Add a printer that knows how to print user-defined columns

pkg/kubectl/custom_column_printer.go

@@ -0,0 +1,107 @@
+/*
+Copyright 2014 The Kubernetes Authors All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package kubectl
+
+import (
+	"fmt"
+	"io"
+	"reflect"
+	"strings"
+	"text/tabwriter"
+
+	"k8s.io/kubernetes/pkg/runtime"
+	"k8s.io/kubernetes/pkg/util/jsonpath"
+)
+
+const (
+	columnwidth       = 10
+	tabwidth          = 4
+	padding           = 3
+	padding_character = ' '
+	flags             = 0
+)
+
+// Column represents a user specified column
+type Column struct {
+	// The header to print above the column, general style is ALL_CAPS
+	Header string
+	// The pointer to the field in the object to print in JSONPath form
+	// e.g. {.ObjectMeta.Name}, see pkg/util/jsonpath for more details.
+	FieldSpec string
+}
+
+// CustomColumnPrinter is a printer that knows how to print arbitrary columns
+// of data from templates specified in the `Columns` array
+type CustomColumnsPrinter struct {
+	Columns []Column
+}
+
+func (s *CustomColumnsPrinter) PrintObj(obj runtime.Object, out io.Writer) error {
+	w := tabwriter.NewWriter(out, columnwidth, tabwidth, padding, padding_character, flags)
+	headers := make([]string, len(s.Columns))
+	for ix := range s.Columns {
+		headers[ix] = s.Columns[ix].Header
+	}
+	fmt.Fprintln(w, strings.Join(headers, "\t"))
+	parsers := make([]*jsonpath.JSONPath, len(s.Columns))
+	for ix := range s.Columns {
+		parsers[ix] = jsonpath.New(fmt.Sprintf("column%d", ix))
+		if err := parsers[ix].Parse(s.Columns[ix].FieldSpec); err != nil {
+			return err
+		}
+	}
+
+	if runtime.IsListType(obj) {
+		objs, err := runtime.ExtractList(obj)
+		if err != nil {
+			return err
+		}
+		for ix := range objs {
+			if err := s.printOneObject(objs[ix], parsers, w); err != nil {
+				return err
+			}
+		}
+	} else {
+		if err := s.printOneObject(obj, parsers, w); err != nil {
+			return err
+		}
+	}
+	return w.Flush()
+}
+
+func (s *CustomColumnsPrinter) printOneObject(obj runtime.Object, parsers []*jsonpath.JSONPath, out io.Writer) error {
+	columns := make([]string, len(parsers))
+	for ix := range parsers {
+		parser := parsers[ix]
+		values, err := parser.FindResults(reflect.ValueOf(obj).Elem().Interface())
+		if err != nil {
+			return err
+		}
+		if len(values) == 0 || len(values[0]) == 0 {
+			fmt.Fprintf(out, "<none>\t")
+		}
+		valueStrings := []string{}
+		for arrIx := range values {
+			for valIx := range values[arrIx] {
+				valueStrings = append(valueStrings, fmt.Sprintf("%v", values[arrIx][valIx].Interface()))
+			}
+		}
+		columns[ix] = strings.Join(valueStrings, ",")
+	}
+	fmt.Fprintln(out, strings.Join(columns, "\t"))
+	return nil
+}