[2376] Disallow missing last unit

Also, simplify the code little bit and make it run faster in the case of
TTL without any units.

src/lib/dns/rrttl.cc

@@ -69,27 +69,41 @@ RRTTL::RRTTL(const std::string& ttlstr) {
     const string::const_iterator end = ttlstr.end();
     string::const_iterator pos = ttlstr.begin();
 
+    // When we detect we have some units
+    bool units_mode = false;
+
     try {
         while (pos != end) {
             // Find the first unit, if there's any.
             const string::const_iterator unit = find_if(pos, end, myIsalpha);
-            // Default multiplication if no unit.
-            uint32_t multiply = 1;
-            if (unit != end) {
-                // Find the unit and get the size.
-                bool found = false;
-                for (size_t i = 0; i < sizeof(units) / sizeof(*units); ++i) {
-                    if (toupper(*unit) == units[i].unit) {
-                        found = true;
-                        multiply = units[i].multiply;
-                        break;
-                    }
+            // No unit
+            if (unit == end) {
+                if (units_mode) {
+                    // We had some units before. The last one is missing unit.
+                    isc_throw(InvalidRRTTL, "Missing the last unit: " <<
+                              ttlstr);
+                } else {
+                    // Case without any units at all. Just convert and store it.
+                    val = boost::lexical_cast<int64_t>(ttlstr);
+                    break;
                 }
-                if (!found) {
-                    isc_throw(InvalidRRTTL, "Unknown unit used: " << *unit <<
-                              " in: " << ttlstr);
+            }
+            // There's a unit now.
+            units_mode = true;
+            // Find the unit and get the size.
+            uint32_t multiply;
+            bool found = false;
+            for (size_t i = 0; i < sizeof(units) / sizeof(*units); ++i) {
+                if (toupper(*unit) == units[i].unit) {
+                    found = true;
+                    multiply = units[i].multiply;
+                    break;
                 }
             }
+            if (!found) {
+                isc_throw(InvalidRRTTL, "Unknown unit used: " << *unit <<
+                          " in: " << ttlstr);
+            }
             // Now extract the number.
             if (unit == pos) {
                 isc_throw(InvalidRRTTL, "Missing number in TTL: " << ttlstr);
@@ -105,12 +119,8 @@ RRTTL::RRTTL(const std::string& ttlstr) {
                 isc_throw(InvalidRRTTL, "Part of TTL out of range: " <<
                           ttlstr);
             }
-            // Move to after the unit (if any). But make sure not to increment
-            // past end, which is, strictly speaking, illegal.
-            pos = unit;
-            if (pos != end) {
-                ++pos;
-            }
+            // Move to after the unit.
+            pos = unit + 1;
         }
     } catch (const boost::bad_lexical_cast&) {
         isc_throw(InvalidRRTTL, "invalid TTL: " << ttlstr);