CSE224 - HTTP server

Required library packages

Http package

net/http: A standard library package in Go to create and handle web-based communication using the HTTP protocol.

• http.HandleFunc(path, handler): When someone visits path, run the handler function. e.g., http.HandleFunc("/", homeHandler)
• http.ListenAndServe(addr, nil): Starts the server and listens on a specific address/port. e.g., http.ListenAndServe(":8080", nil), Listen for HTTP requests on port 8080.
• func(w http.ResponseWriter, r *http.Request): This is what handler functions look like.

func greetHandler(w http.ResponseWriter, r *http.Request) {
    name := r.URL.Query().Get("name") // Reads a query parameter from the URL
    if name == "" {
        name = "Guest"
    }
    fmt.Fprintf(w, "Hello, %s!", name)
}


func main() {
    http.HandleFunc("/", greetoHandler)
    http.ListenAndServe(":8080", nil)
}

Then visit http://localhost:8080/?name=Alice, and will output: Hello, Alice!

• r.URL.Query().Get("id"): Reads a query parameter from the URL, like /student?id=Alice
• r.ParseForm(): Used for reading form data submitted via POST.
• name := r.FormValue("student_name") : Access form values, gives you the first value for that key.
• r.Form["key"]: gives you all values as a slice ([]string)
• http.Redirect(...): Redirects the browser to another URL after a POST request.

html/template package

html/template is a Go standard library package that helps you create HTML pages with dynamic content.

1. Define HTML Template

   <!-- gradeinfo.html -->
   <h2>Student Name: {{.Name}}</h2>
   <h2>Grade: {{.Grade}}</h2>

2. Define a go struct

   type GradeInfo struct {
   	Name  string
   	Grade string
   }

3. Fill the template

   tmpl := template.Must(template.ParseFiles("gradeinfo.html"))
   
   student := GradeInfo{Name: "Alice", Grade: "A+"}
   tmpl.Execute(w, student)

tmpl.Execute(w, students) use template for index.html, fill data from student, dynamically generate a HTML page, and finally write the page to w.