Implement var_str

lib/struct.js

@@ -13,11 +13,11 @@ var bitmessage = require("./");
  * var_int.
  * @see {@link https://bitmessage.org/wiki/Protocol_specification#Variable_length_integer}
  */
-exports.var_int = {
+var var_int = exports.var_int = {
   /**
    * Decode var_int.
    * @param {Buffer} buf - Buffer that starts with encoded var_int
-   * @return {{value: (number|Int64), length: number, rest: number}}
+   * @return {{value: (number|Int64), length: number, rest: Buffer}}
    * Decoded var_int structure.
    */
   decode: function(buf) {
@@ -105,3 +105,35 @@ exports.var_int = {
     return buf;
   },
 };
+
+/**
+ * var_str.
+ * @see {@link https://bitmessage.org/wiki/Protocol_specification#Variable_length_string}
+ */
+exports.var_str = {
+  /**
+   * Decode var_str.
+   * @param {Buffer} buf - Buffer that starts with encoded var_str
+   * @return {{str: string, length: number, rest: Buffer}}
+   * Decoded var_str structure.
+   */
+  decode: function(buf) {
+    var decoded = var_int.decode(buf);
+    var strLength = decoded.value;
+    // XXX(Kagami): Spec doesn't mention encoding, using UTF-8.
+    var str = decoded.rest.slice(0, strLength).toString();
+    var rest = decoded.rest.slice(strLength);
+    return {str: str, length: decoded.length + strLength, rest: rest};
+  },
+
+  /**
+   * Encode string into var_str.
+   * @param {string} str - A string
+   * @return {Buffer} Encoded var_str.
+   */
+  encode: function(str) {
+    // XXX(Kagami): Spec doesn't mention encoding, using UTF-8.
+    var strBuf = new Buffer(str);
+    return Buffer.concat([var_int.encode(strBuf.length), strBuf]);
+  },
+};

test.js

@@ -8,6 +8,7 @@ var Int64 = bitmessage.Int64;
 var Address = bitmessage.Address;
 var wif = bitmessage.wif;
 var var_int = bitmessage.struct.var_int;
+var var_str = bitmessage.struct.var_str;
 var bmcrypto = require("./lib/crypto");
 
 describe("Core structures", function() {
@@ -56,6 +57,26 @@ describe("Core structures", function() {
       expect(var_int.encode.bind(null, "test")).to.throw(Error);
     });
   });
+
+  describe("var_str", function() {
+    it("should decode", function() {
+      var res;
+      res = var_str.decode(Buffer("0474657374", "hex"));
+      expect(res.str).to.equal("test");
+      expect(res.length).to.equal(5);
+      expect(res.rest.toString("hex")).to.equal("");
+
+      res = var_str.decode(Buffer("00", "hex"));
+      expect(res.str).to.equal("");
+      expect(res.length).to.equal(1);
+      expect(res.rest.toString("hex")).to.equal("");
+    });
+
+    it("should encode", function() {
+      expect(var_str.encode("test").toString("hex")).to.equal("0474657374");
+      expect(var_str.encode("").toString("hex")).to.equal("00");
+    });
+  });
 });
 
 describe("WIF", function() {