Add time-to-live (TTL) support to resolver cache
Use the the TTL of the answer as the time a query
shall remain in the resolver cache.
Added some debugging support as well, i.e.
parse answer and print a la dig.
Change-Id: I724d3392245032592f1912f3ca7a81a8987ebbac
diff --git a/libc/netbsd/resolv/res_cache.c b/libc/netbsd/resolv/res_cache.c
index 84194c2..f0c51ab 100644
--- a/libc/netbsd/resolv/res_cache.c
+++ b/libc/netbsd/resolv/res_cache.c
@@ -32,12 +32,15 @@
#include <time.h>
#include "pthread.h"
+#include <errno.h>
+#include "arpa_nameser.h"
+
/* This code implements a small and *simple* DNS resolver cache.
*
- * It is only used to cache DNS answers for a maximum of CONFIG_SECONDS seconds
- * in order to reduce DNS traffic. It is not supposed to be a full DNS cache,
- * since we plan to implement that in the future in a dedicated process running
- * on the system.
+ * It is only used to cache DNS answers for a time defined by the smallest TTL
+ * among the answer records in order to reduce DNS traffic. It is not supposed
+ * to be a full DNS cache, since we plan to implement that in the future in a
+ * dedicated process running on the system.
*
* Note that its design is kept simple very intentionally, i.e.:
*
@@ -47,9 +50,8 @@
* (this means that two similar queries that encode the DNS name
* differently will be treated distinctly).
*
- * - the TTLs of answer RRs are ignored. our DNS resolver library does not use
- * them anyway, but it means that records with a TTL smaller than
- * CONFIG_SECONDS will be kept in the cache anyway.
+ * the smallest TTL value among the answer records are used as the time
+ * to keep an answer in the cache.
*
* this is bad, but we absolutely want to avoid parsing the answer packets
* (and should be solved by the later full DNS cache process).
@@ -141,6 +143,7 @@
/* set to 1 to debug query data */
#define DEBUG_DATA 0
+#undef XLOG
#if DEBUG
# include <logd.h>
# define XLOG(...) \
@@ -149,6 +152,9 @@
#include <stdio.h>
#include <stdarg.h>
+#include <arpa/inet.h>
+#include "resolv_private.h"
+
/** BOUNDED BUFFER FORMATTING
**/
@@ -987,10 +993,50 @@
int querylen;
const uint8_t* answer;
int answerlen;
- time_t when; /* time_t when entry was added to table */
- int id; /* for debugging purpose */
+ time_t expires; /* time_t when the entry isn't valid any more */
+ int id; /* for debugging purpose */
} Entry;
+/**
+ * Parse the answer records and find the smallest
+ * TTL among the answer records.
+ *
+ * The returned TTL is the number of seconds to
+ * keep the answer in the cache.
+ *
+ * In case of parse error zero (0) is returned which
+ * indicates that the answer shall not be cached.
+ */
+static u_long
+answer_getTTL(const void* answer, int answerlen)
+{
+ ns_msg handle;
+ int ancount, n;
+ u_long result, ttl;
+ ns_rr rr;
+
+ result = 0;
+ if (ns_initparse(answer, answerlen, &handle) >= 0) {
+ // get number of answer records
+ ancount = ns_msg_count(handle, ns_s_an);
+ for (n = 0; n < ancount; n++) {
+ if (ns_parserr(&handle, ns_s_an, n, &rr) == 0) {
+ ttl = ns_rr_ttl(rr);
+ if (n == 0 || ttl < result) {
+ result = ttl;
+ }
+ } else {
+ XLOG("ns_parserr failed ancount no = %d. errno = %s\n", n, strerror(errno));
+ }
+ }
+ } else {
+ XLOG("ns_parserr failed. %s\n", strerror(errno));
+ }
+
+ XLOG("TTL = %d\n", result);
+
+ return result;
+}
static void
entry_free( Entry* e )
@@ -1072,8 +1118,6 @@
memcpy( (char*)e->answer, answer, e->answerlen );
- e->when = _time_now();
-
return e;
}
@@ -1183,12 +1227,47 @@
XLOG("%s", temp);
}
+
+static void
+_dump_answer(const void* answer, int answerlen)
+{
+ res_state statep;
+ FILE* fp;
+ char* buf;
+ int fileLen;
+
+ fp = fopen("/data/reslog.txt", "w+");
+ if (fp != NULL) {
+ statep = __res_get_state();
+
+ res_pquery(statep, answer, answerlen, fp);
+
+ //Get file length
+ fseek(fp, 0, SEEK_END);
+ fileLen=ftell(fp);
+ fseek(fp, 0, SEEK_SET);
+ buf = (char *)malloc(fileLen+1);
+ if (buf != NULL) {
+ //Read file contents into buffer
+ fread(buf, fileLen, 1, fp);
+ XLOG("%s\n", buf);
+ free(buf);
+ }
+ fclose(fp);
+ remove("/data/reslog.txt");
+ }
+ else {
+ XLOG("_dump_answer: can't open file\n");
+ }
+}
#endif
#if DEBUG
# define XLOG_QUERY(q,len) _dump_query((q), (len))
+# define XLOG_ANSWER(a, len) _dump_answer((a), (len))
#else
# define XLOG_QUERY(q,len) ((void)0)
+# define XLOG_ANSWER(a,len) ((void)0)
#endif
/* This function tries to find a key within the hash table
@@ -1322,7 +1401,7 @@
now = _time_now();
/* remove stale entries here */
- if ( (unsigned)(now - e->when) >= CONFIG_SECONDS ) {
+ if (now >= e->expires) {
XLOG( " NOT IN CACHE (STALE ENTRY %p DISCARDED)", *lookup );
_cache_remove_p(cache, lookup);
goto Exit;
@@ -1363,6 +1442,7 @@
Entry key[1];
Entry* e;
Entry** lookup;
+ u_long ttl;
/* don't assume that the query has already been cached
*/
@@ -1375,6 +1455,7 @@
XLOG( "%s: query:", __FUNCTION__ );
XLOG_QUERY(query,querylen);
+ XLOG_ANSWER(answer, answerlen);
#if DEBUG_DATA
XLOG( "answer:");
XLOG_BYTES(answer,answerlen);
@@ -1401,9 +1482,13 @@
}
}
- e = entry_alloc( key, answer, answerlen );
- if (e != NULL) {
- _cache_add_p(cache, lookup, e);
+ ttl = answer_getTTL(answer, answerlen);
+ if (ttl > 0) {
+ e = entry_alloc(key, answer, answerlen);
+ if (e != NULL) {
+ e->expires = ttl + _time_now();
+ _cache_add_p(cache, lookup, e);
+ }
}
#if DEBUG
_cache_dump_mru(cache);