[GitHub] [arrow-nanoarrow] lidavidm commented on a diff in pull request #61: Proof-of-concept IPC reader/writer

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

lidavidm commented on code in PR #61:
URL: https://github.com/apache/arrow-nanoarrow/pull/61#discussion_r1002158637


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extensions/nanoarrow_ipc/src/nanoarrow_ipc/nanoarrow_ipc.h:
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@@ -0,0 +1,153 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#ifndef NANOARROW_NANOARROW_IPC_H_INCLUDED
+#define NANOARROW_NANOARROW_IPC_H_INCLUDED
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Extra guard for versions of Arrow without the canonical guard
+#ifndef ARROW_FLAG_DICTIONARY_ORDERED
+
+/// \defgroup nanoarrow-arrow-cdata
+///
+/// The Arrow C Data (https://arrow.apache.org/docs/format/CDataInterface.html)
+/// and Arrow C Stream (https://arrow.apache.org/docs/format/CStreamInterface.html)
+/// interfaces are part of the
+/// Arrow Columnar Format specification
+/// (https://arrow.apache.org/docs/format/Columnar.html). See the Arrow documentation for
+/// documentation of these structures.
+///
+/// @{
+
+#ifndef ARROW_C_DATA_INTERFACE
+#define ARROW_C_DATA_INTERFACE
+
+#define ARROW_FLAG_DICTIONARY_ORDERED 1
+#define ARROW_FLAG_NULLABLE 2
+#define ARROW_FLAG_MAP_KEYS_SORTED 4
+
+struct ArrowSchema {
+  // Array type description
+  const char* format;
+  const char* name;
+  const char* metadata;
+  int64_t flags;
+  int64_t n_children;
+  struct ArrowSchema** children;
+  struct ArrowSchema* dictionary;
+
+  // Release callback
+  void (*release)(struct ArrowSchema*);
+  // Opaque producer-specific data
+  void* private_data;
+};
+
+struct ArrowArray {
+  // Array data description
+  int64_t length;
+  int64_t null_count;
+  int64_t offset;
+  int64_t n_buffers;
+  int64_t n_children;
+  const void** buffers;
+  struct ArrowArray** children;
+  struct ArrowArray* dictionary;
+
+  // Release callback
+  void (*release)(struct ArrowArray*);
+  // Opaque producer-specific data
+  void* private_data;
+};
+
+#endif  // ARROW_C_DATA_INTERFACE
+
+#ifndef ARROW_C_STREAM_INTERFACE
+#define ARROW_C_STREAM_INTERFACE
+
+struct ArrowArrayStream {
+  // Callback to get the stream type
+  // (will be the same for all arrays in the stream).
+  //
+  // Return value: 0 if successful, an `errno`-compatible error code otherwise.
+  //
+  // If successful, the ArrowSchema must be released independently from the stream.
+  int (*get_schema)(struct ArrowArrayStream*, struct ArrowSchema* out);
+
+  // Callback to get the next array
+  // (if no error and the array is released, the stream has ended)
+  //
+  // Return value: 0 if successful, an `errno`-compatible error code otherwise.
+  //
+  // If successful, the ArrowArray must be released independently from the stream.
+  int (*get_next)(struct ArrowArrayStream*, struct ArrowArray* out);
+
+  // Callback to get optional detailed error information.
+  // This must only be called if the last stream operation failed
+  // with a non-0 return code.
+  //
+  // Return value: pointer to a null-terminated character array describing
+  // the last error, or NULL if no description is available.
+  //
+  // The returned pointer is only valid until the next operation on this stream
+  // (including release).
+  const char* (*get_last_error)(struct ArrowArrayStream*);
+
+  // Release callback: release the stream's own resources.
+  // Note that arrays returned by `get_next` must be individually released.
+  void (*release)(struct ArrowArrayStream*);
+
+  // Opaque producer-specific data
+  void* private_data;
+};
+
+#endif  // ARROW_C_STREAM_INTERFACE
+#endif  // ARROW_FLAG_DICTIONARY_ORDERED
+
+#ifdef __cplusplus
+}
+#endif
+
+typedef int ArrowIpcErrorCode;
+
+struct ArrowIpcIO {

Review Comment:
   An alternative might be a push-based API, like [StreamDecoder](https://github.com/apache/arrow/blob/4ce64537e5ee223bf5eea91284efc46f214d6c76/cpp/src/arrow/ipc/reader.h#L309)? (Except maybe instead of a callback, require the user to poll the reader object)



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