yourself).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

color.c

@@ -145,6 +145,11 @@ int color_parse(const char *value, char *dst)
 	return color_parse_mem(value, strlen(value), dst);
 }
 
+void color_set(char *dst, const char *color_bytes)
+{
+	xsnprintf(dst, COLOR_MAXLEN, "%s", color_bytes);
+}
+
 /*
  * Write the ANSI color codes for "c" to "out"; the string should
  * already have the ANSI escape code in it. "out" should have enough

color.h

@@ -75,6 +75,13 @@ extern int color_stdout_is_tty;
 int git_color_config(const char *var, const char *value, void *cb);
 int git_color_default_config(const char *var, const char *value, void *cb);
 
+/*
+ * Set the color buffer (which must be COLOR_MAXLEN bytes)
+ * to the raw color bytes; this is useful for initializing
+ * default color variables.
+ */
+void color_set(char *dst, const char *color_bytes);
+
 int git_config_colorbool(const char *var, const char *value);
 int want_color(int var);
 int color_parse(const char *value, char *dst);

grep.c

@@ -31,14 +31,14 @@ void init_grep_defaults(void)
 	opt->max_depth = -1;
 	opt->pattern_type_option = GREP_PATTERN_TYPE_UNSPECIFIED;
 	opt->extended_regexp_option = 0;
-	strcpy(opt->color_context, "");
-	strcpy(opt->color_filename, "");
-	strcpy(opt->color_function, "");
-	strcpy(opt->color_lineno, "");
-	strcpy(opt->color_match_context, GIT_COLOR_BOLD_RED);
-	strcpy(opt->color_match_selected, GIT_COLOR_BOLD_RED);
-	strcpy(opt->color_selected, "");
-	strcpy(opt->color_sep, GIT_COLOR_CYAN);
+	color_set(opt->color_context, "");
+	color_set(opt->color_filename, "");
+	color_set(opt->color_function, "");
+	color_set(opt->color_lineno, "");
+	color_set(opt->color_match_context, GIT_COLOR_BOLD_RED);
+	color_set(opt->color_match_selected, GIT_COLOR_BOLD_RED);
+	color_set(opt->color_selected, "");
+	color_set(opt->color_sep, GIT_COLOR_CYAN);
 	opt->color = -1;
 }
 
@@ -151,14 +151,14 @@ void grep_init(struct grep_opt *opt, const char *prefix)
 	opt->regflags = def->regflags;
 	opt->relative = def->relative;
 
-	strcpy(opt->color_context, def->color_context);
-	strcpy(opt->color_filename, def->color_filename);
-	strcpy(opt->color_function, def->color_function);
-	strcpy(opt->color_lineno, def->color_lineno);
-	strcpy(opt->color_match_context, def->color_match_context);
-	strcpy(opt->color_match_selected, def->color_match_selected);
-	strcpy(opt->color_selected, def->color_selected);
-	strcpy(opt->color_sep, def->color_sep);
+	color_set(opt->color_context, def->color_context);
+	color_set(opt->color_filename, def->color_filename);
+	color_set(opt->color_function, def->color_function);
+	color_set(opt->color_lineno, def->color_lineno);
+	color_set(opt->color_match_context, def->color_match_context);
+	color_set(opt->color_match_selected, def->color_match_selected);
+	color_set(opt->color_selected, def->color_selected);
+	color_set(opt->color_sep, def->color_sep);
 }
 
 void grep_commit_pattern_type(enum grep_pattern_type pattern_type, struct grep_opt *opt)