refac: removed 7 direct and 12 indirect go modules for custom code instead

api/middleware/cors.go

@@ -0,0 +1,138 @@
+package middleware
+
+import (
+	"net/http"
+	"strconv"
+	"strings"
+)
+
+const (
+	corsAllowAnyOrigin   = "*"
+	corsWildcardMarker   = "*"
+	corsPreflightMaxAge  = 300
+	corsPreflightSuccess = http.StatusNoContent
+)
+
+var (
+	corsAllowedMethods = []string{http.MethodGet, http.MethodPost, http.MethodPut, http.MethodPatch, http.MethodDelete, http.MethodOptions}
+	corsAllowedHeaders = []string{"Accept", "Authorization", "Content-Type", "X-CSRF-Token"}
+	corsExposedHeaders = []string{"Link", "X-Total-Count"}
+)
+
+type originWildcard struct {
+	prefix string
+	suffix string
+}
+
+func (w originWildcard) matches(origin string) bool {
+	return len(origin) >= len(w.prefix)+len(w.suffix) && strings.HasPrefix(origin, w.prefix) && strings.HasSuffix(origin, w.suffix)
+}
+
+type originPolicy struct {
+	anyOrigin bool
+	exact     map[string]struct{}
+	wildcards []originWildcard
+}
+
+func newOriginPolicy(origins []string) originPolicy {
+	policy := originPolicy{exact: map[string]struct{}{}}
+	for _, origin := range origins {
+		origin = strings.ToLower(strings.TrimSpace(origin))
+		prefix, suffix, hasWildcard := strings.Cut(origin, corsWildcardMarker)
+		switch {
+		case origin == "":
+		case origin == corsAllowAnyOrigin:
+			policy.anyOrigin = true
+		case hasWildcard:
+			policy.wildcards = append(policy.wildcards, originWildcard{prefix: prefix, suffix: suffix})
+		default:
+			policy.exact[origin] = struct{}{}
+		}
+	}
+	return policy
+}
+
+func (p originPolicy) allows(origin string) bool {
+	if p.anyOrigin {
+		return true
+	}
+	origin = strings.ToLower(origin)
+	if _, ok := p.exact[origin]; ok {
+		return true
+	}
+	for _, wildcard := range p.wildcards {
+		if wildcard.matches(origin) {
+			return true
+		}
+	}
+	return false
+}
+
+func isPreflight(r *http.Request) bool {
+	return r.Method == http.MethodOptions && r.Header.Get("Access-Control-Request-Method") != ""
+}
+
+func containsFold(allowed []string, value string) bool {
+	for _, candidate := range allowed {
+		if strings.EqualFold(candidate, value) {
+			return true
+		}
+	}
+	return false
+}
+
+func requestedHeadersAllowed(r *http.Request) bool {
+	requested := r.Header.Get("Access-Control-Request-Headers")
+	if requested == "" {
+		return true
+	}
+	for _, header := range strings.Split(requested, ",") {
+		if header = strings.TrimSpace(header); header != "" && !containsFold(corsAllowedHeaders, header) {
+			return false
+		}
+	}
+	return true
+}
+
+func CORS(allowedOrigins []string) func(http.Handler) http.Handler {
+	policy := newOriginPolicy(allowedOrigins)
+
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			origin := r.Header.Get("Origin")
+			if origin == "" {
+				next.ServeHTTP(w, r)
+				return
+			}
+
+			w.Header().Add("Vary", "Origin")
+			if isPreflight(r) {
+				answerPreflight(w, r, origin, policy)
+				return
+			}
+
+			if policy.allows(origin) {
+				w.Header().Set("Access-Control-Allow-Origin", origin)
+				w.Header().Set("Access-Control-Expose-Headers", strings.Join(corsExposedHeaders, ", "))
+			}
+			next.ServeHTTP(w, r)
+		})
+	}
+}
+
+func answerPreflight(w http.ResponseWriter, r *http.Request, origin string, policy originPolicy) {
+	w.Header().Add("Vary", "Access-Control-Request-Method")
+	w.Header().Add("Vary", "Access-Control-Request-Headers")
+
+	method := r.Header.Get("Access-Control-Request-Method")
+	if !policy.allows(origin) || !containsFold(corsAllowedMethods, method) || !requestedHeadersAllowed(r) {
+		w.WriteHeader(http.StatusOK)
+		return
+	}
+
+	w.Header().Set("Access-Control-Allow-Origin", origin)
+	w.Header().Set("Access-Control-Allow-Methods", strings.ToUpper(method))
+	w.Header().Set("Access-Control-Allow-Headers", strings.Join(corsAllowedHeaders, ", "))
+	w.Header().Set("Access-Control-Max-Age", strconv.Itoa(corsPreflightMaxAge))
+	w.WriteHeader(corsPreflightSuccess)
+}