implement structured logging

api/middleware.go

@@ -9,20 +9,36 @@ import (
 
 	"github.com/gin-gonic/gin"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/rs/zerolog/log"
 )
 
 // Only use base path as label value (e.g.: /api/repos) because of time series cardinality
 // See https://prometheus.io/docs/practices/naming/#labels
 func getBasePath(c *gin.Context) string {
-	return fmt.Sprintf("%s%s", getURLSegment(c.Request.URL.Path, 0), getURLSegment(c.Request.URL.Path, 1))
+	segment0, err := getURLSegment(c.Request.URL.Path, 0)
+	if err != nil {
+		return "/"
+	}
+	segment1, err := getURLSegment(c.Request.URL.Path, 1)
+	if err != nil {
+		return *segment0
+	}
+
+	return *segment0 + *segment1
 }
 
-func getURLSegment(url string, idx int) string {
-	var urlSegments = strings.Split(url, "/")
-
+func getURLSegment(url string, idx int) (*string, error) {
+	urlSegments := strings.Split(url, "/")
 	// Remove segment at index 0 because it's an empty string
-	var segmentAtIndex = urlSegments[1:cap(urlSegments)][idx]
-	return fmt.Sprintf("/%s", segmentAtIndex)
+	urlSegments = urlSegments[1:cap(urlSegments)]
+
+	if len(urlSegments) <= idx {
+		return nil, fmt.Errorf("index %d out of range, only has %d url segments", idx, len(urlSegments))
+	}
+
+	segmentAtIndex := urlSegments[idx]
+	s := fmt.Sprintf("/%s", segmentAtIndex)
+	return &s, nil
 }
 
 func instrumentHandlerInFlight(g *prometheus.GaugeVec, pathFunc func(*gin.Context) string) func(*gin.Context) {
@@ -62,3 +78,39 @@ func instrumentHandlerDuration(obs prometheus.ObserverVec, pathFunc func(*gin.Co
 		obs.WithLabelValues(strconv.Itoa(c.Writer.Status()), c.Request.Method, pathFunc(c)).Observe(time.Since(now).Seconds())
 	}
 }
+
+// JSONLogger is a gin middleware that takes an instance of Logger and uses it for writing access
+// logs that include error messages if there are any.
+func JSONLogger() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		// Start timer
+		start := time.Now()
+		path := c.Request.URL.Path
+		raw := c.Request.URL.RawQuery
+
+		// Process request
+		c.Next()
+
+		ts := time.Now()
+		if raw != "" {
+			path = path + "?" + raw
+		}
+
+		errorMessage := strings.TrimSuffix(c.Errors.ByType(gin.ErrorTypePrivate).String(), "\n")
+		l := log.With().Str("remote", c.ClientIP()).Logger().
+			With().Str("method", c.Request.Method).Logger().
+			With().Str("path", path).Logger().
+			With().Str("protocol", c.Request.Proto).Logger().
+			With().Str("code", fmt.Sprint(c.Writer.Status())).Logger().
+			With().Str("latency", ts.Sub(start).String()).Logger().
+			With().Str("agent", c.Request.UserAgent()).Logger()
+
+		if c.Writer.Status() >= 400 && c.Writer.Status() < 500 {
+			l.Warn().Msg(errorMessage)
+		} else if c.Writer.Status() >= 500 {
+			l.Error().Msg(errorMessage)
+		} else {
+			l.Info().Msg(errorMessage)
+		}
+	}
+}