Add global parameter for customizing how .Bytes works in JSON

encoder_json.go

@@ -1,3 +1,4 @@
+//go:build !binary_log
 // +build !binary_log
 
 package zerolog
@@ -21,6 +22,12 @@ func init() {
 	json.JSONMarshalFunc = func(v interface{}) ([]byte, error) {
 		return InterfaceMarshalFunc(v)
 	}
+	if JSONBytesMarshalFunc == nil {
+		JSONBytesMarshalFunc = json.AppendBytesDefault
+	}
+	json.AppendBytesFunc = func(dst, src []byte) []byte {
+		return JSONBytesMarshalFunc(dst, src)
+	}
 }
 
 func appendJSON(dst []byte, j []byte) []byte {

event.go

@@ -290,7 +290,7 @@ func (e *Event) Stringers(key string, vals []fmt.Stringer) *Event {
 // Bytes adds the field key with val as a string to the *Event context.
 //
 // Runes outside of normal ASCII ranges will be hex-encoded in the resulting
-// JSON.
+// JSON. The marshaling can be customized by setting JSONBytesMarshalFunc.
 func (e *Event) Bytes(key string, val []byte) *Event {
 	if e == nil {
 		return e

globals.go

@@ -1,6 +1,7 @@
 package zerolog
 
 import (
+	"encoding/base64"
 	"encoding/json"
 	"strconv"
 	"sync/atomic"
@@ -80,6 +81,12 @@ var (
 		return err
 	}
 
+	// JSONBytesMarshalFunc allows customization of how Bytes() produces JSON output.
+	// The default implementation leaves ASCII characters as-is and encodes Unicode runes as hex escapes.
+	//
+	// The function should append the encoded bytes to dst and return the extended buffer.
+	JSONBytesMarshalFunc func(dst, src []byte) []byte
+
 	// InterfaceMarshalFunc allows customization of interface marshaling.
 	// Default: "encoding/json.Marshal"
 	InterfaceMarshalFunc = json.Marshal
@@ -164,3 +171,17 @@ func DisableSampling(v bool) {
 func samplingDisabled() bool {
 	return atomic.LoadInt32(disableSampling) == 1
 }
+
+// JSONBytesMarshalBase64 returns a function compatible with JSONBytesMarshalFunc that encodes bytes using the given base64 encoder.
+func JSONBytesMarshalBase64(enc *base64.Encoding) func(dst, src []byte) []byte {
+	return func(dst, src []byte) []byte {
+		start := len(dst)
+		targetLen := start + enc.EncodedLen(len(src))
+		for cap(dst) < targetLen {
+			dst = append(dst[:cap(dst)], 0)
+		}
+		dst = dst[:targetLen]
+		enc.Encode(dst[start:], src)
+		return dst
+	}
+}

internal/json/base.go

@@ -8,6 +8,8 @@ package json
 // you might get a nil pointer dereference panic at runtime.
 var JSONMarshalFunc func(v interface{}) ([]byte, error)
 
+var AppendBytesFunc func(dst, src []byte) []byte = AppendBytesDefault
+
 type Encoder struct{}
 
 // AppendKey appends a new key to the output JSON.

internal/json/bytes.go

@@ -5,14 +5,17 @@ import "unicode/utf8"
 // AppendBytes is a mirror of appendString with []byte arg
 func (Encoder) AppendBytes(dst, s []byte) []byte {
 	dst = append(dst, '"')
+	dst = AppendBytesFunc(dst, s)
+	return append(dst, '"')
+}
+
+func AppendBytesDefault(dst, s []byte) []byte {
 	for i := 0; i < len(s); i++ {
 		if !noEscapeTable[s[i]] {
-			dst = appendBytesComplex(dst, s, i)
-			return append(dst, '"')
+			return appendBytesComplex(dst, s, i)
 		}
 	}
-	dst = append(dst, s...)
-	return append(dst, '"')
+	return append(dst, s...)
 }
 
 // AppendHex encodes the input bytes to a hex string and appends

log_json_test.go

@@ -0,0 +1,46 @@
+//go:build !binary_log
+// +build !binary_log
+
+package zerolog
+
+import (
+	"bytes"
+	"encoding/base64"
+	"os"
+	"testing"
+)
+
+func TestJSONBytesMarshalFunc(t *testing.T) {
+	out := &bytes.Buffer{}
+	log := New(out)
+	log.Log().Bytes("bytes", []byte{'a', 'b', 'c', 1, 2, 3, 0xff}).Msg("msg")
+	if got, want := decodeIfBinaryToString(out.Bytes()), `{"bytes":"abc\u0001\u0002\u0003\ufffd","message":"msg"}`+"\n"; got != want {
+		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+	}
+	out.Reset()
+	origBytesMarshalFunc := JSONBytesMarshalFunc
+	defer func() {
+		JSONBytesMarshalFunc = origBytesMarshalFunc
+	}()
+
+	JSONBytesMarshalFunc = JSONBytesMarshalBase64(base64.StdEncoding)
+	log.Log().Bytes("bytes", []byte{'a', 'b', 'c', 1, 2, 3, 0xff}).Msg("msg")
+	if got, want := decodeIfBinaryToString(out.Bytes()), `{"bytes":"YWJjAQID/w==","message":"msg"}`+"\n"; got != want {
+		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+	}
+	out.Reset()
+
+	JSONBytesMarshalFunc = JSONBytesMarshalBase64(base64.RawURLEncoding)
+	log.Log().Bytes("bytes", []byte{'a', 'b', 'c', 1, 2, 3, 0xff}).Msg("msg")
+	if got, want := decodeIfBinaryToString(out.Bytes()), `{"bytes":"YWJjAQID_w","message":"msg"}`+"\n"; got != want {
+		t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+	}
+	out.Reset()
+}
+
+func ExampleJSONBytesMarshalBase64() {
+	log := New(os.Stdout)
+	JSONBytesMarshalFunc = JSONBytesMarshalBase64(base64.StdEncoding)
+	log.Info().Bytes("bytes", []byte{'a', 'b', 'c', 1, 2, 3, 0xff}).Msg("msg")
+	// Output: {"level":"info","bytes":"YWJjAQID/w==","message":"msg"}
+}