Retrieve function logs from controller (#207)

Establish a proxy server from the controller to the log database.

Redirect query commands send from client to database then proxy back the db response.

Use parameter binding instead of fmt.Sprintf to prevent SQL injection.

controller/functionApi.go

@@ -17,14 +17,16 @@ limitations under the License.
 package controller
 
 import (
+	"encoding/base64"
+	"encoding/json"
 	"io/ioutil"
 	"net/http"
+	"net/http/httputil"
+	"net/url"
 
-	"encoding/json"
 	log "github.com/Sirupsen/logrus"
 	"github.com/gorilla/mux"
 
-	"encoding/base64"
 	"github.com/fission/fission"
 )
 
@@ -171,3 +173,33 @@ func (api *API) FunctionApiDelete(w http.ResponseWriter, r *http.Request) {
 
 	api.respondWithSuccess(w, []byte(""))
 }
+
+// FunctionLogsApiPost establishes a proxy server to log database, and redirect
+// query command send from client to database then proxy back the db response.
+func (api *API) FunctionLogsApiPost(w http.ResponseWriter, r *http.Request) {
+	vars := mux.Vars(r)
+	// get dbType from url
+	dbType := vars["dbType"]
+
+	// find correspond db http url
+	dbCnf := api.getLogDBConfig(dbType)
+
+	svcUrl, err := url.Parse(dbCnf.httpURL)
+	if err != nil {
+		log.Printf("Failed to establish proxy server for function logs: %v", err)
+	}
+	// set up proxy server director
+	director := func(req *http.Request) {
+		// only replace url Scheme and Host to remote influxDB
+		// and leave query string intact
+		req.URL.Scheme = svcUrl.Scheme
+		req.URL.Host = svcUrl.Host
+		req.URL.Path = svcUrl.Path
+		// set up http basic auth for database authentication
+		req.SetBasicAuth(dbCnf.username, dbCnf.password)
+	}
+	proxy := &httputil.ReverseProxy{
+		Director: director,
+	}
+	proxy.ServeHTTP(w, r)
+}