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cors.go
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cors.go
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package cors
import (
"bytes"
"io"
"net/http"
"net/url"
"strconv"
"strings"
"time"
config "github.com/go-kratos/gateway/api/gateway/config/v1"
v1 "github.com/go-kratos/gateway/api/gateway/middleware/cors/v1"
"github.com/go-kratos/gateway/middleware"
"google.golang.org/protobuf/proto"
"google.golang.org/protobuf/types/known/anypb"
"google.golang.org/protobuf/types/known/durationpb"
)
var (
defaultAllowCredentials = true
defaultAllowPrivateNetwork = false
defaultCorsMethods = []string{"GET", "POST", "PUT", "DELETE"}
defaultCorsHeaders = []string{"Origin", "Content-Length", "Content-Type"}
// (WebKit/Safari v9 sends the Origin header by default in AJAX requests)
)
const (
corsOptionMethod string = "OPTIONS"
corsAllowOriginHeader string = "Access-Control-Allow-Origin"
corsExposeHeadersHeader string = "Access-Control-Expose-Headers"
corsMaxAgeHeader string = "Access-Control-Max-Age"
corsAllowMethodsHeader string = "Access-Control-Allow-Methods"
corsAllowHeadersHeader string = "Access-Control-Allow-Headers"
corsAllowCredentialsHeader string = "Access-Control-Allow-Credentials"
corsAllowPrivateNetworkHeader string = "Access-Control-Allow-Private-Network"
corsRequestMethodHeader string = "Access-Control-Request-Method"
corsRequestHeadersHeader string = "Access-Control-Request-Headers"
corsRequestPrivateNetwork string = "Access-Control-Request-Private-Network"
corsOriginHeader string = "Origin"
corsVaryHeader string = "Vary"
corsMatchAll string = "*"
)
func init() {
middleware.Register("cors", Middleware)
}
func isOriginAllowed(origin string, allowOriginHosts []string) bool {
originURL, err := url.Parse(origin)
if err != nil {
return false
}
hostname := strings.ToLower(originURL.Hostname())
for _, host := range allowOriginHosts {
host = strings.ToLower(host)
if host[0] != '*' {
if hostname == host {
return true
}
continue
}
if strings.HasSuffix(hostname, strings.TrimPrefix(host, "*")) {
return true
}
}
return false
}
func newResponse(statusCode int, header http.Header) (*http.Response, error) {
return &http.Response{
StatusCode: statusCode,
Header: header,
Body: io.NopCloser(&bytes.Buffer{}),
}, nil
}
// Middleware automatically sets the allow response header.
func Middleware(c *config.Middleware) (middleware.Middleware, error) {
options := &v1.Cors{
AllowCredentials: defaultAllowCredentials,
AllowMethods: defaultCorsMethods,
AllowHeaders: defaultCorsHeaders,
AllowPrivateNetwork: defaultAllowPrivateNetwork,
MaxAge: durationpb.New(time.Minute * 10),
}
if c.Options != nil {
if err := anypb.UnmarshalTo(c.Options, options, proto.UnmarshalOptions{Merge: true}); err != nil {
return nil, err
}
}
preflightHeaders := generatePreflightHeaders(options)
normalHeaders := generateNormalHeaders(options)
return func(next http.RoundTripper) http.RoundTripper {
return middleware.RoundTripperFunc(func(req *http.Request) (*http.Response, error) {
origin := req.Header.Get(corsOriginHeader)
if origin == "" {
// not a cors request
return next.RoundTrip(req)
}
if !isOriginAllowed(origin, options.AllowOrigins) {
return newResponse(http.StatusForbidden, http.Header{})
}
if req.Method == corsOptionMethod {
headers := make(http.Header, len(preflightHeaders)+2)
if options.AllowPrivateNetwork && req.Header.Get(corsRequestPrivateNetwork) == "true" {
headers.Set(corsAllowPrivateNetworkHeader, "true")
}
for key, value := range preflightHeaders {
headers[key] = value
}
headers.Set(corsAllowOriginHeader, origin)
return newResponse(http.StatusOK, headers)
}
resp, err := next.RoundTrip(req)
if err != nil {
return nil, err
}
if resp.Header == nil {
resp.Header = make(http.Header, len(normalHeaders)+1)
}
for key, value := range normalHeaders {
resp.Header[key] = value
}
resp.Header.Set(corsAllowOriginHeader, origin)
return resp, nil
})
}, nil
}
func generateNormalHeaders(c *v1.Cors) http.Header {
headers := make(http.Header)
if c.AllowCredentials {
headers.Set(corsAllowCredentialsHeader, "true")
}
// backport support for early browsers
if len(c.AllowMethods) > 0 {
allowMethods := convert(normalize(c.AllowMethods), strings.ToUpper)
headers.Set(corsAllowMethodsHeader, strings.Join(allowMethods, ","))
}
if len(c.ExposeHeaders) > 0 {
exposeHeaders := convert(normalize(c.ExposeHeaders), http.CanonicalHeaderKey)
headers.Set(corsExposeHeadersHeader, strings.Join(exposeHeaders, ","))
}
headers.Add(corsVaryHeader, corsOriginHeader)
return headers
}
func generatePreflightHeaders(c *v1.Cors) http.Header {
headers := make(http.Header)
if c.AllowCredentials {
headers.Set(corsAllowCredentialsHeader, "true")
}
if len(c.AllowMethods) > 0 {
allowMethods := convert(normalize(c.AllowMethods), strings.ToUpper)
headers.Set(corsAllowMethodsHeader, strings.Join(allowMethods, ","))
}
if len(c.AllowHeaders) > 0 {
allowHeaders := convert(normalize(c.AllowHeaders), http.CanonicalHeaderKey)
headers.Set(corsAllowHeadersHeader, strings.Join(allowHeaders, ","))
}
if c.MaxAge != nil {
maxAge := int64(c.MaxAge.AsDuration() / time.Second)
headers.Set(corsMaxAgeHeader, strconv.FormatInt(maxAge, 10))
}
// Always set Vary headers
// see https://github.com/rs/cors/issues/10,
// https://github.com/rs/cors/commit/dbdca4d95feaa7511a46e6f1efb3b3aa505bc43f#commitcomment-12352001
headers.Add(corsVaryHeader, corsOriginHeader)
headers.Add(corsVaryHeader, corsRequestMethodHeader)
headers.Add(corsVaryHeader, corsRequestHeadersHeader)
return headers
}
func normalize(values []string) []string {
if values == nil {
return nil
}
distinctMap := make(map[string]bool, len(values))
normalized := make([]string, 0, len(values))
for _, value := range values {
value = strings.TrimSpace(value)
value = strings.ToLower(value)
if _, seen := distinctMap[value]; !seen {
normalized = append(normalized, value)
distinctMap[value] = true
}
}
return normalized
}
func convert(s []string, c func(string) string) []string {
out := make([]string, 0, len(s))
for _, i := range s {
out = append(out, c(i))
}
return out
}