Support OSC 4 terminal colour-palette queries.

Markus Gans points out that some applications which (not at all
unreasonably) don't trust $TERM to tell them the full capabilities of
their terminal will use the sequence "OSC 4 ; nn ; ? BEL" to ask for
the colour-palette value in position nn, and they may not particularly
care _what_ the results are but they will use them to decide whether
the right number of colour palette entries even exist.

fuzzterm.c

@@ -81,6 +81,7 @@ Context get_ctx(void *frontend) {
 void free_ctx(Context ctx) { }
 void palette_set(void *frontend, int a, int b, int c, int d) { }
 void palette_reset(void *frontend) { }
+int palette_get(void *frontend, int n, int *r, int *g, int *b) {return FALSE;}
 void write_clip(void *frontend, wchar_t *a, int *b, int c, int d) { }
 void get_clip(void *frontend, wchar_t **w, int *i) { }
 void set_raw_mouse_mode(void *frontend, int m) { }

putty.h

@@ -633,6 +633,7 @@ Context get_ctx(void *frontend);
 void free_ctx(Context);
 void palette_set(void *frontend, int, int, int, int);
 void palette_reset(void *frontend);
+int palette_get(void *frontend, int n, int *r, int *g, int *b);
 void write_aclip(void *frontend, char *, int, int);
 void write_clip(void *frontend, wchar_t *, int *, int, int);
 void get_clip(void *frontend, wchar_t **, int *);

terminal.c

@@ -2727,6 +2727,22 @@ static void do_osc(Terminal *term)
 	    if (!term->no_remote_wintitle)
 		set_title(term->frontend, term->osc_string);
 	    break;
+          case 4:
+            if (term->ldisc && !strcmp(term->osc_string, "?")) {
+                int r, g, b;
+                if (palette_get(term->frontend, toint(term->esc_args[1]),
+                                &r, &g, &b)) {
+                    char *reply_buf = dupprintf(
+                        "\033]4;%u;rgb:%04x/%04x/%04x\007",
+                        term->esc_args[1],
+                        (unsigned)r * 0x0101,
+                        (unsigned)g * 0x0101,
+                        (unsigned)b * 0x0101);
+                    ldisc_send(term->ldisc, reply_buf, strlen(reply_buf), 0);
+                    sfree(reply_buf);
+                }
+            }
+            break;
 	}
     }
 }
@@ -3365,6 +3381,7 @@ static void term_out(Terminal *term)
 		    compatibility(OTHER);
 		    term->termstate = SEEN_OSC;
 		    term->esc_args[0] = 0;
+                    term->esc_nargs = 1;
 		    break;
 		  case '7':		/* DECSC: save cursor */
 		    compatibility(VT100);
@@ -4470,25 +4487,40 @@ static void term_out(Terminal *term)
 		  case '7':
 		  case '8':
 		  case '9':
-		    if (term->esc_args[0] <= UINT_MAX / 10 &&
+		    if (term->esc_args[term->esc_nargs-1] <= UINT_MAX / 10 &&
-			term->esc_args[0] * 10 <= UINT_MAX - c - '0')
+			term->esc_args[term->esc_nargs-1] * 10 <= UINT_MAX - c - '0')
-			term->esc_args[0] = 10 * term->esc_args[0] + c - '0';
+			term->esc_args[term->esc_nargs-1] =
+                            10 * term->esc_args[term->esc_nargs-1] + c - '0';
 		    else
-			term->esc_args[0] = UINT_MAX;
+			term->esc_args[term->esc_nargs-1] = UINT_MAX;
 		    break;
-		  case 'L':
+                  default:
-		    /*
+                    /*
-		     * Grotty hack to support xterm and DECterm title
+                     * _Most_ other characters here terminate the
-		     * sequences concurrently.
+                     * immediate parsing of the OSC sequence and go
-		     */
+                     * into OSC_STRING state, but we deal with a
-		    if (term->esc_args[0] == 2) {
+                     * couple of exceptions first.
-			term->esc_args[0] = 1;
+                     */
-			break;
+                    if (c == 'L' && term->esc_args[0] == 2) {
-		    }
+                        /*
-		    /* else fall through */
+                         * Grotty hack to support xterm and DECterm title
-		  default:
+                         * sequences concurrently.
-		    term->termstate = OSC_STRING;
+                         */
-		    term->osc_strlen = 0;
+                        term->esc_args[0] = 1;
+                    } else if (c == ';' && term->esc_nargs == 1 &&
+                               term->esc_args[0] == 4) {
+                        /*
+                         * xterm's OSC 4 sequence to query the current
+                         * RGB value of a colour takes a second
+                         * numeric argument which is easiest to parse
+                         * using the existing system rather than in
+                         * do_osc.
+                         */
+                        term->esc_args[term->esc_nargs++] = 0;
+                    } else {
+                        term->termstate = OSC_STRING;
+                        term->osc_strlen = 0;
+                    }
 		}
 		break;
 	      case OSC_STRING:

unix/gtkwin.c

@@ -2222,6 +2222,17 @@ void palette_set(void *frontend, int n, int r, int g, int b)
     }
 }
 
+int palette_get(void *frontend, int n, int *r, int *g, int *b)
+{
+    struct gui_data *inst = (struct gui_data *)frontend;
+    if (n < 0 || n >= NALLCOLOURS)
+	return FALSE;
+    *r = inst->cols[n].red >> 8;
+    *g = inst->cols[n].green >> 8;
+    *b = inst->cols[n].blue >> 8;
+    return TRUE;
+}
+
 void palette_reset(void *frontend)
 {
     struct gui_data *inst = (struct gui_data *)frontend;

windows/window.c

@@ -198,6 +198,9 @@ static int descent;
 #define NEXTCOLOURS 240
 #define NALLCOLOURS (NCFGCOLOURS + NEXTCOLOURS)
 static COLORREF colours[NALLCOLOURS];
+struct rgb {
+    int r, g, b;
+} colours_rgb[NALLCOLOURS];
 static HPALETTE pal;
 static LPLOGPALETTE logpal;
 static RGBTRIPLE defpal[NALLCOLOURS];
@@ -1264,6 +1267,19 @@ static void systopalette(void)
     }
 }
 
+static void internal_set_colour(int i, int r, int g, int b)
+{
+    assert(i >= 0);
+    assert(i < NALLCOLOURS);
+    if (pal)
+        colours[i] = PALETTERGB(r, g, b);
+    else
+        colours[i] = RGB(r, g, b);
+    colours_rgb[i].r = r;
+    colours_rgb[i].g = g;
+    colours_rgb[i].b = b;
+}
+
 /*
  * Set up the colour palette.
  */
@@ -1298,15 +1314,9 @@ static void init_palette(void)
 	}
 	ReleaseDC(hwnd, hdc);
     }
-    if (pal)
+    for (i = 0; i < NALLCOLOURS; i++)
-	for (i = 0; i < NALLCOLOURS; i++)
+        internal_set_colour(i, defpal[i].rgbtRed,
-	    colours[i] = PALETTERGB(defpal[i].rgbtRed,
+                            defpal[i].rgbtGreen, defpal[i].rgbtBlue);
-				    defpal[i].rgbtGreen,
-				    defpal[i].rgbtBlue);
-    else
-	for (i = 0; i < NALLCOLOURS; i++)
-	    colours[i] = RGB(defpal[i].rgbtRed,
-			     defpal[i].rgbtGreen, defpal[i].rgbtBlue);
 }
 
 /*
@@ -4865,15 +4875,24 @@ void free_ctx(Context ctx)
 
 static void real_palette_set(int n, int r, int g, int b)
 {
+    internal_set_colour(n, r, g, b);
     if (pal) {
 	logpal->palPalEntry[n].peRed = r;
 	logpal->palPalEntry[n].peGreen = g;
 	logpal->palPalEntry[n].peBlue = b;
 	logpal->palPalEntry[n].peFlags = PC_NOCOLLAPSE;
-	colours[n] = PALETTERGB(r, g, b);
 	SetPaletteEntries(pal, 0, NALLCOLOURS, logpal->palPalEntry);
-    } else
+    }
-	colours[n] = RGB(r, g, b);
+}
+
+int palette_get(void *frontend, int n, int *r, int *g, int *b)
+{
+    if (n < 0 || n >= NALLCOLOURS)
+	return FALSE;
+    *r = colours_rgb[n].r;
+    *g = colours_rgb[n].g;
+    *b = colours_rgb[n].b;
+    return TRUE;
 }
 
 void palette_set(void *frontend, int n, int r, int g, int b)
@@ -4903,17 +4922,14 @@ void palette_reset(void *frontend)
 
     /* And this */
     for (i = 0; i < NALLCOLOURS; i++) {
+        internal_set_colour(i, defpal[i].rgbtRed,
+                            defpal[i].rgbtGreen, defpal[i].rgbtBlue);
 	if (pal) {
 	    logpal->palPalEntry[i].peRed = defpal[i].rgbtRed;
 	    logpal->palPalEntry[i].peGreen = defpal[i].rgbtGreen;
 	    logpal->palPalEntry[i].peBlue = defpal[i].rgbtBlue;
 	    logpal->palPalEntry[i].peFlags = 0;
-	    colours[i] = PALETTERGB(defpal[i].rgbtRed,
+	}
-				    defpal[i].rgbtGreen,
-				    defpal[i].rgbtBlue);
-	} else
-	    colours[i] = RGB(defpal[i].rgbtRed,
-			     defpal[i].rgbtGreen, defpal[i].rgbtBlue);
     }
 
     if (pal) {