In terminal output, unify handling of Unicode and numbered character

escape sequences just like it was earlier implemented for -Thtml.
Do not let control characters other than ASCII 9 (horizontal tab)
propagate to the output, even though groff allows them; but that
really doesn't look like a great idea.

Let mchars_num2char() return int such that we can distinguish invalid \N
syntax from \N'0'.  This also reduces the danger of signed char issues
popping up.

4 files changed, 74 insertions, 47 deletions

diff --git a/chars.c b/chars.c
index e4f3cbcf..e4f522b5 100644
--- a/chars.c
+++ b/chars.c
@@ -107,15 +107,13 @@ mchars_spec2cp(const struct mchars *arg, const char *p, size_t sz)
 	return(ln != NULL ? ln->unicode : sz == 1 ? (unsigned char)*p : -1);
 }
 
-char
+int
 mchars_num2char(const char *p, size_t sz)
 {
 	int	  i;
 
-	if ((i = mandoc_strntoi(p, sz, 10)) < 0)
-		return('\0');
-
-	return(i > 0 && i < 256 && isprint(i) ? i : '\0');
+	i = mandoc_strntoi(p, sz, 10);
+	return(i >= 0 && i < 256 ? i : -1);
 }
 
 int
diff --git a/html.c b/html.c
index 01514937..ff68e6e1 100644
--- a/html.c
+++ b/html.c
@@ -422,9 +422,13 @@ print_encode(struct html *h, const char *p, int norecurse)
 			break;
 		case ESCAPE_NUMBERED:
 			c = mchars_num2char(seq, len);
+			if (c < 0)
+				continue;
 			break;
 		case ESCAPE_SPECIAL:
 			c = mchars_spec2cp(h->symtab, seq, len);
+			if (c <= 0)
+				continue;
 			break;
 		case ESCAPE_NOSPACE:
 			if ('\0' == *p)
@@ -433,9 +437,8 @@ print_encode(struct html *h, const char *p, int norecurse)
 		default:
 			continue;
 		}
-		if (c <= 0)
-			continue;
-		if (c < 0x20 || (c > 0x7E && c < 0xA0))
+		if ((c < 0x20 && c != 0x09) ||
+		    (c > 0x7E && c < 0xA0))
 			c = 0xFFFD;
 		if (c > 0x7E)
 			printf("&#%d;", c);
diff --git a/mandoc.h b/mandoc.h
index f6863368..5a90f20f 100644
--- a/mandoc.h
+++ b/mandoc.h
@@ -425,7 +425,7 @@ __BEGIN_DECLS
 enum mandoc_esc	  mandoc_escape(const char **, const char **, int *);
 struct mchars	 *mchars_alloc(void);
 void		  mchars_free(struct mchars *);
-char		  mchars_num2char(const char *, size_t);
+int		  mchars_num2char(const char *, size_t);
 const char	 *mchars_uc2str(int);
 int		  mchars_num2uc(const char *, size_t);
 int		  mchars_spec2cp(const struct mchars *,
diff --git a/term.c b/term.c
index 10516d14..9b7ccb27 100644
--- a/term.c
+++ b/term.c
@@ -391,7 +391,6 @@ term_word(struct termp *p, const char *word)
 {
 	const char	 nbrsp[2] = { ASCII_NBRSP, 0 };
 	const char	*seq, *cp;
-	char		 c;
 	int		 sz, uc;
 	size_t		 ssz;
 	enum mandoc_esc	 esc;
@@ -443,16 +442,11 @@ term_word(struct termp *p, const char *word)
 		switch (esc) {
 		case ESCAPE_UNICODE:
 			uc = mchars_num2uc(seq + 1, sz - 1);
-			if (p->enc == TERMENC_ASCII) {
-				cp = ascii_uc2str(uc);
-				encode(p, cp, strlen(cp));
-			} else
-				encode1(p, uc);
 			break;
 		case ESCAPE_NUMBERED:
-			c = mchars_num2char(seq, sz);
-			if ('\0' != c)
-				encode(p, &c, 1);
+			uc = mchars_num2char(seq, sz);
+			if (uc < 0)
+				continue;
 			break;
 		case ESCAPE_SPECIAL:
 			if (p->enc == TERMENC_ASCII) {
@@ -465,35 +459,50 @@ term_word(struct termp *p, const char *word)
 				if (uc > 0)
 					encode1(p, uc);
 			}
-			break;
+			continue;
 		case ESCAPE_FONTBOLD:
 			term_fontrepl(p, TERMFONT_BOLD);
-			break;
+			continue;
 		case ESCAPE_FONTITALIC:
 			term_fontrepl(p, TERMFONT_UNDER);
-			break;
+			continue;
 		case ESCAPE_FONTBI:
 			term_fontrepl(p, TERMFONT_BI);
-			break;
+			continue;
 		case ESCAPE_FONT:
 			/* FALLTHROUGH */
 		case ESCAPE_FONTROMAN:
 			term_fontrepl(p, TERMFONT_NONE);
-			break;
+			continue;
 		case ESCAPE_FONTPREV:
 			term_fontlast(p);
-			break;
+			continue;
 		case ESCAPE_NOSPACE:
 			if (TERMP_SKIPCHAR & p->flags)
 				p->flags &= ~TERMP_SKIPCHAR;
 			else if ('\0' == *word)
 				p->flags |= TERMP_NOSPACE;
-			break;
+			continue;
 		case ESCAPE_SKIPCHAR:
 			p->flags |= TERMP_SKIPCHAR;
-			break;
+			continue;
 		default:
-			break;
+			continue;
+		}
+
+		/*
+		 * Common handling for Unicode and numbered
+		 * character escape sequences.
+		 */
+
+		if (p->enc == TERMENC_ASCII) {
+			cp = ascii_uc2str(uc);
+			encode(p, cp, strlen(cp));
+		} else {
+			if ((uc < 0x20 && uc != 0x09) ||
+			    (uc > 0x7E && uc < 0xA0))
+				uc = 0xFFFD;
+			encode1(p, uc);
 		}
 	}
 	p->flags &= ~TERMP_NBRWORD;
@@ -645,7 +654,7 @@ size_t
 term_strlen(const struct termp *p, const char *cp)
 {
 	size_t		 sz, rsz, i;
-	int		 ssz, skip, c;
+	int		 ssz, skip, uc;
 	const char	*seq, *rhs;
 	enum mandoc_esc	 esc;
 	static const char rej[] = { '\\', ASCII_NBRSP, ASCII_HYPH,
@@ -675,44 +684,61 @@ term_strlen(const struct termp *p, const char *cp)
 
 			switch (esc) {
 			case ESCAPE_UNICODE:
-				c = mchars_num2uc(seq + 1, sz - 1);
-				if (p->enc == TERMENC_ASCII) {
-					rhs = ascii_uc2str(c);
-					rsz = strlen(rhs);
-				} else
-					sz += cond_width(p, c, &skip);
+				uc = mchars_num2uc(seq + 1, sz - 1);
 				break;
 			case ESCAPE_NUMBERED:
-				c = mchars_num2char(seq, ssz);
-				if ('\0' != c)
-					sz += cond_width(p, c, &skip);
+				uc = mchars_num2char(seq, ssz);
+				if (uc < 0)
+					continue;
 				break;
 			case ESCAPE_SPECIAL:
-				if (p->enc == TERMENC_ASCII)
+				if (p->enc == TERMENC_ASCII) {
 					rhs = mchars_spec2str(p->symtab,
 					    seq, ssz, &rsz);
-				else {
-					c = mchars_spec2cp(p->symtab,
+					if (rhs != NULL)
+						break;
+				} else {
+					uc = mchars_spec2cp(p->symtab,
 					    seq, ssz);
-					if (c > 0)
-						sz += cond_width(p, c, &skip);
+					if (uc > 0)
+						sz += cond_width(p, uc, &skip);
 				}
-				break;
+				continue;
 			case ESCAPE_SKIPCHAR:
 				skip = 1;
-				break;
+				continue;
 			default:
-				break;
+				continue;
 			}
 
-			if (NULL == rhs)
-				break;
+			/*
+			 * Common handling for Unicode and numbered
+			 * character escape sequences.
+			 */
+
+			if (rhs == NULL) {
+				if (p->enc == TERMENC_ASCII) {
+					rhs = ascii_uc2str(uc);
+					rsz = strlen(rhs);
+				} else {
+					if ((uc < 0x20 && uc != 0x09) ||
+					    (uc > 0x7E && uc < 0xA0))
+						uc = 0xFFFD;
+					sz += cond_width(p, uc, &skip);
+					continue;
+				}
+			}
 
 			if (skip) {
 				skip = 0;
 				break;
 			}
 
+			/*
+			 * Common handling for all escape sequences
+			 * printing more than one character.
+			 */
+
 			for (i = 0; i < rsz; i++)
 				sz += (*p->width)(p, *rhs++);
 			break;