[BugFix] fix HttpResultWriter ill-formatted json string (backport #54590)

be/src/runtime/http_result_writer.cpp

@@ -53,14 +53,14 @@ void HttpResultWriter::_init_profile() {
 
 // transform one row into json format
 Status HttpResultWriter::_transform_row_to_json(const Columns& result_columns, int idx) {
-    int num_columns = result_columns.size();
+    size_t num_columns = result_columns.size();
 
     _row_str.append("{\"data\":[");
-    for (auto& result_column : result_columns) {
+    for (size_t i = 0; i < num_columns; ++i) {
         std::string row;
-        ASSIGN_OR_RETURN(row, cast_type_to_json_str(result_column, idx));
+        ASSIGN_OR_RETURN(row, cast_type_to_json_str(result_columns[i], idx));
         _row_str.append(row);
-        if (result_column != result_columns[num_columns - 1]) {
+        if (i != num_columns - 1) {
             _row_str.append(",");
         }
     }

be/test/CMakeLists.txt

@@ -328,6 +328,7 @@ set(EXEC_FILES
         ./runtime/decimalv3_test.cpp
         ./runtime/external_scan_context_mgr_test.cpp
         ./runtime/fragment_mgr_test.cpp
+        ./runtime/http_result_writer_test.cpp
         ./runtime/int128_arithmetic_ops_test.cpp
         ./runtime/kafka_consumer_pipe_test.cpp
         ./runtime/lake_tablets_channel_test.cpp

be/test/runtime/http_result_writer_test.cpp

@@ -0,0 +1,108 @@
+// Copyright 2021-present StarRocks, Inc. All rights reserved.
+//
+// Licensed 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
+//
+//     https://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 "runtime/http_result_writer.h"
+
+#include <gtest/gtest.h>
+
+#include <memory>
+
+#include "column/vectorized_fwd.h"
+#include "exprs/column_ref.h"
+#include "runtime/buffer_control_block.h"
+#include "storage/chunk_helper.h"
+#include "testutil/assert.h"
+#include "util/uid_util.h"
+
+namespace starrocks {
+
+static ChunkPtr create_chunk(SchemaPtr schema, int col0value, int col1value) {
+    std::vector<int> c0v{col0value};
+    std::vector<int> c1v{col1value};
+    auto c0 = Int32Column::create();
+    auto c1 = Int32Column::create();
+    c0->append_numbers(c0v.data(), c0v.size() * sizeof(int));
+    c1->append_numbers(c1v.data(), c1v.size() * sizeof(int));
+    auto chunk = std::shared_ptr<Chunk>(new Chunk({c0, c1}, schema));
+    chunk->set_slot_id_to_index(0, 0);
+    chunk->set_slot_id_to_index(1, 1);
+    return chunk;
+}
+
+TEST(HttpResultWriterTest, BasicJsonFormat) {
+    // Mock all the necessary data structures
+    RuntimeState dummy_state;
+    SchemaPtr schema(new Schema());
+    auto c0_field = std::make_shared<Field>(0, "c0", TYPE_INT, true);
+    auto c1_field = std::make_shared<Field>(1, "c1", TYPE_INT, true);
+    schema->append(c0_field);
+    schema->append(c1_field);
+    auto c0ref = std::make_unique<ColumnRef>(TypeDescriptor(TYPE_INT), 0);
+    auto c1ref = std::make_unique<ColumnRef>(TypeDescriptor(TYPE_INT), 1);
+    std::vector<std::unique_ptr<ExprContext>> managed_expr_ctxs;
+    std::vector<ExprContext*> expr_ctxs;
+    // create c0/c1 ExprContext
+    managed_expr_ctxs.emplace_back(std::make_unique<ExprContext>(c0ref.get()));
+    expr_ctxs.push_back(managed_expr_ctxs.back().get());
+    managed_expr_ctxs.emplace_back(std::make_unique<ExprContext>(c1ref.get()));
+    expr_ctxs.push_back(managed_expr_ctxs.back().get());
+    ASSERT_OK(Expr::prepare(expr_ctxs, &dummy_state));
+    ASSERT_OK(Expr::open(expr_ctxs, &dummy_state));
+
+    TUniqueId uuid(generate_uuid());
+    RuntimeProfile dummy_profile{"dummy"};
+    auto sinker = std::make_unique<BufferControlBlock>(uuid, 100 * 1024);
+
+    // create the writer
+    HttpResultWriter writer(sinker.get(), expr_ctxs, &dummy_profile, TResultSinkFormatType::type::JSON);
+    writer.init(&dummy_state);
+
+    // generate a chunk with [1,1], check the output json
+    {
+        auto chunk = create_chunk(schema, 1, 1);
+        auto result = writer.process_chunk(chunk.get());
+        EXPECT_TRUE(result.ok()) << result.status();
+        auto resultPtrs = std::move(result.value());
+        EXPECT_EQ(1L, resultPtrs.size());
+        EXPECT_EQ(1L, resultPtrs[0]->result_batch.rows.size());
+        EXPECT_EQ("{\"data\":[1,1]}\n", resultPtrs[0]->result_batch.rows[0]);
+    }
+    // generate a chunk with [2,1], check the output json
+    {
+        auto chunk = create_chunk(schema, 2, 1);
+        auto result = writer.process_chunk(chunk.get());
+        EXPECT_TRUE(result.ok()) << result.status();
+        auto resultPtrs = std::move(result.value());
+        EXPECT_EQ(1L, resultPtrs.size());
+        EXPECT_EQ(1L, resultPtrs[0]->result_batch.rows.size());
+        EXPECT_EQ("{\"data\":[2,1]}\n", resultPtrs[0]->result_batch.rows[0]);
+    }
+    // generate a chunk with reuse of the result columns
+    // `SELECT count(*) as A, count(*) as B FROM t`
+    {
+        std::vector<int> c0v{10};
+        auto c0 = Int32Column::create();
+        c0->append_numbers(c0v.data(), c0v.size() * sizeof(int));
+        auto chunk = std::shared_ptr<Chunk>(new Chunk({c0, c0}, schema));
+        chunk->set_slot_id_to_index(0, 0);
+        chunk->set_slot_id_to_index(1, 1);
+        auto result = writer.process_chunk(chunk.get());
+        EXPECT_TRUE(result.ok()) << result.status();
+        auto resultPtrs = std::move(result.value());
+        EXPECT_EQ(1L, resultPtrs.size());
+        EXPECT_EQ(1L, resultPtrs[0]->result_batch.rows.size());
+        EXPECT_EQ("{\"data\":[10,10]}\n", resultPtrs[0]->result_batch.rows[0]);
+    }
+}
+} // namespace starrocks