Go package for creating net/http middleware handlers to alter the contents of other (net/http) handlers.
Error handler omitted for brevity.
Middleware handler to append custom JavaScript and CSS tags or data attributes to the HTML output of a previous handler.
package main
import (
"io"
"log"
"net/http"
"testing"
)
func baseAppendHandler() http.Handler {
fn := func(rsp http.ResponseWriter, req *http.Request) {
rsp.Header().Set("Content-type", "text/html")
rsp.Write([]byte(`<html><head><title>Test</title></head><body>Hello world</body><html>`))
}
h := http.HandlerFunc(fn)
return h
}
func main() {
append_opts := &AppendResourcesOptions{
JavaScript: []string{"test.js"},
Stylesheets: []string{"test.css"},
DataAttributes: map[string]string{"example": "example"},
}
append_handler := baseAppendHandler()
append_handler = AppendResourcesHandler(append_handler, append_opts)
s := &http.Server{
Addr: ":8080",
Handler: append_handler,
}
defer s.Close()
go s.ListenAndServe()
rsp, _ := http.Get("http://localhost:8080")
defer rsp.Body.Close()
body, _ := io.ReadAll(rsp.Body)
fmt.Println(string(body))
// Prints:
// <html><head><title>Test</title><script type="text/javascript" src="test.js"></script><link type="text/css" rel="stylesheet" href="test.css"/></head><body data-example="example">Hello world</body></html>
}
Middleware handler to rewrite the HTML output of a previous handler.
package main
import (
"golang.org/x/net/html"
"io"
"log"
"net/http"
"testing"
)
func baseRewriteHandler() http.Handler {
fn := func(rsp http.ResponseWriter, req *http.Request) {
rsp.Header().Set("Content-type", "text/html")
rsp.Write([]byte(`<html><head><title>Test</title></head><body><p>hello world</p></body></html>`))
}
h := http.HandlerFunc(fn)
return h
}
func main() {
var rewrite_func RewriteHTMLFunc
rewrite_func = func(n *html.Node, wr io.Writer) {
if n.Type == html.ElementNode && n.Data == "p" {
n.FirstChild.Data = "HELLO WORLD"
}
for c := n.FirstChild; c != nil; c = c.NextSibling {
rewrite_func(c, wr)
}
}
rewrite_handler := baseRewriteHandler()
rewrite_handler = RewriteHTMLHandler(rewrite_handler, rewrite_func)
s := &http.Server{
Addr: ":9434",
Handler: rewrite_handler,
}
defer s.Close()
go s.ListenAndServe()
rsp, _ := http.Get("http://localhost:9434")
defer rsp.Body.Close()
body, _ := io.ReadAll(rsp.Body)
log.Println(string(body))
// Prints
// <html><head><title>Test</title></head><body><p>HELLO WORLD</p></body></html>
}
Middleware handler to modify the http.Request instance passed to another handler before invoking it.
package main
import (
"fmt"
"io"
"log"
"net/http"
"testing"
)
func baseRequestHandler() http.Handler {
fn := func(rsp http.ResponseWriter, req *http.Request) {
msg := req.Header.Get("X-Message")
// See the way there is no input validation on msg? Don't do this in production...
body := fmt.Sprintf("<html><head><title>Test</title></head><body><p>%s</p></body></html>", msg)
rsp.Header().Set("Content-type", "text/html")
rsp.Write([]byte(body))
}
h := http.HandlerFunc(fn)
return h
}
func TestRewriteRequestHandler(t *testing.T) {
rewrite_func := func(req *http.Request) (*http.Request, error) {
req.Header.Set("X-Message", "hello world")
return req, nil
}
request_handler := baseRequestHandler()
request_handler = RewriteRequestHandler(request_handler, rewrite_func)
s := &http.Server{
Addr: ":9664",
Handler: request_handler,
}
defer s.Close()
go s.ListenAndServe()
rsp, _ := http.Get("http://localhost:9664")
defer rsp.Body.Close()
body, _ := io.ReadAll(rsp.Body)
log.Println(string(body))
// Prints:
// <html><head><title>Test</title></head><body><p>hello world</p></body></html>
}