package main | |
import ( | |
"net/http" | |
) | |
type SingleHost struct { | |
handler http.Handler | |
allowedHost string | |
} | |
func NewSingleHost(handler http.Handler, allowedHost string) *SingleHost { | |
return &SingleHost{handler: handler, allowedHost: allowedHost} | |
} | |
func (s *SingleHost) ServeHTTP(w http.ResponseWriter, r *http.Request) { | |
host := r.Host | |
if host == s.allowedHost { | |
s.handler.ServeHTTP(w, r) | |
} else { | |
w.WriteHeader(403) | |
} | |
} | |
func myHandler(w http.ResponseWriter, r *http.Request) { | |
w.Write([]byte("Success!")) | |
} | |
func main() { | |
single := NewSingleHost(http.HandlerFunc(myHandler), "example.com") | |
println("Listening on port 8080") | |
http.ListenAndServe(":8080", single) | |
} |
package main | |
import ( | |
"net/http" | |
) | |
func SingleHost(handler http.Handler, allowedHost string) http.Handler { | |
ourFunc := func(w http.ResponseWriter, r *http.Request) { | |
host := r.Host | |
if host == allowedHost { | |
handler.ServeHTTP(w, r) | |
} else { | |
w.WriteHeader(403) | |
} | |
} | |
return http.HandlerFunc(ourFunc) | |
} | |
func myHandler(w http.ResponseWriter, r *http.Request) { | |
w.Write([]byte("Success!")) | |
} | |
func main() { | |
single := SingleHost(http.HandlerFunc(myHandler), "example.com") | |
println("Listening on port 8080") | |
http.ListenAndServe(":8080", single) | |
} |
package main | |
import ( | |
"net/http" | |
) | |
type AppendMiddleware struct { | |
handler http.Handler | |
} | |
func (a *AppendMiddleware) ServeHTTP(w http.ResponseWriter, r *http.Request) { | |
a.handler.ServeHTTP(w, r) | |
w.Write([]byte("<!-- Middleware says hello! -->")) | |
} | |
func myHandler(w http.ResponseWriter, r *http.Request) { | |
w.Write([]byte("Success!")) | |
} | |
func main() { | |
mid := &AppendMiddleware{http.HandlerFunc(myHandler)} | |
println("Listening on port 8080") | |
http.ListenAndServe(":8080", mid) | |
} |
package main | |
import ( | |
"net/http" | |
"net/http/httptest" | |
) | |
type ModifierMiddleware struct { | |
handler http.Handler | |
} | |
func (m *ModifierMiddleware) ServeHTTP(w http.ResponseWriter, r *http.Request) { | |
rec := httptest.NewRecorder() | |
// passing a ResponseRecorder instead of the original RW | |
m.handler.ServeHTTP(rec, r) | |
// after this finishes, we have the response recorded | |
// and can modify it before copying it to the original RW | |
// we copy the original headers first | |
for k, v := range rec.Header() { | |
w.Header()[k] = v | |
} | |
// and set an additional one | |
w.Header().Set("X-We-Modified-This", "Yup") | |
// only then the status code, as this call writes the headers as well | |
w.WriteHeader(418) | |
// The body hasn't been written (to the real RW) yet, | |
// so we can prepend some data. | |
data := []byte("Middleware says hello again. ") | |
// But the Content-Length might have been set already, | |
// we should modify it by adding the length | |
// of our own data. | |
// Ignoring the error is fine here: | |
// if Content-Length is empty or otherwise invalid, | |
// Atoi() will return zero, | |
// which is just what we'd want in that case. | |
clen, _ := strconv.Atoi(r.Header.Get("Content-Length")) | |
clen += len(data) | |
w.Header.Set("Content-Length", strconv.Itoa(clen)) | |
// finally, write out our data | |
w.Write(data) | |
// then write out the original body | |
w.Write(rec.Body.Bytes()) | |
} | |
func myHandler(w http.ResponseWriter, r *http.Request) { | |
w.Write([]byte("Success!")) | |
} | |
func main() { | |
mid := &ModifierMiddleware{http.HandlerFunc(myHandler)} | |
println("Listening on port 8080") | |
http.ListenAndServe(":8080", mid) | |
} |
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@justinas - Just read your blog as well, I recently pushed a simple "add on" to net/http that does allows middleware style programming, you can take a look here: https://github.com/stevan/httpapp |
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since you have modified the content, why there is no code updating 'content-length' ? |
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Very good resources! I just made one lecture based on your blog about middleware, but that's in Chinese in case you might be interested in https://github.com/Unknwon/go-web-foundation/blob/master/lectures/lecture10/lecture10.md |
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Hi justinas ! |
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There are two problems with 4_modifier.go.
|
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@hartzell, thanks so much. I think @pengfei-xue referred to the same issue, though I had trouble understanding it. I have updated the gist (and the blog post) for #2, though I am not sure about #1. It would make sense to add it everywhere, instead of just that one example, as weird stuff might happen anywhere and in theory, every |
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What would be a good way for your modifier middleware to alter the HTTP Status Code of the response? I found some old discussion on the GoNuts list from 30 months ago but none of what they suggested seems to work anymore! DOH! Nevermind. ResponseRecorder has it. I should have looked closer. Silly Me! |
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@justinas, |
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@Komosa, yes, thank you! |
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Hi, came here from your blog and I'm thinking about writing my next app in go and really appreciate your post about middlewares. It would be really cool if you could share the rest of your stack.