Restructure project

We previously didn't really had any structure in our project apart
from creating a new folder for each package in our project root.
Now that we have accumulated some packages, we use the well-known
Golang project layout in order to clearly communicate our intent
with packages. See https://github.com/golang-standards/project-layout

pkg/logging/logging.go

@@ -0,0 +1,83 @@
+package logging
+
+import (
+	"bufio"
+	"fmt"
+	"github.com/sirupsen/logrus"
+	"net"
+	"net/http"
+	"os"
+	"time"
+)
+
+var log = &logrus.Logger{
+	Out: os.Stderr,
+	Formatter: &logrus.TextFormatter{
+		DisableColors: true,
+		FullTimestamp: true,
+	},
+	Hooks: make(logrus.LevelHooks),
+	Level: logrus.InfoLevel,
+}
+
+func InitializeLogging(loglevel string) {
+	level, err := logrus.ParseLevel(loglevel)
+	if err != nil {
+		log.WithError(err).Fatal("Error parsing loglevel")
+		return
+	}
+	log.SetLevel(level)
+}
+
+func GetLogger(pkg string) *logrus.Entry {
+	return log.WithField("package", pkg)
+}
+
+// loggingResponseWriter wraps the default http.ResponseWriter and catches the status code
+// that is written.
+type loggingResponseWriter struct {
+	http.ResponseWriter
+	statusCode int
+}
+
+func NewLoggingResponseWriter(w http.ResponseWriter) *loggingResponseWriter {
+	return &loggingResponseWriter{w, http.StatusOK}
+}
+
+func (writer *loggingResponseWriter) WriteHeader(code int) {
+	writer.statusCode = code
+	writer.ResponseWriter.WriteHeader(code)
+}
+
+func (writer *loggingResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	conn, rw, err := writer.ResponseWriter.(http.Hijacker).Hijack()
+	if err != nil {
+		return conn, nil, fmt.Errorf("hijacking connection failed: %w", err)
+	}
+	return conn, rw, nil
+}
+
+// HTTPLoggingMiddleware returns an http.Handler that logs different information about every request.
+func HTTPLoggingMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		start := time.Now().UTC()
+		path := r.URL.Path
+
+		lrw := NewLoggingResponseWriter(w)
+		next.ServeHTTP(lrw, r)
+
+		latency := time.Now().UTC().Sub(start)
+		logEntry := log.WithFields(logrus.Fields{
+			"code":       lrw.statusCode,
+			"method":     r.Method,
+			"path":       path,
+			"duration":   latency,
+			"user_agent": r.UserAgent(),
+		})
+		if lrw.statusCode >= http.StatusInternalServerError {
+			logEntry.Warn()
+		} else {
+			logEntry.Debug()
+		}
+	})
+}

pkg/logging/logging_test.go

@@ -0,0 +1,48 @@
+package logging
+
+import (
+	"github.com/sirupsen/logrus"
+	"github.com/sirupsen/logrus/hooks/test"
+	"github.com/stretchr/testify/assert"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func mockHTTPStatusHandler(status int) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(status)
+	})
+}
+
+func TestHTTPMiddlewareWarnsWhenInternalServerError(t *testing.T) {
+	var hook *test.Hook
+	log, hook = test.NewNullLogger()
+	InitializeLogging(logrus.DebugLevel.String())
+
+	request, err := http.NewRequest(http.MethodGet, "/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	recorder := httptest.NewRecorder()
+	HTTPLoggingMiddleware(mockHTTPStatusHandler(500)).ServeHTTP(recorder, request)
+
+	assert.Equal(t, 1, len(hook.Entries))
+	assert.Equal(t, logrus.WarnLevel, hook.LastEntry().Level)
+}
+
+func TestHTTPMiddlewareDebugsWhenStatusOK(t *testing.T) {
+	var hook *test.Hook
+	log, hook = test.NewNullLogger()
+	InitializeLogging(logrus.DebugLevel.String())
+
+	request, err := http.NewRequest(http.MethodGet, "/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	recorder := httptest.NewRecorder()
+	HTTPLoggingMiddleware(mockHTTPStatusHandler(200)).ServeHTTP(recorder, request)
+
+	assert.Equal(t, 1, len(hook.Entries))
+	assert.Equal(t, logrus.DebugLevel, hook.LastEntry().Level)
+}