term.c: Add support for extended number format terminfo files.

ncurses 6.1 introduced an extended number format for terminfo files
which the terminfo parsing in Asterisk is not able to parse. This
results in some TERM values that do support color (screen-256color on
Ubuntu 20.04 for example) to not get a color console.

ASTERISK-29630 #close

Change-Id: I27a4fcfab502219924af2d6b1c46feba92903cb3

main/term.c

@@ -74,7 +74,7 @@ static int opposite(int color)
 }
 
 /* Ripped off from Ross Ridge, but it's public domain code (libmytinfo) */
-static short convshort(char *s)
+static short convshort(unsigned char *s)
 {
 	register int a, b;
 
@@ -89,11 +89,83 @@ static short convshort(char *s)
 	return a + b * 256;
 }
 
+static inline int convint(unsigned char *s)
+{
+	return s[0]
+		| s[1] << 8
+		| s[2] << 16
+		| s[3] << 24;
+}
+
+#define MAGIC_LEGACY (00432)
+#define MAGIC_EXTNUM (01036)
+
+#define HEADER_LEN (12)
+#define MAX_COLORS_INDEX (13)
+
+static int parse_terminfo_file(int fd)
+{
+	int bytes_read, bytes_needed, num_size;
+	short magic, sz_names, sz_bools;
+	unsigned char buffer[1024];
+
+	bytes_read = read(fd, buffer, sizeof(buffer));
+	if (bytes_read < HEADER_LEN) {
+		return 0;
+	}
+
+	magic = convshort(buffer);
+
+	if (magic == MAGIC_LEGACY) {
+		num_size = 2;
+	} else if (magic == MAGIC_EXTNUM) {
+		/* Extended number format (ncurses 6.1) */
+		num_size = 4;
+	} else {
+		/* We don't know how to parse this file */
+		return 0;
+	}
+
+	sz_names = convshort(buffer + 2);
+	sz_bools = convshort(buffer + 4);
+
+	/* From term(5):
+	 * Between the boolean section and the number section, a null byte will be
+	 * inserted, if necessary, to ensure that the number section begins on an
+	 * even byte. */
+	if ((sz_names + sz_bools) & 1) {
+		sz_bools++;
+	}
+
+	bytes_needed = HEADER_LEN + sz_names + sz_bools + ((MAX_COLORS_INDEX + 1) * num_size);
+	if (bytes_needed <= bytes_read) {
+		/* Offset 13 is defined in /usr/include/term.h, though we do not
+		 * include it here, as it conflicts with include/asterisk/term.h */
+		int max_colors;
+		int offset = HEADER_LEN + sz_names + sz_bools + MAX_COLORS_INDEX * num_size;
+
+		if (num_size == 2) {
+			/* In the legacy terminfo format, numbers are signed shorts */
+			max_colors = convshort(buffer + offset);
+		} else {
+			/* Extended number format makes them signed ints */
+			max_colors = convint(buffer + offset);
+		}
+
+		if (max_colors > 0) {
+			vt100compat = 1;
+		}
+
+		return 1;
+	}
+
+	return 0;
+}
+
 int ast_term_init(void)
 {
 	char *term = getenv("TERM");
 	char termfile[256] = "";
-	char buffer[512] = "";
 	int termfd = -1, parseokay = 0, i;
 
 	if (ast_opt_no_color) {
@@ -110,36 +182,15 @@ int ast_term_init(void)
 		return 0;
 	}
 
-	for (i = 0;; i++) {
-		if (termpath[i] == NULL) {
-			break;
-		}
+	for (i = 0; !parseokay && termpath[i]; i++) {
 		snprintf(termfile, sizeof(termfile), "%s/%c/%s", termpath[i], *term, term);
+
 		termfd = open(termfile, O_RDONLY);
 		if (termfd > -1) {
-			break;
-		}
-	}
-	if (termfd > -1) {
-		int actsize = read(termfd, buffer, sizeof(buffer) - 1);
-		short sz_names = convshort(buffer + 2);
-		short sz_bools = convshort(buffer + 4);
-		short n_nums   = convshort(buffer + 6);
-
-		/* if ((sz_names + sz_bools) & 1)
-			sz_bools++; */
-
-		if (sz_names + sz_bools + n_nums < actsize) {
-			/* Offset 13 is defined in /usr/include/term.h, though we do not
-			 * include it here, as it conflicts with include/asterisk/term.h */
-			short max_colors = convshort(buffer + 12 + sz_names + sz_bools + 13 * 2);
-			if (max_colors > 0) {
-				vt100compat = 1;
-			}
-			parseokay = 1;
-		}
+			parseokay = parse_terminfo_file(termfd);
 			close(termfd);
 		}
+	}
 
 	if (!parseokay) {
 		/* These comparisons should not be substrings nor case-insensitive, as