Address Daira's further comments

src/test/torcontrol_tests.cpp

@@ -163,6 +163,16 @@ BOOST_AUTO_TEST_CASE(util_ParseTorReplyMapping)
             {"TwoOctal", "TwoEnd\11"},
         });
 
+    // Special handling for null case
+    // (needed because string comparison reads the null as end-of-string)
+    BOOST_TEST_MESSAGE(std::string("CheckParseTorReplyMapping(Null=\"\\0\")"));
+    auto ret = ParseTorReplyMapping("Null=\"\\0\"");
+    BOOST_CHECK_EQUAL(ret.size(), 1);
+    auto r_it = ret.begin();
+    BOOST_CHECK_EQUAL(r_it->first, "Null");
+    BOOST_CHECK_EQUAL(r_it->second.size(), 1);
+    BOOST_CHECK_EQUAL(r_it->second[0], '\0');
+
     // A more complex valid grammar. PROTOCOLINFO accepts a VersionLine that
     // takes a key=value pair followed by an OptArguments, making this valid.
     // Because an OptArguments contains no semantic data, there is no point in

src/torcontrol.cpp

@@ -327,7 +327,7 @@ static std::map<std::string,std::string> ParseTorReplyMapping(const std::string
                         // Octal escape sequences have a limit of three octal digits,
                         // but terminate at the first character that is not a valid
                         // octal digit if encountered sooner.
-                        for (j = 1; '0' <= value[i+j] && value[i+j] <= '7' && j < 3; ++j) {}
+                        for (j = 1; j < 3 && (i+j) < value.size() && '0' <= value[i+j] && value[i+j] <= '7'; ++j) {}
                         // Tor restricts first digit to 0-3 for three-digit octals.
                         if (j < 3 || ('0' <= value[i] && value[i] <= '3')) {
                             escaped_value.push_back(strtol(value.substr(i, j).c_str(), NULL, 8));