Request filtering and interception techniques and applications of http.Transport in Go language

Request filtering and interception techniques and applications of http.Transport in Go language

1. Introduction
In the http package of Go language, http.Transport is implemented as the underlying HTTP transport layer and provides Powerful function that can be used to initiate HTTP requests. This article will focus on how to use http.Transport to implement request filtering and interception techniques and their applications.

2. Request filtering
2.1 Filtering request method
We can use the RoundTrip method of http.Transport to customize HTTP requests. By defining a structure that implements the http.RoundTripper interface and overriding the RoundTrip method in it, we can filter and modify requests. The following code example shows how to filter request methods.

type FilterTransport struct {
    Transport http.RoundTripper
}

func (t *FilterTransport) RoundTrip(req *http.Request) (*http.Response, error) {
    // 过滤请求方法
    if req.Method == http.MethodGet {
        return nil, errors.New("Method Not Allowed")
    }

    return t.Transport.RoundTrip(req)
}

func main() {
    // 创建一个Transport
    transport := &FilterTransport{
        Transport: http.DefaultTransport,
    }

    // 创建一个Client
    client := &http.Client{
        Transport: transport,
    }

    // 创建一个GET请求
    req, _ := http.NewRequest(http.MethodGet, "http://example.com", nil)

    // 发起请求
    resp, err := client.Do(req)
    if err != nil {
        fmt.Println("Error:", err)
    } else {
        fmt.Println("Response:", resp.Status)
    }
}

In the above code, we created a FilterTransport structure that implements the http.RoundTripper interface, and filtered the GET request in the RoundTrip method. If the request method is GET, an error is returned.

2.2 Filtering request headers
In addition to filtering request methods, we can also filter and modify request headers. The following code example shows how to filter and modify request headers.

type HeaderFilterTransport struct {
    Transport http.RoundTripper
}

func (t *HeaderFilterTransport) RoundTrip(req *http.Request) (*http.Response, error) {
    // 过滤请求头
    req.Header.Del("User-Agent")
    req.Header.Set("User-Agent", "Custom User-Agent")

    return t.Transport.RoundTrip(req)
}

func main() {
    // 创建一个Transport
    transport := &HeaderFilterTransport{
        Transport: http.DefaultTransport,
    }

    // 创建一个Client
    client := &http.Client{
        Transport: transport,
    }

    // 创建一个GET请求
    req, _ := http.NewRequest(http.MethodGet, "http://example.com", nil)

    // 发起请求
    resp, err := client.Do(req)
    if err != nil {
        fmt.Println("Error:", err)
    } else {
        fmt.Println("Response:", resp.Status)
    }
}

In the above code, we created a HeaderFilterTransport structure that implements the http.RoundTripper interface, and filtered and modified the User-Agent request header in the RoundTrip method. We delete the original User-Agent request header and set a custom User-Agent.

3. Request interception
In addition to filtering requests, we can also intercept requests, modify the request body or further process the request. The following code example shows how to intercept a request and modify the request body.

type BodyInterceptorTransport struct {
    Transport http.RoundTripper
}

func (t *BodyInterceptorTransport) RoundTrip(req *http.Request) (*http.Response, error) {
    // 拦截请求并修改请求体
    if req.Method == http.MethodPost {
        // 读取原始请求体
        body, err := ioutil.ReadAll(req.Body)
        if err != nil {
            return nil, err
        }
        req.Body.Close()

        // 修改请求体
        newBody := bytes.NewReader([]byte("Modified Body"))

        // 替换请求体
        req.Body = ioutil.NopCloser(newBody)

        // 设置Content-Type
        req.Header.Set("Content-Type", "text/plain")
    }

    return t.Transport.RoundTrip(req)
}

func main() {
    // 创建一个Transport
    transport := &BodyInterceptorTransport{
        Transport: http.DefaultTransport,
    }

    // 创建一个Client
    client := &http.Client{
        Transport: transport,
    }

    // 创建一个POST请求
    req, _ := http.NewRequest(http.MethodPost, "http://example.com", strings.NewReader("Original Body"))

    // 发起请求
    resp, err := client.Do(req)
    if err != nil {
        fmt.Println("Error:", err)
    } else {
        fmt.Println("Response:", resp.Status)
    }
}

In the above code, we created a BodyInterceptorTransport structure that implements the http.RoundTripper interface, intercepted the POST request in the RoundTrip method, and modified the request body. We read the original request body, then replace it with the custom modified request body, and set the Content-Type to text/plain.

4. Conclusion
By using http.Transport's request filtering and interception techniques, we can customize the filtering, modification and interception of HTTP requests. This is very useful for implementing some special functions and requirements. However, caution is required during use to avoid affecting normal request processing and performance. I hope this article can help you use http.Transport for request filtering and interception in Go language.

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