Return NA values for invalid integer inputs

I had meant to go back and do this, but never did.

Fixes #135

NEWS.md

@@ -1,5 +1,7 @@
 # vroom (development)
 
+* The integer parser now returns NA values for invalid inputs (#135)
+
 * The column created by `id` is now stored as an run length encoded Altrep
   vector, which uses less memory and is much faster for large inputs. (#111)
 

src/vroom_int.cc

@@ -4,9 +4,13 @@
 // A version of strtoi that doesn't need null terminated strings, to avoid
 // needing to copy the data
 int strtoi(const char* begin, const char* end) {
-  int val = 0;
+  double val = 0;
   bool is_neg = false;
 
+  if (begin == end) {
+    return NA_INTEGER;
+  }
+
   if (begin != end && *begin == '-') {
     is_neg = true;
     ++begin;
@@ -16,6 +20,15 @@ int strtoi(const char* begin, const char* end) {
     val = val * 10 + ((*begin++) - '0');
   }
 
+  // If there is more than digits, return NA
+  if (begin != end) {
+    return NA_INTEGER;
+  }
+
+  if (val > INT_MAX) {
+    return NA_INTEGER;
+  }
+
   return is_neg ? -val : val;
 }