In theory, version exchange for client and server works now.

Test rig isn't there yet, so untested at the moment.

Added a simple README

lib/em-bitcoin.rb

@@ -23,23 +23,70 @@ module EventMachine
       end
       PE = ProtocolError
       
+      BTC = ::BtcWireProto
+      
+      # The actor for this peer
+      attr_reader :actor
+
+      # Randomly-generated 32-bit number allowing us to guarantee we're not
+      # connecting to ourselves.
+      attr_reader :connection_nonce
+       
       # The list of methods a valid actor will respond to.
       ACTOR_METHODS = [
+        :network_name,    # Returns a symbol telling us which network to be on
+        :current_time,    # Time instance specifying the current time
+        :sub_version,     # String specifying custom version string
+        :current_height,  # Number of the newest block known to the actor
         :log,             # log(:level, message) - self-evident
         :connection=,     # Called with +self+ to allow actor interaction
         :ready!           # Called when the connection is ready to be used
       ]
 
-      def log(level, data)
-        @actor.log(level, data)
+      # receive_version and receive_verack implementations differ in client &
+      # server, so are implemented there.
+      
+      # Send a 'version' message to the peer.
+      def send_version
+        log(:info, "Sending version message")
+
+        m = build_message(:version, {
+          :services        => {:node_network => 1},
+          :timestamp       => actor.current_time.to_i,
+          :addr_me         => my_netaddr,
+          :addr_you        => peer_netaddr,
+          :nonce           => connection_nonce,
+          :sub_version_num => (actor.sub_version || "em-bitcoin"),
+          :start_height    => actor.current_height
+        })
+        send_data(m.to_binary_s)
       end
       
+      # Send a 'verack' message to the peer
+      def send_verack
+        log(:info, "Sending verack message")
+        send_data(build_message(:verack).to_binary_s)
+      end
+
       protected
       
+      # Puts together a message from the details given. Common fields, like
+      # magic and checksums, are filled in.
+      def build_message(command, payload_opts = {}, header_opts = {})
+        header_opts[:command] = command.to_s
+        header_opts[:magic] ||= BTC::NETWORKS[actor.network_name]
+        m = BTC::Message.new(:header => header_opts, :payload => payload_opts)
+      end
+
+      def log(level, data)
+        actor.log(level, data)
+      end
+      
       def init_state!
         @data = ""
         @ready = nil
-        @actor.connection = self # Tell the actor about the connection
+        @connection_nonce = rand(2**32)
+        actor.connection = self # Tell the actor about the connection
       end
       
       # Checks the current actor object to see if it is valid or not.
@@ -59,7 +106,7 @@ module EventMachine
 
         ACTOR_METHODS.each do |m|
           return [false, "Actor doesn't implement all #{m}"] unless
-            @actor.respond_to?(m)
+            actor.respond_to?(m)
         end  
 
         true
@@ -74,7 +121,7 @@ module EventMachine
         finished = false
         while !finished 
           begin
-            packet = BtcWireProto::Message.read(@data)
+            packet = BTC::Message.read(@data)
             @data.slice!(0, packet.num_bytes - 1) # Remove data from buffer
             if packet.cmd_sym
               m = "receive_#{packet.cmd_sym}"
@@ -94,19 +141,36 @@ module EventMachine
         end
         log(:debug, "Leaving receive_data with #{@data.length} bytes in buffer")
       end
-     
-      # receive_version and receive_verack implementations differ in client &
-      # server, so are implemented there.
       
-      # Send a 'version' message to the peer.
-      def send_version
-        # TODO
+      # Checks whether we can communicate sensibly with a peer of a particular
+      # version. At the moment, we're fairly liberal about who we try to talk to
+      # @param[Fixnum] their_version Version of the peer under question
+      # @return[Boolean] can we communicate with a peer advertising the version?
+      def can_talk_version?(their_version)
+        their_version >= 31402 
       end
       
-      # Send a 'verack' message to the peer
-      def send_verack
-        # TODO
+      # @return[BTC::NetAddr] wire represenation of our own network address
+      def my_netaddr
+        sockaddr = get_sockname
+        raise PE.new("Unable to determine own NetAddr") unless sockaddr
+        port, ip = Socket::unpack_sockaddr_in(sockaddr)
+        BTC::NetAddr.new(
+          :services => {:node_network => 1}, :ip => ip, :port => port
+        )
       end
+      
+      # FIXME: what does node_network mean here?
+      # @return[BTC::NetAddr] wire representation of our peer's network address
+      def peer_netaddr
+        sockaddr = get_peername
+        raise PE.new("Unable to determine peer NetAddr") unless sockaddr
+        port, ip = Socket::unpack_sockaddr_in(sockaddr)
+        BTC::NetAddr.new(
+          :services => {:node_network => 1}, :ip => ip, :port => port
+        )
+      end
+
     end
     
     # EventMachine protocol class that handles an *outgoing* connection to
@@ -122,7 +186,6 @@ module EventMachine
 
       # @param[Object] actor See the BitcoinPeer#valid_actor?
       def initialize(actor)
-        super
         @actor = actor
         result, msg = valid_actor?
         raise ArgumentError.new("Invalid actor: #{msg}") unless result
@@ -154,10 +217,16 @@ module EventMachine
       def receive_version(p)
         raise PE.new("Received version inappropriately") unless
           @ready == :version_sent
-        log(:info, "Peer tells us its version is #{p.payload.version}")
-        send_verack
-        @ready = true
-        @actor.ready!
+        
+        if can_talk_version?(p.payload.version)
+          log(:info, "Valid peer, version is #{p.payload.version}")
+          send_verack
+          @ready = true
+          actor.ready!
+        else
+          log(:info, "Bad peer, can't talk version #{p.payload.version}")
+          unbind
+        end  
       end
     end
     
@@ -173,23 +242,37 @@ module EventMachine
 
       # @param[Object] actor See the BitcoinPeer#valid_actor? method
       def initialize(actor)
-        super
         @actor = actor
         result, msg = valid_actor?
         raise ArgumentError.new("Invalid actor: #{msg}") unless result
         
         init_state!
       end
-      
 
-      # We should receive this as the very first message on the wire
+      # We should receive this as the very first message on the wire.
+      # If we're prepared ot talk to a client with this version, we send a
+      # verack message followed by our own version and wait for a verack to be
+      # received.
       def receive_version(p)
-        # TODO
+        raise PE.new("Received version inappropriately") unless @ready.nil?
+        if can_talk_version?(p.payload.version)
+          log(:info, "Peer version #{p.payload.version}")
+          send_verack
+          send_version
+          @ready = :version_sent
+        else
+          log(:info, "Bad peer - can't talk version #{p.payload.version}")
+          unbind
+        end
       end
       
-      # We should only receive this after sending our own version
+      # We should only receive this after sending our own version. If the client
+      # doesn't like our version, it'll close the connection.
       def receive_verack(p)
-        # TODO
+        raise PE.new("Received verack inappropriately") unless
+          @ready == :version_sent
+        @ready = true
+        actor.ready!
       end
 
     end