Move metadata in RowMark output to stderr

Signed-off-by: Aswin Karthik <[email protected]>

cmd/config.go

@@ -2,6 +2,7 @@ package cmd
 
 import (
 	"errors"
+	"os"
 	"strings"
 
 	"github.com/aswinkarthik/csvdiff/pkg/digest"
@@ -74,10 +75,16 @@ const (
 // based on config.Format
 func (c *Config) Formatter() Formatter {
 	format := strings.ToLower(c.Format)
-	if format == rowmark {
-		return &RowMarkFormatter{}
-	} else if format == jsonFormat {
-		return &JSONFormatter{}
+
+	switch format {
+	case jsonFormat:
+		return &JSONFormatter{
+			Stdout: os.Stdout,
+		}
+	default:
+		return &RowMarkFormatter{
+			Stdout: os.Stdout,
+			Stderr: os.Stderr,
+		}
 	}
-	return &RowMarkFormatter{}
 }

cmd/formatter.go

@@ -11,38 +11,60 @@ import (
 // Formatter defines the interface through which differences
 // can be formatted and displayed
 type Formatter interface {
-	Format(digest.Difference, io.Writer)
+	Format(digest.Difference) error
 }
 
 // RowMarkFormatter formats diff by marking each row as
 // ADDED/MODIFIED. It mutates the row and adds as a new column.
-type RowMarkFormatter struct{}
+type RowMarkFormatter struct {
+	Stdout io.Writer
+	Stderr io.Writer
+}
 
 // Format prints the diff to os.Stdout
-func (f *RowMarkFormatter) Format(diff digest.Difference, w io.Writer) {
-	fmt.Fprintf(w, "Additions %d\n", len(diff.Additions))
-	fmt.Fprintf(w, "Modifications %d\n", len(diff.Modifications))
-	fmt.Fprintf(w, "Rows:\n")
+func (f *RowMarkFormatter) Format(diff digest.Difference) error {
+	fmt.Fprintf(f.Stderr, "Additions %d\n", len(diff.Additions))
+	fmt.Fprintf(f.Stderr, "Modifications %d\n", len(diff.Modifications))
+	fmt.Fprintf(f.Stderr, "Rows:\n")
 
 	for _, added := range diff.Additions {
-		fmt.Fprintf(w, "%s,%s\n", added, "ADDED")
+		_, err := fmt.Fprintf(f.Stdout, "%s,%s\n", added, "ADDED")
+
+		if err != nil {
+			return fmt.Errorf("error when formatting additions with RowMark formatter: %v", err)
+		}
 	}
 
 	for _, modified := range diff.Modifications {
-		fmt.Fprintf(w, "%s,%s\n", modified, "MODIFIED")
+		_, err := fmt.Fprintf(f.Stdout, "%s,%s\n", modified, "MODIFIED")
+
+		if err != nil {
+			return fmt.Errorf("error when formatting modifications with RowMark formatter: %v", err)
+		}
+
 	}
+
+	return nil
 }
 
 // JSONFormatter formats diff to as a JSON Object
-type JSONFormatter struct{}
+type JSONFormatter struct {
+	Stdout io.Writer
+}
 
 // Format prints the diff as a JSON
-func (f *JSONFormatter) Format(diff digest.Difference, w io.Writer) {
+func (f *JSONFormatter) Format(diff digest.Difference) error {
 	data, err := json.MarshalIndent(diff, "", "  ")
 
 	if err != nil {
-		panic(err)
+		return fmt.Errorf("error when serializing with JSON formatter: %v", err)
+	}
+
+	_, err = f.Stdout.Write(data)
+
+	if err != nil {
+		return fmt.Errorf("error when writing to writer with JSON formatter: %v", err)
 	}
 
-	w.Write(data)
+	return nil
 }

cmd/formatter_test.go

@@ -25,12 +25,13 @@ func TestJSONFormat(t *testing.T) {
   ]
 }`
 
-	var buffer bytes.Buffer
+	var stdout bytes.Buffer
 
-	formatter = &cmd.JSONFormatter{}
+	formatter = &cmd.JSONFormatter{Stdout: &stdout}
 
-	formatter.Format(diff, &buffer)
-	assert.Equal(t, expected, buffer.String())
+	err := formatter.Format(diff)
+	assert.NoError(t, err)
+	assert.Equal(t, expected, stdout.String())
 }
 
 func TestRowMarkFormatter(t *testing.T) {
@@ -39,17 +40,22 @@ func TestRowMarkFormatter(t *testing.T) {
 		Additions:     []string{"additions"},
 		Modifications: []string{"modification"},
 	}
-	expected := `Additions 1
+	expectedStdout := `additions,ADDED
+modification,MODIFIED
+`
+	expectedStderr := `Additions 1
 Modifications 1
 Rows:
-additions,ADDED
-modification,MODIFIED
 `
 
-	var buffer bytes.Buffer
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+
+	formatter = &cmd.RowMarkFormatter{Stdout: &stdout, Stderr: &stderr}
 
-	formatter = &cmd.RowMarkFormatter{}
+	err := formatter.Format(diff)
 
-	formatter.Format(diff, &buffer)
-	assert.Equal(t, expected, buffer.String())
+	assert.NoError(t, err)
+	assert.Equal(t, expectedStdout, stdout.String())
+	assert.Equal(t, expectedStderr, stderr.String())
 }

cmd/root.go

@@ -92,7 +92,7 @@ Most suitable for csv files created from database tables`,
 			os.Exit(2)
 		}
 
-		config.Formatter().Format(diff, os.Stdout)
+		config.Formatter().Format(diff)
 
 		return
 	},