Allow data in square brackets in JSONAsString format

src/Formats/FormatFactory.cpp

@@ -162,14 +162,12 @@ InputFormatPtr FormatFactory::getInput(
     if (settings.max_memory_usage_for_user && settings.min_chunk_bytes_for_parallel_parsing * settings.max_threads * 2 > settings.max_memory_usage_for_user)
         parallel_parsing = false;
 
-    if (parallel_parsing && name == "JSONEachRow")
+    if (parallel_parsing)
     {
-        /// FIXME ParallelParsingBlockInputStream doesn't support formats with non-trivial readPrefix() and readSuffix()
-
-        /// For JSONEachRow we can safely skip whitespace characters
-        skipWhitespaceIfAny(buf);
-        if (buf.eof() || *buf.position() == '[')
-            parallel_parsing = false; /// Disable it for JSONEachRow if data is in square brackets (see JSONEachRowRowInputFormat)
+        const auto & non_trivial_prefix_and_suffix_checker = getCreators(name).non_trivial_prefix_and_suffix_checker;
+        /// Disable parallel parsing for input formats with non-trivial readPrefix() and readSuffix().
+        if (non_trivial_prefix_and_suffix_checker && non_trivial_prefix_and_suffix_checker(buf))
+            parallel_parsing = false;
     }
 
     if (parallel_parsing)
@@ -396,6 +394,14 @@ void FormatFactory::registerInputFormatProcessor(const String & name, InputProce
     target = std::move(input_creator);
 }
 
+void FormatFactory::registerNonTrivialPrefixAndSuffixChecker(const String & name, NonTrivialPrefixAndSuffixChecker non_trivial_prefix_and_suffix_checker)
+{
+    auto & target = dict[name].non_trivial_prefix_and_suffix_checker;
+    if (target)
+        throw Exception("FormatFactory: Non trivial prefix and suffix checker " + name + " is already registered", ErrorCodes::LOGICAL_ERROR);
+    target = std::move(non_trivial_prefix_and_suffix_checker);
+}
+
 void FormatFactory::registerOutputFormatProcessor(const String & name, OutputProcessorCreator output_creator)
 {
     auto & target = dict[name].output_processor_creator;

src/Formats/FormatFactory.h

@@ -93,6 +93,11 @@ private:
             const RowOutputFormatParams & params,
             const FormatSettings & settings)>;
 
+    /// Some input formats can have non trivial readPrefix() and readSuffix(),
+    /// so in some cases there is no possibility to use parallel parsing.
+    /// The checker should return true if parallel parsing should be disabled.
+    using NonTrivialPrefixAndSuffixChecker = std::function<bool(ReadBuffer & buf)>;
+
     struct Creators
     {
         InputCreator input_creator;
@@ -102,6 +107,7 @@ private:
         FileSegmentationEngine file_segmentation_engine;
         bool supports_parallel_formatting{false};
         bool is_column_oriented{false};
+        NonTrivialPrefixAndSuffixChecker non_trivial_prefix_and_suffix_checker;
     };
 
     using FormatsDictionary = std::unordered_map<String, Creators>;
@@ -166,6 +172,8 @@ public:
     void registerOutputFormat(const String & name, OutputCreator output_creator);
     void registerFileSegmentationEngine(const String & name, FileSegmentationEngine file_segmentation_engine);
 
+    void registerNonTrivialPrefixAndSuffixChecker(const String & name, NonTrivialPrefixAndSuffixChecker non_trivial_prefix_and_suffix_checker);
+
     void registerInputFormatProcessor(const String & name, InputProcessorCreator input_creator);
     void registerOutputFormatProcessor(const String & name, OutputProcessorCreator output_creator);
 

src/Formats/JSONEachRowUtils.cpp

@@ -83,4 +83,11 @@ std::pair<bool, size_t> fileSegmentationEngineJSONEachRowImpl(ReadBuffer & in, D
     return {loadAtPosition(in, memory, pos), number_of_rows};
 }
 
+bool nonTrivialPrefixAndSuffixCheckerJSONEachRowImpl(ReadBuffer & buf)
+{
+    /// For JSONEachRow we can safely skip whitespace characters
+    skipWhitespaceIfAny(buf);
+    return buf.eof() || *buf.position() == '[';
+}
+
 }

src/Formats/JSONEachRowUtils.h

@@ -5,4 +5,6 @@ namespace DB
 
 std::pair<bool, size_t> fileSegmentationEngineJSONEachRowImpl(ReadBuffer & in, DB::Memory<> & memory, size_t min_chunk_size);
 
+bool nonTrivialPrefixAndSuffixCheckerJSONEachRowImpl(ReadBuffer & buf);
+
 }

src/Formats/registerFormats.cpp

@@ -79,6 +79,9 @@ void registerInputFormatProcessorJSONAsString(FormatFactory & factory);
 void registerInputFormatProcessorLineAsString(FormatFactory & factory);
 void registerInputFormatProcessorCapnProto(FormatFactory & factory);
 
+/// Non trivial prefix and suffix checkers for disabling parallel parsing.
+void registerNonTrivialPrefixAndSuffixCheckerJSONEachRow(FormatFactory & factory);
+void registerNonTrivialPrefixAndSuffixCheckerJSONAsString(FormatFactory & factory);
 
 void registerFormats()
 {
@@ -152,6 +155,9 @@ void registerFormats()
 #if !defined(ARCADIA_BUILD)
     registerInputFormatProcessorCapnProto(factory);
 #endif
+
+    registerNonTrivialPrefixAndSuffixCheckerJSONEachRow(factory);
+    registerNonTrivialPrefixAndSuffixCheckerJSONAsString(factory);
 }
 
 }

src/Processors/Formats/Impl/JSONAsStringRowInputFormat.cpp

@@ -34,6 +34,35 @@ void JSONAsStringRowInputFormat::resetParser()
     buf.reset();
 }
 
+void JSONAsStringRowInputFormat::readPrefix()
+{
+    /// In this format, BOM at beginning of stream cannot be confused with value, so it is safe to skip it.
+    skipBOMIfExists(buf);
+
+    skipWhitespaceIfAny(buf);
+    if (!buf.eof() && *buf.position() == '[')
+    {
+        ++buf.position();
+        data_in_square_brackets = true;
+    }
+}
+
+void JSONAsStringRowInputFormat::readSuffix()
+{
+    skipWhitespaceIfAny(buf);
+    if (data_in_square_brackets)
+    {
+        assertChar(']', buf);
+        skipWhitespaceIfAny(buf);
+    }
+    if (!buf.eof() && *buf.position() == ';')
+    {
+        ++buf.position();
+        skipWhitespaceIfAny(buf);
+    }
+    assertEOF(buf);
+}
+
 void JSONAsStringRowInputFormat::readJSONObject(IColumn & column)
 {
     PeekableReadBufferCheckpoint checkpoint{buf};
@@ -113,7 +142,23 @@ void JSONAsStringRowInputFormat::readJSONObject(IColumn & column)
 
 bool JSONAsStringRowInputFormat::readRow(MutableColumns & columns, RowReadExtension &)
 {
+    if (!allow_new_rows)
+        return false;
+
     skipWhitespaceIfAny(buf);
+    if (!buf.eof())
+    {
+        if (!data_in_square_brackets && *buf.position() == ';')
+        {
+            /// ';' means the end of query, but it cannot be before ']'.
+            return allow_new_rows = false;
+        }
+        else if (data_in_square_brackets && *buf.position() == ']')
+        {
+            /// ']' means the end of query.
+            return allow_new_rows = false;
+        }
+    }
 
     if (!buf.eof())
         readJSONObject(*columns[0]);
@@ -143,4 +188,9 @@ void registerFileSegmentationEngineJSONAsString(FormatFactory & factory)
     factory.registerFileSegmentationEngine("JSONAsString", &fileSegmentationEngineJSONEachRowImpl);
 }
 
+void registerNonTrivialPrefixAndSuffixCheckerJSONAsString(FormatFactory & factory)
+{
+    factory.registerNonTrivialPrefixAndSuffixChecker("JSONAsString", nonTrivialPrefixAndSuffixCheckerJSONEachRowImpl);
+}
+
 }

src/Processors/Formats/Impl/JSONAsStringRowInputFormat.h

@@ -22,10 +22,17 @@ public:
     String getName() const override { return "JSONAsStringRowInputFormat"; }
     void resetParser() override;
 
+    void readPrefix() override;
+    void readSuffix() override;
+
 private:
     void readJSONObject(IColumn & column);
 
     PeekableReadBuffer buf;
+
+    /// This flag is needed to know if data is in square brackets.
+    bool data_in_square_brackets = false;
+    bool allow_new_rows = true;
 };
 
 }

src/Processors/Formats/Impl/JSONEachRowRowInputFormat.cpp

@@ -359,4 +359,10 @@ void registerFileSegmentationEngineJSONEachRow(FormatFactory & factory)
     factory.registerFileSegmentationEngine("JSONStringsEachRow", &fileSegmentationEngineJSONEachRowImpl);
 }
 
+void registerNonTrivialPrefixAndSuffixCheckerJSONEachRow(FormatFactory & factory)
+{
+    factory.registerNonTrivialPrefixAndSuffixChecker("JSONEachRow", nonTrivialPrefixAndSuffixCheckerJSONEachRowImpl);
+    factory.registerNonTrivialPrefixAndSuffixChecker("JSONStringsEachRow", nonTrivialPrefixAndSuffixCheckerJSONEachRowImpl);
+}
+
 }

tests/queries/0_stateless/01232_json_as_string_format.sh

@@ -28,21 +28,59 @@ echo '
     "array" : [3, 2, 1],
     "map" : {
         "z" : 1,
-        "y" : 2, 
+        "y" : 2,
         "x" : 3
     }
 }
 {
-    "id" : 3, 
-    "date" : "01.03.2020", 
-    "string" : "one more string", 
-    "array" : [3,1,2], 
+    "id" : 3,
+    "date" : "01.03.2020",
+    "string" : "one more string",
+    "array" : [3,1,2],
     "map" : {
-        "{" : 1, 
+        "{" : 1,
         "}}" : 2
     }
 }' | $CLICKHOUSE_CLIENT --query="INSERT INTO json_as_string FORMAT JSONAsString";
 
+echo '
+[
+    {
+        "id" : 1,
+        "date" : "01.01.2020",
+        "string" : "123{{{\"\\",
+        "array" : [1, 2, 3],
+        "map": {
+            "a" : 1,
+            "b" : 2,
+            "c" : 3
+        }
+    },
+    {
+        "id" : 2,
+        "date" : "01.02.2020",
+        "string" : "{another\"
+        string}}",
+        "array" : [3, 2, 1],
+        "map" : {
+            "z" : 1,
+            "y" : 2,
+            "x" : 3
+        }
+    }
+    {
+        "id" : 3,
+        "date" : "01.03.2020",
+        "string" : "one more string",
+        "array" : [3,1,2],
+        "map" : {
+            "{" : 1,
+            "}}" : 2
+        }
+    }
+]' | $CLICKHOUSE_CLIENT --query="INSERT INTO json_as_string FORMAT JSONAsString";
+
+
 $CLICKHOUSE_CLIENT --query="SELECT * FROM json_as_string";
 $CLICKHOUSE_CLIENT --query="DROP TABLE json_as_string"
 

tests/queries/0_stateless/01925_json_as_string_data_in_square_brackets.reference

@@ -0,0 +1,2 @@
+{"id": 1, "name": "name1"}
+{"id": 2, "name": "name2"}

tests/queries/0_stateless/01925_json_as_string_data_in_square_brackets.sql

@@ -0,0 +1,9 @@
+DROP TABLE IF EXISTS json_square_brackets;
+CREATE TABLE json_square_brackets (field String) ENGINE = Memory;
+INSERT INTO json_square_brackets FORMAT JSONAsString [{"id": 1, "name": "name1"}, {"id": 2, "name": "name2"}];
+INSERT INTO json_square_brackets FORMAT JSONAsString[];
+INSERT INTO json_square_brackets FORMAT JSONAsString [  ]  ;
+INSERT INTO json_square_brackets FORMAT JSONEachRow ;
+
+SELECT * FROM json_square_brackets;
+DROP TABLE IF EXISTS json_square_brackets;

tests/queries/0_stateless/01926_json_as_string_array.reference

@@ -0,0 +1 @@
+1000000

tests/queries/0_stateless/01926_json_as_string_array.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+set -e
+
+CUR_DIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+# shellcheck source=../shell_config.sh
+. "$CUR_DIR"/../shell_config.sh
+
+${CLICKHOUSE_LOCAL} --query "SELECT '[' || arrayStringConcat(arrayMap(x -> '{\"id\": 1, \"name\": \"name1\"}', range(1000000)), ',') || ']'" | ${CLICKHOUSE_LOCAL} --query "SELECT count() FROM table" --input-format JSONAsString --structure 'field String'