mangaBookmark/backend/internal/httpmw/middleware.go

package httpmw

import (
	"compress/gzip"
	"context"
	"log"
	"net/http"
	"strings"

	"bookmarkmanager/backend/internal/store"
	"bookmarkmanager/backend/internal/token"
)

const bearerPrefix = "Bearer "

type ctxKey int

// readerCtxKey is where Auth stashes the authenticated Reader id.
const readerCtxKey ctxKey = iota

// ReaderID returns the Reader id Auth authenticated, for handlers that take
// the acting Reader from the request rather than from a fixed field.
func ReaderID(r *http.Request) int64 { return r.Context().Value(readerCtxKey).(int64) }

// ResolveReader maps a presented credential to a Reader. The credential is
// hashed and matched against readers.token_sha256 — an equality on 32-byte
// values, never a comparison of the credential itself. The same resolution
// backs the API bearer header and the userscript download path, so a Reader
// has exactly one credential with one blast radius.
func ResolveReader(s *store.Store, cred string) (int64, bool) {
	readerID, ok, err := s.ReaderIDForTokenHash(token.Hash(cred))
	if err != nil {
		log.Printf("auth: reader lookup: %v", err)
		return 0, false
	}
	return readerID, ok
}

// Auth guards a handler with a per-Reader bearer credential. The acting
// Reader travels in the request context, so a handler scopes every store call
// to exactly the Reader that authenticated.
func Auth(s *store.Store, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		h := r.Header.Get("Authorization")
		if !strings.HasPrefix(h, bearerPrefix) {
			http.Error(w, "unauthorized", http.StatusUnauthorized)
			return
		}
		readerID, ok := ResolveReader(s, strings.TrimPrefix(h, bearerPrefix))
		if !ok {
			http.Error(w, "unauthorized", http.StatusUnauthorized)
			return
		}
		next.ServeHTTP(w, r.WithContext(context.WithValue(r.Context(), readerCtxKey, readerID)))
	})
}

// gzipWriter compresses the body and drops Content-Length, which no longer
// describes what goes on the wire. WriteHeader is where the decision is made:
// only then is Content-Type known.
type gzipWriter struct {
	http.ResponseWriter
	gz      *gzip.Writer
	decided bool
}

// compressible covers what this server actually serves in bulk: HTML, CSS, JS
// and JSON. Fonts are woff2, which is already compressed — gzipping them costs
// CPU to add bytes.
func compressible(contentType string) bool {
	ct, _, _ := strings.Cut(contentType, ";")
	switch strings.TrimSpace(ct) {
	case "text/html", "text/css", "text/javascript", "application/javascript",
		"application/json", "text/plain":
		return true
	}
	return false
}

func (w *gzipWriter) WriteHeader(status int) {
	if !w.decided {
		w.decided = true
		if compressible(w.Header().Get("Content-Type")) {
			w.Header().Set("Content-Encoding", "gzip")
			w.Header().Del("Content-Length")
			w.gz = gzip.NewWriter(w.ResponseWriter)
		}
	}
	w.ResponseWriter.WriteHeader(status)
}

func (w *gzipWriter) Write(b []byte) (int, error) {
	if !w.decided {
		w.WriteHeader(http.StatusOK)
	}
	if w.gz != nil {
		return w.gz.Write(b)
	}
	return w.ResponseWriter.Write(b)
}

// Gzip compresses text responses for clients that ask. The templates,
// stylesheet and htmx together are ~120 KB uncompressed and roughly a quarter
// of that gzipped, which is the difference between a fast and a slow first load
// on mobile data.
func Gzip(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if !strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") {
			next.ServeHTTP(w, r)
			return
		}
		w.Header().Add("Vary", "Accept-Encoding")
		gw := &gzipWriter{ResponseWriter: w}
		defer func() {
			if gw.gz != nil {
				gw.gz.Close()
			}
		}()
		next.ServeHTTP(gw, r)
	})
}

// CORS reflects the request Origin only when it is in allowed, answers
// preflight OPTIONS with 204, and passes everything else through. It wraps the
// auth middleware so preflight (which carries no Authorization header) is never
// rejected by auth.
func CORS(allowed []string, next http.Handler) http.Handler {
	set := make(map[string]struct{}, len(allowed))
	for _, o := range allowed {
		set[o] = struct{}{}
	}
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		origin := r.Header.Get("Origin")
		if _, ok := set[origin]; ok && origin != "" {
			w.Header().Set("Access-Control-Allow-Origin", origin)
			w.Header().Add("Vary", "Origin")
			w.Header().Set("Access-Control-Allow-Methods", "GET,PUT,DELETE,OPTIONS")
			w.Header().Set("Access-Control-Allow-Headers", "Authorization,Content-Type")
			w.Header().Set("Access-Control-Max-Age", "86400")
		}
		if r.Method == http.MethodOptions {
			w.WriteHeader(http.StatusNoContent)
			return
		}
		next.ServeHTTP(w, r)
	})
}