Metrics data is stored as structure, HTTP requests logging, got rid of context.

Metrics data now stored as structures. This is a first step for autodiscovery
helping for NMSes.

HTTP requests now logged.

Got rid of context.Context for getting metric data in applications
because context.Context is useless here.

internal/httpserver/handler.go

@@ -1,11 +1,26 @@
 package httpserver
 
 import (
-	"context"
+	"encoding/json"
+	"errors"
+	"log"
 	"net/http"
+	"strconv"
 	"strings"
+	"time"
 
 	"go.dev.pztrn.name/metricator/internal/common"
+	"go.dev.pztrn.name/metricator/internal/models"
+)
+
+var (
+	errInvalidAPIVersion  = errors.New("invalid API version")
+	errInvalidApplication = errors.New("invalid application")
+	errInvalidPath        = errors.New("invalid path")
+	errNoAppsRegistered   = errors.New("no applications registered")
+	errNoData             = errors.New("no data")
+
+	supportedAPIVersions = []int{1}
 )
 
 // HTTP requests handler.
@@ -13,41 +28,135 @@ type handler struct {
 	handlers map[string]common.HTTPHandlerFunc
 }
 
+// Gets applications list from handlers map.
+func (h *handler) getAppsList() ([]byte, error) {
+	apps := make([]string, 0, len(h.handlers))
+
+	for appName := range h.handlers {
+		apps = append(apps, appName)
+	}
+
+	appsList, err := json.Marshal(apps)
+	if err != nil {
+		// ToDo: log error
+
+		return nil, errNoAppsRegistered
+	}
+
+	return appsList, nil
+}
+
+// Gets request information from URL. Returns a structure with filled request
+// info and error if it occurs.
+func (h *handler) getRequestInfo(r *http.Request) (*models.RequestInfo, error) {
+	// Request isn't for API or isn't versioned.
+	if !strings.HasPrefix(r.URL.Path, "/api/v") {
+		return nil, errInvalidPath
+	}
+
+	// Note: first element will always be empty!
+	pathSplitted := strings.Split(r.URL.Path, "/")
+
+	// Request is for API but not enough items in URL was passed.
+	if len(pathSplitted) < 4 {
+		return nil, errInvalidPath
+	}
+
+	var (
+		appName     string
+		metricName  string
+		requestType string
+	)
+
+	// Parse API version.
+	apiVersionRaw := strings.TrimLeft(pathSplitted[2], "v")
+	apiVersion, err := strconv.Atoi(apiVersionRaw)
+	if err != nil {
+		// ToDo: log error
+		return nil, errInvalidAPIVersion
+	}
+
+	// Get request type and key.
+	requestType = pathSplitted[3]
+	if len(pathSplitted) >= 5 {
+		appName = pathSplitted[4]
+	}
+	if len(pathSplitted) >= 6 {
+		metricName = strings.Join(pathSplitted[5:], "/")
+	}
+
+	reqInfo := &models.RequestInfo{
+		ApiVersion:  apiVersion,
+		Application: appName,
+		Metric:      metricName,
+		RequestType: requestType,
+	}
+
+	return reqInfo, nil
+}
+
 // Registers request's handler.
-func (h *handler) register(name string, hndl common.HTTPHandlerFunc) {
-	h.handlers[name] = hndl
+func (h *handler) register(appName string, hndl common.HTTPHandlerFunc) {
+	h.handlers[appName] = hndl
 }
 
 // ServeHTTP handles every HTTP request.
 func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	if !strings.HasPrefix(r.URL.Path, "/api") {
+	startTime := time.Now()
+	defer func() {
+		requestDuration := time.Now().Sub(startTime)
+
+		log.Printf("[HTTP Request] from %s to %s, duration %.4fs\n", r.RemoteAddr, r.URL.Path, requestDuration.Seconds())
+	}()
+
+	// Validate request and extract needed info.
+	rInfo, err := h.getRequestInfo(r)
+	if err != nil {
 		w.WriteHeader(http.StatusBadRequest)
-		_, _ = w.Write([]byte("400 Bad Request - invalid path"))
+		_, _ = w.Write([]byte("400 bad request - " + err.Error()))
 
 		return
 	}
 
-	// Request validation.
-	pathSplitted := strings.Split(r.URL.Path, "/")
-	if len(pathSplitted) < 3 {
-		w.WriteHeader(http.StatusBadRequest)
-		_, _ = w.Write([]byte("400 Bad Request - invalid path"))
-	}
+	// Process request type. Here we process only known requests types,
+	// by default request should go to specific application's handler.
+	switch rInfo.RequestType {
+	// ToDo: move to constants.
+	case "apps_list":
+		appsList, err := h.getAppsList()
+		if err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+			_, _ = w.Write([]byte("400 bad request - " + err.Error()))
 
-	handler, found := h.handlers[pathSplitted[2]]
-	if !found {
-		w.WriteHeader(http.StatusBadRequest)
-		_, _ = w.Write([]byte("400 Bad Request - invalid application name"))
+			return
+		}
+
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write(appsList)
+
+		return
+	case "metrics":
+		handler, found := h.handlers[rInfo.Application]
+		if !found {
+			w.WriteHeader(http.StatusBadRequest)
+			_, _ = w.Write([]byte("400 bad request - " + errInvalidApplication.Error()))
+
+			return
+		}
+
+		// Get data from handler.
+		data := handler(rInfo)
+		if data == "" {
+			w.WriteHeader(http.StatusBadRequest)
+			_, _ = w.Write([]byte("400 bad request - " + errNoData.Error()))
+		}
+
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write([]byte(data))
 
 		return
 	}
 
-	requestContext := r.Context()
-
-	// Compose metric name.
-	metricName := strings.Join(pathSplitted[3:], "/")
-	ctx := context.WithValue(requestContext, common.ContextKeyMetric, metricName)
-
-	w.WriteHeader(http.StatusOK)
-	_, _ = w.Write([]byte(handler(ctx)))
+	w.WriteHeader(http.StatusBadRequest)
+	_, _ = w.Write([]byte("400 bad request - " + errInvalidPath.Error()))
 }