encoding/json: make use of Buffer.AvailableBuffer

Use the explicit API for acquiring an empty available buffer,
rather than the hack that's implemented in terms of Bytes and Len.

Change-Id: If286ed42693acd61ffe28dc849ed4b76c3ae4434
Reviewed-on: https://go-review.googlesource.com/c/go/+/476337
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>
Auto-Submit: Joseph Tsai <[email protected]>
Run-TryBot: Joseph Tsai <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: dsnet

src/encoding/json/encode.go

@@ -259,10 +259,6 @@ type encodeState struct {
 	ptrSeen  map[any]struct{}
 }
 
-func (e *encodeState) AvailableBuffer() []byte {
-	return availableBuffer(&e.Buffer)
-}
-
 const startDetectingCyclesAfter = 1000
 
 var encodeStatePool sync.Pool
@@ -445,7 +441,7 @@ func marshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	b, err := m.MarshalJSON()
 	if err == nil {
 		e.Grow(len(b))
-		out := availableBuffer(&e.Buffer)
+		out := e.AvailableBuffer()
 		out, err = appendCompact(out, b, opts.escapeHTML)
 		e.Buffer.Write(out)
 	}
@@ -464,7 +460,7 @@ func addrMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	b, err := m.MarshalJSON()
 	if err == nil {
 		e.Grow(len(b))
-		out := availableBuffer(&e.Buffer)
+		out := e.AvailableBuffer()
 		out, err = appendCompact(out, b, opts.escapeHTML)
 		e.Buffer.Write(out)
 	}

src/encoding/json/indent.go

@@ -6,19 +6,14 @@ package json
 
 import "bytes"
 
-// TODO(https://go.dev/issue/53685): Use bytes.Buffer.AvailableBuffer instead.
-func availableBuffer(b *bytes.Buffer) []byte {
-	return b.Bytes()[b.Len():]
-}
-
 // HTMLEscape appends to dst the JSON-encoded src with <, >, &, U+2028 and U+2029
 // characters inside string literals changed to \u003c, \u003e, \u0026, \u2028, \u2029
 // so that the JSON will be safe to embed inside HTML <script> tags.
 // For historical reasons, web browsers don't honor standard HTML
 // escaping within <script> tags, so an alternative JSON encoding must be used.
 func HTMLEscape(dst *bytes.Buffer, src []byte) {
 	dst.Grow(len(src))
-	dst.Write(appendHTMLEscape(availableBuffer(dst), src))
+	dst.Write(appendHTMLEscape(dst.AvailableBuffer(), src))
 }
 
 func appendHTMLEscape(dst, src []byte) []byte {
@@ -45,7 +40,7 @@ func appendHTMLEscape(dst, src []byte) []byte {
 // insignificant space characters elided.
 func Compact(dst *bytes.Buffer, src []byte) error {
 	dst.Grow(len(src))
-	b := availableBuffer(dst)
+	b := dst.AvailableBuffer()
 	b, err := appendCompact(b, src, false)
 	dst.Write(b)
 	return err
@@ -114,7 +109,7 @@ const indentGrowthFactor = 2
 // if src ends in a trailing newline, so will dst.
 func Indent(dst *bytes.Buffer, src []byte, prefix, indent string) error {
 	dst.Grow(indentGrowthFactor * len(src))
-	b := availableBuffer(dst)
+	b := dst.AvailableBuffer()
 	b, err := appendIndent(b, src, prefix, indent)
 	dst.Write(b)
 	return err