Add ability to customize internal json marshaler

Added a package level variable "JSONMarshaler".
It's used to marshal interface to JSON encoded
byte slice, mostly when event.Interface("key", v)
is called.

This enables user to replace the internal json
marshaler at runtime, but will potentially cause
data race if used improperly.

encoder.go

@@ -1,10 +1,23 @@
 package zerolog
 
 import (
+	"encoding/json"
 	"net"
 	"time"
 )
 
+var (
+	// JSONMarshaler is used to marshal interface
+	// to JSON encoded byte slice when an interface
+	// is passed for logging.
+	// Default: "encoding/json.Marshal"
+	JSONMarshaler InterfaceMarshaler = json.Marshal
+)
+
+// InterfaceMarshaler represents a way to marshal
+// interface to byte slice.
+type InterfaceMarshaler func(v interface{}) ([]byte, error)
+
 type encoder interface {
 	AppendArrayDelim(dst []byte) []byte
 	AppendArrayEnd(dst []byte) []byte

encoder_cbor.go

@@ -14,6 +14,13 @@ var (
 	enc = cbor.Encoder{}
 )
 
+func init() {
+	// using closure to reflect the changes at runtime.
+	cbor.JSONMarshaler = func(v interface{}) ([]byte, error) {
+		return JSONMarshaler(v)
+	}
+}
+
 func appendJSON(dst []byte, j []byte) []byte {
 	return cbor.AppendEmbeddedJSON(dst, j)
 }

encoder_json.go

@@ -15,6 +15,13 @@ var (
 	enc = json.Encoder{}
 )
 
+func init() {
+	// using closure to reflect the changes at runtime.
+	json.JSONMarshaler = func(v interface{}) ([]byte, error) {
+		return JSONMarshaler(v)
+	}
+}
+
 func appendJSON(dst []byte, j []byte) []byte {
 	return append(dst, j...)
 }

internal/cbor/base.go

@@ -1,5 +1,13 @@
 package cbor
 
+// JSONMarshaler knows how to marshal an interface to JSON encoded byte slice.
+// Making it package level instead of embedded in Encoder brings
+// some extra efforts at importing, but avoids value copy when
+// the functions of Encoder being invoked.
+// DO REMEMBER to set this variable at importing, or
+// you might get a nil pointer dereference panic at runtime.
+var JSONMarshaler func(v interface{}) ([]byte, error)
+
 type Encoder struct{}
 
 // AppendKey adds a key (string) to the binary encoded log message
@@ -8,4 +16,4 @@ func (e Encoder) AppendKey(dst []byte, key string) []byte {
 		dst = e.AppendBeginMarker(dst)
 	}
 	return e.AppendString(dst, key)
-}
+}

internal/cbor/types.go

@@ -1,7 +1,6 @@
 package cbor
 
 import (
-	"encoding/json"
 	"fmt"
 	"math"
 	"net"
@@ -432,7 +431,7 @@ func (e Encoder) AppendFloats64(dst []byte, vals []float64) []byte {
 
 // AppendInterface takes an arbitrary object and converts it to JSON and embeds it dst.
 func (e Encoder) AppendInterface(dst []byte, i interface{}) []byte {
-	marshaled, err := json.Marshal(i)
+	marshaled, err := JSONMarshaler(i)
 	if err != nil {
 		return e.AppendString(dst, fmt.Sprintf("marshaling error: %v", err))
 	}

internal/json/base.go

@@ -1,5 +1,13 @@
 package json
 
+// JSONMarshaler knows how to marshal an interface to JSON encoded byte slice.
+// Making it package level instead of embedded in Encoder brings
+// some extra efforts at importing, but avoids value copy when
+// the functions of Encoder being invoked.
+// DO REMEMBER to set this variable at importing, or
+// you might get a nil pointer dereference panic at runtime.
+var JSONMarshaler func(v interface{}) ([]byte, error)
+
 type Encoder struct{}
 
 // AppendKey appends a new key to the output JSON.

internal/json/types.go

@@ -1,7 +1,6 @@
 package json
 
 import (
-	"encoding/json"
 	"fmt"
 	"math"
 	"net"
@@ -363,7 +362,7 @@ func (Encoder) AppendFloats64(dst []byte, vals []float64) []byte {
 // AppendInterface marshals the input interface to a string and
 // appends the encoded string to the input byte slice.
 func (e Encoder) AppendInterface(dst []byte, i interface{}) []byte {
-	marshaled, err := json.Marshal(i)
+	marshaled, err := JSONMarshaler(i)
 	if err != nil {
 		return e.AppendString(dst, fmt.Sprintf("marshaling error: %v", err))
 	}