添加 iox.JSONReader{

iox/json_reader.go

@@ -0,0 +1,50 @@
+// Copyright 2021 ecodeclub
+//
+// 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 iox
+
+import (
+	"bytes"
+	"encoding/json"
+)
+
+type JSONReader struct {
+	val any
+	bf  *bytes.Reader
+}
+
+func (j *JSONReader) Read(p []byte) (n int, err error) {
+	if j.bf == nil {
+		var data []byte
+		data, err = json.Marshal(j.val)
+		if err == nil {
+			j.bf = bytes.NewReader(data)
+		}
+	}
+	if err != nil {
+		return
+	}
+	return j.bf.Read(p)
+}
+
+// NewJSONReader 用于解决将一个结构体序列化为 JSON 之后，再封装为 io.Reader 的场景。
+// 该实现没有做任何输入检查。
+// 也就是你需要自己确保 val 是一个可以被 json 正确处理的东西。
+// 非线程安全。
+// 如果你传入的是 nil，那么读到的结果应该是 null。务必小心。
+func NewJSONReader(val any) *JSONReader {
+	return &JSONReader{
+		val: val,
+	}
+}

iox/json_reader_test.go

@@ -0,0 +1,61 @@
+// Copyright 2021 ecodeclub
+//
+// 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 iox
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestJSONReader(t *testing.T) {
+	testCases := []struct {
+		name  string
+		input []byte
+		val   any
+
+		wantRes []byte
+		wantN   int
+		wantErr error
+	}{
+		{
+			name:    "正常读取",
+			input:   make([]byte, 10),
+			wantN:   10,
+			val:     User{Name: "Tom"},
+			wantRes: []byte(`{"name":"T`),
+		},
+		{
+			name:    "输入 nil",
+			input:   make([]byte, 7),
+			wantN:   4,
+			wantRes: append([]byte(`null`), 0, 0, 0),
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			reader := NewJSONReader(tc.val)
+			n, err := reader.Read(tc.input)
+			assert.Equal(t, tc.wantErr, err)
+			assert.Equal(t, tc.wantN, n)
+			assert.Equal(t, tc.wantRes, tc.input)
+		})
+	}
+}
+
+type User struct {
+	Name string `json:"name"`
+}