Extract event signing into its own class

lib/nostr/crypto.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+module Nostr
+  # Performs cryptographic operations on a +Nostr::Event+.
+  class Crypto
+    # Uses the private key to generate an event id and sign the event
+    #
+    # @api public
+    #
+    # @example Signing an event
+    #   crypto = Nostr::Crypto.new
+    #   crypto.sign(event, private_key)
+    #   event.id # => an id
+    #   event.sig # => a signature
+    #
+    # @param event [Event] The event to be signed
+    # @param private_key [String] 32-bytes hex-encoded private key.
+    #
+    # @return [Event] An unsigned event.
+    #
+    def sign_event(event, private_key)
+      event_digest = hash_event(event)
+
+      hex_private_key = Array(private_key).pack('H*')
+      hex_message     = Array(event_digest).pack('H*')
+      event_signature = Schnorr.sign(hex_message, hex_private_key).encode.unpack1('H*')
+
+      event.id = event_digest
+      event.sig = event_signature
+
+      event
+    end
+
+    private
+
+    # Generates a SHA256 hash of a +Nostr::Event+
+    #
+    # @api private
+    #
+    # @param event [Event] The event to be hashed
+    #
+    # @return [String] A SHA256 digest of the event
+    #
+    def hash_event(event)
+      Digest::SHA256.hexdigest(JSON.dump(event.serialize))
+    end
+  end
+end

lib/nostr/event.rb

@@ -70,9 +70,13 @@ module Nostr
     # @example Getting the event id
     #   event.id # => 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460'
     #
+    # @example Setting the event id
+    #   event.id = 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460'
+    #   event.id # => 'ccf9fdf3e1466d7c20969c71ec98defcf5f54aee088513e1b73ccb7bd770d460'
+    #
     # @return [String|nil]
     #
-    attr_reader :id
+    attr_accessor :id
 
     # 64-bytes signature of the sha256 hash of the serialized event data, which is
     # the same as the "id" field
@@ -82,9 +86,13 @@ module Nostr
     # @example Getting the event signature
     #   event.sig # => ''
     #
+    # @example Setting the event signature
+    #   event.sig = '058613f8d34c053294cc28b7f9e1f8f0e80fd1ac94fb20f2da6ca514e7360b39'
+    #   event.sig # => '058613f8d34c053294cc28b7f9e1f8f0e80fd1ac94fb20f2da6ca514e7360b39'
+    #
     # @return [String|nil]
     #
-    attr_reader :sig
+    attr_accessor :sig
 
     # Instantiates a new Event
     #
@@ -130,6 +138,22 @@ module Nostr
       @content = content
     end
 
+    # Signs an event with the user's private key
+    #
+    # @api public
+    #
+    # @example Signing an event
+    #   event.sign(private_key)
+    #
+    # @param private_key [String] 32-bytes hex-encoded private key.
+    #
+    # @return [Event] A signed event.
+    #
+    def sign(private_key)
+      crypto = Crypto.new
+      crypto.sign_event(self, private_key)
+    end
+
     # Serializes the event, to obtain a SHA256 digest of it
     #
     # @api public

lib/nostr/user.rb

@@ -57,36 +57,8 @@ module Nostr
     # @return [Event]
     #
     def create_event(event_attributes)
-      event_fragment = EventFragment.new(**event_attributes.merge(pubkey: keypair.public_key))
-      event_sha256 = Digest::SHA256.hexdigest(JSON.dump(event_fragment.serialize))
-
-      signature = sign(event_sha256)
-
-      Event.new(
-        id: event_sha256,
-        pubkey: event_fragment.pubkey,
-        created_at: event_fragment.created_at,
-        kind: event_fragment.kind,
-        tags: event_fragment.tags,
-        content: event_fragment.content,
-        sig: signature
-      )
-    end
-
-    private
-
-    # Signs an event with the user's private key
-    #
-    # @api private
-    #
-    # @param event_sha256 [String] The SHA256 hash of the event.
-    #
-    # @return [String] The signature of the event.
-    #
-    def sign(event_sha256)
-      hex_private_key = Array(keypair.private_key).pack('H*')
-      hex_message = Array(event_sha256).pack('H*')
-      Schnorr.sign(hex_message, hex_private_key).encode.unpack1('H*')
+      event = Event.new(**event_attributes.merge(pubkey: keypair.public_key))
+      event.sign(keypair.private_key)
     end
   end
 end