Add support for OSC color sequences

Reference:
https://git.suckless.org/st/commit/8e310303903792c010d03c046ba75f8b18f7d3a7.html

Author: sighook

config.def.h

@@ -115,14 +115,22 @@ static const char *colorname[] = {
   [13] = "#d3869b", /* magenta */
   [14] = "#8ec07c", /* cyan    */
   [15] = "#ebdbb2", /* white   */
+
+  [255] = 0,
+
+  /* More colors can be added after 255 to use with DefaultXX. */
+  "#cccccc",
+  "#555555",
+  "gray90", /* default foreground color */
+  "black", /* default background color */
 };
 
 /* Default colors (colorname index).
  */
-unsigned int defaultfg = 15;           /* foreground color     */
-unsigned int defaultbg = 0;            /* background color     */
-static unsigned int defaultcs = 15;    /* cursor color         */
-static unsigned int defaultrcs = 257;  /* reverse cursor color */
+unsigned int defaultfg = 15;    /* foreground color     */
+unsigned int defaultbg = 0;     /* background color     */
+unsigned int defaultcs = 15;    /* cursor color         */
+unsigned int defaultrcs = 258;  /* reverse cursor color */
 
 /*********************************************************************
  * [VimBrowse] settings and appearance.

st.c

@@ -174,6 +174,8 @@ static void csidump(void);
 static void csihandle(void);
 static void csiparse(void);
 static void csireset(void);
+static void osc4_color_response(int num);
+static void osc_color_response(int index, int num);
 static int eschandle(uchar);
 static void strdump(void);
 static void strhandle(void);
@@ -1932,6 +1934,42 @@ csireset(void)
 	memset(&csiescseq, 0, sizeof(csiescseq));
 }
 
+void
+osc4_color_response(int num)
+{
+	int n;
+	char buf[32];
+	unsigned char r, g, b;
+
+	if (xgetcolor(num, &r, &g, &b)) {
+		fprintf(stderr, "erresc: failed to fetch osc4 color %d\n", num);
+		return;
+	}
+
+	n = snprintf(buf, sizeof buf, "\033]4;%d;rgb:%02x%02x/%02x%02x/%02x%02x\007",
+		     num, r, r, g, g, b, b);
+
+	ttywrite(buf, n, 1);
+}
+
+void
+osc_color_response(int index, int num)
+{
+	int n;
+	char buf[32];
+	unsigned char r, g, b;
+
+	if (xgetcolor(index, &r, &g, &b)) {
+		fprintf(stderr, "erresc: failed to fetch osc color %d\n", index);
+		return;
+	}
+
+	n = snprintf(buf, sizeof buf, "\033]%d;rgb:%02x%02x/%02x%02x/%02x%02x\007",
+		     num, r, r, g, g, b, b);
+
+	ttywrite(buf, n, 1);
+}
+
 void
 strhandle(void)
 {
@@ -1970,14 +2008,56 @@ strhandle(void)
 				}
 			}
 			return;
+		case 10:
+			if (narg < 2)
+				break;
+
+			p = strescseq.args[1];
+
+			if (!strcmp(p, "?"))
+				osc_color_response(defaultfg, 10);
+			else if (xsetcolorname(defaultfg, p))
+				fprintf(stderr, "erresc: invalid foreground color: %s\n", p);
+			else
+				redraw();
+			break;
+		case 11:
+			if (narg < 2)
+				break;
+
+			p = strescseq.args[1];
+
+			if (!strcmp(p, "?"))
+				osc_color_response(defaultbg, 11);
+			else if (xsetcolorname(defaultbg, p))
+				fprintf(stderr, "erresc: invalid background color: %s\n", p);
+			else
+				redraw();
+			break;
+		case 12:
+			if (narg < 2)
+				break;
+
+			p = strescseq.args[1];
+
+			if (!strcmp(p, "?"))
+				osc_color_response(defaultcs, 12);
+			else if (xsetcolorname(defaultcs, p))
+				fprintf(stderr, "erresc: invalid cursor color: %s\n", p);
+			else
+				redraw();
+			break;
 		case 4: /* color set */
 			if (narg < 3)
 				break;
 			p = strescseq.args[2];
 			/* FALLTHROUGH */
 		case 104: /* color reset, here p = NULL */
 			j = (narg > 1) ? atoi(strescseq.args[1]) : -1;
-			if (xsetcolorname(j, p)) {
+
+			if (!strcmp(p, "?"))
+				osc4_color_response(j);
+			else if (xsetcolorname(j, p)) {
 				if (par == 104 && narg <= 1)
 					return; /* color reset without parameter */
 				fprintf(stderr, "erresc: invalid color j=%d, p=%s\n",

st.h

@@ -123,6 +123,7 @@ void *xmalloc(size_t);
 void *xrealloc(void *, size_t);
 char *xstrdup(const char *);
 
+int xgetcolor(int x, unsigned char *r, unsigned char *g, unsigned char *b);
 /*
  * config.h globals
  */
@@ -137,6 +138,7 @@ extern char *termname;
 extern unsigned int tabspaces;
 extern unsigned int defaultfg;
 extern unsigned int defaultbg;
+extern unsigned int defaultcs;
 
 /*
  * copyurl

x.c

@@ -838,6 +838,19 @@ xloadcols(void)
 	loaded = 1;
 }
 
+int
+xgetcolor(int x, unsigned char *r, unsigned char *g, unsigned char *b)
+{
+	if (!BETWEEN(x, 0, dc.collen))
+		return 1;
+
+	*r = dc.col[x].color.red >> 8;
+	*g = dc.col[x].color.green >> 8;
+	*b = dc.col[x].color.blue >> 8;
+
+	return 0;
+}
+
 int
 xsetcolorname(int x, const char *name)
 {