Context-based tracing

Author: ashald

context/context.go

@@ -0,0 +1,90 @@
+package context
+
+import (
+	"fmt"
+	"github.com/oklog/ulid"
+	"github.com/sirupsen/logrus"
+	"io"
+	"math/rand"
+	"time"
+)
+
+const (
+	Error   = 0
+	Warning = 1
+	Info    = 2
+	Debug   = 3
+	Trace   = 4
+)
+
+var allLevels = []logrus.Level{
+	logrus.ErrorLevel,
+	logrus.WarnLevel,
+	logrus.InfoLevel,
+	logrus.DebugLevel,
+	logrus.TraceLevel,
+}
+
+type Fields map[string]interface{}
+
+type Context struct {
+	Trace string
+	index uint64 // given Context is intended to be used in single-threaded fashion so we use uint instead of ULID
+
+	level  logrus.Level
+	fields map[string]interface{}
+}
+
+func Init(level int, output io.Writer) {
+	logrus.SetFormatter(&logrus.JSONFormatter{})
+	logrus.SetOutput(output)
+	logrus.SetLevel(convertLevel(level))
+}
+
+func New() (ctx *Context) {
+	ctx = new(Context)
+	ctx.Trace = newULID()
+	ctx.fields = make(map[string]interface{})
+	return
+}
+
+func (ctx *Context) Derived() (derived *Context) {
+	ctx.index += 1
+	derived = New()
+	derived.Trace = fmt.Sprintf("%s.%d", ctx.Trace, ctx.index)
+	return
+}
+
+func (ctx *Context) Level(level int) *Context {
+	ctx.level = convertLevel(level)
+	return ctx
+}
+
+func (ctx *Context) Field(name string, value interface{}) *Context {
+	ctx.fields[name] = value
+	return ctx
+}
+
+func (ctx *Context) Message(message string) {
+	ctx.fields["::trace"] = ctx.Trace
+
+	logrus.WithFields(ctx.fields).Log(ctx.level, message)
+}
+
+func convertLevel(level int) logrus.Level {
+	if level < 0 || level >= len(allLevels) {
+		panic(
+			fmt.Sprintf(
+				"Wrong log level '%d' - only '0' (least verbose) to '%d' (most verbose) supported",
+				level, len(allLevels)-1))
+	}
+
+	return allLevels[level]
+}
+
+func newULID() string {
+	t := time.Now()
+	entropy := ulid.Monotonic(rand.New(rand.NewSource(t.UnixNano())), 0)
+	value := ulid.MustNew(ulid.Timestamp(t), entropy)
+	return value.String()
+}