1 /*
2  * Copyright (c) 2021 Omar Polo <op@omarpolo.com>
3  *
4  * Permission to use, copy, modify, and distribute this software for any
5  * purpose with or without fee is hereby granted, provided that the above
6  * copyright notice and this permission notice appear in all copies.
7  *
8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15  */
16 
17 #include <stddef.h>
18 #include <stdint.h>
19 #include <string.h>
20 
21 #include "gmid.h"
22 
23 #define BASE	36
24 #define TMIN	1
25 #define TMAX	26
26 #define SKEW	38
27 #define DAMP	700
28 #define IBIAS	72
29 #define IN	128
30 
31 static int
32 adapt(int delta, int numpoints, int firsttime)
33 {
34 	int k;
35 
36 	if (firsttime)
37 		delta = delta / DAMP;
38 	else
39 		delta = delta / 2;
40 
41 	delta += (delta / numpoints);
42 
43 	k = 0;
44 	while (delta > ((BASE - TMIN) * TMAX) / 2) {
45 		delta = delta / (BASE - TMIN);
46 		k += BASE;
47 	}
48 	return k + (((BASE - TMIN + 1) * delta) / (delta + SKEW));
49 }
50 
51 static const char *
52 copy_until_delimiter(const char *s, char *out, size_t len)
53 {
54 	char *end, *t;
55 	size_t l;
56 
57 	end = strchr(s, '\0');
58 	l = end - s;
59 	if (l > len)
60 		return NULL;
61 
62 	for (t = end; t >= s; --t)
63 		if (*t == '-')
64 			break;
65 
66 	if (t < s)
67 		t = end;
68 
69 	for (; s < t; ++s, ++out) {
70 		if (*s > 'z')
71 			return NULL;
72 		*out = *s;
73 	}
74 
75 	return s;
76 }
77 
78 static unsigned int
79 digit_value(char c)
80 {
81 	if ('A' <= c && c <= 'Z')
82 		return c - 'A';
83 
84 	if ('a' <= c && c <= 'z')
85 		return c - 'a';
86 
87 	if ('0' <= c && c <= '9')
88 		return 26 + c - '0';
89 
90 	return c;
91 }
92 
93 static int
94 insert(char *out, size_t len, int codepoint, size_t i)
95 {
96 	int l;
97 	char *t;
98 
99 	if (codepoint <= 0x7F)
100 		return 0;
101 	else if (codepoint <= 0x7FF)
102 		l = 2;
103 	else if (codepoint <= 0xFFFF)
104 		l = 3;
105 	else if (codepoint <= 0x10FFFF)
106 		l = 4;
107 	else
108 		return 0;
109 
110 	if ((t = utf8_nth(out, i)) == NULL)
111 		return 0;
112 	if (t + l >= out + len)
113 		return 0;
114 
115 	memmove(t + l, t, strlen(t));
116 
117 	switch (l) {
118 	case 2:
119 		t[1] = ( codepoint        & 0x3F) + 0x80;
120 		t[0] = ((codepoint >> 6)  & 0x1F) + 0xC0;
121 		break;
122 	case 3:
123 		t[2] = ( codepoint        & 0x3F) + 0x80;
124 		t[1] = ((codepoint >> 6)  & 0x3F) + 0x80;
125 		t[0] = ((codepoint >> 12) & 0x0F) + 0xE0;
126 		break;
127 	case 4:
128 		t[3] = ( codepoint        & 0x3F) + 0x80;
129 		t[2] = ((codepoint >> 6)  & 0x3F) + 0x80;
130 		t[1] = ((codepoint >> 12) & 0x3F) + 0x80;
131 		t[0] = ((codepoint >> 18) & 0x07) + 0xF0;
132 		break;
133 	}
134 	return 1;
135 }
136 
137 static int
138 decode(const char *str, char *out, size_t len)
139 {
140 	size_t i;
141 	uint32_t n;
142 	unsigned int oldi, bias, w, k, digit, t;
143 	unsigned int numpoints;
144 	const char *s;
145 
146 	if (!starts_with(str, "xn--")) {
147 		strncpy(out, str, len);
148 		return 1;
149 	}
150 
151 	/* skip the xn-- */
152 	str += 4;
153 
154 	if (strchr(str, '-') != NULL) {
155 		if ((s = copy_until_delimiter(str, out, len)) == NULL)
156 			return 0;
157 		if (*s == '-')
158 			s++;
159 	} else
160 		s = str;
161 
162 	numpoints = strlen(out);
163 
164 	n = IN;
165 	i = 0;
166 	bias = IBIAS;
167 
168 	while (*s != '\0') {
169 		oldi = i;
170 		w = 1;
171 
172 		for (k = BASE; ; k += BASE) {
173 			if (*s == '\0')
174 				return 0;
175 			/* fail eventually? */
176 			digit = digit_value(*s);
177 			s++;
178 
179 			/* fail on overflow */
180 			i += digit * w;
181 
182 			if (k <= bias)
183 				t = TMIN;
184 			else if (k >= bias + TMAX)
185 				t = TMAX;
186 			else
187 				t = k - bias;
188 
189 			if (digit < t)
190 				break;
191 			w *= (BASE - t);
192 		}
193 
194 		bias = adapt(i - oldi, numpoints+1, oldi == 0);
195 		n += i / (numpoints+1); /* fail on overflow */
196 		i = i % (numpoints+1);
197 
198 		if (!insert(out, len, n, i))
199 			return 0;
200 		numpoints++;
201 		++i;
202 	}
203 
204 	return 1;
205 }
206 
207 static const char *
208 end_of_component(const char *hostname)
209 {
210 	for (; *hostname != '\0' && *hostname != '.'; ++hostname)
211 		;		/* nop */
212 	return hostname;
213 }
214 
215 int
216 puny_decode(const char *hostname, char *out, size_t len)
217 {
218 	char comp[DOMAIN_NAME_LEN];
219 	const char *s, *end;
220 	size_t l;
221 
222 	memset(out, 0, len);
223 	if (hostname == NULL)
224 		return 1;
225 
226 	s = hostname;
227 	for (;;) {
228 		end = end_of_component(s);
229 		l = end - s;
230 		if (l >= sizeof(comp))
231 			return 0;
232 
233 		memcpy(comp, s, end - s);
234 		comp[end - s] = '\0';
235 
236 		if (!decode(comp, out, len))
237 			return 0;
238 
239 		if (*end == '\0')
240 			return 1;
241 
242 		if (strlcat(out, ".", len) >= len)
243 			return 0;
244 
245 		l = strlen(out);
246 		if (l >= len)
247 			return 0;
248 		out += l;
249 		len -= l;
250 
251 		s = end+1;
252 	}
253 }