1 | /* vi: set sw=4 ts=4: */
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2 |
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3 | /* RFC1035 domain compression routines (C) 2007 Gabriel Somlo <somlo at cmu.edu>
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4 | *
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5 | * Loosely based on the isc-dhcpd implementation by dhankins@isc.org
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6 | *
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7 | * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
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8 | */
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9 |
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10 | #if ENABLE_FEATURE_RFC3397
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11 |
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12 | #include "common.h"
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13 | #include "options.h"
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14 |
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15 | #define NS_MAXDNAME 1025 /* max domain name length */
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16 | #define NS_MAXCDNAME 255 /* max compressed domain name length */
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17 | #define NS_MAXLABEL 63 /* max label length */
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18 | #define NS_MAXDNSRCH 6 /* max domains in search path */
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19 | #define NS_CMPRSFLGS 0xc0 /* name compression pointer flag */
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20 |
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21 |
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22 | /* expand a RFC1035-compressed list of domain names "cstr", of length "clen";
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23 | * returns a newly allocated string containing the space-separated domains,
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24 | * prefixed with the contents of string pre, or NULL if an error occurs.
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25 | */
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26 | char *dname_dec(const uint8_t *cstr, int clen, const char *pre)
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27 | {
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28 | const uint8_t *c;
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29 | int crtpos, retpos, depth, plen = 0, len = 0;
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30 | char *dst = NULL;
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31 |
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32 | if (!cstr)
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33 | return NULL;
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34 |
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35 | if (pre)
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36 | plen = strlen(pre);
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37 |
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38 | /* We make two passes over the cstr string. First, we compute
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39 | * how long the resulting string would be. Then we allocate a
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40 | * new buffer of the required length, and fill it in with the
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41 | * expanded content. The advantage of this approach is not
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42 | * having to deal with requiring callers to supply their own
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43 | * buffer, then having to check if it's sufficiently large, etc.
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44 | */
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45 |
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46 | while (!dst) {
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47 |
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48 | if (len > 0) { /* second pass? allocate dst buffer and copy pre */
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49 | dst = xmalloc(len + plen);
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50 | memcpy(dst, pre, plen);
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51 | }
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52 |
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53 | crtpos = retpos = depth = len = 0;
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54 |
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55 | while (crtpos < clen) {
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56 | c = cstr + crtpos;
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57 |
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58 | if ((*c & NS_CMPRSFLGS) != 0) { /* pointer */
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59 | if (crtpos + 2 > clen) /* no offset to jump to? abort */
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60 | return NULL;
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61 | if (retpos == 0) /* toplevel? save return spot */
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62 | retpos = crtpos + 2;
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63 | depth++;
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64 | crtpos = ((*c & 0x3f) << 8) | (*(c + 1) & 0xff); /* jump */
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65 | } else if (*c) { /* label */
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66 | if (crtpos + *c + 1 > clen) /* label too long? abort */
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67 | return NULL;
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68 | if (dst)
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69 | memcpy(dst + plen + len, c + 1, *c);
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70 | len += *c + 1;
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71 | crtpos += *c + 1;
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72 | if (dst)
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73 | *(dst + plen + len - 1) = '.';
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74 | } else { /* null: end of current domain name */
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75 | if (retpos == 0) { /* toplevel? keep going */
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76 | crtpos++;
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77 | } else { /* return to toplevel saved spot */
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78 | crtpos = retpos;
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79 | retpos = depth = 0;
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80 | }
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81 | if (dst)
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82 | *(dst + plen + len - 1) = ' ';
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83 | }
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84 |
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85 | if (depth > NS_MAXDNSRCH || /* too many jumps? abort, it's a loop */
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86 | len > NS_MAXDNAME * NS_MAXDNSRCH) /* result too long? abort */
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87 | return NULL;
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88 | }
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89 |
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90 | if (!len) /* expanded string has 0 length? abort */
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91 | return NULL;
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92 |
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93 | if (dst)
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94 | *(dst + plen + len - 1) = '\0';
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95 | }
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96 |
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97 | return dst;
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98 | }
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99 |
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100 | /* Convert a domain name (src) from human-readable "foo.blah.com" format into
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101 | * RFC1035 encoding "\003foo\004blah\003com\000". Return allocated string, or
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102 | * NULL if an error occurs.
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103 | */
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104 | static uint8_t *convert_dname(const char *src)
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105 | {
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106 | uint8_t c, *res, *lp, *rp;
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107 | int len;
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108 |
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109 | res = xmalloc(strlen(src) + 2);
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110 | rp = lp = res;
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111 | rp++;
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112 |
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113 | for (;;) {
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114 | c = (uint8_t)*src++;
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115 | if (c == '.' || c == '\0') { /* end of label */
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116 | len = rp - lp - 1;
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117 | /* label too long, too short, or two '.'s in a row? abort */
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118 | if (len > NS_MAXLABEL || len == 0 || (c == '.' && *src == '.')) {
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119 | free(res);
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120 | return NULL;
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121 | }
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122 | *lp = len;
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123 | lp = rp++;
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124 | if (c == '\0' || *src == '\0') /* end of dname */
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125 | break;
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126 | } else {
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127 | if (c >= 0x41 && c <= 0x5A) /* uppercase? convert to lower */
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128 | c += 0x20;
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129 | *rp++ = c;
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130 | }
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131 | }
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132 |
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133 | *lp = 0;
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134 | if (rp - res > NS_MAXCDNAME) { /* dname too long? abort */
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135 | free(res);
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136 | return NULL;
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137 | }
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138 | return res;
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139 | }
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140 |
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141 | /* returns the offset within cstr at which dname can be found, or -1
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142 | */
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143 | static int find_offset(const uint8_t *cstr, int clen, const uint8_t *dname)
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144 | {
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145 | const uint8_t *c, *d;
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146 | int off, inc;
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147 |
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148 | /* find all labels in cstr */
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149 | off = 0;
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150 | while (off < clen) {
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151 | c = cstr + off;
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152 |
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153 | if ((*c & NS_CMPRSFLGS) != 0) { /* pointer, skip */
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154 | off += 2;
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155 | } else if (*c) { /* label, try matching dname */
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156 | inc = *c + 1;
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157 | d = dname;
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158 | while (*c == *d && memcmp(c + 1, d + 1, *c) == 0) {
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159 | if (*c == 0) /* match, return offset */
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160 | return off;
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161 | d += *c + 1;
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162 | c += *c + 1;
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163 | if ((*c & NS_CMPRSFLGS) != 0) /* pointer, jump */
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164 | c = cstr + (((*c & 0x3f) << 8) | (*(c + 1) & 0xff));
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165 | }
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166 | off += inc;
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167 | } else { /* null, skip */
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168 | off++;
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169 | }
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170 | }
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171 |
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172 | return -1;
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173 | }
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174 |
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175 | /* computes string to be appended to cstr so that src would be added to
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176 | * the compression (best case, it's a 2-byte pointer to some offset within
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177 | * cstr; worst case, it's all of src, converted to rfc3011 format).
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178 | * The computed string is returned directly; its length is returned via retlen;
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179 | * NULL and 0, respectively, are returned if an error occurs.
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180 | */
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181 | uint8_t *dname_enc(const uint8_t *cstr, int clen, const char *src, int *retlen)
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182 | {
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183 | uint8_t *d, *dname;
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184 | int off;
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185 |
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186 | dname = convert_dname(src);
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187 | if (dname == NULL) {
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188 | *retlen = 0;
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189 | return NULL;
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190 | }
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191 |
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192 | for (d = dname; *d != 0; d += *d + 1) {
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193 | off = find_offset(cstr, clen, d);
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194 | if (off >= 0) { /* found a match, add pointer and terminate string */
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195 | *d++ = NS_CMPRSFLGS;
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196 | *d = off;
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197 | break;
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198 | }
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199 | }
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200 |
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201 | *retlen = d - dname + 1;
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202 | return dname;
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203 | }
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204 |
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205 | #endif /* ENABLE_FEATURE_RFC3397 */
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