cli: add flag to specify log format (console, json)

Signed-off-by: VirtualTam <virtualtam@flibidi.net>

Dockerfile

@@ -40,6 +40,7 @@ ENV \
     SPARKLEMUFFIN_LISTEN_ADDR="0.0.0.0:8080" \
     SPARKLEMUFFIN_METRICS_LISTEN_ADDR="127.0.0.1:8081" \
     SPARKLEMUFFIN_PUBLIC_ADDR="http://localhost:8080" \
+    SPARKLEMUFFIN_LOG_FORMAT="json" \
     SPARKLEMUFFIN_LOG_LEVEL="info"
 
 EXPOSE 8080

cmd/sparklemuffin/command/root.go

@@ -47,6 +47,7 @@ const (
 var (
 	defaultLogLevelValue string = zerolog.LevelInfoValue
 	logLevelValue        string
+	logFormat            string
 
 	versionDetails *version.Details
 
@@ -84,8 +85,6 @@ func NewRootCommand() *cobra.Command {
 				return nil
 			}
 
-			var err error
-
 			// Configuration file lookup paths
 			home, err := os.UserHomeDir()
 			if err != nil {
@@ -105,15 +104,10 @@ func NewRootCommand() *cobra.Command {
 			}
 
 			// Global logger configuration
-			var logLevel zerolog.Level
-
-			if err := logLevel.UnmarshalText([]byte(logLevelValue)); err != nil {
-				log.Error().Err(err).Msg("invalid log level")
+			if err := config.SetupGlobalLogger(logFormat, logLevelValue); err != nil {
 				return err
 			}
 
-			zerolog.SetGlobalLevel(logLevel)
-
 			if configFileUsed := v.ConfigFileUsed(); configFileUsed != "" {
 				log.Info().Str("config_file", v.ConfigFileUsed()).Msg("configuration: using file")
 			} else {
@@ -175,23 +169,19 @@ func NewRootCommand() *cobra.Command {
 		},
 	}
 
-	var logLevelValues = []string{
-		zerolog.LevelTraceValue,
-		zerolog.LevelDebugValue,
-		zerolog.LevelInfoValue,
-		zerolog.LevelWarnValue,
-		zerolog.LevelErrorValue,
-		zerolog.LevelFatalValue,
-		zerolog.LevelPanicValue,
-	}
-
+	cmd.PersistentFlags().StringVar(
+		&logFormat,
+		"log-format",
+		config.LogFormatConsole,
+		fmt.Sprintf("Log format (%s, %s)", config.LogFormatJSON, config.LogFormatConsole),
+	)
 	cmd.PersistentFlags().StringVar(
 		&logLevelValue,
 		"log-level",
 		defaultLogLevelValue,
 		fmt.Sprintf(
 			"Log level (%s)",
-			strings.Join(logLevelValues, ", "),
+			strings.Join(config.LogLevelValues, ", "),
 		),
 	)
 

cmd/sparklemuffin/config/logger.go

@@ -0,0 +1,65 @@
+// Copyright (c) VirtualTam
+// SPDX-License-Identifier: MIT
+
+package config
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/rs/zerolog"
+	"github.com/rs/zerolog/log"
+)
+
+const (
+	// Format log messages as pretty-printed key-value pairs.
+	LogFormatConsole = "console"
+
+	// Format log messages as JSON documents.
+	LogFormatJSON = "json"
+)
+
+var (
+	// Available logger levels.
+	LogLevelValues = []string{
+		zerolog.LevelTraceValue,
+		zerolog.LevelDebugValue,
+		zerolog.LevelInfoValue,
+		zerolog.LevelWarnValue,
+		zerolog.LevelErrorValue,
+		zerolog.LevelFatalValue,
+		zerolog.LevelPanicValue,
+	}
+)
+
+// SetupGlobalLogger configures the global zerolog.Logger.
+func SetupGlobalLogger(logFormat string, logLevelValue string) error {
+	zerolog.SetGlobalLevel(zerolog.InfoLevel)
+
+	switch logFormat {
+	case LogFormatConsole:
+		log.Logger = log.Output(zerolog.ConsoleWriter{
+			Out:        os.Stderr,
+			TimeFormat: time.RFC3339,
+		})
+
+	case LogFormatJSON:
+		log.Logger = log.Output(os.Stderr)
+
+	default:
+		log.Error().Str("format", logFormat).Msg("log: invalid format")
+		return fmt.Errorf("log: invalid format %q", logFormat)
+	}
+
+	var logLevel zerolog.Level
+
+	if err := logLevel.UnmarshalText([]byte(logLevelValue)); err != nil {
+		log.Error().Err(err).Msg("invalid log level")
+		return err
+	}
+
+	zerolog.SetGlobalLevel(logLevel)
+
+	return nil
+}

cmd/sparklemuffin/main.go

@@ -4,22 +4,11 @@
 package main
 
 import (
-	"os"
-	"time"
-
-	"github.com/rs/zerolog"
-	"github.com/rs/zerolog/log"
 	"github.com/spf13/cobra"
 	"github.com/virtualtam/sparklemuffin/cmd/sparklemuffin/command"
 )
 
 func main() {
-	zerolog.SetGlobalLevel(zerolog.InfoLevel)
-	log.Logger = log.Output(zerolog.ConsoleWriter{
-		Out:        os.Stderr,
-		TimeFormat: time.RFC3339,
-	})
-
 	rootCommand := command.NewRootCommand()
 
 	commands := []*cobra.Command{

docker-compose.yml

@@ -32,6 +32,7 @@ services:
         condition: service_healthy
     environment:
       SPARKLEMUFFIN_PUBLIC_ADDR: https://sparklemuffin.domain.tld
+      SPARKLEMUFFIN_LOG_FORMAT: console
       SPARKLEMUFFIN_LOG_LEVEL: debug
       SPARKLEMUFFIN_METRICS_LISTEN_ADDR: "0.0.0.0:8081"
     ports:

docs/src/users/observability.md

@@ -3,11 +3,10 @@
 SparkleMuffin logs information on the standard error (stderr) stream,
 using a structured log message format (JSON or logfmt).
 
-The log level can be specified via [configuration](./configuration.md).
-
-TODO: add command-line flag to configure the log format (JSON or logfmt).
+The log format and level can be specified via [configuration](./configuration.md).
 
 ### Example logs: program startup
+#### Format: `console`
 ```shell
 2024-01-20T17:03:52+01:00 INF configuration: no file found config_paths=["/etc","/home/dev/.config","."]
 2024-01-20T17:03:53+01:00 INF database: successfully created connection pool database_addr=localhost:15432 database_driver=pgx database_name=sparklemuffin
@@ -20,6 +19,18 @@ TODO: add command-line flag to configure the log format (JSON or logfmt).
 2024-01-20T17:04:44+01:00 INF handle request duration_ms=7.072792 host=localhost:8080 method=GET path=/static/www.css remote_addr=127.0.0.1:51440 request_id=localhost.local/96bRV2ceWt-000002 size=5402 status=200
 ```
 
+#### Format: `json`
+```json
+{"level":"info","config_paths":["/etc","/home/dev/.config","."],"time":"2024-01-22T22:56:30+01:00","message":"configuration: no file found"}
+{"level":"info","database_driver":"pgx","database_addr":"localhost:15432","database_name":"sparklemuffin","time":"2024-01-22T22:56:30+01:00","message":"database: successfully created connection pool"}
+{"level":"info","log_level":"info","version":"devel","time":"2024-01-22T22:56:30+01:00","message":"global: setting up services"}
+{"level":"info","metrics_addr":"127.0.0.1:8081","time":"2024-01-22T22:56:30+01:00","message":"metrics: listening for HTTP requests"}
+{"level":"info","http_addr":"0.0.0.0:8080","time":"2024-01-22T22:56:30+01:00","message":"sparklemuffin: listening for HTTP requests"}
+{"level":"info","duration_ms":69.373458,"host":"localhost:8080","method":"GET","path":"/bookmarks","remote_addr":"127.0.0.1:50857","request_id":"localhost.local/dqPgOolnvF-000001","size":26808,"status":200,"time":"2024-01-22T22:57:12+01:00","message":"handle request"}
+{"level":"info","duration_ms":5.552375,"host":"localhost:8080","method":"GET","path":"/static/awesomplete.css","remote_addr":"127.0.0.1:50857","request_id":"localhost.local/dqPgOolnvF-000002","size":236,"status":200,"time":"2024-01-22T22:57:12+01:00","message":"handle request"}
+{"level":"info","duration_ms":12.052417,"host":"localhost:8080","method":"GET","path":"/static/easymde.css","remote_addr":"127.0.0.1:50860","request_id":"localhost.local/dqPgOolnvF-000003","size":1000,"status":200,"time":"2024-01-22T22:57:12+01:00","message":"handle request"}
+```
+
 ## Prometheus Metrics
 SparkleMuffin exposes [Prometheus metrics](https://prometheus.io/docs/concepts/metric_types/),
 providing useful information that can be used for monitoring and alerting.