follow-up scriptpubkeys

Author: SomberNight

docs/protocol-changes.rst

@@ -195,10 +195,7 @@ Changes
     the :func:`server.version` message must be the first message sent.
     That is, version negotiation must happen before any other messages.
   * The `blockchain.scripthash.*` methods are all replaced with `blockchain.scriptpubkey.*`
-    methods. Note: `sha256(scriptPubKey) == scripthash`. This should be easy to implement:
-    previously clients were calculating the sha256 hash prior to sending a request,
-    now the server can decide whether to apply sha256 when processing the request.
-    (some server implementations might want to apply sha256, to keep the same DB structure)
+    methods. Note: `sha256(scriptPubKey) == scripthash`.
   * The status of a scripthash/scriptpubkey has its definition tightened in a
     backwards-compatible way: mempool txs now have a canonical ordering
     defined for the calculation (previously their order was undefined).

docs/protocol-methods.rst

@@ -518,10 +518,19 @@ Subscribe to a :ref:`scriptPubKey <scriptpubkeys>`.
 
 **Notifications**
 
-  The client will receive a notification when the :ref:`status <status>` of the script
-  hash changes.  Its signature is
-
-    .. function:: blockchain.scriptpubkey.subscribe(scriptpubkey, status)
+  The client will receive a notification when the :ref:`status <status>` of the
+  scriptPubKey changes. Importantly, the notifications use :ref:`script hash <script hashes>`
+  instead of scriptPubKey. The scripthash corresponds to the scriptPubKey from the
+  original request.
+  The client is expected to maintain a mapping scripthash->scriptpubkey, or similar,
+  to be able to figure out what the notification refers to.
+  Notably, this way servers do not have to store in memory the scriptpubkey corresponding
+  to the original request (which can be up to 10 KB in size, as per Bitcoin consensus),
+  only the scripthash (which is fixed size). Also, this limits upstream bandwidth usage
+  of servers.
+  The signature is
+
+    .. function:: blockchain.scriptpubkey.subscribe(scripthash, status)
        :noindex:
 
 blockchain.scriptpubkey.unsubscribe