http_calls.md

HTTP client and server

HTTP client and server implementations are available in net/http package. This is a huge package. The package documentation can be found here

Response struct has Status StatusCode, Body (io.ReadCloser), etc. io.ReadCloser is an interface that has two interface inside it i.e. Reader and Closer interface. These two interfaces have Read and Close names functions in it respectively.

In Reader, the Read function's signature takes byte slice as a paramter. This means user will provide the byte slice the implementation of Read will modify the slice (remember slice is passed by reference). The function should return an int i.e. the number of bytes read and error i.e. error if encountered any.

resp, err := http.Get("http://google.com")
if err != nil {
    fmt.Println("Error:", err)
    os.Exit(1)
}
// Read will take place till the byte slice is full or object to read is complete
var bs = make([]byte, 99999)
resp.Body.Read(bs)
fmt.Println(string(bs))

Writer interface can be used to print a []byte data. Ih has the function Write which receives a byte slice and returns an integer and error.

To implement both of these (Reader and Writer) simultaneously, io.Copy is used. It takes a Writer and Reader. Reads data from somewhere and writes it to somewhere.

_, err := io.Copy(os.Stdout, resp.Body)

Here is an example to a custom struct that implements Writer.

func (logWriter) Write(bs []byte) (int, error) {
	fmt.Println(string(bs))
	return len(bs), nil
}

lw := logWriter{}
io.Copy(lw, resp.Body)