infra: add logging wrapping

Resolves issues with gcp cloud logging quirks such as field names

go/internal/utils/env.go

@@ -2,7 +2,8 @@ package utils
 
 import (
 	"os"
-	"log/slog"
+
+	"github.com/flowy-live/llink/internal/utils/flog"
 )
 
 // EnvVar enumerates the env vars referenced via this package.
@@ -15,7 +16,7 @@ func MustGetEnv[T string | EnvVar](key T) string {
 	keyString := string(key)
 	value := os.Getenv(keyString)
 	if value == "" {
-		slog.Errorf("Missing required environment variable %s", key)
+		flog.Error("missing required environment variable", "key", key)
 		panic("Missing required environment variable")
 	}
 
@@ -26,7 +27,7 @@ func MustGetEnv[T string | EnvVar](key T) string {
 func GetEnv(key string) string {
 	value := os.Getenv(key)
 	if value == "" {
-	    slog.Warnf("Missing optional environment variable %s", key)
+		flog.Warn("missing optional environment variable", "key", key)
 	}
 	return value
 }

go/internal/utils/flog/flog.go

@@ -0,0 +1,58 @@
+// Package flog is a structured logger formatted for GCP Cloud Logging.
+//
+// The API mirrors log/slog: a message string followed by alternating key/value
+// pairs. Each kv pair becomes a JSON field in the emitted record, which Cloud
+// Logging promotes to a queryable jsonPayload field.
+//
+//	flog.Info("particle processed", "particleID", id, "elapsed", dt)
+package flog
+
+import (
+	"os"
+
+	"github.com/sirupsen/logrus"
+)
+
+// Prepares global logger for GCP Cloud Logging's quirks
+var log = func() *logrus.Logger {
+	logger := logrus.New()
+	logger.SetFormatter(&logrus.JSONFormatter{
+		FieldMap: logrus.FieldMap{
+			logrus.FieldKeyLevel: "severity",
+			logrus.FieldKeyMsg:   "message",
+			logrus.FieldKeyTime:  "timestamp",
+		},
+	})
+	logger.SetOutput(os.Stderr)
+	logger.SetLevel(logrus.DebugLevel)
+	return logger
+}()
+
+// fields converts alternating key/value args into a logrus.Fields map. A
+// trailing odd arg or non-string key is stored under "!BADKEY" to match
+// slog's behavior.
+func fields(args []any) logrus.Fields {
+	if len(args) == 0 {
+		return nil
+	}
+	f := make(logrus.Fields, len(args)/2+1)
+	for i := 0; i < len(args); i += 2 {
+		if i+1 >= len(args) {
+			f["!BADKEY"] = args[i]
+			break
+		}
+		key, ok := args[i].(string)
+		if !ok {
+			f["!BADKEY"] = args[i]
+			continue
+		}
+		f[key] = args[i+1]
+	}
+	return f
+}
+
+func Debug(msg string, args ...any) { log.WithFields(fields(args)).Debug(msg) }
+func Info(msg string, args ...any)  { log.WithFields(fields(args)).Info(msg) }
+func Warn(msg string, args ...any)  { log.WithFields(fields(args)).Warn(msg) }
+func Error(msg string, args ...any) { log.WithFields(fields(args)).Error(msg) }
+func Fatal(msg string, args ...any) { log.WithFields(fields(args)).Fatal(msg) }