[GitHub] [arrow] lidavidm commented on a change in pull request #11849: ARROW-14905: [C++] Enable CSV Writer to handle quoting

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

lidavidm commented on a change in pull request #11849:
URL: https://github.com/apache/arrow/pull/11849#discussion_r766875020



##########
File path: cpp/src/arrow/csv/writer.cc
##########
@@ -155,27 +161,64 @@ class UnquotedColumnPopulator : public ColumnPopulator {
     return Status::OK();
   }
 
-  void PopulateColumns(char* output, int32_t* offsets) const override {
-    VisitArrayDataInline<StringType>(
-        *casted_array_->data(),
-        [&](arrow::util::string_view s) {
-          int32_t next_column_offset = static_cast<int32_t>(s.length()) + /*end_char*/ 1;
-          memcpy((output + *offsets - next_column_offset), s.data(), s.length());
-          *(output + *offsets - 1) = end_char_;
-          *offsets -= next_column_offset;
-          offsets++;
-        },
-        [&]() {
-          // For nulls, the configured null value string is copied into the output.
-          int32_t next_column_offset =
-              static_cast<int32_t>(null_string_->size()) + /*end_char*/ 1;
-          memcpy((output + *offsets - next_column_offset), null_string_->data(),
-                 null_string_->size());
-          *(output + *offsets - 1) = end_char_;
-          *offsets -= next_column_offset;
-          offsets++;
-        });
+  Status PopulateColumns(char* output, int32_t* offsets) const override {
+    // Function applied to valid values cast to string.
+    auto valid_function = [&](arrow::util::string_view s) {
+      int32_t next_column_offset = static_cast<int32_t>(s.length()) + /*end_char*/ 1;
+      memcpy((output + *offsets - next_column_offset), s.data(), s.length());
+      *(output + *offsets - 1) = end_char_;
+      *offsets -= next_column_offset;
+      offsets++;
+      return Status::OK();
+    };
+
+    // Function applied to null values cast to string.
+    auto null_function = [&]() {
+      // For nulls, the configured null value string is copied into the output.
+      int32_t next_column_offset =
+          static_cast<int32_t>(null_string_->size()) + /*end_char*/ 1;
+      memcpy((output + *offsets - next_column_offset), null_string_->data(),
+             null_string_->size());
+      *(output + *offsets - 1) = end_char_;
+      *offsets -= next_column_offset;
+      offsets++;
+      return Status::OK();
+    };
+
+    if (reject_values_with_quotes_) {
+      // When using this UnquotedColumnPopulator on values that, after casting, could
+      // produce quotes, we need to return an error in accord with RFC4180. We need to
+      // precede valid_func with a check.
+      return VisitArrayDataInline<StringType>(
+          *casted_array_->data(),
+          [&](arrow::util::string_view s) {
+            ARROW_RETURN_NOT_OK(CheckStringHasNoStructuralChars(s));
+            return valid_function(s);
+          },
+          null_function);
+    } else {
+      // Populate without checking and rejecting values with quotes.
+      return VisitArrayDataInline<StringType>(*casted_array_->data(), valid_function,
+                                              null_function);
+    }
+  }
+
+ private:
+  // Returns an error status if s has any structural characters.
+  static Status CheckStringHasNoStructuralChars(const util::string_view& s) {
+    if (std::any_of(s.begin(), s.end(), [](const char& c) {

Review comment:
       I filed ARROW-15064 so we don't forget this, though we need writer benchmarks (ARROW-14993).




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