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Implement CORs #13
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Implement CORs #13
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,123 @@ | ||
| package middleware | ||
|
|
||
| import ( | ||
| "net/http" | ||
| "strconv" | ||
| "strings" | ||
| "time" | ||
|
|
||
| "github.com/gin-gonic/gin" | ||
| ) | ||
|
|
||
| // CORSConfig configures the CORS middleware. | ||
| type CORSConfig struct { | ||
| // AllowedOrigins is the list of exact origins permitted to access the API | ||
| // from a browser, e.g. "https://fmsg.io". A single entry of "*" allows any | ||
| // origin (only valid when credentials are not used). An empty list | ||
| // disables CORS entirely. | ||
| AllowedOrigins []string | ||
| // AllowedMethods are the HTTP methods returned in the preflight response. | ||
| AllowedMethods []string | ||
| // AllowedHeaders are the request headers returned in the preflight response. | ||
| AllowedHeaders []string | ||
| // MaxAge controls how long browsers may cache the preflight result. | ||
| MaxAge time.Duration | ||
| } | ||
|
|
||
| // DefaultCORSConfig returns a CORSConfig populated with values appropriate for | ||
| // this API: GET/POST/PUT/DELETE/OPTIONS plus Authorization and Content-Type | ||
| // request headers, with a 10 minute preflight cache. Callers must still set | ||
| // AllowedOrigins. | ||
| func DefaultCORSConfig() CORSConfig { | ||
| return CORSConfig{ | ||
| AllowedMethods: []string{"GET", "POST", "PUT", "DELETE", "OPTIONS"}, | ||
| AllowedHeaders: []string{"Authorization", "Content-Type"}, | ||
| MaxAge: 10 * time.Minute, | ||
| } | ||
| } | ||
|
|
||
| // NewCORS returns a Gin middleware that handles CORS preflight requests and | ||
| // adds the Access-Control-Allow-* headers to matching cross-origin responses. | ||
| // | ||
| // Behaviour: | ||
| // - Requests without an Origin header pass through untouched. | ||
| // - When Origin matches an entry in AllowedOrigins (or AllowedOrigins is | ||
| // {"*"}), the appropriate Access-Control-Allow-* headers are added. | ||
| // - OPTIONS preflight requests are short-circuited with 204 so they never | ||
| // reach downstream auth middleware (which would reject them for missing | ||
| // the Authorization header). | ||
| // - When Origin is present but not allowed, the request is allowed to | ||
| // continue without CORS headers; the browser will then block the | ||
| // response, which is the standard CORS failure mode. | ||
| func NewCORS(cfg CORSConfig) gin.HandlerFunc { | ||
| if len(cfg.AllowedOrigins) == 0 { | ||
| // CORS disabled; return a no-op middleware. | ||
| return func(c *gin.Context) { c.Next() } | ||
| } | ||
|
|
||
| trimmedOrigins := make([]string, 0, len(cfg.AllowedOrigins)) | ||
| allowed := make(map[string]struct{}, len(cfg.AllowedOrigins)) | ||
| for _, o := range cfg.AllowedOrigins { | ||
| origin := strings.TrimSpace(o) | ||
| if origin == "" { | ||
| continue | ||
| } | ||
| trimmedOrigins = append(trimmedOrigins, origin) | ||
| allowed[origin] = struct{}{} | ||
| } | ||
| if len(trimmedOrigins) == 0 { | ||
| // CORS disabled; return a no-op middleware. | ||
| return func(c *gin.Context) { c.Next() } | ||
| } | ||
| allowAny := len(trimmedOrigins) == 1 && trimmedOrigins[0] == "*" | ||
|
|
||
| methods := strings.Join(cfg.AllowedMethods, ", ") | ||
| headers := strings.Join(cfg.AllowedHeaders, ", ") | ||
| maxAge := strconv.Itoa(int(cfg.MaxAge.Seconds())) | ||
|
|
||
| return func(c *gin.Context) { | ||
| origin := c.GetHeader("Origin") | ||
| if origin == "" { | ||
| c.Next() | ||
| return | ||
| } | ||
|
|
||
| // Always advertise that the response varies by Origin so caches | ||
| // (browser + intermediaries) don't serve a response keyed only on | ||
| // the URL across different origins. | ||
| c.Writer.Header().Add("Vary", "Origin") | ||
|
|
||
| _, ok := allowed[origin] | ||
| if !ok && !allowAny { | ||
| // Not an allowed origin. Don't add CORS headers; let the request | ||
| // proceed (the browser will block the response). | ||
| c.Next() | ||
| return | ||
| } | ||
|
|
||
| if allowAny { | ||
| c.Writer.Header().Set("Access-Control-Allow-Origin", "*") | ||
| } else { | ||
| c.Writer.Header().Set("Access-Control-Allow-Origin", origin) | ||
| } | ||
|
|
||
| if c.Request.Method == http.MethodOptions { | ||
| // Preflight. | ||
| c.Writer.Header().Add("Vary", "Access-Control-Request-Method") | ||
| c.Writer.Header().Add("Vary", "Access-Control-Request-Headers") | ||
| if methods != "" { | ||
|
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|
||
| c.Writer.Header().Set("Access-Control-Allow-Methods", methods) | ||
| } | ||
| if headers != "" { | ||
| c.Writer.Header().Set("Access-Control-Allow-Headers", headers) | ||
| } | ||
| if cfg.MaxAge > 0 { | ||
| c.Writer.Header().Set("Access-Control-Max-Age", maxAge) | ||
| } | ||
| c.AbortWithStatus(http.StatusNoContent) | ||
| return | ||
| } | ||
|
|
||
| c.Next() | ||
| } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,129 @@ | ||
| package middleware | ||
|
|
||
| import ( | ||
| "net/http" | ||
| "net/http/httptest" | ||
| "testing" | ||
|
|
||
| "github.com/gin-gonic/gin" | ||
| ) | ||
|
|
||
| func init() { | ||
| gin.SetMode(gin.TestMode) | ||
| } | ||
|
|
||
| func newCORSTestRouter(origins []string) *gin.Engine { | ||
| r := gin.New() | ||
| cfg := DefaultCORSConfig() | ||
| cfg.AllowedOrigins = origins | ||
| r.Use(NewCORS(cfg)) | ||
| r.GET("/x", func(c *gin.Context) { c.String(http.StatusOK, "ok") }) | ||
| r.POST("/x", func(c *gin.Context) { c.String(http.StatusOK, "ok") }) | ||
| return r | ||
| } | ||
|
|
||
| func TestCORS_NoOriginPassesThrough(t *testing.T) { | ||
| r := newCORSTestRouter([]string{"https://fmsg.io"}) | ||
| w := httptest.NewRecorder() | ||
| req := httptest.NewRequest(http.MethodGet, "/x", nil) | ||
| r.ServeHTTP(w, req) | ||
|
|
||
| if w.Code != http.StatusOK { | ||
| t.Fatalf("status = %d, want 200", w.Code) | ||
| } | ||
| if got := w.Header().Get("Access-Control-Allow-Origin"); got != "" { | ||
| t.Errorf("Access-Control-Allow-Origin = %q, want empty", got) | ||
| } | ||
| } | ||
|
|
||
| func TestCORS_AllowedOriginGetsHeaders(t *testing.T) { | ||
| r := newCORSTestRouter([]string{"https://fmsg.io"}) | ||
| w := httptest.NewRecorder() | ||
| req := httptest.NewRequest(http.MethodGet, "/x", nil) | ||
| req.Header.Set("Origin", "https://fmsg.io") | ||
| r.ServeHTTP(w, req) | ||
|
|
||
| if w.Code != http.StatusOK { | ||
| t.Fatalf("status = %d, want 200", w.Code) | ||
| } | ||
| if got := w.Header().Get("Access-Control-Allow-Origin"); got != "https://fmsg.io" { | ||
| t.Errorf("Access-Control-Allow-Origin = %q, want https://fmsg.io", got) | ||
| } | ||
| if got := w.Header().Get("Vary"); got == "" { | ||
| t.Errorf("Vary header missing") | ||
| } | ||
| } | ||
|
|
||
| func TestCORS_DisallowedOriginGetsNoHeaders(t *testing.T) { | ||
| r := newCORSTestRouter([]string{"https://fmsg.io"}) | ||
| w := httptest.NewRecorder() | ||
| req := httptest.NewRequest(http.MethodGet, "/x", nil) | ||
| req.Header.Set("Origin", "https://evil.example") | ||
| r.ServeHTTP(w, req) | ||
|
|
||
| if w.Code != http.StatusOK { | ||
| t.Fatalf("status = %d, want 200", w.Code) | ||
| } | ||
| if got := w.Header().Get("Access-Control-Allow-Origin"); got != "" { | ||
| t.Errorf("Access-Control-Allow-Origin = %q, want empty", got) | ||
| } | ||
| } | ||
|
|
||
| func TestCORS_PreflightShortCircuits(t *testing.T) { | ||
| r := gin.New() | ||
| cfg := DefaultCORSConfig() | ||
| cfg.AllowedOrigins = []string{"https://fmsg.io"} | ||
| r.Use(NewCORS(cfg)) | ||
| // Downstream middleware that would reject if reached. | ||
| r.Use(func(c *gin.Context) { | ||
| c.AbortWithStatus(http.StatusUnauthorized) | ||
| }) | ||
| r.POST("/x", func(c *gin.Context) { c.String(http.StatusOK, "ok") }) | ||
|
|
||
| w := httptest.NewRecorder() | ||
| req := httptest.NewRequest(http.MethodOptions, "/x", nil) | ||
| req.Header.Set("Origin", "https://fmsg.io") | ||
| req.Header.Set("Access-Control-Request-Method", "POST") | ||
| req.Header.Set("Access-Control-Request-Headers", "Authorization, Content-Type") | ||
| r.ServeHTTP(w, req) | ||
|
|
||
| if w.Code != http.StatusNoContent { | ||
| t.Fatalf("status = %d, want 204", w.Code) | ||
| } | ||
| if got := w.Header().Get("Access-Control-Allow-Origin"); got != "https://fmsg.io" { | ||
| t.Errorf("Access-Control-Allow-Origin = %q", got) | ||
| } | ||
| if got := w.Header().Get("Access-Control-Allow-Methods"); got == "" { | ||
| t.Errorf("Access-Control-Allow-Methods missing") | ||
| } | ||
| if got := w.Header().Get("Access-Control-Allow-Headers"); got == "" { | ||
| t.Errorf("Access-Control-Allow-Headers missing") | ||
| } | ||
| if got := w.Header().Get("Access-Control-Max-Age"); got == "" { | ||
| t.Errorf("Access-Control-Max-Age missing") | ||
| } | ||
| } | ||
|
|
||
| func TestCORS_Wildcard(t *testing.T) { | ||
| r := newCORSTestRouter([]string{"*"}) | ||
| w := httptest.NewRecorder() | ||
| req := httptest.NewRequest(http.MethodGet, "/x", nil) | ||
| req.Header.Set("Origin", "https://anything.example") | ||
| r.ServeHTTP(w, req) | ||
|
|
||
| if got := w.Header().Get("Access-Control-Allow-Origin"); got != "*" { | ||
| t.Errorf("Access-Control-Allow-Origin = %q, want *", got) | ||
| } | ||
| } | ||
|
|
||
| func TestCORS_DisabledWhenNoOrigins(t *testing.T) { | ||
| r := newCORSTestRouter(nil) | ||
| w := httptest.NewRecorder() | ||
| req := httptest.NewRequest(http.MethodGet, "/x", nil) | ||
| req.Header.Set("Origin", "https://fmsg.io") | ||
| r.ServeHTTP(w, req) | ||
|
|
||
| if got := w.Header().Get("Access-Control-Allow-Origin"); got != "" { | ||
| t.Errorf("Access-Control-Allow-Origin = %q, want empty", got) | ||
| } | ||
| } |
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