From d91f47246197c5c82ea911933f1e6520a480e78c Mon Sep 17 00:00:00 2001
From: Sarat Chandra <me@saratchandra.in>
Date: Thu, 7 Jul 2022 14:59:07 +0530
Subject: [PATCH] feat: Add default options to opts which gets logged with
 every log.

---
 README.md         | 25 ++++++++++---------------
 benchmark_test.go | 11 +++++++++++
 examples/main.go  |  1 +
 log.go            | 33 +++++++++++++++++++++++++++------
 log_test.go       | 13 +++++++++++++
 5 files changed, 62 insertions(+), 21 deletions(-)

diff --git a/README.md b/README.md
index 23a3cf1..2e48fd8 100644
--- a/README.md
+++ b/README.md
@@ -16,23 +16,23 @@
 package main
 
 import (
-	"os"
 	"time"
 
 	"github.com/zerodha/logf"
 )
 
 func main() {
-	logger := logf.New(os.Stderr)
-
-	// Basic log.
+	logger := logf.New(logf.Opts{
+		EnableColor:          true,
+		Level:                logf.DebugLevel,
+		CallerSkipFrameCount: 3,
+		EnableCaller:         true,
+		TimestampFormat:      time.RFC3339Nano,
+		DefaultFields:        []any{"scope", "example"},
+	})
+
+	// Basic logs.
 	logger.Info("starting app")
-
-	// Enable colored output.
-	logger.SetColorOutput(true)
-
-	// Change verbosity on the fly.
-	logger.SetLevel(logf.DebugLevel)
 	logger.Debug("meant for debugging app")
 
 	// Add extra keys to the log.
@@ -41,11 +41,6 @@ func main() {
 	// Log with error key.
 	logger.Error("error fetching details", "error", "this is a dummy error")
 
-	// Enable `caller` field in the log and specify the number of frames to skip to get the caller.
-	logger.SetCallerFrame(true, 3)
-	// Change the default timestamp format.
-	logger.SetTimestampFormat(time.RFC3339Nano)
-
 	// Log the error and set exit code as 1.
 	logger.Fatal("goodbye world")
 }
diff --git a/benchmark_test.go b/benchmark_test.go
index 4a61394..c9bc555 100644
--- a/benchmark_test.go
+++ b/benchmark_test.go
@@ -30,6 +30,17 @@ func BenchmarkOneField(b *testing.B) {
 	})
 }
 
+func BenchmarkOneFieldWithDefaultFields(b *testing.B) {
+	logger := logf.New(logf.Opts{Writer: io.Discard, DefaultFields: []any{"component", "logf"}})
+	b.ReportAllocs()
+	b.ResetTimer()
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			logger.Info("hello world", "stack", "testing")
+		}
+	})
+}
+
 func BenchmarkThreeFields(b *testing.B) {
 	logger := logf.New(logf.Opts{Writer: io.Discard})
 	b.ReportAllocs()
diff --git a/examples/main.go b/examples/main.go
index 15a3140..74792f0 100644
--- a/examples/main.go
+++ b/examples/main.go
@@ -13,6 +13,7 @@ func main() {
 		CallerSkipFrameCount: 3,
 		EnableCaller:         true,
 		TimestampFormat:      time.RFC3339Nano,
+		DefaultFields:        []any{"scope", "example"},
 	})
 
 	// Basic logs.
diff --git a/log.go b/log.go
index e0f11aa..413030e 100644
--- a/log.go
+++ b/log.go
@@ -29,6 +29,9 @@ type Opts struct {
 	EnableColor          bool
 	EnableCaller         bool
 	CallerSkipFrameCount int
+
+	// These fields will be printed with every log.
+	DefaultFields []any
 }
 
 // Logger is the interface for all log operations
@@ -180,19 +183,37 @@ func (l Logger) handleLog(msg string, lvl Level, fields ...any) {
 	// Format the line as logfmt.
 	var (
 		// count is find out if this is the last key in while itering fields.
-		count int
-		key   string
-		val   any
+		count      int
+		fieldCount = len(l.DefaultFields) + len(fields)
+		key        string
+		val        any
 	)
 
 	// If there are odd number of fields, ignore the last.
-	if len(fields)%2 != 0 {
-		fields = fields[0 : len(fields)-1]
+	if fieldCount%2 != 0 {
+		fields = fields[0 : fieldCount-1]
+	}
+
+	for i := range l.DefaultFields {
+		space := false
+		if count != fieldCount-1 {
+			space = true
+		}
+
+		if i%2 == 0 {
+			key = l.DefaultFields[i].(string)
+			continue
+		} else {
+			val = l.DefaultFields[i]
+		}
+
+		writeToBuf(buf, key, val, lvl, l.Opts.EnableColor, space)
+		count++
 	}
 
 	for i := range fields {
 		space := false
-		if count != len(fields)-1 {
+		if count != fieldCount-1 {
 			space = true
 		}
 
diff --git a/log_test.go b/log_test.go
index c9a3964..aeaf389 100644
--- a/log_test.go
+++ b/log_test.go
@@ -66,6 +66,19 @@ func TestLogFormat(t *testing.T) {
 	buf.Reset()
 }
 
+func TestLogFormatWithDefaultFields(t *testing.T) {
+	buf := &bytes.Buffer{}
+	l := New(Opts{Writer: buf, DefaultFields: []any{"defaultkey", "defaultvalue"}})
+
+	l.Info("hello world")
+	assert.Contains(t, buf.String(), `level=info message="hello world" defaultkey=defaultvalue`)
+	buf.Reset()
+
+	l.Info("hello world", "component", "logf")
+	assert.Contains(t, buf.String(), `level=info message="hello world" defaultkey=defaultvalue component=logf`)
+	buf.Reset()
+}
+
 func TestOddNumberedFields(t *testing.T) {
 	buf := &bytes.Buffer{}
 	l := New(Opts{Writer: buf})