Implement structs.message

lib/structs.js

@@ -7,6 +7,83 @@
 "use strict";
 
 var assert = require("assert");
+var bufferEqual = require("buffer-equal");
+var bmcrypto = require("./crypto");
+
+function isAscii(str) {
+  for (var i = 0; i < str.length; i++) {
+    if (str.charCodeAt(i) > 127) {
+      return false;
+    }
+  }
+  return true;
+}
+
+function getchecksum(data) {
+  return bmcrypto.sha512(data).slice(0, 4);
+}
+
+/**
+ * Message structure.
+ * @see {@link https://bitmessage.org/wiki/Protocol_specification#Message_structure}
+ * @namespace
+ * @static
+ */
+var message = exports.message = {
+  /** Bitmessage magic value. */
+  MAGIC: 0xE9BEB4D9,
+
+  /**
+   * Decode message structure.
+   * @param {Buffer} buf - Buffer that starts with encoded message
+   * structure
+   * @return {{command: string, payload: Buffer, length: number, rest: Buffer}}
+   * Decoded message structure.
+   */
+  decode: function(buf) {
+    assert(buf.length >= 24, "Buffer is too small");
+    assert(buf.readUInt32BE(0, true) === message.MAGIC, "Wrong magic");
+    var command = buf.slice(4, 16);
+    var firstNonNull;
+    for (var i = 11; i >=0; i--) {
+      assert(command[i] <= 127, "Non-ASCII characters in command");
+      if (firstNonNull === undefined && command[i] !== 0) {
+        firstNonNull = i;
+      }
+    }
+    command = command.slice(0, firstNonNull + 1).toString("ascii");
+    var payloadLength = buf.readUInt32BE(16, true);
+    assert(payloadLength <= 262144, "Payload is too big");
+    var checksum = buf.slice(20, 24);
+    var length = 24 + payloadLength;
+    var payload = buf.slice(24, length);
+    assert(bufferEqual(checksum, getchecksum(payload)), "Bad checkum");
+    var rest = buf.slice(length);
+    return {command: command, payload: payload, length: length, rest: rest};
+  },
+
+  /**
+   * Encode message structure.
+   * @param {string} command - ASCII string identifying the packet
+   * content
+   * @param {Buffer} payload - The actual data, a message or an object
+   * @return {Buffer} Encoded message structure.
+   */
+  encode: function(command, payload) {
+    assert(command.length <= 12, "Command is too long");
+    assert(isAscii(command), "Non-ASCII characters in command");
+    assert(payload.length <= 262144, "Payload is too big");
+    var buf = new Buffer(24 + payload.length);
+    buf.fill(0);
+    buf.writeUInt32BE(message.MAGIC, 0, true);
+    buf.write(command, 4);
+    buf.writeUInt32BE(payload.length, 16, true);
+    getchecksum(payload).copy(buf, 20);
+    payload.copy(buf, 24);
+    return buf;
+  },
+};
+
 
 /**
  * var_int.

test.js

@@ -5,6 +5,7 @@ var allTests = typeof window === "undefined" ?
 
 var bmcrypto = require("./lib/crypto");
 var bitmessage = require("./lib");
+var message = bitmessage.structs.message;
 var var_int = bitmessage.structs.var_int;
 var var_str = bitmessage.structs.var_str;
 var var_int_list = bitmessage.structs.var_int_list;
@@ -49,6 +50,21 @@ describe("Crypto", function() {
 });
 
 describe("Common structures", function() {
+  describe("message", function() {
+    it("should encode", function() {
+      expect(message.encode("test", Buffer("payload")).toString("hex")).to.equal("e9beb4d97465737400000000000000000000000770b33ce97061796c6f6164");
+    });
+
+    it("should decode", function() {
+      var res;
+      res = message.decode(Buffer("e9beb4d97465737400000000000000000000000770b33ce97061796c6f6164", "hex"));
+      expect(res.command).to.equal("test");
+      expect(res.payload.toString()).to.equal("payload");
+      expect(res.length).to.equal(31);
+      expect(res.rest.toString("hex")).to.equal("");
+    });
+  });
+
   describe("var_int", function() {
     it("should decode", function() {
       var res;