| 1 | package aviso |
| 2 | |
| 3 | import ( |
| 4 | "crypto/ecdh" |
| 5 | "encoding/base64" |
| 6 | "encoding/json" |
| 7 | "errors" |
| 8 | "io" |
| 9 | "net/http" |
| 10 | "strings" |
| 11 | |
| 12 | "amadan.net/rastrillo/rastrillo/csrf" |
| 13 | "amadan.net/rastrillo/rastrillo/sessions" |
| 14 | ) |
| 15 | |
| 16 | const maxSubscribeBody = 8192 |
| 17 | |
| 18 | // PublicKey answers GET with {"publicKey": ...}. no-cache so a rotated |
| 19 | // key reaches browsers on their next load rather than after a cache |
| 20 | // expiry nobody chose. |
| 21 | func (s *Service) PublicKey(w http.ResponseWriter, r *http.Request) { |
| 22 | if r.Method != http.MethodGet { |
| 23 | w.Header().Set("Allow", http.MethodGet) |
| 24 | http.Error(w, "method not allowed", http.StatusMethodNotAllowed) |
| 25 | return |
| 26 | } |
| 27 | w.Header().Set("Content-Type", "application/json") |
| 28 | w.Header().Set("Cache-Control", "no-cache") |
| 29 | _ = json.NewEncoder(w).Encode(map[string]string{"publicKey": s.pub}) |
| 30 | } |
| 31 | |
| 32 | // gate is what both mutations require: POST, a session with a subject, |
| 33 | // and a same-origin request. It writes the refusal and returns "" when |
| 34 | // the caller must stop. |
| 35 | func (s *Service) gate(w http.ResponseWriter, r *http.Request) string { |
| 36 | if r.Method != http.MethodPost { |
| 37 | w.Header().Set("Allow", http.MethodPost) |
| 38 | http.Error(w, "method not allowed", http.StatusMethodNotAllowed) |
| 39 | return "" |
| 40 | } |
| 41 | sess, ok := sessions.Current(r) |
| 42 | if !ok || sess.Subject == "" { |
| 43 | http.Error(w, "sign in first", http.StatusUnauthorized) |
| 44 | return "" |
| 45 | } |
| 46 | if !csrf.SameOrigin(r, s.cfg.Origin) { |
| 47 | http.Error(w, "cross-origin request refused", http.StatusForbidden) |
| 48 | return "" |
| 49 | } |
| 50 | return sess.Subject |
| 51 | } |
| 52 | |
| 53 | // decodeBody reads at most maxSubscribeBody bytes of JSON into into. |
| 54 | // Unknown fields are tolerated on purpose: a browser's |
| 55 | // PushSubscription.toJSON() carries expirationTime and whatever a |
| 56 | // future spec adds, and refusing those would refuse every genuine |
| 57 | // subscription. The byte cap and field validation are the defence. |
| 58 | func decodeBody(w http.ResponseWriter, r *http.Request, into any) bool { |
| 59 | body := http.MaxBytesReader(w, r.Body, maxSubscribeBody) |
| 60 | dec := json.NewDecoder(body) |
| 61 | tooLarge := func(err error) bool { |
| 62 | var mbe *http.MaxBytesError |
| 63 | return errors.As(err, &mbe) |
| 64 | } |
| 65 | if err := dec.Decode(into); err != nil { |
| 66 | if tooLarge(err) { |
| 67 | http.Error(w, "body too large", http.StatusRequestEntityTooLarge) |
| 68 | return false |
| 69 | } |
| 70 | http.Error(w, "bad request body", http.StatusBadRequest) |
| 71 | return false |
| 72 | } |
| 73 | // Exactly one JSON value: a second Decode must hit EOF. Anything |
| 74 | // else — trailing garbage, a second document — is refused rather |
| 75 | // than silently dropped, so a mangled body cannot half-apply. |
| 76 | if err := dec.Decode(new(json.RawMessage)); !errors.Is(err, io.EOF) { |
| 77 | if tooLarge(err) { |
| 78 | http.Error(w, "body too large", http.StatusRequestEntityTooLarge) |
| 79 | return false |
| 80 | } |
| 81 | http.Error(w, "bad request body", http.StatusBadRequest) |
| 82 | return false |
| 83 | } |
| 84 | return true |
| 85 | } |
| 86 | |
| 87 | // canonicalKeys checks the two RFC 8291 inputs the way webpush-go will |
| 88 | // before it encrypts — p256dh an uncompressed P-256 point, auth 16 |
| 89 | // bytes, both base64url with or without padding — and returns them |
| 90 | // re-encoded canonically. Stored canonical, not as sent: Go's decoder |
| 91 | // forgives a stray CR/LF that webpush-go's padding arithmetic does |
| 92 | // not, so a key that "validated" verbatim could still fail every |
| 93 | // send. Refusing bad keys here keeps a mangled re-subscribe from |
| 94 | // replacing working keys or deleting previousEndpoint. |
| 95 | func canonicalKeys(p256dh, auth string) (string, string, error) { |
| 96 | decode := func(s string) ([]byte, error) { |
| 97 | if strings.ContainsAny(s, "\r\n \t") { |
| 98 | return nil, errors.New("whitespace") |
| 99 | } |
| 100 | if b, err := base64.RawURLEncoding.DecodeString(s); err == nil { |
| 101 | return b, nil |
| 102 | } |
| 103 | return base64.URLEncoding.DecodeString(s) |
| 104 | } |
| 105 | point, err := decode(p256dh) |
| 106 | if err != nil { |
| 107 | return "", "", errors.New("p256dh is not base64url") |
| 108 | } |
| 109 | if _, err := ecdh.P256().NewPublicKey(point); err != nil { |
| 110 | return "", "", errors.New("p256dh is not a P-256 point") |
| 111 | } |
| 112 | secret, err := decode(auth) |
| 113 | if err != nil || len(secret) != 16 { |
| 114 | return "", "", errors.New("auth is not 16 base64url bytes") |
| 115 | } |
| 116 | return base64.RawURLEncoding.EncodeToString(point), base64.RawURLEncoding.EncodeToString(secret), nil |
| 117 | } |
| 118 | |
| 119 | type subscribeRequest struct { |
| 120 | Subscription struct { |
| 121 | Endpoint string `json:"endpoint"` |
| 122 | Keys struct { |
| 123 | P256dh string `json:"p256dh"` |
| 124 | Auth string `json:"auth"` |
| 125 | } `json:"keys"` |
| 126 | } `json:"subscription"` |
| 127 | PublicKey string `json:"publicKey"` |
| 128 | PreviousEndpoint string `json:"previousEndpoint"` |
| 129 | } |
| 130 | |
| 131 | // Subscribe stores the caller's subscription. 409 when the endpoint is |
| 132 | // another subject's or the browser subscribed under a key that is not |
| 133 | // ours — storing that row would be storing one nothing can sign for. |
| 134 | func (s *Service) Subscribe(w http.ResponseWriter, r *http.Request) { |
| 135 | subject := s.gate(w, r) |
| 136 | if subject == "" { |
| 137 | return |
| 138 | } |
| 139 | var req subscribeRequest |
| 140 | if !decodeBody(w, r, &req) { |
| 141 | return |
| 142 | } |
| 143 | if req.PublicKey != s.pub { |
| 144 | http.Error(w, "subscribed under a different application server key; re-enrol", http.StatusConflict) |
| 145 | return |
| 146 | } |
| 147 | if err := validateEndpoint(req.Subscription.Endpoint); err != nil { |
| 148 | http.Error(w, "endpoint refused", http.StatusBadRequest) |
| 149 | return |
| 150 | } |
| 151 | p256dh, auth, err := canonicalKeys(req.Subscription.Keys.P256dh, req.Subscription.Keys.Auth) |
| 152 | if err != nil { |
| 153 | http.Error(w, "subscription keys refused: "+err.Error(), http.StatusBadRequest) |
| 154 | return |
| 155 | } |
| 156 | if req.PreviousEndpoint != "" && validateEndpoint(req.PreviousEndpoint) != nil { |
| 157 | http.Error(w, "previousEndpoint refused", http.StatusBadRequest) |
| 158 | return |
| 159 | } |
| 160 | sub := Subscription{Endpoint: req.Subscription.Endpoint, P256dh: p256dh, Auth: auth} |
| 161 | switch err := s.put(r.Context(), subject, sub, req.PreviousEndpoint); { |
| 162 | case errors.Is(err, ErrOwnedElsewhere): |
| 163 | http.Error(w, "endpoint enrolled by another account", http.StatusConflict) |
| 164 | case err != nil: |
| 165 | s.cfg.Logger.Error("aviso: subscribe", "err", err) |
| 166 | http.Error(w, "could not store subscription", http.StatusInternalServerError) |
| 167 | default: |
| 168 | w.WriteHeader(http.StatusNoContent) |
| 169 | } |
| 170 | } |
| 171 | |
| 172 | // Unsubscribe removes the caller's own row for the endpoint. 204 |
| 173 | // whether or not it existed: the endpoint's existence is not the |
| 174 | // caller's to learn unless they own it. |
| 175 | func (s *Service) Unsubscribe(w http.ResponseWriter, r *http.Request) { |
| 176 | subject := s.gate(w, r) |
| 177 | if subject == "" { |
| 178 | return |
| 179 | } |
| 180 | var req struct { |
| 181 | Endpoint string `json:"endpoint"` |
| 182 | } |
| 183 | if !decodeBody(w, r, &req) { |
| 184 | return |
| 185 | } |
| 186 | if req.Endpoint == "" || len(req.Endpoint) > maxEndpointLen { |
| 187 | http.Error(w, "endpoint missing", http.StatusBadRequest) |
| 188 | return |
| 189 | } |
| 190 | if err := s.deleteOwn(r.Context(), subject, req.Endpoint); err != nil { |
| 191 | s.cfg.Logger.Error("aviso: unsubscribe", "err", err) |
| 192 | http.Error(w, "could not remove subscription", http.StatusInternalServerError) |
| 193 | return |
| 194 | } |
| 195 | w.WriteHeader(http.StatusNoContent) |
| 196 | } |
| 197 | |
amadan