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 /* to make the linker happy */
32 struct conf conf;
33 
34 static int
35 adapt(int delta, int numpoints, int firsttime)
36 {
37 	int k;
38 
39 	if (firsttime)
40 		delta = delta / DAMP;
41 	else
42 		delta = delta / 2;
43 
44 	delta += (delta / numpoints);
45 
46 	k = 0;
47 	while (delta > ((BASE - TMIN) * TMAX) / 2) {
48 		delta = delta / (BASE - TMIN);
49 		k += BASE;
50 	}
51 	return k + (((BASE - TMIN + 1) * delta) / (delta + SKEW));
52 }
53 
54 static const char *
55 copy_label(const char *s, char *out, size_t len)
56 {
57 	char *end, *t;
58 	size_t l;
59 
60 	end = strchr(s, '\0');
61 	l = end - s;
62 	if (l > len)
63 		return NULL;
64 
65 	for (t = end; t >= s; --t)
66 		if (*t == '-')
67 			break;
68 
69 	if (t < s)
70 		t = end;
71 
72 	for (; s < t; ++s, ++out) {
73 		if (*s > 'z')
74 			return NULL;
75 		*out = *s;
76 	}
77 
78 	return s;
79 }
80 
81 static unsigned int
82 digit_value(char c)
83 {
84 	if ('A' <= c && c <= 'Z')
85 		return c - 'A';
86 
87 	if ('a' <= c && c <= 'z')
88 		return c - 'a';
89 
90 	if ('0' <= c && c <= '9')
91 		return 26 + c - '0';
92 
93 	return c;
94 }
95 
96 static int
97 insert(char *out, size_t len, int codepoint, size_t i, const char **err)
98 {
99 	int l;
100 	char *t;
101 
102 	if (codepoint <= 0x7F) {
103 		*err = "puny: invalid decoded character (ASCII range)";
104 		return 0;
105 	} else if (codepoint <= 0x7FF) {
106 		l = 2;
107 	} else if (codepoint <= 0xFFFF) {
108 		l = 3;
109 	} else if (codepoint <= 0x10FFFF) {
110 		l = 4;
111 	} else {
112 		*err = "puny: invalid decoded character";
113 		return 0;
114 	}
115 
116 	if ((t = utf8_nth(out, i)) == NULL) {
117 		*err = "puny: invalid insert position";
118 		return 0;
119 	}
120 
121 	if (t + l >= out + len) {
122 		*err = "puny: insert would overflow";
123 		return 0;
124 	}
125 
126 	memmove(t + l, t, strlen(t));
127 
128 	switch (l) {
129 	case 2:
130 		t[1] = ( codepoint        & 0x3F) + 0x80;
131 		t[0] = ((codepoint >>  6) & 0x1F) + 0xC0;
132 		break;
133 	case 3:
134 		t[2] = ( codepoint        & 0x3F) + 0x80;
135 		t[1] = ((codepoint >>  6) & 0x3F) + 0x80;
136 		t[0] = ((codepoint >> 12) & 0x0F) + 0xE0;
137 		break;
138 	case 4:
139 		t[3] = ( codepoint        & 0x3F) + 0x80;
140 		t[2] = ((codepoint >>  6) & 0x3F) + 0x80;
141 		t[1] = ((codepoint >> 12) & 0x3F) + 0x80;
142 		t[0] = ((codepoint >> 18) & 0x07) + 0xF0;
143 		break;
144 	}
145 	return 1;
146 }
147 
148 static int
149 decode(const char *str, char *out, size_t len, const char **err)
150 {
151 	size_t i;
152 	uint32_t n;
153 	unsigned int oldi, bias, w, k, digit, t;
154 	unsigned int numpoints;
155 	const char *s;
156 
157 	if (!starts_with(str, "xn--")) {
158 		strncpy(out, str, len);
159 		return 1;
160 	}
161 
162 	/* skip the xn-- */
163 	str += 4;
164 
165 	if (strchr(str, '-') != NULL) {
166 		if ((s = copy_label(str, out, len)) == NULL) {
167 			*err = "puny: invalid label";
168 			return 0;
169 		}
170 		if (*s == '-')
171 			s++;
172 	} else
173 		s = str;
174 
175 	numpoints = strlen(out);
176 
177 	n = IN;
178 	i = 0;
179 	bias = IBIAS;
180 
181 	while (*s != '\0') {
182 		oldi = i;
183 		w = 1;
184 
185 		for (k = BASE; ; k += BASE) {
186 			if (*s == '\0') {
187 				*err = "puny: label truncated?";
188 				return 0;
189 			}
190 			/* fail eventually? */
191 			digit = digit_value(*s);
192 			s++;
193 
194 			/* fail on overflow */
195 			i += digit * w;
196 
197 			if (k <= bias)
198 				t = TMIN;
199 			else if (k >= bias + TMAX)
200 				t = TMAX;
201 			else
202 				t = k - bias;
203 
204 			if (digit < t)
205 				break;
206 			w *= (BASE - t);
207 		}
208 
209 		bias = adapt(i - oldi, numpoints+1, oldi == 0);
210 		n += i / (numpoints+1); /* fail on overflow */
211 		i = i % (numpoints+1);
212 
213 		if (!insert(out, len, n, i, err))
214 			return 0;
215 		numpoints++;
216 		++i;
217 	}
218 
219 	return 1;
220 }
221 
222 static const char *
223 end_of_label(const char *hostname)
224 {
225 	for (; *hostname != '\0' && *hostname != '.'; ++hostname)
226 		;		/* nop */
227 	return hostname;
228 }
229 
230 int
231 puny_decode(const char *hostname, char *out, size_t len, const char **err)
232 {
233 	char label[LABEL_LEN];
234 	const char *s, *end;
235 	size_t l;
236 
237 	memset(out, 0, len);
238 	if (hostname == NULL)
239 		return 1;
240 
241 	s = hostname;
242 	for (;;) {
243 		end = end_of_label(s);
244 		l = end - s;
245 		if (l >= sizeof(label)) {
246 			*err = "label too long";
247 			return 0;
248 		}
249 
250 		memcpy(label, s, l);
251 		label[l] = '\0';
252 
253 		if (!decode(label, out, len, err))
254 			return 0;
255 
256 		if (*end == '\0')
257 			return 1;
258 
259 		if (strlcat(out, ".", len) >= len) {
260 			*err = "domain name too long";
261 			return 0;
262 		}
263 
264 		l = strlen(out);
265 		if (l >= len) {
266 			*err = "domain name too long";
267 			return 0;
268 		}
269 		out += l;
270 		len -= l;
271 
272 		s = end+1;
273 	}
274 }