HTTP Servers

Response Model

A response combines a status code, body text, and headers.

response Server code fills a response value so the caller can inspect status, body, and headers.

Response Model

userID
response_model.go
Replay: real traced execution (multi-file project)
package main

import "fmt"

type response struct {
	Status  int
	Body    string
	Headers map[string]string
}

func main() {
	var userID = "42"
	res := response{Status: 200, Body: "user " + userID, Headers: map[string]string{}}

	if userID == "missing" {
		res.Status = 404
		res.Body = "user not found"
	}
	res.Headers["Content-Type"] = "text/plain"

	fmt.Println("userID=", userID)
	fmt.Println("status=", res.Status)
	fmt.Println("body=", res.Body)
	fmt.Println("contentType=", res.Headers["Content-Type"])
}

package main

import "fmt"

type response struct {
	Status  int
	Body    string
	Headers map[string]string
}

func main() {
	var userID = "7"
	res := response{Status: 200, Body: "user " + userID, Headers: map[string]string{}}

	if userID == "missing" {
		res.Status = 404
		res.Body = "user not found"
	}
	res.Headers["Content-Type"] = "text/plain"

	fmt.Println("userID=", userID)
	fmt.Println("status=", res.Status)
	fmt.Println("body=", res.Body)
	fmt.Println("contentType=", res.Headers["Content-Type"])
}

package main

import "fmt"

type response struct {
	Status  int
	Body    string
	Headers map[string]string
}

func main() {
	var userID = "missing"
	res := response{Status: 200, Body: "user " + userID, Headers: map[string]string{}}

	if userID == "missing" {
		res.Status = 404
		res.Body = "user not found"
	}
	res.Headers["Content-Type"] = "text/plain"

	fmt.Println("userID=", userID)
	fmt.Println("status=", res.Status)
	fmt.Println("body=", res.Body)
	fmt.Println("contentType=", res.Headers["Content-Type"])
}

  1. userID ← "42", res ← main.response{Status:200, Body:"user 42", Headers:map[string]string{}}

    11func main() {12  var userID→ "42" = "42" //@userID="7", "missing"13  res→ main.response{Status:200, Body:"user 42", Headers:map[string]string{}} := response{Status: 200, Body: "user " + userID"42", Headers: map[string]string{}}1415  if userID == "missing" {16    res.Status = 40417    res.Body = "user not found"18  }19  res.Headers["Content-Type"]→ "text/plain" = "text/plain"2021  fmt.Println("userID=", userID"42")22  fmt.Println("status=", res.Status200)23  fmt.Println("body=", res.Body"user 42")24  fmt.Println("contentType=", res.Headers["Content-Type"]"text/plain")25}
    outputuserID= 42
status= 200
body= user 42
contentType= text/plain

  1. userID ← "7", res ← main.response{Status:200, Body:"user 7", Headers:map[string]string{}}

    11func main() {12  var userID→ "7" = "7"13  res→ main.response{Status:200, Body:"user 7", Headers:map[string]string{}} := response{Status: 200, Body: "user " + userID"7", Headers: map[string]string{}}1415  if userID == "missing" {16    res.Status = 40417    res.Body = "user not found"18  }19  res.Headers["Content-Type"]→ "text/plain" = "text/plain"2021  fmt.Println("userID=", userID"7")22  fmt.Println("status=", res.Status200)23  fmt.Println("body=", res.Body"user 7")24  fmt.Println("contentType=", res.Headers["Content-Type"]"text/plain")25}
    outputuserID= 7
status= 200
body= user 7
contentType= text/plain

  1. userID ← "missing", res ← main.response{Status:200, Body:"user missing", Headers:map[string]string{}}

    11func main() {12  var userID→ "missing" = "missing"13  res→ main.response{Status:200, Body:"user missing", Headers:map[string]string{}} := response{Status: 200, Body: "user " + userID"missing", Headers: map[string]string{}}

  2. res.Status ← 404, res.Body ← "user not found"

    15if userID"missing" == "missing" {16  res.Status→ 404 = 40417  res.Body→ "user not found" = "user not found"18}

  3. res.Headers["Content-Type"] ← "text/plain"

    18  }19  res.Headers["Content-Type"]→ "text/plain" = "text/plain"2021  fmt.Println("userID=", userID"missing")22  fmt.Println("status=", res.Status404)23  fmt.Println("body=", res.Body"user not found")24  fmt.Println("contentType=", res.Headers["Content-Type"]"text/plain")25}
    outputuserID= missing
status= 404
body= user not found
contentType= text/plain