FormatPartValueByName for flexible custom formatting for ConsoleWriter (#541)

Author: sted

README.md

@@ -366,6 +366,37 @@ log.Info().Str("foo", "bar").Msg("Hello World")
 // Output: 2006-01-02T15:04:05Z07:00 | INFO  | ***Hello World**** foo:BAR
 ```
 
+To use custom advanced formatting:
+
+```go
+output := zerolog.ConsoleWriter{Out: os.Stdout, NoColor: true,
+    PartsOrder:    []string{"level", "one", "two", "three", "message"},
+    FieldsExclude: []string{"one", "two", "three"}}
+output.FormatLevel = func(i interface{}) string { return strings.ToUpper(fmt.Sprintf("%-6s", i)) }
+output.FormatFieldName = func(i interface{}) string { return fmt.Sprintf("%s:", i) }
+output.FormatPartValueByName = func(i interface{}, s string) string {
+    var ret string
+    switch s {
+    case "one":
+        ret = strings.ToUpper(fmt.Sprintf("%s", i))
+    case "two":
+        ret = strings.ToLower(fmt.Sprintf("%s", i))
+    case "three":
+        ret = strings.ToLower(fmt.Sprintf("(%s)", i))
+    }
+    return ret
+}
+log := zerolog.New(output)
+
+log.Info().Str("foo", "bar").
+    Str("two", "TEST_TWO").
+    Str("one", "test_one").
+    Str("three", "test_three").
+    Msg("Hello World")
+    
+// Output: INFO   TEST_ONE test_two (test_three) Hello World foo:bar
+```
+
 ### Sub dictionary
 
 ```go

console.go

@@ -47,6 +47,10 @@ const (
 // Formatter transforms the input into a formatted string.
 type Formatter func(interface{}) string
 
+// FormatterByFieldName transforms the input into a formatted string,
+// being able to differentiate formatting based on field name.
+type FormatterByFieldName func(interface{}, string) string
+
 // ConsoleWriter parses the JSON input and writes it in an
 // (optionally) colorized, human-friendly format to Out.
 type ConsoleWriter struct {
@@ -85,6 +89,9 @@ type ConsoleWriter struct {
 	FormatFieldValue    Formatter
 	FormatErrFieldName  Formatter
 	FormatErrFieldValue Formatter
+	// If this is configured it is used for "part" values and
+	// has precedence on FormatFieldValue
+	FormatPartValueByName FormatterByFieldName
 
 	FormatExtra func(map[string]interface{}, *bytes.Buffer) error
 
@@ -282,6 +289,7 @@ func (w ConsoleWriter) writeFields(evt map[string]interface{}, buf *bytes.Buffer
 // writePart appends a formatted part to buf.
 func (w ConsoleWriter) writePart(buf *bytes.Buffer, evt map[string]interface{}, p string) {
 	var f Formatter
+	var fvn FormatterByFieldName
 
 	if len(w.PartsExclude) > 0 {
 		for _, exclude := range w.PartsExclude {
@@ -317,14 +325,21 @@ func (w ConsoleWriter) writePart(buf *bytes.Buffer, evt map[string]interface{},
 			f = w.FormatCaller
 		}
 	default:
-		if w.FormatFieldValue == nil {
-			f = consoleDefaultFormatFieldValue
-		} else {
+		if w.FormatPartValueByName != nil {
+			fvn = w.FormatPartValueByName
+		} else if w.FormatFieldValue != nil {
 			f = w.FormatFieldValue
+		} else {
+			f = consoleDefaultFormatFieldValue
 		}
 	}
 
-	var s = f(evt[p])
+	var s string
+	if f == nil {
+		s = fvn(evt[p], p)
+	} else {
+		s = f(evt[p])
+	}
 
 	if len(s) > 0 {
 		if buf.Len() > 0 {

console_test.go

@@ -30,6 +30,34 @@ func ExampleConsoleWriter_customFormatters() {
 	// Output: <nil> INFO  | Hello World foo:BAR
 }
 
+func ExampleConsoleWriter_partValueFormatter() {
+	out := zerolog.ConsoleWriter{Out: os.Stdout, NoColor: true,
+		PartsOrder:    []string{"level", "one", "two", "three", "message"},
+		FieldsExclude: []string{"one", "two", "three"}}
+	out.FormatLevel = func(i interface{}) string { return strings.ToUpper(fmt.Sprintf("%-6s", i)) }
+	out.FormatFieldName = func(i interface{}) string { return fmt.Sprintf("%s:", i) }
+	out.FormatPartValueByName = func(i interface{}, s string) string {
+		var ret string
+		switch s {
+		case "one":
+			ret = strings.ToUpper(fmt.Sprintf("%s", i))
+		case "two":
+			ret = strings.ToLower(fmt.Sprintf("%s", i))
+		case "three":
+			ret = strings.ToLower(fmt.Sprintf("(%s)", i))
+		}
+		return ret
+	}
+	log := zerolog.New(out)
+
+	log.Info().Str("foo", "bar").
+		Str("two", "TEST_TWO").
+		Str("one", "test_one").
+		Str("three", "test_three").
+		Msg("Hello World")
+	// Output: INFO   TEST_ONE test_two (test_three) Hello World foo:bar
+}
+
 func ExampleNewConsoleWriter() {
 	out := zerolog.NewConsoleWriter()
 	out.NoColor = true // For testing purposes only