Improve the InfluxDB through-put performance

This changes the current use of the InfluxDB client to instead use a
baked-in client that uses the fasthttp library.

This allows for significantly smaller allocations, the re-use of http
body buffers, and the re-use of the actual bytes of the line-protocol
metric representations.

plugins/outputs/influxdb/influxdb_test.go

@@ -20,22 +20,123 @@ func TestUDPInflux(t *testing.T) {
 	require.NoError(t, err)
 	err = i.Write(testutil.MockMetrics())
 	require.NoError(t, err)
+	require.NoError(t, i.Close())
 }
 
 func TestHTTPInflux(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		w.WriteHeader(http.StatusOK)
-		w.Header().Set("Content-Type", "application/json")
-		fmt.Fprintln(w, `{"results":[{}]}`)
+		switch r.URL.Path {
+		case "/write":
+			// test that database is set properly
+			if r.FormValue("db") != "test" {
+				w.WriteHeader(http.StatusTeapot)
+				w.Header().Set("Content-Type", "application/json")
+			}
+			// test that user agent is set properly
+			if r.UserAgent() != "telegraf" {
+				w.WriteHeader(http.StatusTeapot)
+				w.Header().Set("Content-Type", "application/json")
+			}
+			w.WriteHeader(http.StatusNoContent)
+			w.Header().Set("Content-Type", "application/json")
+		case "/query":
+			w.WriteHeader(http.StatusOK)
+			w.Header().Set("Content-Type", "application/json")
+			fmt.Fprintln(w, `{"results":[{}]}`)
+		}
 	}))
 	defer ts.Close()
 
-	i := InfluxDB{
-		URLs: []string{ts.URL},
-	}
+	i := newInflux()
+	i.URLs = []string{ts.URL}
+	i.Database = "test"
+	i.UserAgent = "telegraf"
 
 	err := i.Connect()
 	require.NoError(t, err)
 	err = i.Write(testutil.MockMetrics())
 	require.NoError(t, err)
+	require.NoError(t, i.Close())
+}
+
+func TestUDPConnectError(t *testing.T) {
+	i := InfluxDB{
+		URLs: []string{"udp://foobar:8089"},
+	}
+
+	err := i.Connect()
+	require.Error(t, err)
+
+	i = InfluxDB{
+		URLs: []string{"udp://localhost:9999999"},
+	}
+
+	err = i.Connect()
+	require.Error(t, err)
+}
+
+func TestHTTPConnectError_InvalidURL(t *testing.T) {
+	i := InfluxDB{
+		URLs: []string{"http://foobar:8089"},
+	}
+
+	err := i.Connect()
+	require.Error(t, err)
+
+	i = InfluxDB{
+		URLs: []string{"http://localhost:9999999"},
+	}
+
+	err = i.Connect()
+	require.Error(t, err)
+}
+
+func TestHTTPConnectError_DatabaseCreateFail(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/query":
+			w.WriteHeader(http.StatusNotFound)
+			w.Header().Set("Content-Type", "application/json")
+			fmt.Fprintln(w, `{"results":[{}],"error":"test error"}`)
+		}
+	}))
+	defer ts.Close()
+
+	i := InfluxDB{
+		URLs:     []string{ts.URL},
+		Database: "test",
+	}
+
+	// database creation errors do not return an error from Connect
+	// they are only logged.
+	err := i.Connect()
+	require.NoError(t, err)
+	require.NoError(t, i.Close())
+}
+
+func TestHTTPError_DatabaseNotFound(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/write":
+			w.WriteHeader(http.StatusNotFound)
+			w.Header().Set("Content-Type", "application/json")
+			fmt.Fprintln(w, `{"results":[{}],"error":"database not found"}`)
+		case "/query":
+			w.WriteHeader(http.StatusNotFound)
+			w.Header().Set("Content-Type", "application/json")
+			fmt.Fprintln(w, `{"results":[{}],"error":"database not found"}`)
+		}
+	}))
+	defer ts.Close()
+
+	i := InfluxDB{
+		URLs:     []string{ts.URL},
+		Database: "test",
+	}
+
+	err := i.Connect()
+	require.NoError(t, err)
+	err = i.Write(testutil.MockMetrics())
+	require.Error(t, err)
+	require.NoError(t, i.Close())
 }