Go CORS handler 
CORS is a net/http handler implementing Cross Origin Resource Sharing W3 specification in Golang.
Getting Started
After installing Go and setting up your GOPATH, create your first .go file. We'll call it server.go.
package main
import (
"net/http"
"github.com/rs/cors"
)
func main() {
mux := http.NewServeMux()
mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Type", "application/json")
w.Write([]byte("{\"hello\": \"world\"}"))
})
// cors.Default() setup the middleware with default options being
// all origins accepted with simple methods (GET, POST). See
// documentation below for more options.
handler := cors.Default().Handler(mux)
http.ListenAndServe(":8080", handler)
}
Install cors:
go get github.com/rs/cors
Then run your server:
go run server.go
The server now runs on localhost:8080:
$ curl -D - -H 'Origin: http://foo.com' http://localhost:8080/
HTTP/1.1 200 OK
Access-Control-Allow-Origin: foo.com
Content-Type: application/json
Date: Sat, 25 Oct 2014 03:43:57 GMT
Content-Length: 18
{"hello": "world"}
Allow * With Credentials Security Protection
This library has been modified to avoid a well known security issue when configured with AllowedOrigins to * and AllowCredentials to true. Such setup used to make the library reflects the request Origin header value, working around a security protection embedded into the standard that makes clients to refuse such configuration. This behavior has been removed with #55 and #57.
If you depend on this behavior and understand the implications, you can restore it using the AllowOriginFunc with func(origin string) {return true}.
Please refer to #55 for more information about the security implications.
More Examples
net/http: examples/nethttp/server.go- Goji: examples/goji/server.go
- Martini: examples/martini/server.go
- Negroni: examples/negroni/server.go
- Alice: examples/alice/server.go
- HttpRouter: examples/httprouter/server.go
- Gorilla: examples/gorilla/server.go
- Buffalo: examples/buffalo/server.go
- Gin: examples/gin/server.go
- Chi: examples/chi/server.go
Parameters
Parameters are passed to the middleware thru the cors.New method as follow:
c := cors.New(cors.Options{
AllowedOrigins: []string{"http://foo.com", "http://foo.com:8080"},
AllowCredentials: true,
// Enable Debugging for testing, consider disabling in production
Debug: true,
})
// Insert the middleware
handler = c.Handler(handler)
- AllowedOrigins
[]string: A list of origins a cross-domain request can be executed from. If the special*value is present in the list, all origins will be allowed. An origin may contain a wildcard (*) to replace 0 or more characters (i.e.:http://*.domain.com). Usage of wildcards implies a small performance penality. Only one wildcard can be used per origin. The default value is*. - AllowOriginFunc
func (origin string) bool: A custom function to validate the origin. It takes the origin as an argument and returns true if allowed, or false otherwise. If this option is set, the content ofAllowedOriginsis ignored. - AllowOriginRequestFunc
func (r *http.Request origin string) bool: A custom function to validate the origin. It takes the HTTP Request object and the origin as argument and returns true if allowed or false otherwise. If this option is set, the content ofAllowedOriginsandAllowOriginFuncis ignored - AllowedMethods
[]string: A list of methods the client is allowed to use with cross-domain requests. Default value is simple methods (GETandPOST). - AllowedHeaders
[]string: A list of non simple headers the client is allowed to use with cross-domain requests. - ExposedHeaders
[]string: Indicates which headers are safe to expose to the API of a CORS API specification - AllowCredentials
bool: Indicates whether the request can include user credentials like cookies, HTTP authentication or client side SSL certificates. The default isfalse. - MaxAge
int: Indicates how long (in seconds) the results of a preflight request can be cached. The default is0which stands for no max age. - OptionsPassthrough
bool: Instructs preflight to let other potential next handlers to process theOPTIONSmethod. Turn this on if your application handlesOPTIONS. - Debug
bool: Debugging flag adds additional output to debug server side CORS issues.
See API documentation for more info.
Benchmarks
BenchmarkWithout 20000000 64.6 ns/op 8 B/op 1 allocs/op
BenchmarkDefault 3000000 469 ns/op 114 B/op 2 allocs/op
BenchmarkAllowedOrigin 3000000 608 ns/op 114 B/op 2 allocs/op
BenchmarkPreflight 20000000 73.2 ns/op 0 B/op 0 allocs/op
BenchmarkPreflightHeader 20000000 73.6 ns/op 0 B/op 0 allocs/op
BenchmarkParseHeaderList 2000000 847 ns/op 184 B/op 6 allocs/op
BenchmarkParse…Single 5000000 290 ns/op 32 B/op 3 allocs/op
BenchmarkParse…Normalized 2000000 776 ns/op 160 B/op 6 allocs/op
Licenses
All source code is licensed under the MIT License.
![[help] Access-Control-Allow-Credentials: true, Access-Control-Allow-Origin cannot be *, but I did not find the corresponding implementation](https://avatars.githubusercontent.com/u/3955934?v=4)
