support OSC color sequences

cherry picked from upstream:

* a0467c8 Fix null pointer access in strhandle
* 273db5c follow-up fix for OSC color sequences, return
* 8e31030 Add support for OSC color sequences

config.def.h

@@ -117,18 +117,20 @@ static const char *colorname[] = {
   [15] = "#ffffff", /* white   */
 
   /* special colors */
-  [256] = "#282a36", /* background */
-  [257] = "#f8f8f2", /* foreground */
+  [256] = "#f8f8f2", /* cursor */
+  [257] = "#282a36", /* reverse cursor */
+  [258] = "#f8f8f2", /* foreground */
+  [259] = "#282a36", /* background */
 };
 
 /*
  * Default colors (colorname index)
- * foreground, background, cursor
+ * cursor, reverse cursor foreground, background
  */
-unsigned int defaultfg = 257;
-unsigned int defaultbg = 256;
-static unsigned int defaultcs = 257;
+static unsigned int defaultcs = 256;
 static unsigned int defaultrcs = 257;
+unsigned int defaultfg = 258;
+unsigned int defaultbg = 259;
 
 /*
  * Colors used, when the specific fg == defaultfg. So in reverse mode this

st.c

@@ -1904,6 +1904,42 @@ 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)
 {
@@ -1942,14 +1978,56 @@ 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();
+			return;
+		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();
+			return;
+		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();
+			return;
 		case 4: /* color set */
 			if (narg < 3)
 				break;
 			p = strescseq.args[2];
 			/* FALLTHROUGH */
-		case 104: /* color reset, here p = NULL */
+		case 104: /* color reset */
 			j = (narg > 1) ? atoi(strescseq.args[1]) : -1;
-			if (xsetcolorname(j, p)) {
+
+			if (p && !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

@@ -113,6 +113,8 @@ 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 */
 extern char *utmp;
 extern char *scroll;
@@ -125,3 +127,4 @@ extern char *termname;
 extern unsigned int tabspaces;
 extern unsigned int defaultfg;
 extern unsigned int defaultbg;
+extern unsigned int defaultcs;

x.c

@@ -790,6 +790,19 @@ 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)
 {
@@ -2045,12 +2058,12 @@ xrdb_load(void)
 		  // this looks confusing because we are chaining off of the if
 		  // in the macro. probably we should be wrapping everything blocks
 		  // so this isn't possible...
-		  defaultcs = defaultfg;
+		  colorname[defaultcs] = xstrdup(colorname[defaultfg]);
 		}
 		XRESOURCE_LOAD_STRING("reverse-cursor", colorname[defaultrcs])
 		else {
 		  // see above.
-		  defaultrcs = defaultbg;
+		  colorname[defaultrcs] = xstrdup(colorname[defaultbg]);
 		}
 
 		XRESOURCE_LOAD_STRING("font", font);