Add support for setting log fields from env vars

Setting env vars in the form LOG_VAR_field_name=value now adds fields
fields to the logger (e.g. zap.String("field_name", "value") in this
example).

Author: prydie

cmd/oci-cloud-controller-manager/main.go

@@ -30,7 +30,7 @@ import (
 	_ "k8s.io/kubernetes/pkg/client/metrics/prometheus" // for client metric registration
 	_ "k8s.io/kubernetes/pkg/version/prometheus"        // for version metric registration
 
-	logutil "github.com/oracle/oci-cloud-controller-manager/pkg/log"
+	"github.com/oracle/oci-cloud-controller-manager/pkg/logging"
 	_ "github.com/oracle/oci-cloud-controller-manager/pkg/oci"
 )
 
@@ -40,7 +40,7 @@ var build string
 func main() {
 	rand.Seed(time.Now().UTC().UnixNano())
 
-	logger := logutil.Logger()
+	logger := logging.Logger()
 	defer logger.Sync()
 	zap.ReplaceGlobals(logger)
 

pkg/log/log.go renamed to pkg/logging/logging.go

@@ -12,10 +12,12 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package log
+package logging
 
 import (
 	"flag"
+	"os"
+	"strings"
 	"sync"
 
 	"go.uber.org/zap"
@@ -61,7 +63,15 @@ func Logger() *zap.Logger {
 		cfg = zap.NewProductionConfig()
 	}
 
-	options := []zap.Option{zap.AddStacktrace(zapcore.FatalLevel)}
+	// Extract log fields from environment variables.
+	envFields := FieldsFromEnv(os.Environ())
+
+	options := []zap.Option{
+		zap.AddStacktrace(zapcore.FatalLevel),
+		zap.WrapCore(func(c zapcore.Core) zapcore.Core {
+			return c.With(envFields)
+		}),
+	}
 
 	if len(logfilePath) > 0 {
 		w := zapcore.AddSync(&lumberjack.Logger{
@@ -99,3 +109,27 @@ func Logger() *zap.Logger {
 
 	return logger
 }
+
+// FieldsFromEnv extracts log fields from environment variables.
+// If an environment variable starts with LOG_FIELD_, the suffix is extracted
+// and split on =. The first part is used for the name and the second for the
+// value.
+// For example, LOG_FIELD_foo=bar would result in a field named "foo" with the
+// value "bar".
+func FieldsFromEnv(env []string) []zapcore.Field {
+	const logfieldPrefix = "LOG_FIELD_"
+
+	fields := []zapcore.Field{}
+	for _, s := range env {
+		if !strings.HasPrefix(s, logfieldPrefix) || len(s) < (len(logfieldPrefix)+1) {
+			continue
+		}
+		s = s[len(logfieldPrefix):]
+		parts := strings.SplitN(s, "=", 2)
+		if len(parts) != 2 {
+			continue
+		}
+		fields = append(fields, zap.String(parts[0], parts[1]))
+	}
+	return fields
+}

pkg/logging/logging_test.go

@@ -0,0 +1,81 @@
+// Copyright 2018 Oracle and/or its affiliates. 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 logging
+
+import (
+	"reflect"
+	"testing"
+
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+)
+
+func TestFieldsFromEnv(t *testing.T) {
+	testCases := map[string]struct {
+		env    []string
+		fields []zapcore.Field
+	}{
+		"single": {
+			env: []string{"LOG_FIELD_foo=bar"},
+			fields: []zapcore.Field{
+				zap.String("foo", "bar"),
+			},
+		},
+		"multiple": {
+			env: []string{
+				"LOG_FIELD_foo=bar",
+				"LOG_FIELD_bar=baz",
+			},
+			fields: []zapcore.Field{
+				zap.String("foo", "bar"),
+				zap.String("bar", "baz"),
+			},
+		},
+		"handles_equals_in_value": {
+			env: []string{
+				"LOG_FIELD_foo=a=b",
+			},
+			fields: []zapcore.Field{
+				zap.String("foo", "a=b"),
+			},
+		},
+		"handles_empty_value": {
+			env: []string{
+				"LOG_FIELD_foo=",
+			},
+			fields: []zapcore.Field{
+				zap.String("foo", ""),
+			},
+		},
+		"ignores_non_log_field": {
+			env: []string{
+				"LOG_FIELD_foo=bar",
+				"NOT_A_FIELD=1",
+			},
+			fields: []zapcore.Field{
+				zap.String("foo", "bar"),
+			},
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			fields := FieldsFromEnv(tc.env)
+			if !reflect.DeepEqual(fields, tc.fields) {
+				t.Errorf("Got incorrect fields:\nexpected=%+v\nactual=%+v", tc.fields, fields)
+			}
+		})
+	}
+}