[GitHub] [arrow] pitrou commented on a change in pull request #6213: ARROW-7592: [C++] Fix crashes on corrupt IPC input

[GitBox <gi...@apache.org>]

pitrou commented on a change in pull request #6213:
URL: https://github.com/apache/arrow/pull/6213#discussion_r442423611



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File path: cpp/src/arrow/type.cc
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@@ -501,20 +501,35 @@ Status Decimal128Type::Make(int32_t precision, int32_t scale,
 // ----------------------------------------------------------------------
 // Dictionary-encoded type
 
+Status DictionaryType::ValidateParameters(const DataType& index_type,
+                                          const DataType& value_type) {
+  const bool index_type_ok = is_integer(index_type.id()) &&
+                             checked_cast<const IntegerType&>(index_type).is_signed();
+  if (!index_type_ok) {
+    return Status::TypeError("Dictionary index type should be signed integer, got ",

Review comment:
       I'm not sure about the history (@wesm could tell more), but it's specified here:
   https://arrow.apache.org/docs/format/Columnar.html#dictionary-encoded-layout
   
   > When a field is dictionary encoded, the values are represented by an array of signed integers representing the index of the value in the dictionary. 




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