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package restful
// Copyright 2013 Ernest Micklei. All rights reserved.
// Use of this source code is governed by a license
// that can be found in the LICENSE file.
import (
"regexp"
"strconv"
"strings"
)
// CrossOriginResourceSharing is used to create a Container Filter that implements CORS.
// Cross-origin resource sharing (CORS) is a mechanism that allows JavaScript on a web page
// to make XMLHttpRequests to another domain, not the domain the JavaScript originated from.
//
// http://en.wikipedia.org/wiki/Cross-origin_resource_sharing
// http://enable-cors.org/server.html
// http://www.html5rocks.com/en/tutorials/cors/#toc-handling-a-not-so-simple-request
type CrossOriginResourceSharing struct {
ExposeHeaders []string // list of Header names
AllowedHeaders []string // list of Header names
AllowedDomains []string // list of allowed values for Http Origin. An allowed value can be a regular expression to support subdomain matching. If empty all are allowed.
AllowedMethods []string
MaxAge int // number of seconds before requiring new Options request
CookiesAllowed bool
Container *Container
allowedOriginPatterns []*regexp.Regexp // internal field for origin regexp check.
}
// Filter is a filter function that implements the CORS flow as documented on http://enable-cors.org/server.html
// and http://www.html5rocks.com/static/images/cors_server_flowchart.png
func (c CrossOriginResourceSharing) Filter(req *Request, resp *Response, chain *FilterChain) {
origin := req.Request.Header.Get(HEADER_Origin)
if len(origin) == 0 {
if trace {
traceLogger.Print("no Http header Origin set")
}
chain.ProcessFilter(req, resp)
return
}
if !c.isOriginAllowed(origin) { // check whether this origin is allowed
if trace {
traceLogger.Printf("HTTP Origin:%s is not part of %v, neither matches any part of %v", origin, c.AllowedDomains, c.allowedOriginPatterns)
}
chain.ProcessFilter(req, resp)
return
}
if req.Request.Method != "OPTIONS" {
c.doActualRequest(req, resp)
chain.ProcessFilter(req, resp)
return
}
if acrm := req.Request.Header.Get(HEADER_AccessControlRequestMethod); acrm != "" {
c.doPreflightRequest(req, resp)
} else {
c.doActualRequest(req, resp)
chain.ProcessFilter(req, resp)
return
}
}
func (c CrossOriginResourceSharing) doActualRequest(req *Request, resp *Response) {
c.setOptionsHeaders(req, resp)
// continue processing the response
}
func (c *CrossOriginResourceSharing) doPreflightRequest(req *Request, resp *Response) {
if len(c.AllowedMethods) == 0 {
if c.Container == nil {
c.AllowedMethods = DefaultContainer.computeAllowedMethods(req)
} else {
c.AllowedMethods = c.Container.computeAllowedMethods(req)
}
}
acrm := req.Request.Header.Get(HEADER_AccessControlRequestMethod)
if !c.isValidAccessControlRequestMethod(acrm, c.AllowedMethods) {
if trace {
traceLogger.Printf("Http header %s:%s is not in %v",
HEADER_AccessControlRequestMethod,
acrm,
c.AllowedMethods)
}
return
}
acrhs := req.Request.Header.Get(HEADER_AccessControlRequestHeaders)
if len(acrhs) > 0 {
for _, each := range strings.Split(acrhs, ",") {
if !c.isValidAccessControlRequestHeader(strings.Trim(each, " ")) {
if trace {
traceLogger.Printf("Http header %s:%s is not in %v",
HEADER_AccessControlRequestHeaders,
acrhs,
c.AllowedHeaders)
}
return
}
}
}
resp.AddHeader(HEADER_AccessControlAllowMethods, strings.Join(c.AllowedMethods, ","))
resp.AddHeader(HEADER_AccessControlAllowHeaders, acrhs)
c.setOptionsHeaders(req, resp)
// return http 200 response, no body
}
func (c CrossOriginResourceSharing) setOptionsHeaders(req *Request, resp *Response) {
c.checkAndSetExposeHeaders(resp)
c.setAllowOriginHeader(req, resp)
c.checkAndSetAllowCredentials(resp)
if c.MaxAge > 0 {
resp.AddHeader(HEADER_AccessControlMaxAge, strconv.Itoa(c.MaxAge))
}
}
func (c CrossOriginResourceSharing) isOriginAllowed(origin string) bool {
if len(origin) == 0 {
return false
}
if len(c.AllowedDomains) == 0 {
return true
}
allowed := false
for _, domain := range c.AllowedDomains {
if domain == origin {
allowed = true
break
}
}
if !allowed {
if len(c.allowedOriginPatterns) == 0 {
// compile allowed domains to allowed origin patterns
allowedOriginRegexps, err := compileRegexps(c.AllowedDomains)
if err != nil {
return false
}
c.allowedOriginPatterns = allowedOriginRegexps
}
for _, pattern := range c.allowedOriginPatterns {
if allowed = pattern.MatchString(origin); allowed {
break
}
}
}
return allowed
}
func (c CrossOriginResourceSharing) setAllowOriginHeader(req *Request, resp *Response) {
origin := req.Request.Header.Get(HEADER_Origin)
if c.isOriginAllowed(origin) {
resp.AddHeader(HEADER_AccessControlAllowOrigin, origin)
}
}
func (c CrossOriginResourceSharing) checkAndSetExposeHeaders(resp *Response) {
if len(c.ExposeHeaders) > 0 {
resp.AddHeader(HEADER_AccessControlExposeHeaders, strings.Join(c.ExposeHeaders, ","))
}
}
func (c CrossOriginResourceSharing) checkAndSetAllowCredentials(resp *Response) {
if c.CookiesAllowed {
resp.AddHeader(HEADER_AccessControlAllowCredentials, "true")
}
}
func (c CrossOriginResourceSharing) isValidAccessControlRequestMethod(method string, allowedMethods []string) bool {
for _, each := range allowedMethods {
if each == method {
return true
}
}
return false
}
func (c CrossOriginResourceSharing) isValidAccessControlRequestHeader(header string) bool {
for _, each := range c.AllowedHeaders {
if strings.ToLower(each) == strings.ToLower(header) {
return true
}
}
return false
}
// Take a list of strings and compile them into a list of regular expressions.
func compileRegexps(regexpStrings []string) ([]*regexp.Regexp, error) {
regexps := []*regexp.Regexp{}
for _, regexpStr := range regexpStrings {
r, err := regexp.Compile(regexpStr)
if err != nil {
return regexps, err
}
regexps = append(regexps, r)
}
return regexps, nil
}
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