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GH-51470: [C++] Delimit JSON documents without parsing them #51472

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Merged
pitrou merged 2 commits into from
Sep 28, 2026
Merged

GH-51470: [C++] Delimit JSON documents without parsing them #51472

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8bcb93c
[C++] Delimit JSON documents without parsing them
taepper Sep 23, 2026
333f4fe
keep the structure more similar to the previous version
taepper Sep 23, 2026
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21 changes: 6 additions & 15 deletions cpp/src/arrow/json/chunker.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -42,17 +42,8 @@ int64_t ConsumeWhitespace(std::string_view view) {
return static_cast<int64_t>(ws_count);
}

Status ConsumeDocument(simdjson::ondemand::document_stream::iterator& it) {
ARROW_ASSIGN_OR_RAISE(
auto document, internal::ResolveSimdjsonResult(*it, "Failed to get JSON document"));
ARROW_ASSIGN_OR_RAISE(
auto value,
internal::ResolveSimdjsonResult(document.get_value(), "Failed to get JSON value"));
return internal::ConsumeJsonValue(value);
}

// A BoundaryFinder implementation that assumes JSON objects can contain raw newlines,
// and uses actual JSON parsing to delimit them.
// and uses the structural indexes computed by simdjson to delimit them.
class ParsingBoundaryFinder : public BoundaryFinder {
public:
explicit ParsingBoundaryFinder(MemoryPool* pool) : pool_(pool) {}
Expand Down Expand Up @@ -122,8 +113,8 @@ class ParsingBoundaryFinder : public BoundaryFinder {
}

// Find the first or last JSON object (depending on `find_last`)
// and return the consumed JSON byte length, or 0 if no valid document
// can be parsed.
// and return the consumed JSON byte length, or 0 if no complete document
// can be found.
Result<size_t> FindDocument(simdjson::padded_string_view input, bool find_last) {
simdjson::ondemand::document_stream stream;
// XXX Should be pass a specific batch_size?
Expand All @@ -137,8 +128,8 @@ class ParsingBoundaryFinder : public BoundaryFinder {

int64_t consumed_length = 0;
if (!find_last) {
// Parsing the first document only.
if (!ConsumeDocument(it).ok()) {
// Delimiting the first document only.
if (it.error()) {
// Could be either a partial document or invalid JSON, we'll let
// followup chunker or parser calls decide.
return 0;
Expand All @@ -148,7 +139,7 @@ class ParsingBoundaryFinder : public BoundaryFinder {
consumed_length = it.current_index() + it.source().size();
} else {
while (it != stream.end()) {
if (!ConsumeDocument(it).ok()) {
if (it.error()) {
// Could be either a partial document or invalid JSON, we'll let
// followup chunker or parser calls decide.
break;
Expand Down
9 changes: 1 addition & 8 deletions cpp/src/arrow/json/reader_test.cc
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Expand Up @@ -743,16 +743,9 @@ TEST_P(StreamingReaderTest, PropagateErrorsNonLinewiseChunker) {
read_options_.block_size = 10;
parse_options_.newlines_in_values = true;

ASSERT_OK_AND_ASSIGN(reader, MakeReader(bad_first_block));
AssertReadNext(reader, &batch);
EXPECT_EQ(reader->bytes_processed(), 7);
ASSERT_BATCHES_EQUAL(*RecordBatchFromJSON(test_schema, "[{\"i\":0}]"), *batch);

EXPECT_RAISES_WITH_MESSAGE_THAT(Invalid,
::testing::StartsWith("Invalid: JSON parse error"),
reader->ReadNext(&batch));
EXPECT_EQ(reader->bytes_processed(), 7);
AssertReadEnd(reader);
MakeReader(bad_first_block));

ASSERT_OK_AND_ASSIGN(reader, MakeReader(bad_middle_blocks));
AssertReadNext(reader, &batch);
Expand Down
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