Setting HTTP headers

Question

I m trying to set a header in my Go web server  I m using gorilla mux and net http packages   I d like to set Access-Control-Allow-Origin    to allow cross domain AJAX   Here s my Go code   func saveHandler w http ResponseWriter  r  http Request       do some stuff with the request data    func main         r    mux NewRouter       r HandleFunc   save   saveHandler      http Handle      r      http ListenAndServe     port  nil      The net http package has documentation describing sending http request headers as if it were a client - I m not exactly sure how to set response headers

User · Answer

If you don t want to override your router  if you don t have your app configured in a way that supports this  or want to configure CORS on a route by route basis   add an OPTIONS handler to handle the pre flight request   Ie  with Gorilla Mux your routes would look like   accounts    router Path   accounts   Subrouter   accounts Methods  POST   Handler AccountsCreate  accounts Methods  OPTIONS   Handler AccountsCreatePreFlight    Note above that in addition to our POST handler  we re defining a specific OPTIONS method handler   And then to actual handle the OPTIONS preflight method  you could define AccountsCreatePreFlight like so      Check the origin is valid  origin    r Header Get  Origin   validOrigin  err    validateOrigin origin  if err    nil       return err       If it is  allow CORS  if validOrigin       w Header   Set  Access-Control-Allow-Origin   origin      w Header   Set  Access-Control-Allow-Methods    POST       w Header   Set  Access-Control-Allow-Headers            Accept  Content-Type  Content-Length  Accept-Encoding  X-CSRF-Token  Authorization       What really made this all click for me  in addition to actually understanding how CORS works  is that the HTTP Method of a preflight request is different from the HTTP Method of the actual request  To initiate CORS  the browser sends a preflight request with HTTP Method OPTIONS  which you have to handle explicitly in your router  and then  if it receives the appropriate response  Access-Control-Allow-Origin   origin  or     for all  from your application  it initiates the actual request   I also believe that you can only do     for standard types of requests  ie  GET   but for others you ll have to explicitly set the origin like I do above

User · Answer

Never mind  I figured it out - I used the Set   method on Header    doh    My handler looks like this now   func saveHandler w http ResponseWriter  r  http Request           allow cross domain AJAX requests     w Header   Set  Access-Control-Allow-Origin            Maybe this will help someone as caffeine deprived as myself sometime

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All of the above answers are wrong because they fail to handle the OPTIONS preflight request  the solution is to override the mux router s interface  See AngularJS  http get request failed with custom header  alllowed in CORS   func main         r    mux NewRouter       r HandleFunc   save   saveHandler      http Handle       amp MyServer r       http ListenAndServe   8080   nil       type MyServer struct       r  mux Router    func  s  MyServer  ServeHTTP rw http ResponseWriter  req  http Request        if origin    req Header Get  Origin    origin                 rw Header   Set  Access-Control-Allow-Origin   origin          rw Header   Set  Access-Control-Allow-Methods    POST  GET  OPTIONS  PUT  DELETE           rw Header   Set  Access-Control-Allow-Headers                Accept  Content-Type  Content-Length  Accept-Encoding  X-CSRF-Token  Authorization                Stop here if its Preflighted OPTIONS request     if req Method     OPTIONS            return              Lets Gorilla work     s r ServeHTTP rw  req

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Do not use     for Origin  until You really need a completely public behavior  As Wikipedia says       The value of     is special in that it does not allow requests to supply credentials     meaning HTTP authentication  client-side SSL certificates  nor does it allow cookies    to be sent     That means  you ll get a lot of errors  especially in Chrome when you ll try to implement for example a simple authentication   Here is a corrected wrapper      Code has not been tested  func addDefaultHeaders fn http HandlerFunc  http HandlerFunc       return func w http ResponseWriter  r  http Request            if origin    r Header Get  Origin    origin                     w Header   Set  Access-Control-Allow-Origin   origin                    w Header   Set  Access-Control-Allow-Methods    POST  GET  OPTIONS  PUT  DELETE           w Header   Set  Access-Control-Allow-Headers    Content-Type  Content-Length  Accept-Encoding  X-CSRF-Token           w Header   Set  Access-Control-Allow-Credentials    true           fn w  r            And don t forget to reply all these headers to the preflight OPTIONS request

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Set a proper golang middleware  so you can reuse on any endpoint   Helper Type and Function  type Adapter func http Handler  http Handler    Adapt h with all specified adapters  func Adapt h http Handler  adapters    Adapter  http Handler       for    adapter    range adapters           h   adapter h            return h     Actual middleware  func EnableCORS   Adapter       return func h http Handler  http Handler           return http HandlerFunc func w http ResponseWriter  r  http Request                 if origin    r Header Get  Origin    origin                         w Header   Set  Access-Control-Allow-Origin   origin                  w Header   Set  Access-Control-Allow-Methods    POST  GET  OPTIONS  PUT  DELETE                   w Header   Set  Access-Control-Allow-Headers                        Accept  Content-Type  Content-Length  Accept-Encoding  X-CSRF-Token  Authorization                                Stop here if its Preflighted OPTIONS request             if r Method     OPTIONS                    return                           h ServeHTTP w  r                       Endpoint  REMEBER  Middlewares get applyed on reverse order  ExpectGET   gets fires first   mux Handle   watcher  action   device   Adapt api SerialHandler mux       api EnableCORS        api ExpectGET

User · Answer

I create wrapper for this case   func addDefaultHeaders fn http HandlerFunc  http HandlerFunc       return func w http ResponseWriter  r  http Request            w Header   Set  Access-Control-Allow-Origin                fn w  r

User · Answer

I had the same issue as described above the solutions given above are correct  the set up I have is as follows 1  Angularjs for the Client  2  Beego framework for GO server  Please following these points 1  CORS settings must be enabled only on GO server  2  Do NOT add any type of headers in angularJS except for this    config    httpProvider   function  httpProvider             httpProvider defaults useXDomain   true          delete  httpProvider defaults headers common  X-Requested-With              In you GO server add the CORS settings before the request starts to get processed so that the preflight request receives a 200 OK after which the the OPTIONS method will get converted to GET POST PUT or what ever is your request type

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I know this is a different twist on the answer  but isn t this more of a concern for a web server   For example  nginx  could help      The ngx http headers module module allows adding the    Expires    and    Cache-Control    header fields  and arbitrary fields  to a response header        location     lt REGXP MATCHING CORS ROUTES gt        add header Access-Control-Allow-Methods POST                 Adding nginx in front of your go service in production seems wise   It provides a lot more feature for authorizing  logging and modifying requests   Also  it gives the ability to control who has access to your service and not only that but one can specify different behavior for specific locations in your app  as demonstrated above   I could go on about why to use a web server with your go api  but I think that s a topic for another discussion

[http] Setting HTTP headers

Examples related to http

Examples related to go

Examples related to cors

Examples related to http-headers