net: avoid memory copy calling absDomainName

Change-Id: I8ea9bec8bc33e29b8c265fbca40871bc23667144
Reviewed-on: https://go-review.googlesource.com/c/go/+/330470
Reviewed-by: Damien Neil <dneil@google.com>
Trust: Damien Neil <dneil@google.com>
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

src/net/cgo_unix.go

@@ -323,7 +323,7 @@ func cgoLookupAddrPTR(addr string, sa *C.struct_sockaddr, salen C.socklen_t) (na
 			break
 		}
 	}
-	return []string{absDomainName(b)}, nil
+	return []string{absDomainName(string(b))}, nil
 }
 
 func cgoReverseLookup(result chan<- reverseLookupResult, addr string, sa *C.struct_sockaddr, salen C.socklen_t) {

src/net/dnsclient.go

@@ -5,6 +5,7 @@
 package net
 
 import (
+	"internal/bytealg"
 	"internal/itoa"
 	"sort"
 
@@ -136,18 +137,11 @@ func isDomainName(s string) bool {
 // It's hard to tell so we settle on the heuristic that names without dots
 // (like "localhost" or "myhost") do not get trailing dots, but any other
 // names do.
-func absDomainName(b []byte) string {
+func absDomainName(s string) string {
-	hasDots := false
+	if bytealg.IndexByteString(s, '.') != -1 && s[len(s)-1] != '.' {
-	for _, x := range b {
+		s += "."
-		if x == '.' {
-			hasDots = true
-			break
 	}
-	}
+	return s
-	if hasDots && b[len(b)-1] != '.' {
-		b = append(b, '.')
-	}
-	return string(b)
 }
 
 // An SRV represents a single DNS SRV record.

src/net/hosts.go

@@ -82,10 +82,10 @@ func readHosts() {
 			continue
 		}
 		for i := 1; i < len(f); i++ {
-			name := absDomainName([]byte(f[i]))
+			name := absDomainName(f[i])
 			h := []byte(f[i])
 			lowerASCIIBytes(h)
-			key := absDomainName(h)
+			key := absDomainName(string(h))
 			hs[key] = append(hs[key], addr)
 			is[addr] = append(is[addr], name)
 		}
@@ -106,11 +106,12 @@ func lookupStaticHost(host string) []string {
 	defer hosts.Unlock()
 	readHosts()
 	if len(hosts.byName) != 0 {
-		// TODO(jbd,bradfitz): avoid this alloc if host is already all lowercase?
+		if hasUpperCase(host) {
-		// or linear scan the byName map if it's small enough?
 			lowerHost := []byte(host)
 			lowerASCIIBytes(lowerHost)
-		if ips, ok := hosts.byName[absDomainName(lowerHost)]; ok {
+			host = string(lowerHost)
+		}
+		if ips, ok := hosts.byName[absDomainName(host)]; ok {
 			ipsCp := make([]string, len(ips))
 			copy(ipsCp, ips)
 			return ipsCp

src/net/hosts_test.go

@@ -70,7 +70,7 @@ func TestLookupStaticHost(t *testing.T) {
 }
 
 func testStaticHost(t *testing.T, hostsPath string, ent staticHostEntry) {
-	ins := []string{ent.in, absDomainName([]byte(ent.in)), strings.ToLower(ent.in), strings.ToUpper(ent.in)}
+	ins := []string{ent.in, absDomainName(ent.in), strings.ToLower(ent.in), strings.ToUpper(ent.in)}
 	for _, in := range ins {
 		addrs := lookupStaticHost(in)
 		if !reflect.DeepEqual(addrs, ent.out) {
@@ -141,7 +141,7 @@ func TestLookupStaticAddr(t *testing.T) {
 func testStaticAddr(t *testing.T, hostsPath string, ent staticHostEntry) {
 	hosts := lookupStaticAddr(ent.in)
 	for i := range ent.out {
-		ent.out[i] = absDomainName([]byte(ent.out[i]))
+		ent.out[i] = absDomainName(ent.out[i])
 	}
 	if !reflect.DeepEqual(hosts, ent.out) {
 		t.Errorf("%s, lookupStaticAddr(%s) = %v; want %v", hostsPath, ent.in, hosts, ent.out)

src/net/lookup_plan9.go

@@ -262,8 +262,8 @@ func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (cn
 		if !(portOk && priorityOk && weightOk) {
 			continue
 		}
-		addrs = append(addrs, &SRV{absDomainName([]byte(f[5])), uint16(port), uint16(priority), uint16(weight)})
+		addrs = append(addrs, &SRV{absDomainName(f[5]), uint16(port), uint16(priority), uint16(weight)})
-		cname = absDomainName([]byte(f[0]))
+		cname = absDomainName(f[0])
 	}
 	byPriorityWeight(addrs).sort()
 	return
@@ -280,7 +280,7 @@ func (*Resolver) lookupMX(ctx context.Context, name string) (mx []*MX, err error
 			continue
 		}
 		if pref, _, ok := dtoi(f[2]); ok {
-			mx = append(mx, &MX{absDomainName([]byte(f[3])), uint16(pref)})
+			mx = append(mx, &MX{absDomainName(f[3]), uint16(pref)})
 		}
 	}
 	byPref(mx).sort()
@@ -297,7 +297,7 @@ func (*Resolver) lookupNS(ctx context.Context, name string) (ns []*NS, err error
 		if len(f) < 3 {
 			continue
 		}
-		ns = append(ns, &NS{absDomainName([]byte(f[2]))})
+		ns = append(ns, &NS{absDomainName(f[2])})
 	}
 	return
 }
@@ -329,7 +329,7 @@ func (*Resolver) lookupAddr(ctx context.Context, addr string) (name []string, er
 		if len(f) < 3 {
 			continue
 		}
-		name = append(name, absDomainName([]byte(f[2])))
+		name = append(name, absDomainName(f[2]))
 	}
 	return
 }

src/net/lookup_windows.go

@@ -226,7 +226,7 @@ func (*Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
 	// windows returns DNS_INFO_NO_RECORDS if there are no CNAME-s
 	if errno, ok := e.(syscall.Errno); ok && errno == syscall.DNS_INFO_NO_RECORDS {
 		// if there are no aliases, the canonical name is the input name
-		return absDomainName([]byte(name)), nil
+		return absDomainName(name), nil
 	}
 	if e != nil {
 		return "", &DNSError{Err: winError("dnsquery", e).Error(), Name: name}
@@ -235,7 +235,7 @@ func (*Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
 
 	resolved := resolveCNAME(syscall.StringToUTF16Ptr(name), r)
 	cname := windows.UTF16PtrToString(resolved)
-	return absDomainName([]byte(cname)), nil
+	return absDomainName(cname), nil
 }
 
 func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
@@ -258,10 +258,10 @@ func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (st
 	srvs := make([]*SRV, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_SRV, target) {
 		v := (*syscall.DNSSRVData)(unsafe.Pointer(&p.Data[0]))
-		srvs = append(srvs, &SRV{absDomainName([]byte(syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Target))[:]))), v.Port, v.Priority, v.Weight})
+		srvs = append(srvs, &SRV{absDomainName(syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Target))[:])), v.Port, v.Priority, v.Weight})
 	}
 	byPriorityWeight(srvs).sort()
-	return absDomainName([]byte(target)), srvs, nil
+	return absDomainName(target), srvs, nil
 }
 
 func (*Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
@@ -278,7 +278,7 @@ func (*Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
 	mxs := make([]*MX, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_MX, name) {
 		v := (*syscall.DNSMXData)(unsafe.Pointer(&p.Data[0]))
-		mxs = append(mxs, &MX{absDomainName([]byte(windows.UTF16PtrToString(v.NameExchange))), v.Preference})
+		mxs = append(mxs, &MX{absDomainName(windows.UTF16PtrToString(v.NameExchange)), v.Preference})
 	}
 	byPref(mxs).sort()
 	return mxs, nil
@@ -298,7 +298,7 @@ func (*Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) {
 	nss := make([]*NS, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_NS, name) {
 		v := (*syscall.DNSPTRData)(unsafe.Pointer(&p.Data[0]))
-		nss = append(nss, &NS{absDomainName([]byte(syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Host))[:])))})
+		nss = append(nss, &NS{absDomainName(syscall.UTF16ToString((*[256]uint16)(unsafe.Pointer(v.Host))[:]))})
 	}
 	return nss, nil
 }
@@ -344,7 +344,7 @@ func (*Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error)
 	ptrs := make([]string, 0, 10)
 	for _, p := range validRecs(r, syscall.DNS_TYPE_PTR, arpa) {
 		v := (*syscall.DNSPTRData)(unsafe.Pointer(&p.Data[0]))
-		ptrs = append(ptrs, absDomainName([]byte(windows.UTF16PtrToString(v.Host))))
+		ptrs = append(ptrs, absDomainName(windows.UTF16PtrToString(v.Host)))
 	}
 	return ptrs, nil
 }

src/net/lookup_windows_test.go

@@ -220,14 +220,14 @@ func nslookupMX(name string) (mx []*MX, err error) {
 	rx := regexp.MustCompile(`(?m)^([a-z0-9.\-]+)\s+mail exchanger\s*=\s*([0-9]+)\s*([a-z0-9.\-]+)$`)
 	for _, ans := range rx.FindAllStringSubmatch(r, -1) {
 		pref, _, _ := dtoi(ans[2])
-		mx = append(mx, &MX{absDomainName([]byte(ans[3])), uint16(pref)})
+		mx = append(mx, &MX{absDomainName(ans[3]), uint16(pref)})
 	}
 	// windows nslookup syntax
 	// gmail.com       MX preference = 30, mail exchanger = alt3.gmail-smtp-in.l.google.com
 	rx = regexp.MustCompile(`(?m)^([a-z0-9.\-]+)\s+MX preference\s*=\s*([0-9]+)\s*,\s*mail exchanger\s*=\s*([a-z0-9.\-]+)$`)
 	for _, ans := range rx.FindAllStringSubmatch(r, -1) {
 		pref, _, _ := dtoi(ans[2])
-		mx = append(mx, &MX{absDomainName([]byte(ans[3])), uint16(pref)})
+		mx = append(mx, &MX{absDomainName(ans[3]), uint16(pref)})
 	}
 	return
 }
@@ -241,7 +241,7 @@ func nslookupNS(name string) (ns []*NS, err error) {
 	// golang.org      nameserver = ns1.google.com.
 	rx := regexp.MustCompile(`(?m)^([a-z0-9.\-]+)\s+nameserver\s*=\s*([a-z0-9.\-]+)$`)
 	for _, ans := range rx.FindAllStringSubmatch(r, -1) {
-		ns = append(ns, &NS{absDomainName([]byte(ans[2]))})
+		ns = append(ns, &NS{absDomainName(ans[2])})
 	}
 	return
 }
@@ -258,7 +258,7 @@ func nslookupCNAME(name string) (cname string, err error) {
 	for _, ans := range rx.FindAllStringSubmatch(r, -1) {
 		last = ans[2]
 	}
-	return absDomainName([]byte(last)), nil
+	return absDomainName(last), nil
 }
 
 func nslookupTXT(name string) (txt []string, err error) {
@@ -299,7 +299,7 @@ func lookupPTR(name string) (ptr []string, err error) {
 	ptr = make([]string, 0, 10)
 	rx := regexp.MustCompile(`(?m)^Pinging\s+([a-zA-Z0-9.\-]+)\s+\[.*$`)
 	for _, ans := range rx.FindAllStringSubmatch(r, -1) {
-		ptr = append(ptr, absDomainName([]byte(ans[1])))
+		ptr = append(ptr, absDomainName(ans[1]))
 	}
 	return
 }

src/net/parse.go

@@ -208,6 +208,16 @@ func last(s string, b byte) int {
 	return i
 }
 
+// hasUpperCase tells whether the given string contains at least one upper-case.
+func hasUpperCase(s string) bool {
+	for i := range s {
+		if 'A' <= s[i] && s[i] <= 'Z' {
+			return true
+		}
+	}
+	return false
+}
+
 // lowerASCIIBytes makes x ASCII lowercase in-place.
 func lowerASCIIBytes(x []byte) {
 	for i, b := range x {