diff --git a/lib/base64-decode.c b/lib/base64-decode.c
index b89db7ac..51db2679 100644
--- a/lib/base64-decode.c
+++ b/lib/base64-decode.c
@@ -91,3 +91,99 @@ lws_b64_encode_string(const char *in, int in_len, char *out, int out_size)
 
 	return done;
 }
+
+/*
+ * returns length of decoded string in out, or -1 if out was too small
+ * according to out_size
+ */
+
+LWS_VISIBLE int
+lws_b64_decode_string(const char *in, char *out, int out_size)
+{
+	int len;
+	int i;
+	int done = 0;
+	unsigned char v;
+	unsigned char quad[4];
+
+	while (*in) {
+
+		len = 0;
+		for (i = 0; i < 4 && *in; i++) {
+
+			v = 0;
+			while (*in && !v) {
+
+				v = *in++;
+				v = (v < 43 || v > 122) ? 0 : decode[v - 43];
+				if (v)
+					v = (v == '$') ? 0 : v - 61;
+				if (*in) {
+					len++;
+					if (v)
+						quad[i] = v - 1;
+				} else
+					quad[i] = 0;
+			}
+		}
+		if (!len)
+			continue;
+
+		if (out_size < (done + len - 1))
+			/* out buffer is too small */
+			return -1;
+
+		if (len >= 2)
+			*out++ = quad[0] << 2 | quad[1] >> 4;
+		if (len >= 3)
+			*out++ = quad[1] << 4 | quad[2] >> 2;
+		if (len >= 4)
+			*out++ = ((quad[2] << 6) & 0xc0) | quad[3];
+
+		done += len - 1;
+	}
+
+	if (done + 1 >= out_size)
+		return -1;
+
+	*out++ = '\0';
+
+	return done;
+}
+
+int
+lws_b64_selftest(void)
+{
+	char buf[64];
+	int n;
+	int test;
+	static const char * const plaintext[] = {
+		"sanity check base 64"
+	};
+	static const char * const coded[] = {
+		"c2FuaXR5IGNoZWNrIGJhc2UgNjQ="
+	};
+
+	for (test = 0; test < sizeof plaintext / sizeof(plaintext[0]); test++) {
+
+		buf[sizeof(buf) - 1] = '\0';
+		n = lws_b64_encode_string(plaintext[test],
+				      strlen(plaintext[test]), buf, sizeof buf);
+		if (n != strlen(coded[test]) || strcmp(buf, coded[test])) {
+			lwsl_err("Failed lws_b64 encode selftest "
+					   "%d result '%s' %d\n", test, buf, n);
+			return -1;
+		}
+
+		buf[sizeof(buf) - 1] = '\0';
+		n = lws_b64_decode_string(coded[test], buf, sizeof buf);
+		if (n != strlen(plaintext[test]) ||
+						 strcmp(buf, plaintext[test])) {
+			lwsl_err("Failed lws_b64 decode selftest "
+					   "%d result '%s' %d\n", test, buf, n);
+			return -1;
+		}
+	}
+
+	return 0;
+}