[mavericks] avoid using istream::putback when the param is not the latest char.

this has been a bug, but it's now critical as libc++ makes it errors
for ifstream.

src/lib/cc/data.cc

@@ -275,11 +275,11 @@ skipChars(std::istream& in, const char* chars, int& line, int& pos) {
 }
 
 // skip on the input stream to one of the characters in chars
-// if another character is found this function returns false
+// if another character is found this function throws JSONError
 // unless that character is specified in the optional may_skip
 //
-// the character found is left on the stream
-void
+// It returns the found character (as an int value).
+int
 skipTo(std::istream& in, const std::string& file, int& line,
        int& pos, const char* chars, const char* may_skip="")
 {
@@ -298,13 +298,12 @@ skipTo(std::istream& in, const std::string& file, int& line,
                 if (in.peek() == '\n') {
                     pos = 1;
                     ++line;
+                } else {
+                    ++pos;
                 }
                 in.ignore();
-                ++pos;
             }
-            in.putback(c);
-            --pos;
-            return;
+            return (c);
         } else {
             throwJSONError(std::string("'") + std::string(1, c) + "' read, one of \"" + chars + "\" expected", file, line, pos);
         }
@@ -466,10 +465,11 @@ fromStringstreamList(std::istream& in, const std::string& file, int& line,
         if (in.peek() != ']') {
             cur_list_element = Element::fromJSON(in, file, line, pos);
             list->add(cur_list_element);
-            skipTo(in, file, line, pos, ",]", WHITESPACE);
+            c = skipTo(in, file, line, pos, ",]", WHITESPACE);
+        } else {
+            c = in.get();
+            ++pos;
         }
-        c = in.get();
-        pos++;
     }
     return (list);
 }
@@ -492,15 +492,11 @@ fromStringstreamMap(std::istream& in, const std::string& file, int& line,
 
             skipTo(in, file, line, pos, ":", WHITESPACE);
             // skip the :
-            in.ignore();
-            pos++;
 
             ConstElementPtr value = Element::fromJSON(in, file, line, pos);
             map->set(key, value);
 
-            skipTo(in, file, line, pos, ",}", WHITESPACE);
-            c = in.get();
-            pos++;
+            c = skipTo(in, file, line, pos, ",}", WHITESPACE);
         }
     }
     return (map);
@@ -596,6 +592,7 @@ Element::fromJSON(std::istream& in, const std::string& file, int& line,
             case '+':
             case '.':
                 in.putback(c);
+                --pos;
                 element = fromStringstreamNumber(in, pos);
                 el_read = true;
                 break;
@@ -604,17 +601,20 @@ Element::fromJSON(std::istream& in, const std::string& file, int& line,
             case 'f':
             case 'F':
                 in.putback(c);
+                --pos;
                 element = fromStringstreamBool(in, file, line, pos);
                 el_read = true;
                 break;
             case 'n':
             case 'N':
                 in.putback(c);
+                --pos;
                 element = fromStringstreamNull(in, file, line, pos);
                 el_read = true;
                 break;
             case '"':
                 in.putback('"');
+                --pos;
                 element = fromStringstreamString(in, file, line, pos);
                 el_read = true;
                 break;

src/lib/cc/tests/data_unittests.cc

@@ -98,16 +98,24 @@ TEST(Element, from_and_to_json) {
     sv.push_back("\"\xFF\"");
 
     BOOST_FOREACH(const std::string& s, sv) {
-        // test << operator, which uses Element::str()
-        std::ostringstream stream;
-        el = Element::fromJSON(s);
-        stream << *el;
-        EXPECT_EQ(s, stream.str());
-
-        // test toWire(ostream), which should also be the same now
-        std::ostringstream wire_stream;
-        el->toWire(wire_stream);
-        EXPECT_EQ(s, wire_stream.str());
+        // Test two types of fromJSON(): with string and istream.
+        for (int i = 0; i < 2; ++i) {
+            // test << operator, which uses Element::str()
+            if (i == 0) {
+                el = Element::fromJSON(s);
+            } else {
+                std::istringstream iss(s);
+                el = Element::fromJSON(iss);
+            }
+            std::ostringstream stream;
+            stream << *el;
+            EXPECT_EQ(s, stream.str());
+
+            // test toWire(ostream), which should also be the same now
+            std::ostringstream wire_stream;
+            el->toWire(wire_stream);
+            EXPECT_EQ(s, wire_stream.str());
+        }
     }
 
     // some parse errors