add the uint32Value data type

The golang buildin package `flag` doesn't support `uint32` data
type, so we need to support it via the `flag.Var`.

Signed-off-by: Benjamin Wang <wachao@vmware.com>

pkg/flags/uint32.go

@@ -0,0 +1,45 @@
+// Copyright 2022 The etcd 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 flags
+
+import (
+	"flag"
+	"strconv"
+)
+
+type uint32Value uint32
+
+// NewUint32Value creates an uint32 instance with the provided value.
+func NewUint32Value(v uint32) *uint32Value {
+	val := new(uint32Value)
+	*val = uint32Value(v)
+	return val
+}
+
+// Set parses a command line uint32 value.
+// Implements "flag.Value" interface.
+func (i *uint32Value) Set(s string) error {
+	v, err := strconv.ParseUint(s, 0, 32)
+	*i = uint32Value(v)
+	return err
+}
+
+func (i *uint32Value) String() string { return strconv.FormatUint(uint64(*i), 10) }
+
+// Uint32FromFlag return the uint32 value of a flag with the given name
+func Uint32FromFlag(fs *flag.FlagSet, name string) uint32 {
+	val := *fs.Lookup(name).Value.(*uint32Value)
+	return uint32(val)
+}

pkg/flags/uint32_test.go

@@ -0,0 +1,111 @@
+// Copyright 2022 The etcd 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 flags
+
+import (
+	"flag"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUint32Value(t *testing.T) {
+	cases := []struct {
+		name        string
+		s           string
+		expectedVal uint32
+		expectError bool
+	}{
+		{
+			name:        "normal uint32 value",
+			s:           "200",
+			expectedVal: 200,
+		},
+		{
+			name:        "zero value",
+			s:           "0",
+			expectedVal: 0,
+		},
+		{
+			name:        "negative int value",
+			s:           "-200",
+			expectError: true,
+		},
+		{
+			name:        "invalid integer value",
+			s:           "invalid",
+			expectError: true,
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			var val uint32Value
+			err := val.Set(tc.s)
+
+			if tc.expectError {
+				if err == nil {
+					t.Errorf("Expected failure on parsing uint32 value from %s", tc.s)
+				}
+			} else {
+				if err != nil {
+					t.Errorf("Unexpected error when parsing %s: %v", tc.s, err)
+				}
+				assert.Equal(t, uint32(val), tc.expectedVal)
+			}
+		})
+	}
+}
+
+func TestUint32FromFlag(t *testing.T) {
+	const flagName = "max-concurrent-streams"
+
+	cases := []struct {
+		name        string
+		defaultVal  uint32
+		arguments   []string
+		expectedVal uint32
+	}{
+		{
+			name:        "only default value",
+			defaultVal:  15,
+			arguments:   []string{},
+			expectedVal: 15,
+		},
+		{
+			name:        "argument has different value from the default one",
+			defaultVal:  16,
+			arguments:   []string{"--max-concurrent-streams", "200"},
+			expectedVal: 200,
+		},
+		{
+			name:        "argument has the same value from the default one",
+			defaultVal:  105,
+			arguments:   []string{"--max-concurrent-streams", "105"},
+			expectedVal: 105,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			fs := flag.NewFlagSet("etcd", flag.ContinueOnError)
+			fs.Var(NewUint32Value(tc.defaultVal), flagName, "Maximum concurrent streams that each client can open at a time.")
+			if err := fs.Parse(tc.arguments); err != nil {
+				t.Fatalf("Unexpected error: %v\n", err)
+			}
+			actualMaxStream := Uint32FromFlag(fs, flagName)
+			assert.Equal(t, actualMaxStream, tc.expectedVal)
+		})
+	}
+}