implement new dns backend, res_send and other legacy resolver functions

this is the second phase of the "resolver overhaul" project.

the key additions in this commit are the __res_msend and __res_mkquery
functions, which have been factored so as to provide a backend for
both the legacy res_* functions and the standard getaddrinfo and
getnameinfo functions. the latter however are still using the old
backend code; there is code duplication which still needs to be
removed, and this will be the next phase of the resolver overhaul.

__res_msend is derived from the old __dns_doqueries function, but
generalized to send arbitrary caller-provided packets in parallel
rather than producing the parallel queries itself. this allows it to
be used (completely trivially) as a backend for res_send. the
factored-out query generation code, with slightly more generality, is
now part of __res_mkquery.

1 files changed, 41 insertions, 0 deletions

diff --git a/src/network/res_mkquery.c b/src/network/res_mkquery.c
new file mode 100644
index 00000000..f7e4e9c6
--- /dev/null
+++ b/src/network/res_mkquery.c
@@ -0,0 +1,41 @@
+#include <resolv.h>
+#include <string.h>
+#include <time.h>
+#include "libc.h"
+
+int __res_mkquery(int op, const char *dname, int class, int type,
+	const unsigned char *data, int datalen,
+	const unsigned char *newrr, unsigned char *buf, int buflen)
+{
+	int id, i, j;
+	unsigned char q[280];
+	struct timespec ts;
+	size_t l = strnlen(dname, 256);
+
+	if (l-1>=254 || buflen<18+l || op>15u || class>255u || type>255u)
+		return -1;
+
+	/* Construct query template - ID will be filled later */
+	memset(q, 0, 18+l);
+	q[2] = op*8 + 1;
+	q[5] = 1;
+	memcpy((char *)q+13, dname, l);
+	for (i=13; q[i]; i=j+1) {
+		for (j=i; q[j] && q[j] != '.'; j++);
+		if (j-i-1u > 62u) return -1;
+		q[i-1] = j-i;
+	}
+	q[i+1] = type;
+	q[i+3] = class;
+
+	/* Make a reasonably unpredictable id */
+	clock_gettime(CLOCK_REALTIME, &ts);
+	id = ts.tv_nsec + ts.tv_nsec/65536UL & 0xffff;
+	q[0] = id/256;
+	q[1] = id;
+
+	memcpy(buf, q, 18+l);
+	return 18+l;
+}
+
+weak_alias(__res_mkquery, res_mkquery);