Go Req
last modified August 24, 2023
Go Req tutorial shows how to create HTTP requests with Req http client. An http client sends HTTP requests and receives HTTP responses from a resource identified by an URL.
$ go version go version go1.18.1 linux/amd64
We use Go version 1.18.
HTTP
The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems. HTTP protocol is the foundation of data communication for the World Wide Web.
Req
Req is a third-party HTTP client with plenty of features. It has many convenience functions for easy configuring, debugging and testing.
Response status code
HTTP response status codes indicate whether a specific HTTP request has been successfully completed. There are five groups available:
- Informational responses (100–199)
- Successful responses (200–299)
- Redirects (300–399)
- Client errors (400–499)
- Server errors (500–599)
package main
import (
"fmt"
"log"
"github.com/imroc/req/v3"
)
func main() {
res, err := req.Get("http://webcode.me")
if err != nil {
log.Fatal(err)
}
fmt.Println(res.Status)
fmt.Println(res.StatusCode)
}
The example creates a GET request to a small website. We get the status code of the request.
import (
"fmt"
"log"
"github.com/imroc/req/v3"
)
We import the req package.
res, err := req.Get("http://webcode.me")
We generate a GET request with Get.
fmt.Println(res.Status) fmt.Println(res.StatusCode)
The Status gives the status as a string and the
StatusCode as a number.
Go Req DevMode
With DevMode function, we enable the development mode. In this mode
we the HTTP commands, HTTP headers and the response is automatically printed
to the console.
package main
import (
"log"
"github.com/imroc/req/v3"
)
func main() {
req.DevMode()
_, err := req.Get("http://webcode.me")
if err != nil {
log.Fatal(err)
}
}
We create a simple GET request in the development mode.
$ go run main.go 2022/05/31 12:39:14.685055 DEBUG [req] HTTP/1.1 GET http://webcode.me GET / HTTP/1.1 Host: webcode.me User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) ... Accept-Encoding: gzip HTTP/1.1 200 OK Server: nginx/1.6.2 Date: Tue, 31 May 2022 10:39:14 GMT Content-Type: text/html ...
Go Req GET request
The following example creates a simple GET request in Req.
package main
import (
"fmt"
"log"
"github.com/imroc/req/v3"
)
func main() {
res, err := req.Get("http://webcode.me")
if err != nil {
log.Fatal(err)
}
fmt.Println(res)
bytes, err := res.ToBytes()
if err != nil {
log.Fatal(err)
}
fmt.Println(string(bytes))
}
We create a GET request to the webcode.me.
res, err := req.Get("http://webcode.me")
A get request is issued with the Get function.
if err != nil {
log.Fatal(err)
}
We check for the error.
fmt.Println(res)
We print the response.
bytes, err := res.ToBytes() ... fmt.Println(string(bytes))
Alternatively, we can get the bytes and transform them into string.
Go Req HEAD request
The HTTP HEAD method requests the headers that are returned if the specified resource would be requested with an HTTP GET method.
package main
import (
"fmt"
"log"
"github.com/imroc/req/v3"
)
func main() {
res, err := req.Head("http://webcode.me")
if err != nil {
log.Fatal(err)
}
for k, v := range res.Header {
fmt.Printf("%s %s\n", k, v)
}
}
The example issues a HEAD request with Head and prints all
key/value pairs from the response header.
$ go run main.go Connection [keep-alive] Etag ["61ed305d-18a"] Content-Type [text/html] Content-Length [394] Last-Modified [Sun, 23 Jan 2022 10:39:25 GMT] Server [nginx/1.6.2] Date [Tue, 31 May 2022 10:50:54 GMT] Accept-Ranges [bytes]
Go Req User-Agent
The User-Agent request header is a string that lets servers and
network peers identify the application, operating system, vendor, and/or version
of the requesting user agent.
package main
import (
"fmt"
"log"
"github.com/imroc/req/v3"
)
func main() {
res, err := req.C().SetUserAgent("Go program").
R().Get("http://webcode.me/ua.php")
if err != nil {
log.Fatal(err)
}
fmt.Println(res)
}
The example sets a User-Agent header with SetUserAgent. The
requested resource simply returns the client's User-Agent string.
res, err := req.C().SetUserAgent("Go program").
R().Get("http://webcode.me/ua.php")
The C is a helper function to create a client while the
R is a helper function to create a request.
$ go run main.go Go program
Query parameters
Query parameters are the part of a uniform resource locator (URL) which assigns values to specified parameters. This is one way of sending data to the destination server.
http://example.com/api/users?name=John%20Doe&occupation=gardener
The query parameters are specified after the ? character. Multiple fields are
separated with the &. Special characters, such as spaces, are encoded. In
the above string, the space is encoded with the %20
value.
package main
import (
"fmt"
"log"
"github.com/imroc/req/v3"
)
func main() {
res, err := req.C().R().Get("http://localhost:8080/hello?name=Peter")
if err != nil {
log.Fatal(err)
}
fmt.Println(res)
}
In the example, we add a query paramter (name=Peter) to the request
URL. Alternatively, we could also use the request's SetQueryParam
function.
In order to test the example, we create a simple server with the Echo framework.
package main
import (
"fmt"
"net/http"
"github.com/labstack/echo/v4"
)
func main() {
e := echo.New()
e.GET("/hello/:name/", func(c echo.Context) error {
name := c.Param("name")
msg := fmt.Sprintf("Hello %s!", name)
return c.String(http.StatusOK, msg)
})
e.Logger.Fatal(e.Start(":8080"))
}
The server processes the request, retrieves the query parameter with
Param and returns a message back to the client.
Path parameters
Values can be send to the server via query parameters or path parameters. The path parameter is specified directly inside the URL path.
package main
import (
"fmt"
"log"
"github.com/imroc/req/v3"
)
func main() {
res, err := req.C().R().SetPathParam("name", "Peter").
Get("http://localhost:8080/hello/{name}/")
if err != nil {
log.Fatal(err)
}
fmt.Println(res)
}
We set the path parameter with SetPathParam.
The following server example processes a request with a path variable.
package main
import (
"fmt"
"net/http"
"github.com/labstack/echo/v4"
)
func main() {
e := echo.New()
e.GET("/hello/:name/", func(c echo.Context) error {
name := c.Param("name")
msg := fmt.Sprintf("Hello %s!", name)
return c.String(http.StatusOK, msg)
})
e.Logger.Fatal(e.Start(":8080"))
}
In the server application, we designate a path variable with a colon character.
We get the variable with Param, build a message and send it to the
client.
Download file
The following example downloads a binary file.
package main
import (
"log"
"github.com/imroc/req/v3"
)
func main() {
client := req.C()
url := "http://webcode.me/favicon.ico"
_, err := client.R().SetOutputFile("favicon.ico").Get(url)
if err != nil {
log.Fatal(err)
}
}
The SetOutputFile function sets the file that response body will be
downloaded to.
Upload file
The next example uploads a binary file.
package main
import (
"fmt"
"log"
"github.com/imroc/req/v3"
)
func main() {
client := req.C()
res, err := client.R().
SetFile("file", "sid.png").
Post("http://localhost:8080/upload")
if err != nil {
log.Fatal(err)
}
fmt.Println(res.Status)
}
The SetFile function sets up a multipart form from file path to
upload, which read file from filePath automatically to upload.
We create a server to process the request.
package main
import (
"io"
"net/http"
"os"
"github.com/labstack/echo/v4"
)
func upload(c echo.Context) error {
file, err := c.FormFile("file")
if err != nil {
return err
}
src, err := file.Open()
if err != nil {
return err
}
defer src.Close()
dst, err := os.Create(file.Filename)
if err != nil {
return err
}
defer dst.Close()
if _, err = io.Copy(dst, src); err != nil {
return err
}
return c.HTML(http.StatusOK, "File uploaded")
}
func main() {
e := echo.New()
e.POST("/upload", upload)
e.Logger.Fatal(e.Start(":8080"))
}
The server reads the binary data from the request and writes it to the filesystem.
In this article we have worked with the Req HTTP client.
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