From 877b7b64021410c1bb686cad562e7446eb65c318 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Anton=20Luka=20=C5=A0ijanec?= <anton@sijanec.eu>
Date: Mon, 2 May 2022 00:45:48 +0200
Subject: dns server. untested. compiles.

---
 domain2name.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 135 insertions(+)
 create mode 100644 domain2name.c

(limited to 'domain2name.c')

diff --git a/domain2name.c b/domain2name.c
new file mode 100644
index 0000000..47bfdad
--- /dev/null
+++ b/domain2name.c
@@ -0,0 +1,135 @@
+int domain2name_len (const char * s, int l) {	/* TODO	make domain2name FAIL at empty label (..) */
+	int r = 1; /* ending terminator */	/*	make functions FAIL at label.length > 63 */
+	int o = 0; /* label offset */		/*	currently domain2name never fails */
+	for (int i = 0; i < l; i++) {		/* NOTE when using BOTH _len, check that they are */
+		if (s[i] == '.') {		/*	NOT negative. d2n_len may fail in d future */
+			if (!o) /* double period or starting period, label is empty */
+				break; /* we could return -1 here if r == 1 */
+			o = 0;
+			continue;
+		}
+		if (!o) /* label has started */
+			r++;
+		if (o < 63) { /* we cap label length at 64 bytes. we could return -2 here. */
+			r++;
+			o++;
+		}
+	}
+	return r;
+}
+int domain2name (char * n /* at least _len bytes */, const char * s, int l) { /* l is length of s */
+	char * c = n; /* where to write the label size when done with label */
+	char * w = n;
+	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-n; /* we return number of bytes written */
+} /* no compression, it's 2022, net bandwidth is unlimited. n2d OFC does decompress ptrs acc2 std. */
+int name2domain_len (const char * u, int s /* size of u */, const char * n /* name */) {
+#define N2DO(x) (ntohs(x) & ~(1 << 15 | 1 << 14)) /* pointer offset */
+	int r = 0;
+	char f[s/8+1];
+	memset(f, '\0', s/8+1);
+	if (n < u+s && *n == '\0') {
+		return 2;
+	}
+	while (n < u+s) {
+		if (*n & 1 << 7) {
+			if (!(*n & 1 << 6))
+				return -1; /* 10xx xxxx not implemented - reserved for future use */
+			if (n+1 >= u+s)
+				return -2; /* malformed packet */
+			if (f[(n-u)/8] & 1 << (n-u)%8)
+				return -3; /* infinite pointer loop detected */
+			f[(n-u)/8] |= 1 << (n-u)%8;
+			n = u + N2DO(*(uint16_t *) n);
+			continue;
+		}
+		if (*n & 1 << 6)
+			return -4; /* 01xx xxxx not implemented - reserved for future use */
+		if (!*n)
+			return r+1;
+		r += *n+1;
+		n += *n+1;
+	}
+	return -5; /* malformed packet */
+} /* returns number of bytes needed for buffer, passed as the first argument of name2domain(). */
+const char * name2domain (char * d /* >= _len B */, const char * u, int s, const char * n) {
+	char * w = d; /* if d is NULL nothing is written and last byte of name is returned */
+	const char * r = NULL;
+	char f[s/8+1];
+	memset(f, '\0', s/8+1);
+	if (n < u+s && *n == '\0') {
+		*w++ = '.';
+		*w++ = '\0';
+		return n;
+	}
+	while (n < u+s) {
+		if (*n & 1 << 7) {
+			if (!(*n & 1 << 6))
+				return NULL; /* 10xx xxxx N/I - reserved for future use as per RFC */
+			if (n+1 >= u+s)
+				return NULL;
+			r = n+1;
+			if (f[(n-u)/8] & 1 << (n-u)%8)
+				return NULL; /* infinite pointer loop detected */
+			f[(n-u)/8] |= 1 << (n-u)%8;
+			n = u + N2DO(*(uint16_t *) n);
+			continue;
+		}
+		if (*n & 1 << 6)
+			return NULL; /* 01xx xxxx N/I - reserved for future use as per RFC */
+		if (!*n) { /* end of name */
+			if (w)
+				*w++ = '\0';
+			return r ? r : n;
+		}
+		const char * x = n+*n;
+		n++;
+		if (!(x < u+s))
+			return NULL; /* malformed packet */
+		while (n <= x)
+			if (w)
+				*w++ = *n++;
+			else
+				n++;
+		if (w)
+			*w++ = '.';
+	}
+	return NULL; /* malformed packet */
+} /* Returns ptr to last byte of name - '\0' or dnsptr. Ret. NULL on fail (_len also returned < 0) */
+int normalizedomain_len (const char * s, int l) {
+	int ž = domain2name_len(s, l);
+	if (ž < 0)
+		return -6;
+	char b[ž];
+	if (domain2name(b, s, l) != ž)
+		return -7;
+	return name2domain_len(b, ž, b);
+}
+int normalizedomain (char * d /* at least _len bytes */, const char * s, int l) {
+	int ž = domain2name_len(s, l);
+	if (ž < 0)
+		return -6;
+	char b[ž];
+	if (domain2name(b, s, l) != ž)
+		return -7;
+	if (!name2domain(d, b, ž, b))
+		return -8;
+	return 0;
+}
-- 
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