all: implement AppendText alongside MarshalText (#9207)

This eventually allows encoding packages that may respect
the proposed encoding.TextAppender interface.
The performance gains from this is between 10-30%.

Updates tailscale/corp#14379

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

types/key/chal.go

@@ -72,9 +72,14 @@ func (k ChallengePublic) String() string {
 	return string(bs)
 }
 
+// AppendText implements encoding.TextAppender.
+func (k ChallengePublic) AppendText(b []byte) ([]byte, error) {
+	return appendHexKey(b, chalPublicHexPrefix, k.k[:]), nil
+}
+
 // MarshalText implements encoding.TextMarshaler.
 func (k ChallengePublic) MarshalText() ([]byte, error) {
-	return toHex(k.k[:], chalPublicHexPrefix), nil
+	return k.AppendText(nil)
 }
 
 // UnmarshalText implements encoding.TextUnmarshaler.

types/key/disco.go

@@ -127,9 +127,14 @@ func (k DiscoPublic) String() string {
 	return string(bs)
 }
 
+// AppendText implements encoding.TextAppender.
+func (k DiscoPublic) AppendText(b []byte) ([]byte, error) {
+	return appendHexKey(b, discoPublicHexPrefix, k.k[:]), nil
+}
+
 // MarshalText implements encoding.TextMarshaler.
 func (k DiscoPublic) MarshalText() ([]byte, error) {
-	return toHex(k.k[:], discoPublicHexPrefix), nil
+	return k.AppendText(nil)
 }
 
 // MarshalText implements encoding.TextUnmarshaler.

types/key/machine.go

@@ -67,9 +67,14 @@ func (k MachinePrivate) Public() MachinePublic {
 	return ret
 }
 
+// AppendText implements encoding.TextAppender.
+func (k MachinePrivate) AppendText(b []byte) ([]byte, error) {
+	return appendHexKey(b, machinePrivateHexPrefix, k.k[:]), nil
+}
+
 // MarshalText implements encoding.TextMarshaler.
 func (k MachinePrivate) MarshalText() ([]byte, error) {
-	return toHex(k.k[:], machinePrivateHexPrefix), nil
+	return k.AppendText(nil)
 }
 
 // MarshalText implements encoding.TextUnmarshaler.
@@ -243,9 +248,14 @@ func (k MachinePublic) String() string {
 	return string(bs)
 }
 
+// AppendText implements encoding.TextAppender.
+func (k MachinePublic) AppendText(b []byte) ([]byte, error) {
+	return appendHexKey(b, machinePublicHexPrefix, k.k[:]), nil
+}
+
 // MarshalText implements encoding.TextMarshaler.
 func (k MachinePublic) MarshalText() ([]byte, error) {
-	return toHex(k.k[:], machinePublicHexPrefix), nil
+	return k.AppendText(nil)
 }
 
 // MarshalText implements encoding.TextUnmarshaler.

types/key/nl.go

@@ -61,9 +61,14 @@ func (k *NLPrivate) UnmarshalText(b []byte) error {
 	return parseHex(k.k[:], mem.B(b), mem.S(nlPrivateHexPrefix))
 }
 
+// AppendText implements encoding.TextAppender.
+func (k NLPrivate) AppendText(b []byte) ([]byte, error) {
+	return appendHexKey(b, nlPrivateHexPrefix, k.k[:]), nil
+}
+
 // MarshalText implements encoding.TextMarshaler.
 func (k NLPrivate) MarshalText() ([]byte, error) {
-	return toHex(k.k[:], nlPrivateHexPrefix), nil
+	return k.AppendText(nil)
 }
 
 // Equal reports whether k and other are the same key.
@@ -132,10 +137,15 @@ func (k *NLPublic) UnmarshalText(b []byte) error {
 	return parseHex(k.k[:], mem.B(b), mem.S(nlPublicHexPrefix))
 }
 
+// AppendText implements encoding.TextAppender.
+func (k NLPublic) AppendText(b []byte) ([]byte, error) {
+	return appendHexKey(b, nlPublicHexPrefix, k.k[:]), nil
+}
+
 // MarshalText implements encoding.TextMarshaler, emitting a
 // representation of the form nlpub:<hex>.
 func (k NLPublic) MarshalText() ([]byte, error) {
-	return toHex(k.k[:], nlPublicHexPrefix), nil
+	return k.AppendText(nil)
 }
 
 // CLIString returns a marshalled representation suitable for use
@@ -143,7 +153,7 @@ func (k NLPublic) MarshalText() ([]byte, error) {
 // the nlpub:<hex> form emitted by MarshalText. Both forms can
 // be decoded by UnmarshalText.
 func (k NLPublic) CLIString() string {
-	return string(toHex(k.k[:], nlPublicHexPrefixCLI))
+	return string(appendHexKey(nil, nlPublicHexPrefixCLI, k.k[:]))
 }
 
 // Verifier returns a ed25519.PublicKey that can be used to

types/key/node.go

@@ -103,9 +103,14 @@ func (k NodePrivate) Public() NodePublic {
 	return ret
 }
 
+// AppendText implements encoding.TextAppender.
+func (k NodePrivate) AppendText(b []byte) ([]byte, error) {
+	return appendHexKey(b, nodePrivateHexPrefix, k.k[:]), nil
+}
+
 // MarshalText implements encoding.TextMarshaler.
 func (k NodePrivate) MarshalText() ([]byte, error) {
-	return toHex(k.k[:], nodePrivateHexPrefix), nil
+	return k.AppendText(nil)
 }
 
 // MarshalText implements encoding.TextUnmarshaler.
@@ -308,9 +313,14 @@ func (k NodePublic) String() string {
 	return string(bs)
 }
 
+// AppendText implements encoding.TextAppender.
+func (k NodePublic) AppendText(b []byte) ([]byte, error) {
+	return appendHexKey(b, nodePublicHexPrefix, k.k[:]), nil
+}
+
 // MarshalText implements encoding.TextMarshaler.
 func (k NodePublic) MarshalText() ([]byte, error) {
-	return toHex(k.k[:], nodePublicHexPrefix), nil
+	return k.AppendText(nil)
 }
 
 // MarshalText implements encoding.TextUnmarshaler.

types/key/util.go

@@ -10,6 +10,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"slices"
 
 	"go4.org/mem"
 )
@@ -49,11 +50,19 @@ func clamp25519Private(b []byte) {
 	b[31] = (b[31] & 127) | 64
 }
 
-func toHex(k []byte, prefix string) []byte {
-	ret := make([]byte, len(prefix)+len(k)*2)
-	copy(ret, prefix)
-	hex.Encode(ret[len(prefix):], k)
-	return ret
+func appendHexKey(dst []byte, prefix string, key []byte) []byte {
+	dst = slices.Grow(dst, len(prefix)+hex.EncodedLen(len(key)))
+	dst = append(dst, prefix...)
+	dst = hexAppendEncode(dst, key)
+	return dst
+}
+
+// TODO(https://go.dev/issue/53693): Use hex.AppendEncode instead.
+func hexAppendEncode(dst, src []byte) []byte {
+	n := hex.EncodedLen(len(src))
+	dst = slices.Grow(dst, n)
+	hex.Encode(dst[len(dst):][:n], src)
+	return dst[:len(dst)+n]
 }
 
 // parseHex decodes a key string of the form "<prefix><hex string>"

types/logid/id.go

@@ -38,8 +38,12 @@ func ParsePrivateID(in string) (out PrivateID, err error) {
 	return out, err
 }
 
+func (id PrivateID) AppendText(b []byte) ([]byte, error) {
+	return hexAppendEncode(b, id[:]), nil
+}
+
 func (id PrivateID) MarshalText() ([]byte, error) {
-	return formatID(id), nil
+	return id.AppendText(nil)
 }
 
 func (id *PrivateID) UnmarshalText(in []byte) error {
@@ -47,7 +51,7 @@ func (id *PrivateID) UnmarshalText(in []byte) error {
 }
 
 func (id PrivateID) String() string {
-	return string(formatID(id))
+	return string(hexAppendEncode(nil, id[:]))
 }
 
 func (id PrivateID) IsZero() bool {
@@ -70,8 +74,12 @@ func ParsePublicID(in string) (out PublicID, err error) {
 	return out, err
 }
 
+func (id PublicID) AppendText(b []byte) ([]byte, error) {
+	return hexAppendEncode(b, id[:]), nil
+}
+
 func (id PublicID) MarshalText() ([]byte, error) {
-	return formatID(id), nil
+	return id.AppendText(nil)
 }
 
 func (id *PublicID) UnmarshalText(in []byte) error {
@@ -79,7 +87,7 @@ func (id *PublicID) UnmarshalText(in []byte) error {
 }
 
 func (id PublicID) String() string {
-	return string(formatID(id))
+	return string(hexAppendEncode(nil, id[:]))
 }
 
 func (id1 PublicID) Less(id2 PublicID) bool {
@@ -98,10 +106,12 @@ func (id PublicID) Prefix64() uint64 {
 	return binary.BigEndian.Uint64(id[:8])
 }
 
-func formatID(in [32]byte) []byte {
-	var hexArr [2 * len(in)]byte
-	hex.Encode(hexArr[:], in[:])
-	return hexArr[:]
+// TODO(https://go.dev/issue/53693): Use hex.AppendEncode instead.
+func hexAppendEncode(dst, src []byte) []byte {
+	n := hex.EncodedLen(len(src))
+	dst = slices.Grow(dst, n)
+	hex.Encode(dst[len(dst):][:n], src)
+	return dst[:len(dst)+n]
 }
 
 func parseID[Bytes []byte | string](funcName string, out *[32]byte, in Bytes) (err error) {