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 
56 	end = strchr(s, '\0');
57 	if (end - s  > len)
58 		return NULL;
59 
60 	for (t = end; t >= s; --t)
61 		if (*t == '-')
62 			break;
63 
64 	if (t < s)
65 		t = end;
66 
67 	for (; s < t; ++s, ++out) {
68 		if (*s > 'z')
69 			return NULL;
70 		*out = *s;
71 	}
72 
73 	return s;
74 }
75 
76 static unsigned int
77 digit_value(char c)
78 {
79 	if ('A' <= c && c <= 'Z')
80 		return c - 'A';
81 
82 	if ('a' <= c && c <= 'z')
83 		return c - 'a';
84 
85 	if ('0' <= c && c <= '9')
86 		return 26 + c - '0';
87 
88 	return c;
89 }
90 
91 static int
92 insert(char *out, size_t len, int codepoint, size_t i)
93 {
94 	int l;
95 	size_t outlen;
96 	char *t;
97 
98 	if (codepoint <= 0x7F)
99 		return 0;
100 	else if (codepoint <= 0x7FF)
101 		l = 2;
102 	else if (codepoint <= 0xFFFF)
103 		l = 3;
104 	else if (codepoint <= 0x10FFFF)
105 		l = 4;
106 	else
107 		return 0;
108 
109 	if ((t = utf8_nth(out, i)) == NULL)
110 		return 0;
111 	if (t + l >= out + len)
112 		return 0;
113 
114 	memmove(t + l, t, strlen(t));
115 
116 	switch (l) {
117 	case 2:
118 		t[1] = ( codepoint        & 0x3F) + 0x80;
119 		t[0] = ((codepoint >> 6)  & 0x1F) + 0xC0;
120 		break;
121 	case 3:
122 		t[2] = ( codepoint        & 0x3F) + 0x80;
123 		t[1] = ((codepoint >> 6)  & 0x3F) + 0x80;
124 		t[0] = ((codepoint >> 12) & 0x0F) + 0xE0;
125 		break;
126 	case 4:
127 		t[3] = ( codepoint        & 0x3F) + 0x80;
128 		t[2] = ((codepoint >> 6)  & 0x3F) + 0x80;
129 		t[1] = ((codepoint >> 12) & 0x3F) + 0x80;
130 		t[0] = ((codepoint >> 18) & 0x07) + 0xF0;
131 		break;
132 	}
133 	return 1;
134 }
135 
136 static int
137 decode(const char *str, char *out, size_t len)
138 {
139 	size_t i;
140 	uint32_t n;
141 	unsigned int oldi, bias, w, k, digit, t;
142 	unsigned int numpoints;
143 	const char *s;
144 
145 	if (str == NULL || len <= 4)
146 		return 0;
147 
148 	/* todo: starts_with */
149 	if (strstr(str, "xn--") != str) {
150 		strncpy(out, str, len);
151 		return 1;
152 	}
153 
154 	/* skip the xn-- */
155 	str += 4;
156 
157 	if (strchr(str, '-') != NULL) {
158 		if ((s = copy_until_delimiter(str, out, len)) == NULL)
159 			return 0;
160 		if (*s == '-')
161 			s++;
162 	} else
163 		s = str;
164 
165 	numpoints = strlen(out);
166 
167 	n = IN;
168 	i = 0;
169 	bias = IBIAS;
170 
171 	while (*s != '\0') {
172 		oldi = i;
173 		w = 1;
174 
175 		for (k = BASE; ; k += BASE) {
176 			if (*s == '\0')
177 				return 0;
178 			/* fail eventually? */
179 			digit = digit_value(*s);
180 			s++;
181 
182 			/* fail on overflow */
183 			i += digit * w;
184 
185 			if (k <= bias)
186 				t = TMIN;
187 			else if (k >= bias + TMAX)
188 				t = TMAX;
189 			else
190 				t = k - bias;
191 
192 			if (digit < t)
193 				break;
194 			w *= (BASE - t);
195 		}
196 
197 		bias = adapt(i - oldi, numpoints+1, oldi == 0);
198 		n += i / (numpoints+1); /* fail on overflow */
199 		i = i % (numpoints+1);
200 
201 		if (!insert(out, len, n, i))
202 			return 0;
203 		numpoints++;
204 		++i;
205 	}
206 
207 	return 1;
208 }
209 
210 const char *
211 end_of_component(const char *hostname)
212 {
213 	for (; *hostname != '\0' && *hostname != '.'; ++hostname)
214 		;		/* nop */
215 	return hostname;
216 }
217 
218 int
219 puny_decode(const char *hostname, char *out, size_t len)
220 {
221 	char comp[DOMAIN_NAME_LEN];
222 	const char *s, *end;
223 	size_t l;
224 
225 	memset(out, 0, len);
226 
227 	s = hostname;
228 	for (;;) {
229 		end = end_of_component(s);
230 		if (end - s >= 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 }