57 lines
2.2 KiB
Go
57 lines
2.2 KiB
Go
package handler
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import (
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"net/http"
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"codeberg.org/VARASYS/ZDDC/zddc/internal/config"
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)
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// CORSMiddleware applies a per-origin CORS policy keyed off cfg.CORSOrigins.
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//
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// On any request whose Origin header exactly matches an entry in the
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// allowlist, the middleware echoes that origin in Access-Control-Allow-Origin
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// and sets Access-Control-Allow-Credentials: true (we use credentials so the
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// reverse-proxy-set email header / cookies cross the boundary). Vary: Origin
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// is always set when the allowlist is non-empty so caches do not collapse
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// per-origin responses.
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//
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// OPTIONS preflight requests are answered directly with 204 + the appropriate
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// allow-methods/headers, bypassing later middleware (so preflight does not
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// require auth). Non-OPTIONS requests pass through to the next handler.
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//
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// Requests with no Origin header, or an Origin that does not match the
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// allowlist, get no CORS response headers — the browser blocks them
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// naturally. An empty allowlist disables CORS entirely.
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func CORSMiddleware(cfg config.Config, next http.Handler) http.Handler {
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if len(cfg.CORSOrigins) == 0 {
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return next
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}
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allow := make(map[string]struct{}, len(cfg.CORSOrigins))
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for _, o := range cfg.CORSOrigins {
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allow[o] = struct{}{}
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}
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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origin := r.Header.Get("Origin")
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if origin != "" {
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if _, ok := allow[origin]; ok {
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h := w.Header()
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h.Set("Access-Control-Allow-Origin", origin)
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h.Set("Access-Control-Allow-Credentials", "true")
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h.Add("Vary", "Origin")
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if r.Method == http.MethodOptions {
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if reqHeaders := r.Header.Get("Access-Control-Request-Headers"); reqHeaders != "" {
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h.Set("Access-Control-Allow-Headers", reqHeaders)
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}
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h.Set("Access-Control-Allow-Methods", "GET, HEAD, PUT, DELETE, POST, OPTIONS")
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// Expose ETag and the file API's source / destination headers
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// so cross-origin clients can read them after a write.
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h.Set("Access-Control-Expose-Headers", "ETag, X-ZDDC-Source, X-ZDDC-Destination")
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h.Set("Access-Control-Max-Age", "600")
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w.WriteHeader(http.StatusNoContent)
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return
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}
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}
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}
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next.ServeHTTP(w, r)
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})
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}
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