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int domain2name_len (const char * s, int l) {
int r = 1; /* ending terminator */
int o = 0; /* label offset */
for (int i = 0; i < l; i++) {
if (s[i] == '.') {
if (!o) /* double period or starting period, label is empty */
break;
o = 0;
continue;
}
if (!o) /* label has started */
r++;
r++;
o++;
}
return r;
}
int domain2name (char * d, const char * s, int l) { /* l is length of s */
char * c = d; /* where to write the label size when done with label */
char * w = d;
int o = 0; /* label offset */
for (int i = 0; i <= l /* yes, we go one more ... */; i++) {
if (i == l /* ... here */ || s[i] == '.') { /* end of label or end of last label */
if (!o) /* double period or starting period, label is empty */
break;
if (o <= 63) /* max length of label (six bits) */
*c = o;
o = 0;
continue;
}
if (!o++) /* label has started */
c = w++; /* to be filled with length */
if (o <= 63)
*w++ = s[i];
if (o == 64) /* if this label is too long, instead of writing it, we silently cap */
*c = 63; /* it at 63 bytes */
}
*w++ = '\0'; /* luckily this makes domain2name kind of safe for handling as a string (: */
return w-d; /* we return number of bytes written */
} /* d must be allocated for at least _len. */
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