Fix univalue handling of \u0000 characters.

Univalue's parsing of \u escape sequences did not handle NUL characters
correctly.  They were, effectively, dropped.  The extended test-case
fails with the old code, and is fixed with this patch.

src/test/univalue_tests.cpp

@@ -286,7 +286,7 @@ BOOST_AUTO_TEST_CASE(univalue_object)
 }
 
 static const char *json1 =
-"[1.10000000,{\"key1\":\"str\",\"key2\":800,\"key3\":{\"name\":\"martian\"}}]";
+"[1.10000000,{\"key1\":\"str\\u0000\",\"key2\":800,\"key3\":{\"name\":\"martian\"}}]";
 
 BOOST_AUTO_TEST_CASE(univalue_readwrite)
 {
@@ -306,7 +306,9 @@ BOOST_AUTO_TEST_CASE(univalue_readwrite)
     BOOST_CHECK_EQUAL(obj.size(), 3);
 
     BOOST_CHECK(obj["key1"].isStr());
-    BOOST_CHECK_EQUAL(obj["key1"].getValStr(), "str");
+    std::string correctValue("str");
+    correctValue.push_back('\0');
+    BOOST_CHECK_EQUAL(obj["key1"].getValStr(), correctValue);
     BOOST_CHECK(obj["key2"].isNum());
     BOOST_CHECK_EQUAL(obj["key2"].getValStr(), "800");
     BOOST_CHECK(obj["key3"].isObject());

src/univalue/univalue_read.cpp

@@ -188,25 +188,22 @@ enum jtokentype getJsonToken(string& tokenVal, unsigned int& consumed,
                 case 't':  valStr += "\t"; break;
 
                 case 'u': {
-                    char buf[4] = {0,0,0,0};
-                    char *last = &buf[0];
                     unsigned int codepoint;
                     if (hatoui(raw + 1, raw + 1 + 4, codepoint) !=
                                raw + 1 + 4)
                         return JTOK_ERR;
 
                     if (codepoint <= 0x7f)
-                         *last = (char)codepoint;
+                        valStr.push_back((char)codepoint);
                     else if (codepoint <= 0x7FF) {
-                        *last++ = (char)(0xC0 | (codepoint >> 6));
-                        *last = (char)(0x80 | (codepoint & 0x3F));
+                        valStr.push_back((char)(0xC0 | (codepoint >> 6)));
+                        valStr.push_back((char)(0x80 | (codepoint & 0x3F)));
                     } else if (codepoint <= 0xFFFF) {
-                        *last++ = (char)(0xE0 | (codepoint >> 12));
-                        *last++ = (char)(0x80 | ((codepoint >> 6) & 0x3F));
-                        *last = (char)(0x80 | (codepoint & 0x3F));
+                        valStr.push_back((char)(0xE0 | (codepoint >> 12)));
+                        valStr.push_back((char)(0x80 | ((codepoint >> 6) & 0x3F)));
+                        valStr.push_back((char)(0x80 | (codepoint & 0x3F)));
                     }
 
-                    valStr += buf;
                     raw += 4;
                     break;
                     }