[ASTERIXDB-2877] Fix multi-byte character handling in CSV output

[ongdisheng]

Description

There are two bugs in writeUTF8StringAsCSV in PrintTools.java:

1. Incorrect loop step in the quoting scan:
   The loop that checks whether a string needs quoting advanced one byte at a time (i++). Since multi-byte characters span 2 to 4 bytes, this might actually cause charAt() to be called at offsets pointing to the middle of a character.

2. Incorrect character writing:
   Characters were written using PrintStream.print(char), which converts the char through the platform default charset before writing. For multi-byte characters such as é and CJK characters (e.g. 中), this re-encoding could produce incorrect bytes if the platform default charset is not UTF-8. Writing the raw UTF-8 bytes directly from the array is always correct regardless of platform.

Fix

Added a fix for the quoting scan loop so that it now advances by UTF8StringUtil.charSize() per iteration and charAt() is always called at a valid character boundary. Characters are now written as raw UTF-8 bytes directly, which is also consistent with how writeUTF8StringAsJSON already handles the same data.

How to Reproduce and Verify

Setup

disheng@LAPTOP-UPFH5KC9:~/asterixdb$ curl --data-urlencode 'statement=
DROP DATAVERSE test IF EXISTS;
CREATE DATAVERSE test;
USE test;
CREATE TYPE TweetType AS { id: int, text: string };
CREATE DATASET tweets(TweetType) PRIMARY KEY id;
' "http://localhost:19002/query/service"

disheng@LAPTOP-UPFH5KC9:~/asterixdb$ curl --data-urlencode 'statement=
USE test;                                                       
INSERT INTO tweets ({"id": 1, "text": "@ScapegoatHelp Walked out on being scapegoated again. Saw Narcs mask slip & that sneer. No more 💪🦋"});
' "http://localhost:19002/query/service"

Before fix

disheng@LAPTOP-UPFH5KC9:~/asterixdb$ curl --data-urlencode "statement=USE test; SELECT text FROM tweets;"      "http://localhost:19002/query/service"
{
        "requestID": "3056c5df-fb14-4ff8-90b6-dcc62662a563",
        "signature": {
                "*": "*"
        },
        "results": [ {"text":"@ScapegoatHelp Walked out on being scapegoated again. Saw Narcs mask slip & that sneer. No more 💪🦋"} ]
        ,
        "plans":{},
        "status": "success",
        "metrics": {
                "elapsedTime": "28.199702ms",
                "executionTime": "26.761674ms",
                "compileTime": "10.872533ms",
                "queueWaitTime": "0ns",
                "resultCount": 1,
                "resultSize": 111,
                "processedObjects": 1
        }
}
disheng@LAPTOP-UPFH5KC9:~/asterixdb$ curl --data-urlencode "statement=USE test; SELECT text FROM tweets;"      "http://localhost:19002/query/service?format=csv&header=absent"
{
        "requestID": "6bbf0b3d-05a3-43e5-ad61-d3ebeee20e5e",
        "type": "text/csv; header=absent",
        "signature": {
                "*": "*"
        },
        "errors": [{ 
                "code": 1,              "msg": "java.lang.IllegalArgumentException" } 
        ],
        "status": "fatal",
        "metrics": {
                "elapsedTime": "26.795447ms",
                "executionTime": "25.588135ms",
                "compileTime": "11.320646ms",
                "queueWaitTime": "0ns",
                "resultCount": 0,
                "resultSize": 0,
                "processedObjects": 0,
                "bufferCacheHitRatio": "0.00%",
                "bufferCachePageReadCount": 0,
                "errorCount": 1
        }
}

After fix

disheng@LAPTOP-UPFH5KC9:~/asterixdb$ curl --data-urlencode "statement=USE test; SELECT text FROM tweets;" \
     "http://localhost:19002/query/service"
{
        "requestID": "6f404f34-1726-42d7-ba7a-990d9b08cd0d",
        "signature": {
                "*": "*"
        },
        "results": [ {"text":"@ScapegoatHelp Walked out on being scapegoated again. Saw Narcs mask slip & that sneer. No more 💪🦋"} ]
        ,
        "plans":{},
        "status": "success",
        "metrics": {
                "elapsedTime": "138.660107ms",
                "executionTime": "134.309116ms",
                "compileTime": "43.763632ms",
                "queueWaitTime": "0ns",
                "resultCount": 1,
                "resultSize": 111,
                "processedObjects": 1
        }
}
disheng@LAPTOP-UPFH5KC9:~/asterixdb$ curl --data-urlencode "statement=USE test; SELECT text FROM tweets;" \
     "http://localhost:19002/query/service?format=csv&header=absent"
{
        "requestID": "855ebc1a-6816-49ef-bbcb-7e99fe6e5ef0",
        "type": "text/csv; header=absent",
        "signature": {
                "*": "*"
        },
        "results": [ "@ScapegoatHelp Walked out on being scapegoated again. Saw Narcs mask slip & that sneer. No more 💪🦋" ]
        ,
        "plans":{},
        "status": "success",
        "metrics": {
                "elapsedTime": "34.516791ms",
                "executionTime": "32.945963ms",
                "compileTime": "11.91599ms",
                "queueWaitTime": "1ms",
                "resultCount": 1,
                "resultSize": 102,
                "processedObjects": 1
        }
}

JIRA Issue

https://issues.apache.org/jira/browse/ASTERIXDB-2877