[common][log] Init filter

- Based on Logrus's code
- Add Logger
- Add Entry
- Add Filter
- Add PkgFilter

common/log/README.md

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+# Log that support filter by field
+
+- [ ] thread safe
+- [ ] log to stdout
+- [ ] leveled logging 
+- [ ] support filed
+- [ ] filter by field

common/log/doc.go

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+/*
+Package log can filter log by field and support multiple level
+*/
+package log

common/log/entry.go

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+package log
+
+type Entry struct {
+	Fields Fields
+}

common/log/filter.go

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+package log
+
+type Set map[string]bool
+
+// Filter determines if the entry should be logged
+type Filter interface {
+	Filter(entry *Entry) bool
+}
+
+// PkgFilter only allows entry without `pkg` field or `pkg` value in the allow set to pass
+type PkgFilter struct {
+	allow Set
+}
+
+func (filter *PkgFilter) Filter(entry *Entry) bool {
+	pkg, ok := entry.Fields["pkg"]
+	// entry without pkg is not filtered
+	if !ok {
+		return true
+	}
+	_, ok = filter.allow[pkg]
+	return ok
+}
+
+func NewPkgFilter(allow Set) *PkgFilter {
+	return &PkgFilter{
+		allow: allow,
+	}
+}

common/log/filter_test.go

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+package log
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFilterInterface(t *testing.T) {
+	assert := assert.New(t)
+
+	allow := make(map[string]bool)
+	allow["ayi.app.git"] = true
+	f := NewPkgFilter(allow)
+	entryWithoutField := &Entry{}
+	assert.True(f.Filter(entryWithoutField))
+	field := make(map[string]string, 1)
+	field["pkg"] = "ayi.app.git"
+	entryWithAllowedPkg := &Entry{Fields: field}
+	assert.True(f.Filter(entryWithAllowedPkg))
+	field["pkg"] = "ayi.app.web"
+	entryWithDisallowedPkg := &Entry{Fields: field}
+	assert.False(f.Filter(entryWithDisallowedPkg))
+
+}

common/log/logger.go

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+package log
+
+import (
+	"io"
+	"os"
+	"sync"
+)
+
+// Level is log level
+type Level uint8
+
+const (
+	// PanicLevel log error and call painc
+	PanicLevel Level = iota
+	// FatalLevel log error and call `os.Exit(1)`
+	FatalLevel
+	// ErrorLevel log error
+	ErrorLevel
+	// WarnLevel log warning
+	WarnLevel
+	// InfoLevel log info
+	InfoLevel
+	// DebugLevel log debug message, user should enable DebugLevel logging when report bug
+	DebugLevel
+	// TraceLevel is used by developer only, user should stop at DebugLevel if they just want to report
+	TraceLevel
+)
+
+// Fields is key-value string pair to annotate the log and can be used by filter
+type Fields map[string]string
+
+type Logger struct {
+	Out   io.Writer
+	Level Level
+	mu    sync.Mutex
+}
+
+// NewLogger returns a new logger using StdOut and InfoLevel
+func NewLogger() *Logger {
+	return &Logger{
+		Out:   os.Stdout,
+		Level: InfoLevel,
+	}
+}
+
+func (log *Logger) AddFilter(filter Filter, level Level) {
+}