messages.getCommand

lib/messages.js

@@ -18,6 +18,30 @@ var util = require("./_util");
 var message = structs.message;
 var ServicesBitfield = structs.ServicesBitfield;
 
+/**
+ * Try to get command for the given encoded message.
+ * Note that this function doesn't do any validation because it is
+ * already provided by `message.decode` routine. Normally you call this
+ * for each incoming message and then call decode function of the
+ * appropriate message handler.
+ * @param {Buffer} buf - Buffer that starts with encoded message
+ * @return {?string} Message's command if any
+ */
+exports.getCommand = function(buf) {
+  if (buf.length < 16) {
+    return;
+  }
+  var command = buf.slice(4, 16);
+  var firstNonNull = 0;
+  for (var i = 11; i >=0; i--) {
+    if (command[i] !== 0) {
+      firstNonNull = i + 1;
+      break;
+    }
+  }
+  return command.slice(0, firstNonNull).toString("ascii");
+};
+
 /**
  * `version` message.
  * @see {@link https://bitmessage.org/wiki/Protocol_specification#version}

lib/structs.js

@@ -41,7 +41,6 @@ var message = exports.message = {
    * Decode message structure.
    * NOTE: `payload` is copied, `rest` references input buffer.
    * @param {Buffer} buf - Buffer that starts with encoded message
-   * structure
    * @return {{command: string, payload: Buffer, length: number, rest: Buffer}}
    * Decoded message structure.
    */
@@ -56,7 +55,10 @@ var message = exports.message = {
         firstNonNull = i + 1;
       }
     }
-    // Command could be empty.
+    // NOTE(Kagami): Command can be empty.
+    // NOTE(Kagami): "ascii" encoding is not necessary here since we
+    // already validated the command but that should be quite faster
+    // than default "utf-8" encoding.
     command = command.slice(0, firstNonNull).toString("ascii");
     var payloadLength = buf.readUInt32BE(16, true);
     assert(payloadLength <= 262144, "Payload is too big");

test.js

@@ -363,6 +363,12 @@ describe("Common structures", function() {
 
 // TODO(Kagami): Add tests for encodePayload/decodePayload as well.
 describe("Message types", function() {
+  it("should get command for encoded message", function() {
+    var encoded = message.encode("test", Buffer(0));
+    expect(messages.getCommand(encoded)).to.equal("test");
+    expect(messages.getCommand(Buffer("test"))).to.be.undefined;
+  });
+
   describe("version", function() {
     it("should encode and decode", function() {
       var encoded = version.encode({