Revert "net: halve the allocs in ParseCIDR by sharing slice backing"

This reverts CL 129118 (commit aff3aaa4)

Reason for revert: It was retracted by the author in a comment on the PR
but that doesn't get synced to Gerrit, and the Gerrit CL wasn't closed
when the PR was closed.

Change-Id: I5ad16e96f98a927972187dc5c9df3a0e9b9fafa8
Reviewed-on: https://go-review.googlesource.com/c/go/+/206377
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

src/net/ip.go

@@ -78,20 +78,10 @@ func CIDRMask(ones, bits int) IPMask {
 	if ones < 0 || ones > bits {
 		return nil
 	}
-	return putCIDRMask(nil, ones, bits/8)
-}
-
-// putCIDRMask will put an IPMask into `m` consisting of `ones` 1 bits
-// followed by 0s up to a total length of `bits' bits if the length
-// of m is < `l` bytes and returns the same slice m. If m did not have
-// sufficient length for the mask l a new m is returned instead.
-func putCIDRMask(m IPMask, ones, bits int) IPMask {
-	if len(m) < bits {
-		m = make(IPMask, bits)
-	}
-
+	l := bits / 8
+	m := make(IPMask, l)
 	n := uint(ones)
-	for i := 0; i < bits; i++ {
+	for i := 0; i < l; i++ {
 		if n >= 8 {
 			m[i] = 0xff
 			n -= 8
@@ -256,13 +246,6 @@ func allFF(b []byte) bool {
 
 // Mask returns the result of masking the IP address ip with mask.
 func (ip IP) Mask(mask IPMask) IP {
-	return ipMaskWithBuf(nil, ip, mask)
-}
-
-// ipMaskWithBuf implements the IP.Mask method, but containing an
-// opitional optional bufer to use for the return value. If the buf is
-// too small, a new one is allocated.
-func ipMaskWithBuf(buf, ip IP, mask IPMask) []byte {
 	if len(mask) == IPv6len && len(ip) == IPv4len && allFF(mask[:12]) {
 		mask = mask[12:]
 	}
@@ -273,13 +256,11 @@ func ipMaskWithBuf(buf, ip IP, mask IPMask) []byte {
 	if n != len(mask) {
 		return nil
 	}
-	if len(buf) < n {
-		buf = make(IP, n)
-	}
+	out := make(IP, n)
 	for i := 0; i < n; i++ {
-		buf[i] = ip[i] & mask[i]
+		out[i] = ip[i] & mask[i]
 	}
-	return buf
+	return out
 }
 
 // ubtoa encodes the string form of the integer v to dst[start:] and
@@ -556,35 +537,28 @@ func (n *IPNet) String() string {
 // Parse IPv4 address (d.d.d.d).
 func parseIPv4(s string) IP {
 	var p [IPv4len]byte
-	if !parseIntoIPv4(p[:], s) {
-		return nil
-	}
-	return IPv4(p[0], p[1], p[2], p[3])
-}
-
-// parseIntoIPv4 parses s as an IPv4 address and parses it into
-// p, which must be at least IPv4len bytes long. It reports
-// whether the parse was successful.
-func parseIntoIPv4(p []byte, s string) bool {
 	for i := 0; i < IPv4len; i++ {
 		if len(s) == 0 {
 			// Missing octets.
-			return false
+			return nil
 		}
 		if i > 0 {
 			if s[0] != '.' {
-				return false
+				return nil
 			}
 			s = s[1:]
 		}
 		n, c, ok := dtoi(s)
 		if !ok || n > 0xFF {
-			return false
+			return nil
 		}
 		s = s[c:]
 		p[i] = byte(n)
 	}
-	return len(s) == 0
+	if len(s) != 0 {
+		return nil
+	}
+	return IPv4(p[0], p[1], p[2], p[3])
 }
 
 // parseIPv6Zone parses s as a literal IPv6 address and its associated zone
@@ -597,16 +571,7 @@ func parseIPv6Zone(s string) (IP, string) {
 // parseIPv6 parses s as a literal IPv6 address described in RFC 4291
 // and RFC 5952.
 func parseIPv6(s string) (ip IP) {
-	if ip = make(IP, IPv6len); !parseIntoIPv6(ip, s) {
-		ip = nil
-	}
-	return
-}
-
-// parseIntoIPv6 parses s as a literal IPv6 address described in RFC
-// 4291 and RFC 5952 and populates ip. It reports whether the parse
-// was successful.
-func parseIntoIPv6(ip IP, s string) bool {
+	ip = make(IP, IPv6len)
 	ellipsis := -1 // position of ellipsis in ip
 
 	// Might have leading ellipsis
@@ -615,7 +580,7 @@ func parseIntoIPv6(ip IP, s string) bool {
 		s = s[2:]
 		// Might be only ellipsis
 		if len(s) == 0 {
-			return true
+			return ip
 		}
 	}
 
@@ -625,22 +590,22 @@ func parseIntoIPv6(ip IP, s string) bool {
 		// Hex number.
 		n, c, ok := xtoi(s)
 		if !ok || n > 0xFFFF {
-			return false
+			return nil
 		}
 
 		// If followed by dot, might be in trailing IPv4.
 		if c < len(s) && s[c] == '.' {
 			if ellipsis < 0 && i != IPv6len-IPv4len {
 				// Not the right place.
-				return false
+				return nil
 			}
 			if i+IPv4len > IPv6len {
 				// Not enough room.
-				return false
+				return nil
 			}
 			ip4 := parseIPv4(s)
 			if ip4 == nil {
-				return false
+				return nil
 			}
 			ip[i] = ip4[12]
 			ip[i+1] = ip4[13]
@@ -664,14 +629,14 @@ func parseIntoIPv6(ip IP, s string) bool {
 
 		// Otherwise must be followed by colon and more.
 		if s[0] != ':' || len(s) == 1 {
-			return false
+			return nil
 		}
 		s = s[1:]
 
 		// Look for ellipsis.
 		if s[0] == ':' {
 			if ellipsis >= 0 { // already have one
-				return false
+				return nil
 			}
 			ellipsis = i
 			s = s[1:]
@@ -683,13 +648,13 @@ func parseIntoIPv6(ip IP, s string) bool {
 
 	// Must have used entire string.
 	if len(s) != 0 {
-		return false
+		return nil
 	}
 
 	// If didn't parse enough, expand ellipsis.
 	if i < IPv6len {
 		if ellipsis < 0 {
-			return false
+			return nil
 		}
 		n := IPv6len - i
 		for j := i - 1; j >= ellipsis; j-- {
@@ -700,9 +665,9 @@ func parseIntoIPv6(ip IP, s string) bool {
 		}
 	} else if ellipsis >= 0 {
 		// Ellipsis must represent at least one 0 group.
-		return false
+		return nil
 	}
-	return true
+	return ip
 }
 
 // ParseIP parses s as an IP address, returning the result.
@@ -711,29 +676,15 @@ func parseIntoIPv6(ip IP, s string) bool {
 // If s is not a valid textual representation of an IP address,
 // ParseIP returns nil.
 func ParseIP(s string) IP {
-	switch n := strToIPvLen(s); n {
-	case IPv4len:
-		return parseIPv4(s)
-	case IPv6len:
-		return parseIPv6(s)
-	default:
-		return nil
-	}
-}
-
-// strToIPvLen reports the expected length of the parsed IP adress
-// given its ASCII representation in s. It returns IPv4len, IPv6len,
-// or -1.
-func strToIPvLen(s string) int {
 	for i := 0; i < len(s); i++ {
 		switch s[i] {
 		case '.':
-			return IPv4len
+			return parseIPv4(s)
 		case ':':
-			return IPv6len
+			return parseIPv6(s)
 		}
 	}
-	return -1
+	return nil
 }
 
 // parseIPZone parses s as an IP address, return it and its associated zone
@@ -763,53 +714,17 @@ func ParseCIDR(s string) (IP, *IPNet, error) {
 	if i < 0 {
 		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
 	}
-
-	iplen := strToIPvLen(s[:i])
-	if iplen < 0 {
-		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
+	addr, mask := s[:i], s[i+1:]
+	iplen := IPv4len
+	ip := parseIPv4(addr)
+	if ip == nil {
+		iplen = IPv6len
+		ip = parseIPv6(addr)
 	}
-
-	nwlen, y, ok := dtoi(s[i+1:])
-	if !ok || y != len(s[i+1:]) || nwlen < 0 || nwlen > 8*iplen {
+	n, i, ok := dtoi(mask)
+	if ip == nil || !ok || i != len(mask) || n < 0 || n > 8*iplen {
 		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
 	}
-
-	var (
-		buf []byte
-		ipn *IPNet
-	)
-	switch iplen {
-	case IPv4len:
-		var block struct {
-			ipn IPNet
-			arr [IPv6len + (IPv4len * 2)]byte
-		}
-		ipn = &block.ipn
-		buf = block.arr[:]
-		copy(buf, v4InV6Prefix)
-		if !parseIntoIPv4(buf[len(v4InV6Prefix):], s[:i]) {
-			return nil, nil, &ParseError{Type: "CIDR address", Text: s}
-		}
-	case IPv6len:
-		var block struct {
-			ipn IPNet
-			arr [IPv6len * 3]byte
-		}
-		ipn = &block.ipn
-		buf = block.arr[:]
-		if !parseIntoIPv6(buf, s[:i]) {
-			return nil, nil, &ParseError{Type: "CIDR address", Text: s}
-		}
-	default:
-		return nil, nil, &ParseError{Type: "CIDR address", Text: s}
-	}
-
-	ip := buf[:IPv6len:IPv6len]
-	buf = buf[IPv6len:]
-
-	ipn.Mask = putCIDRMask(buf[:iplen:iplen], nwlen, iplen)
-	buf = buf[iplen:]
-
-	ipn.IP = ipMaskWithBuf(buf[:iplen:iplen], ip, ipn.Mask)
-	return ip, ipn, nil
+	m := CIDRMask(n, 8*iplen)
+	return ip, &IPNet{IP: ip.Mask(m), Mask: m}, nil
 }

src/net/ip_test.go

@@ -46,18 +46,14 @@ var parseIPTests = []struct {
 
 func TestParseIP(t *testing.T) {
 	for _, tt := range parseIPTests {
-		out := ParseIP(tt.in)
-		if !reflect.DeepEqual(out, tt.out) {
+		if out := ParseIP(tt.in); !reflect.DeepEqual(out, tt.out) {
 			t.Errorf("ParseIP(%q) = %v, want %v", tt.in, out, tt.out)
 		}
-		if exp, got := cap(out), len(out); exp != got {
-			t.Fatalf("ParseIP(%q) cap %v; want %v", tt.in, exp, got)
-		}
 		if tt.in == "" {
 			// Tested in TestMarshalEmptyIP below.
 			continue
 		}
-		out = nil
+		var out IP
 		if err := out.UnmarshalText([]byte(tt.in)); !reflect.DeepEqual(out, tt.out) || (tt.out == nil) != (err != nil) {
 			t.Errorf("IP.UnmarshalText(%q) = %v, %v, want %v", tt.in, out, err, tt.out)
 		}
@@ -111,7 +107,6 @@ func BenchmarkParseIP(b *testing.B) {
 	testHookUninstaller.Do(uninstallTestHooks)
 
 	for i := 0; i < b.N; i++ {
-		b.ReportAllocs()
 		for _, tt := range parseIPTests {
 			ParseIP(tt.in)
 		}
@@ -371,41 +366,12 @@ func TestParseCIDR(t *testing.T) {
 		if !reflect.DeepEqual(err, tt.err) {
 			t.Errorf("ParseCIDR(%q) = %v, %v; want %v, %v", tt.in, ip, net, tt.ip, tt.net)
 		}
-		if err != nil {
-			continue
-		}
-		if !tt.ip.Equal(ip) || !tt.net.IP.Equal(net.IP) || !reflect.DeepEqual(net.Mask, tt.net.Mask) {
+		if err == nil && (!tt.ip.Equal(ip) || !tt.net.IP.Equal(net.IP) || !reflect.DeepEqual(net.Mask, tt.net.Mask)) {
 			t.Errorf("ParseCIDR(%q) = %v, {%v, %v}; want %v, {%v, %v}", tt.in, ip, net.IP, net.Mask, tt.ip, tt.net.IP, tt.net.Mask)
 		}
-		if exp, got := cap(ip), len(ip); exp != got {
-			t.Fatalf("ParseCIDR(%q) ip cap %v; want %v", tt.in, exp, got)
-		}
-		if exp, got := cap(net.IP), len(net.IP); exp != got {
-			t.Fatalf("ParseCIDR(%q) net.IP cap %v; want %v", tt.in, exp, got)
-		}
-		if exp, got := cap(net.Mask), len(net.Mask); exp != got {
-			t.Fatalf("ParseCIDR(%q) net.Mask cap %v; want %v", tt.in, exp, got)
-		}
 	}
 }
 
-func BenchmarkParseCIDR(b *testing.B) {
-	testHookUninstaller.Do(uninstallTestHooks)
-
-	b.Run("IPv4", func(b *testing.B) {
-		b.ReportAllocs()
-		for i := 0; i < b.N; i++ {
-			ParseCIDR("135.104.0.1/24")
-		}
-	})
-	b.Run("IPv6", func(b *testing.B) {
-		b.ReportAllocs()
-		for i := 0; i < b.N; i++ {
-			ParseCIDR("2001:DB8::1/48")
-		}
-	})
-}
-
 var ipNetContainsTests = []struct {
 	ip  IP
 	net *IPNet