1 files changed, 40 insertions, 0 deletions

diff --git a/domain2name.c b/domain2name.c
new file mode 100644
index 0000000..46fd2a3
--- /dev/null
+++ b/domain2name.c
@@ -0,0 +1,40 @@
+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. */