How to Parse Pipelined HTTP Requests and Responses from a Text File in Go?

Parsing HTTP Requests and Responses from a Text File in Go

In a typical scenario, we encounter pipelines of HTTP requests and responses stored in text files. The challenge arises when we need to parse these pipelined messages into a structured format for analysis or further processing. This article will guide you through the steps of parsing both HTTP requests and responses from such a text file in Go.

Request Parsing

The Go standard library provides a convenient function, http.ReadRequest, which simplifies the parsing of HTTP requests. It reads the request line, headers, and body (if specified by the Content-Length header) from a *bufio.Reader.

req, err := http.ReadRequest(buf)
if err != nil {
    return err
}

Response Parsing

The http.ReadResponse function performs a similar task for HTTP responses. It reads the status line, headers, and body from the *bufio.Reader.

resp, err := http.ReadResponse(buf, req)
if err != nil {
    return err
}

Preserving Response Body

The http.ReadResponse function automatically closes the response body upon returning. To preserve the body for later use, we need to manually copy it into another buffer.

b := new(bytes.Buffer)
io.Copy(b, resp.Body)
resp.Body.Close()
resp.Body = ioutil.NopCloser(b)

Parsing the File

To parse the HTTP pipeline from a file, we use the bufio package to read the file line by line and create a slice of Connection structs to store the parsed requests and responses.

stream := make([]Connection, 0)
for {
    req, err := http.ReadRequest(buf)
    if err == io.EOF {
        break
    }
    resp, err := http.ReadResponse(buf, req)
    if err != nil {
        return err
    }
    ...
    stream = append(stream, Connection{Request: req, Response: resp})
}

Dumping for Inspection

For verification purposes, we can use httputil.DumpRequest and httputil.DumpResponse to dump the parsed requests and responses into strings for inspection.

b, err := httputil.DumpRequest(c.Request, true)
if err != nil {
    log.Fatal(err)
}
fmt.Println(string(b))
b, err = httputil.DumpResponse(c.Response, true)
if err != nil {
    log.Fatal(err)
}
fmt.Println(string(b))

Conclusion

By leveraging the http.ReadRequest and http.ReadResponse functions along with careful body handling, we can effectively parse HTTP pipelined requests and responses from a text file in Go. This approach enables us to analyze, process, or test HTTP communication scenarios in a convenient and reliable manner.

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