[GitHub] [arrow-adbc] lidavidm commented on a diff in pull request #65: [C] Basic libpq-based driver

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

lidavidm commented on code in PR #65:
URL: https://github.com/apache/arrow-adbc/pull/65#discussion_r946050839


##########
c/drivers/postgres/statement.cc:
##########
@@ -0,0 +1,283 @@
+// 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.
+
+#include "statement.h"
+
+#include <netinet/in.h>
+#include <cerrno>
+#include <cstring>
+#include <iostream>
+#include <memory>
+#include <vector>
+
+#include <adbc.h>
+#include <libpq-fe.h>
+#include <nanoarrow.h>
+
+#include "connection.h"
+#include "util.h"
+
+namespace adbcpq {
+
+namespace {
+/// \brief An ArrowArrayStream that reads tuples from a PGresult.
+class TupleReader {
+ public:
+  explicit TupleReader(PGresult* result) : result_(result) {}
+
+  int GetSchema(struct ArrowSchema* out) {
+    std::memset(out, 0, sizeof(*out));
+    const int num_fields = PQnfields(result_);
+    NA_RETURN_NOT_OK(ArrowSchemaInit(out, NANOARROW_TYPE_STRUCT));
+    NA_RETURN_NOT_OK(ArrowSchemaAllocateChildren(out, num_fields));
+    for (int i = 0; i < num_fields; i++) {
+      ArrowType field_type = NANOARROW_TYPE_NA;
+      const Oid pg_type = PQftype(result_, i);
+      switch (pg_type) {
+        // TODO: at startup, query pg_type to build up this mapping instead of hardcoding
+        // it
+        case 16:  // BOOLOID
+          field_type = NANOARROW_TYPE_BOOL;
+          break;
+        case 20:  // INT8OID
+          field_type = NANOARROW_TYPE_INT64;
+          break;
+        case 21:  // INT2OID
+          field_type = NANOARROW_TYPE_INT16;
+          break;
+        case 23:  // INT4OID
+          field_type = NANOARROW_TYPE_INT32;
+          break;
+        default:
+          last_error_ =
+              StringBuilder("[libpq] Column #", i + 1, " (\"", PQfname(result_, i),
+                            "\") has unknown type code ", pg_type);
+          return ENOTSUP;
+      }
+      NA_RETURN_NOT_OK(ArrowSchemaInit(out->children[i], field_type));
+      NA_RETURN_NOT_OK(ArrowSchemaSetName(out->children[i], PQfname(result_, i)));
+    }
+
+    NA_RETURN_NOT_OK(ArrowSchemaDeepCopy(out, &schema_));
+    return 0;
+  }
+
+  int GetNext(struct ArrowArray* out) {
+    if (!result_) {
+      out->release = nullptr;
+      return 0;
+    }
+
+    const int num_rows = PQntuples(result_);
+
+    NA_RETURN_NOT_OK(ArrowArrayInit(out, NANOARROW_TYPE_STRUCT));
+    NA_RETURN_NOT_OK(ArrowArrayAllocateChildren(out, schema_.n_children));
+
+    std::vector<struct ArrowSchemaView> fields(schema_.n_children);
+
+    for (int col = 0; col < schema_.n_children; col++) {
+      NA_RETURN_NOT_OK(ArrowSchemaViewInit(&fields[col], schema_.children[col], nullptr));
+      NA_RETURN_NOT_OK(ArrowArrayInit(out->children[col], fields[col].data_type));
+      NA_RETURN_NOT_OK(
+          ArrowBitmapReserve(ArrowArrayValidityBitmap(out->children[col]), num_rows));
+      switch (fields[col].data_type) {
+        case NANOARROW_TYPE_INT32:
+          NA_RETURN_NOT_OK(ArrowBufferReserve(ArrowArrayBuffer(out->children[col], 1),
+                                              num_rows * sizeof(int32_t)));
+          break;
+        default:
+          last_error_ = StringBuilder("[libpq] Column #", col + 1, " (\"",
+                                      schema_.children[col]->name,
+                                      "\") has unsupported type ", fields[col].data_type);
+          return ENOTSUP;
+      }
+    }
+
+    for (int row = 0; row < num_rows; row++) {
+      for (int col = 0; col < schema_.n_children; col++) {
+        struct ArrowBitmap* bitmap = ArrowArrayValidityBitmap(out->children[col]);
+        NA_RETURN_NOT_OK(ArrowBitmapAppend(bitmap, !PQgetisnull(result_, row, col), 1));
+
+        switch (fields[col].data_type) {
+          case NANOARROW_TYPE_INT32: {
+            struct ArrowBuffer* buffer = ArrowArrayBuffer(out->children[col], 1);
+            // TODO: assert PQgetlength is 4
+            NA_RETURN_NOT_OK(ArrowBufferAppendInt32(
+                buffer, ntohl(*(reinterpret_cast<int*>(PQgetvalue(result_, row, col))))));
+            break;
+          }
+          default:
+            last_error_ = StringBuilder(
+                "[libpq] Column #", col + 1, " (\"", schema_.children[col]->name,
+                "\") has unsupported type ", fields[col].data_type);
+            return ENOTSUP;
+        }
+      }
+    }
+
+    for (int col = 0; col < schema_.n_children; col++) {
+      NA_RETURN_NOT_OK(ArrowArrayFinishBuilding(out->children[col], 0));
+      out->children[col]->length = num_rows;
+    }
+    NA_RETURN_NOT_OK(ArrowArrayFinishBuilding(out, 0));
+    out->length = num_rows;
+
+    Release();
+    return 0;
+  }
+
+  const char* last_error() const { return last_error_.c_str(); }
+
+  void Release() {
+    if (result_) {
+      PQclear(result_);
+      result_ = nullptr;
+    }
+    if (schema_.release) {
+      schema_.release(&schema_);
+      schema_.release = nullptr;

Review Comment:
   Fixed - thanks for catching that!



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