feat: allow adding attribute via context function (#25)

This is useful if you only have access to the context values via functions.

Author: teleivo

README.md

@@ -125,7 +125,15 @@ customLogger := sloggorm.New(
 
 	slogGorm.WithErrorField("err"),     // instead of "error" (by default)
 
-	slogGorm.WithContextValue("slogAttrName", "ctxKey"), // adds an slog.Attr if a value if found for this key in the Gorm's query context
+	slogGorm.WithContextValue("slogAttrName1", "ctxKey"), // adds an slog.Attr if a value is found for this key in the Gorm's query context
+
+	slogGorm.WithContextFunc("slogAttrName2", func(ctx context.Context) (slog.Value, bool) {
+        v, ok := ctx.Value(ctxKey1).(time.Duration)
+        if !ok {
+            return slog.Value{}, false
+        }
+        return slog.DurationValue(v), true
+    }), // adds an slog.Attr if the given function returns an slog.Value and true
 )
 ```
 

logger.go

@@ -68,6 +68,7 @@ type logger struct {
 	logLevel                  map[LogType]slog.Level
 	gormLevel                 gormlogger.LogLevel
 	contextKeys               map[string]string
+	contextFuncs              map[string]func(context.Context) (slog.Value, bool)
 
 	sourceField string
 	errorField  string
@@ -201,5 +202,10 @@ func (l logger) appendContextAttributes(ctx context.Context, args []any) []any {
 			args = append(args, slog.Any(k, value))
 		}
 	}
+	for k, f := range l.contextFuncs {
+		if value, ok := f(ctx); ok {
+			args = append(args, slog.Any(k, value))
+		}
+	}
 	return args
 }

logger_test.go

@@ -92,7 +92,23 @@ func Test_logger_LogMode(t *testing.T) {
 }
 
 func Test_logger(t *testing.T) {
-	receiver, gormLogger := getReceiverAndLogger([]Option{WithContextValue("attrKey", "ctxKey")})
+	receiver, gormLogger := getReceiverAndLogger([]Option{
+		WithContextValue("attrKeyViaValue", "ctxKey"),
+		WithContextFunc("attrKeyViaFunc1", func(ctx context.Context) (slog.Value, bool) {
+			v, ok := ctx.Value(ctxKey1).(string)
+			if !ok {
+				return slog.Value{}, false
+			}
+			return slog.StringValue(v), true
+		}),
+		WithContextFunc("attrKeyViaFunc2", func(ctx context.Context) (slog.Value, bool) {
+			v, ok := ctx.Value(ctxKey2).(time.Duration)
+			if !ok {
+				return slog.Value{}, false
+			}
+			return slog.DurationValue(v), true
+		}),
+	})
 	expectedMsg := "awesome message"
 
 	tests := []struct {
@@ -111,6 +127,24 @@ func Test_logger(t *testing.T) {
 			wantMsg:   expectedMsg,
 			wantLevel: slog.LevelInfo,
 		},
+		{
+			name: "with context value and func",
+			ctx: context.WithValue(
+				context.WithValue(
+					context.WithValue(context.Background(), "ctxKey", "ctxVal"),
+					ctxKey1, "ctxValFunc1",
+				),
+				ctxKey2, time.Second,
+			),
+			function: gormLogger.Info,
+			wantMsg:  expectedMsg,
+			wantAttributes: map[string]slog.Attr{
+				"attrKeyViaValue": slog.Any("attrKeyViaValue", "ctxVal"),
+				"attrKeyViaFunc1": slog.String("attrKeyViaFunc1", "ctxValFunc1"),
+				"attrKeyViaFunc2": slog.Duration("attrKeyViaFunc2", time.Second),
+			},
+			wantLevel: slog.LevelInfo,
+		},
 		{
 			name:      "Warn",
 			ctx:       context.Background(),
@@ -130,7 +164,7 @@ func Test_logger(t *testing.T) {
 			ctx:            context.WithValue(context.Background(), "ctxKey", "ctxVal"),
 			function:       gormLogger.Error,
 			wantMsg:        expectedMsg,
-			wantAttributes: map[string]slog.Attr{"attrKey": slog.Any("attrKey", "ctxVal")},
+			wantAttributes: map[string]slog.Attr{"attrKeyViaValue": slog.Any("attrKeyViaValue", "ctxVal")},
 			wantLevel:      slog.LevelError,
 		},
 	}
@@ -389,7 +423,7 @@ func Test_logger_Trace(t *testing.T) {
 	}
 }
 
-// private functions
+// private helpers
 
 func getReceiverAndLogger(options []Option) (*DummyHandler, *logger) {
 	receiver := NewDummyHandler()
@@ -398,6 +432,13 @@ func getReceiverAndLogger(options []Option) (*DummyHandler, *logger) {
 	return receiver, New(options...)
 }
 
+type ctxKey int
+
+const (
+	ctxKey1 ctxKey = iota
+	ctxKey2
+)
+
 // Mock
 
 func NewDummyHandler() *DummyHandler {

options.go

@@ -1,6 +1,7 @@
 package slogGorm
 
 import (
+	"context"
 	"log/slog"
 	"time"
 )
@@ -83,3 +84,16 @@ func WithContextValue(slogAttrName, contextKey string) Option {
 		l.contextKeys[slogAttrName] = contextKey
 	}
 }
+
+// WithContextFunc adds an attribute with the given name and slog.Value returned by the given
+// function if the function returns true. No attribute will be added if the function returns false.
+// Use this over WithContextValue if your context keys are not strings or only accessible via
+// functions.
+func WithContextFunc(slogAttrName string, slogValueFunc func(ctx context.Context) (slog.Value, bool)) Option {
+	return func(l *logger) {
+		if l.contextFuncs == nil {
+			l.contextFuncs = make(map[string]func(context.Context) (slog.Value, bool))
+		}
+		l.contextFuncs[slogAttrName] = slogValueFunc
+	}
+}