4718. [func] Avoid seaching for a owner name compression pointer

more than once when writing out a RRset. [RT #45802]

CHANGES

@@ -1,3 +1,6 @@
+4718.	[func]		Avoid seaching for a owner name compression pointer
+			more than once when writing out a RRset. [RT #45802]
+
 4717.	[bug]		Treat replies with QCOUNT=0 as truncated if TC=1,
 			FORMERR if TC=0, and log the error correctly.
 			[RT #45836]

lib/dns/include/dns/name.h

@@ -739,6 +739,9 @@ dns_name_fromwire(dns_name_t *name, isc_buffer_t *source,
 isc_result_t
 dns_name_towire(const dns_name_t *name, dns_compress_t *cctx,
 		isc_buffer_t *target);
+isc_result_t
+dns_name_towire2(const dns_name_t *name, dns_compress_t *cctx,
+		 isc_buffer_t *target, isc_uint16_t *comp_offsetp);
 /*%<
  * Convert 'name' into wire format, compressing it as specified by the
  * compression context 'cctx', and storing the result in 'target'.

lib/dns/name.c

@@ -1987,6 +1987,13 @@ dns_name_fromwire(dns_name_t *name, isc_buffer_t *source,
 isc_result_t
 dns_name_towire(const dns_name_t *name, dns_compress_t *cctx,
 		isc_buffer_t *target)
+{
+	return (dns_name_towire2(name, cctx, target, NULL));
+}
+
+isc_result_t
+dns_name_towire2(const dns_name_t *name, dns_compress_t *cctx,
+		 isc_buffer_t *target, isc_uint16_t *comp_offsetp)
 {
 	unsigned int methods;
 	isc_uint16_t offset;
@@ -2005,6 +2012,23 @@ dns_name_towire(const dns_name_t *name, dns_compress_t *cctx,
 	REQUIRE(cctx != NULL);
 	REQUIRE(ISC_BUFFER_VALID(target));
 
+	/*
+	 * If this exact name was already rendered before, and the
+	 * offset of the previously rendered name is passed to us, write
+	 * a compression pointer directly.
+	 */
+	methods = dns_compress_getmethods(cctx);
+	if (comp_offsetp != NULL && *comp_offsetp < 0x4000 &&
+	    (name->attributes & DNS_NAMEATTR_NOCOMPRESS) == 0 &&
+	    (methods & DNS_COMPRESS_GLOBAL14) != 0) {
+		if (ISC_UNLIKELY(target->length - target->used < 2))
+			return (ISC_R_NOSPACE);
+		offset = *comp_offsetp;
+		offset |= 0xc000;
+		isc_buffer_putuint16(target, offset);
+		return (ISC_R_SUCCESS);
+	}
+
 	/*
 	 * If 'name' doesn't have an offsets table, make a clone which
 	 * has one.
@@ -2022,8 +2046,6 @@ dns_name_towire(const dns_name_t *name, dns_compress_t *cctx,
 
 	offset = target->used;	/*XXX*/
 
-	methods = dns_compress_getmethods(cctx);
-
 	if ((name->attributes & DNS_NAMEATTR_NOCOMPRESS) == 0 &&
 	    (methods & DNS_COMPRESS_GLOBAL14) != 0)
 		gf = dns_compress_findglobal(cctx, name, &gp, &go);
@@ -2034,7 +2056,7 @@ dns_name_towire(const dns_name_t *name, dns_compress_t *cctx,
 	 * If the offset is too high for 14 bit global compression, we're
 	 * out of luck.
 	 */
-	if (gf && go >= 0x4000)
+	if (gf && ISC_UNLIKELY(go >= 0x4000))
 		gf = ISC_FALSE;
 
 	/*
@@ -2044,25 +2066,32 @@ dns_name_towire(const dns_name_t *name, dns_compress_t *cctx,
 		gf = ISC_FALSE;
 
 	if (gf) {
-		if (target->length - target->used < gp.length)
+		if (ISC_UNLIKELY(target->length - target->used < gp.length))
 			return (ISC_R_NOSPACE);
 		(void)memmove((unsigned char *)target->base + target->used,
 			      gp.ndata, (size_t)gp.length);
 		isc_buffer_add(target, gp.length);
-		go |= 0xc000;
+		if (ISC_UNLIKELY(target->length - target->used < 2))
-		if (target->length - target->used < 2)
 			return (ISC_R_NOSPACE);
-		isc_buffer_putuint16(target, go);
+		isc_buffer_putuint16(target, go | 0xc000);
-		if (gp.length != 0)
+		if (gp.length != 0) {
 			dns_compress_add(cctx, name, &gp, offset);
+			if (comp_offsetp != NULL)
+				*comp_offsetp = offset;
+		} else if (comp_offsetp != NULL) {
+			*comp_offsetp = go;
+		}
 	} else {
-		if (target->length - target->used < name->length)
+		if (ISC_UNLIKELY(target->length - target->used < name->length))
 			return (ISC_R_NOSPACE);
 		(void)memmove((unsigned char *)target->base + target->used,
 			      name->ndata, (size_t)name->length);
 		isc_buffer_add(target, name->length);
 		dns_compress_add(cctx, name, name, offset);
+		if (comp_offsetp != NULL)
+			*comp_offsetp = offset;
 	}
+
 	return (ISC_R_SUCCESS);
 }
 

lib/dns/rdataset.c

@@ -324,6 +324,7 @@ towiresorted(dns_rdataset_t *rdataset, const dns_name_t *owner_name,
 	struct towire_sort *out = out_fixed;
 	dns_fixedname_t fixed;
 	dns_name_t *name;
+	isc_uint16_t offset;
 
 	UNUSED(state);
 
@@ -464,6 +465,7 @@ towiresorted(dns_rdataset_t *rdataset, const dns_name_t *owner_name,
 	name = dns_fixedname_name(&fixed);
 	dns_name_copy(owner_name, name, NULL);
 	dns_rdataset_getownercase(rdataset, name);
+	offset = 0xffff;
 
 	name->attributes |= owner_name->attributes &
 		DNS_NAMEATTR_NOCOMPRESS;
@@ -475,7 +477,7 @@ towiresorted(dns_rdataset_t *rdataset, const dns_name_t *owner_name,
 
 		rrbuffer = *target;
 		dns_compress_setmethods(cctx, DNS_COMPRESS_GLOBAL14);
-		result = dns_name_towire(name, cctx, target);
+		result = dns_name_towire2(name, cctx, target, &offset);
 		if (result != ISC_R_SUCCESS)
 			goto rollback;
 		headlen = sizeof(dns_rdataclass_t) + sizeof(dns_rdatatype_t);