feat(ipc): Support run-end encoded arrays in the IPC reader

src/nanoarrow/ipc/decoder.c

@@ -1203,6 +1203,22 @@ static int ArrowIpcDecoderSetTypeUnion(struct ArrowSchema* schema,
   return ArrowIpcDecoderSetTypeSimpleNested(schema, union_types_str, error);
 }
 
+static int ArrowIpcDecoderSetTypeRunEndEncoded(struct ArrowSchema* schema,
+                                               int64_t n_children,
+                                               struct ArrowError* error) {
+  // The RunEndEncoded type table has no parameters: the run ends and values
+  // types are carried by its two children (run_ends, then values)
+  if (n_children != 2) {
+    ArrowErrorSet(error,
+                  "Expected RunEndEncoded field to have exactly two children but found "
+                  "%" PRId64,
+                  n_children);
+    return EINVAL;
+  }
+
+  return ArrowIpcDecoderSetTypeSimpleNested(schema, "+r", error);
+}
+
 static int ArrowIpcDecoderSetType(struct ArrowSchema* schema, ns(Field_table_t) field,
                                   int64_t n_children, struct ArrowError* error) {
   ns(Type_union_type_t) type_type = ns(Field_type_type(field));
@@ -1266,8 +1282,7 @@ static int ArrowIpcDecoderSetType(struct ArrowSchema* schema, ns(Field_table_t)
     case ns(Type_Union):
       return ArrowIpcDecoderSetTypeUnion(schema, type, n_children, error);
     case ns(Type_RunEndEncoded):
-      ArrowErrorSet(error, "RunEndEncoded not yet supported in IPC reader");
-      return ENOTSUP;
+      return ArrowIpcDecoderSetTypeRunEndEncoded(schema, n_children, error);
     default:
       ArrowErrorSet(error, "Unrecognized Field type with value %d", type_type);
       return EINVAL;

src/nanoarrow/ipc/decoder_test.cc

@@ -2039,6 +2039,10 @@ INSTANTIATE_TEST_SUITE_P(
         arrow::dense_union({arrow::field("col1", arrow::int32()),
                             arrow::field("col2", arrow::utf8())},
                            {126, 127}),
+        // Run-end encoded
+        arrow::run_end_encoded(arrow::int16(), arrow::utf8()),
+        arrow::run_end_encoded(arrow::int32(), arrow::int64()),
+        arrow::run_end_encoded(arrow::int64(), arrow::float64()),
 
         // Type with nested metadata
         arrow::list(arrow::field("some_custom_name", arrow::int32(),

src/nanoarrow/ipc/files_test.cc

@@ -620,7 +620,7 @@ INSTANTIATE_TEST_SUITE_P(
         TestFile::OK("cpp-21.0.0/generated_nested_dictionary.stream"),
         TestFile::NotSupported("cpp-21.0.0/generated_list_view.stream"),
         TestFile::NotSupported("cpp-21.0.0/generated_binary_view.stream"),
-        TestFile::NotSupported("cpp-21.0.0/generated_run_end_encoded.stream")
+        TestFile::OK("cpp-21.0.0/generated_run_end_encoded.stream")
         // Comment to keep line from wrapping
         ));