Add ability to customize internal json marshaler (#318)

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

encoder_cbor.go

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

globals.go

@@ -1,6 +1,7 @@
 package zerolog
 
 import (
+	"encoding/json"
 	"strconv"
 	"sync/atomic"
 	"time"
@@ -75,6 +76,10 @@ var (
 		return err
 	}
 
+	// InterfaceMarshalFunc allows customization of interface marshaling.
+	// Default: "encoding/json.Marshal"
+	InterfaceMarshalFunc = json.Marshal
+
 	// TimeFieldFormat defines the time format of the Time field type. If set to
 	// TimeFormatUnix, TimeFormatUnixMs or TimeFormatUnixMicro, the time is formatted as an UNIX
 	// timestamp as integer.

internal/cbor/base.go

@@ -1,5 +1,13 @@
 package cbor
 
+// JSONMarshalFunc is used to marshal 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 JSONMarshalFunc func(v interface{}) ([]byte, error)
+
 type Encoder struct{}
 
 // AppendKey adds a key (string) to the binary encoded log message

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 := JSONMarshalFunc(i)
 	if err != nil {
 		return e.AppendString(dst, fmt.Sprintf("marshaling error: %v", err))
 	}

internal/json/base.go

@@ -1,5 +1,13 @@
 package json
 
+// JSONMarshalFunc is used to marshal 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 JSONMarshalFunc 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 := JSONMarshalFunc(i)
 	if err != nil {
 		return e.AppendString(dst, fmt.Sprintf("marshaling error: %v", err))
 	}