如何在Golang中实现HTTP请求缓存

type CacheTransport struct {
    transport http.RoundTripper
    cache     map[string]cachedResponse
    mu        sync.RWMutex
}

type cachedResponse struct {
    once      sync.Once
    resp      *http.Response
    bodyBytes []byte
}

func NewCacheTransport() *CacheTransport {
    return &CacheTransport{
        transport: http.DefaultTransport,
        cache:     make(map[string]cachedResponse),
    }
}

func (c *CacheTransport) RoundTrip(req *http.Request) (*http.Response, error) {
    key := req.Method + ":" + req.URL.String()

    c.mu.RLock()
    if cached, found := c.cache[key]; found {
        c.mu.RUnlock()
        // 返回缓存响应的副本，避免引用被修改
        respCopy := cached.resp.Clone(req.Context())
        body := bytes.NewReader(cached.bodyBytes)
        respCopy.Body = io.NopCloser(body)
        return respCopy, nil
    }
    c.mu.RUnlock()

    // 发起真实请求
    resp, err := c.transport.RoundTrip(req)
    if err != nil {
        return nil, err
    }

    // 读取响应体并缓存
    bodyBytes, err := io.ReadAll(resp.Body)
    if err != nil {
        resp.Body.Close()
        return nil, err
    }
    resp.Body.Close()

    respCopy := resp.Clone(req.Context())
    respCopy.Body = io.NopCloser(bytes.NewReader(bodyBytes))

    c.mu.Lock()
    c.cache[key] = cachedResponse{
        resp:      respCopy,
        bodyBytes: bodyBytes,
    }
    c.mu.Unlock()

    return respCopy, nil
}

client := &http.Client{
    Transport: NewCacheTransport(),
}

resp, err := client.Get("https://api.example.com/data")