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/*
Package cors is net/http handler to handle CORS related requests
as defined by http://www.w3.org/TR/cors/
You can configure it by passing an option struct to cors.New:
c := cors.New(cors.Options{
AllowedOrigins: []string{"foo.com"},
AllowedMethods: []string{"GET", "POST", "DELETE"},
AllowCredentials: true,
})
Then insert the handler in the chain:
handler = c.Handler(handler)
See Options documentation for more options.
The resulting handler is a standard net/http handler.
*/
package cors
import (
"log"
"net/http"
"os"
"strconv"
"strings"
"github.com/rs/xhandler"
"golang.org/x/net/context"
)
// Options is a configuration container to setup the CORS middleware.
type Options struct {
// AllowedOrigins is 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.
// Default value is ["*"]
AllowedOrigins []string
// AllowOriginFunc is a custom function to validate the origin. It take the origin
// as argument and returns true if allowed or false otherwise. If this option is
// set, the content of AllowedOrigins is ignored.
AllowOriginFunc func(origin string) bool
// AllowedMethods is a list of methods the client is allowed to use with
// cross-domain requests. Default value is simple methods (GET and POST)
AllowedMethods []string
// AllowedHeaders is list of non simple headers the client is allowed to use with
// cross-domain requests.
// If the special "*" value is present in the list, all headers will be allowed.
// Default value is [] but "Origin" is always appended to the list.
AllowedHeaders []string
// ExposedHeaders indicates which headers are safe to expose to the API of a CORS
// API specification
ExposedHeaders []string
// AllowCredentials indicates whether the request can include user credentials like
// cookies, HTTP authentication or client side SSL certificates.
AllowCredentials bool
// MaxAge indicates how long (in seconds) the results of a preflight request
// can be cached
MaxAge int
// OptionsPassthrough instructs preflight to let other potential next handlers to
// process the OPTIONS method. Turn this on if your application handles OPTIONS.
OptionsPassthrough bool
// Debugging flag adds additional output to debug server side CORS issues
Debug bool
}
// Cors http handler
type Cors struct {
// Debug logger
Log *log.Logger
// Set to true when allowed origins contains a "*"
allowedOriginsAll bool
// Normalized list of plain allowed origins
allowedOrigins []string
// List of allowed origins containing wildcards
allowedWOrigins []wildcard
// Optional origin validator function
allowOriginFunc func(origin string) bool
// Set to true when allowed headers contains a "*"
allowedHeadersAll bool
// Normalized list of allowed headers
allowedHeaders []string
// Normalized list of allowed methods
allowedMethods []string
// Normalized list of exposed headers
exposedHeaders []string
allowCredentials bool
maxAge int
optionPassthrough bool
}
// New creates a new Cors handler with the provided options.
func New(options Options) *Cors {
c := &Cors{
exposedHeaders: convert(options.ExposedHeaders, http.CanonicalHeaderKey),
allowOriginFunc: options.AllowOriginFunc,
allowCredentials: options.AllowCredentials,
maxAge: options.MaxAge,
optionPassthrough: options.OptionsPassthrough,
}
if options.Debug {
c.Log = log.New(os.Stdout, "[cors] ", log.LstdFlags)
}
// Normalize options
// Note: for origins and methods matching, the spec requires a case-sensitive matching.
// As it may error prone, we chose to ignore the spec here.
// Allowed Origins
if len(options.AllowedOrigins) == 0 {
// Default is all origins
c.allowedOriginsAll = true
} else {
c.allowedOrigins = []string{}
c.allowedWOrigins = []wildcard{}
for _, origin := range options.AllowedOrigins {
// Normalize
origin = strings.ToLower(origin)
if origin == "*" {
// If "*" is present in the list, turn the whole list into a match all
c.allowedOriginsAll = true
c.allowedOrigins = nil
c.allowedWOrigins = nil
break
} else if i := strings.IndexByte(origin, '*'); i >= 0 {
// Split the origin in two: start and end string without the *
w := wildcard{origin[0:i], origin[i+1 : len(origin)]}
c.allowedWOrigins = append(c.allowedWOrigins, w)
} else {
c.allowedOrigins = append(c.allowedOrigins, origin)
}
}
}
// Allowed Headers
if len(options.AllowedHeaders) == 0 {
// Use sensible defaults
c.allowedHeaders = []string{"Origin", "Accept", "Content-Type"}
} else {
// Origin is always appended as some browsers will always request for this header at preflight
c.allowedHeaders = convert(append(options.AllowedHeaders, "Origin"), http.CanonicalHeaderKey)
for _, h := range options.AllowedHeaders {
if h == "*" {
c.allowedHeadersAll = true
c.allowedHeaders = nil
break
}
}
}
// Allowed Methods
if len(options.AllowedMethods) == 0 {
// Default is spec's "simple" methods
c.allowedMethods = []string{"GET", "POST"}
} else {
c.allowedMethods = convert(options.AllowedMethods, strings.ToUpper)
}
return c
}
// Default creates a new Cors handler with default options
func Default() *Cors {
return New(Options{})
}
// Handler apply the CORS specification on the request, and add relevant CORS headers
// as necessary.
func (c *Cors) Handler(h http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
if r.Method == "OPTIONS" {
c.logf("Handler: Preflight request")
c.handlePreflight(w, r)
// Preflight requests are standalone and should stop the chain as some other
// middleware may not handle OPTIONS requests correctly. One typical example
// is authentication middleware ; OPTIONS requests won't carry authentication
// headers (see #1)
if c.optionPassthrough {
h.ServeHTTP(w, r)
} else {
w.WriteHeader(http.StatusOK)
}
} else {
c.logf("Handler: Actual request")
c.handleActualRequest(w, r)
h.ServeHTTP(w, r)
}
})
}
// HandlerC is net/context aware handler
func (c *Cors) HandlerC(h xhandler.HandlerC) xhandler.HandlerC {
return xhandler.HandlerFuncC(func(ctx context.Context, w http.ResponseWriter, r *http.Request) {
if r.Method == "OPTIONS" {
c.logf("Handler: Preflight request")
c.handlePreflight(w, r)
// Preflight requests are standalone and should stop the chain as some other
// middleware may not handle OPTIONS requests correctly. One typical example
// is authentication middleware ; OPTIONS requests won't carry authentication
// headers (see #1)
if c.optionPassthrough {
h.ServeHTTPC(ctx, w, r)
} else {
w.WriteHeader(http.StatusOK)
}
} else {
c.logf("Handler: Actual request")
c.handleActualRequest(w, r)
h.ServeHTTPC(ctx, w, r)
}
})
}
// HandlerFunc provides Martini compatible handler
func (c *Cors) HandlerFunc(w http.ResponseWriter, r *http.Request) {
if r.Method == "OPTIONS" {
c.logf("HandlerFunc: Preflight request")
c.handlePreflight(w, r)
} else {
c.logf("HandlerFunc: Actual request")
c.handleActualRequest(w, r)
}
}
// Negroni compatible interface
func (c *Cors) ServeHTTP(w http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
if r.Method == "OPTIONS" {
c.logf("ServeHTTP: Preflight request")
c.handlePreflight(w, r)
// Preflight requests are standalone and should stop the chain as some other
// middleware may not handle OPTIONS requests correctly. One typical example
// is authentication middleware ; OPTIONS requests won't carry authentication
// headers (see #1)
if c.optionPassthrough {
next(w, r)
} else {
w.WriteHeader(http.StatusOK)
}
} else {
c.logf("ServeHTTP: Actual request")
c.handleActualRequest(w, r)
next(w, r)
}
}
// handlePreflight handles pre-flight CORS requests
func (c *Cors) handlePreflight(w http.ResponseWriter, r *http.Request) {
headers := w.Header()
origin := r.Header.Get("Origin")
if r.Method != "OPTIONS" {
c.logf(" Preflight aborted: %s!=OPTIONS", r.Method)
return
}
// Always set Vary headers
// see https://github.com/rs/cors/issues/10,
// https://github.com/rs/cors/commit/dbdca4d95feaa7511a46e6f1efb3b3aa505bc43f#commitcomment-12352001
headers.Add("Vary", "Origin")
headers.Add("Vary", "Access-Control-Request-Method")
headers.Add("Vary", "Access-Control-Request-Headers")
if origin == "" {
c.logf(" Preflight aborted: empty origin")
return
}
if !c.isOriginAllowed(origin) {
c.logf(" Preflight aborted: origin '%s' not allowed", origin)
return
}
reqMethod := r.Header.Get("Access-Control-Request-Method")
if !c.isMethodAllowed(reqMethod) {
c.logf(" Preflight aborted: method '%s' not allowed", reqMethod)
return
}
reqHeaders := parseHeaderList(r.Header.Get("Access-Control-Request-Headers"))
if !c.areHeadersAllowed(reqHeaders) {
c.logf(" Preflight aborted: headers '%v' not allowed", reqHeaders)
return
}
headers.Set("Access-Control-Allow-Origin", origin)
// Spec says: Since the list of methods can be unbounded, simply returning the method indicated
// by Access-Control-Request-Method (if supported) can be enough
headers.Set("Access-Control-Allow-Methods", strings.ToUpper(reqMethod))
if len(reqHeaders) > 0 {
// Spec says: Since the list of headers can be unbounded, simply returning supported headers
// from Access-Control-Request-Headers can be enough
headers.Set("Access-Control-Allow-Headers", strings.Join(reqHeaders, ", "))
}
if c.allowCredentials {
headers.Set("Access-Control-Allow-Credentials", "true")
}
if c.maxAge > 0 {
headers.Set("Access-Control-Max-Age", strconv.Itoa(c.maxAge))
}
c.logf(" Preflight response headers: %v", headers)
}
// handleActualRequest handles simple cross-origin requests, actual request or redirects
func (c *Cors) handleActualRequest(w http.ResponseWriter, r *http.Request) {
headers := w.Header()
origin := r.Header.Get("Origin")
if r.Method == "OPTIONS" {
c.logf(" Actual request no headers added: method == %s", r.Method)
return
}
// Always set Vary, see https://github.com/rs/cors/issues/10
headers.Add("Vary", "Origin")
if origin == "" {
c.logf(" Actual request no headers added: missing origin")
return
}
if !c.isOriginAllowed(origin) {
c.logf(" Actual request no headers added: origin '%s' not allowed", origin)
return
}
// Note that spec does define a way to specifically disallow a simple method like GET or
// POST. Access-Control-Allow-Methods is only used for pre-flight requests and the
// spec doesn't instruct to check the allowed methods for simple cross-origin requests.
// We think it's a nice feature to be able to have control on those methods though.
if !c.isMethodAllowed(r.Method) {
c.logf(" Actual request no headers added: method '%s' not allowed", r.Method)
return
}
headers.Set("Access-Control-Allow-Origin", origin)
if len(c.exposedHeaders) > 0 {
headers.Set("Access-Control-Expose-Headers", strings.Join(c.exposedHeaders, ", "))
}
if c.allowCredentials {
headers.Set("Access-Control-Allow-Credentials", "true")
}
c.logf(" Actual response added headers: %v", headers)
}
// convenience method. checks if debugging is turned on before printing
func (c *Cors) logf(format string, a ...interface{}) {
if c.Log != nil {
c.Log.Printf(format, a...)
}
}
// isOriginAllowed checks if a given origin is allowed to perform cross-domain requests
// on the endpoint
func (c *Cors) isOriginAllowed(origin string) bool {
if c.allowOriginFunc != nil {
return c.allowOriginFunc(origin)
}
if c.allowedOriginsAll {
return true
}
origin = strings.ToLower(origin)
for _, o := range c.allowedOrigins {
if o == origin {
return true
}
}
for _, w := range c.allowedWOrigins {
if w.match(origin) {
return true
}
}
return false
}
// isMethodAllowed checks if a given method can be used as part of a cross-domain request
// on the endpoing
func (c *Cors) isMethodAllowed(method string) bool {
if len(c.allowedMethods) == 0 {
// If no method allowed, always return false, even for preflight request
return false
}
method = strings.ToUpper(method)
if method == "OPTIONS" {
// Always allow preflight requests
return true
}
for _, m := range c.allowedMethods {
if m == method {
return true
}
}
return false
}
// areHeadersAllowed checks if a given list of headers are allowed to used within
// a cross-domain request.
func (c *Cors) areHeadersAllowed(requestedHeaders []string) bool {
if c.allowedHeadersAll || len(requestedHeaders) == 0 {
return true
}
for _, header := range requestedHeaders {
header = http.CanonicalHeaderKey(header)
found := false
for _, h := range c.allowedHeaders {
if h == header {
found = true
}
}
if !found {
return false
}
}
return true
}
|