Add helper function to read webhook port number from env var (#1162)

* Add helper function to read port number from env var

* Add check for port == 0

* Add the unit test

* Update error message

Co-Authored-By: savitaashture <sashture@redhat.com>

* Panic when env var is set but invalid

* Rename the func to be PortFromEnv.

* Apply suggestions from code review on error message

Co-authored-by: Victor Agababov <vagababov@gmail.com>

* Join defers

Co-authored-by: savitaashture <sashture@redhat.com>
Co-authored-by: Victor Agababov <vagababov@gmail.com>

webhook/env.go

@@ -0,0 +1,39 @@
+/*
+Copyright 2020 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package webhook
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+)
+
+const portEnvKey = "WEBHOOK_PORT"
+
+// PortFromEnv returns the webhook port set by portEnvKey, or default port if env var is not set.
+func PortFromEnv(defaultPort int) int {
+	if os.Getenv(portEnvKey) == "" {
+		return defaultPort
+	}
+	port, err := strconv.Atoi(os.Getenv(portEnvKey))
+	if err != nil {
+		panic(fmt.Sprintf("failed to convert the environment variable %q : %v", portEnvKey, err))
+	} else if port == 0 {
+		panic(fmt.Sprintf("the environment variable %q can't be zero", portEnvKey))
+	}
+	return port
+}

webhook/env_test.go

@@ -0,0 +1,83 @@
+/*
+Copyright 2020 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package webhook
+
+import (
+	"os"
+	"testing"
+)
+
+const (
+	testDefaultPort      = 8888
+	testMissingInputName = "MissingInput" // portEnvKey is not found.
+)
+
+type portTest struct {
+	name      string
+	in        string
+	want      int
+	wantPanic bool
+}
+
+func TestPort(t *testing.T) {
+	tests := []portTest{{
+		name: testMissingInputName,
+		want: testDefaultPort,
+	}, {
+		name: "EmptyInput",
+		in:   "",
+		want: testDefaultPort,
+	}, {
+		name:      "InvalidInputNonNumeric",
+		in:        "invalid",
+		wantPanic: true,
+	}, {
+		name:      "InvalidInputTrailingSpace",
+		in:        "8443 ",
+		wantPanic: true,
+	}, {
+		name:      "InvalidInputZero",
+		in:        "0",
+		wantPanic: true,
+	}, {
+		name: "ValidInput",
+		in:   "443",
+		want: 443,
+	}}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			// portEnvKey is unset when testing missing input.
+			if tc.name != testMissingInputName {
+				os.Setenv(portEnvKey, tc.in)
+			}
+
+			defer func() {
+				if r := recover(); r == nil && tc.wantPanic {
+					t.Error("Did not panic")
+				} else if r != nil && !tc.wantPanic {
+					t.Error("Got unexpected panic")
+				}
+				os.Unsetenv(portEnvKey)
+			}()
+
+			if got := PortFromEnv(testDefaultPort); got != tc.want {
+				t.Errorf("PortFromEnv = %d, want: %d", got, tc.want)
+			}
+		})
+	}
+}