[-] fix JSON serialization of different error types in task execution logging

[MaxaiZer]

Task errors are currently serialized inconsistently. If ExecuteSQLCommand fails during this block:

if len(paramValues) == 0 { 
  ct, e := executor.Exec(ctx, task.Command)
  pge.LogTaskExecution(context.Background(), task, errCodes[e != nil], ct.String(), "") 
  return e
}

message_data.error in the "Task execution failed" log will contain a full pgconn.PgError struct:

{"task": 1, "vxid": 1, "chain": 1, "error": {"Code": "42P02", "File": "parse_expr.c", "Hint": "", "Line": 901, "Where": "", "Detail": "", "Message": "there is no parameter $1", "Routine": "transformParamRef", "Position": 175, "Severity": "ERROR", "TableName": "", "ColumnName": "", "SchemaName": "", "DataTypeName": "", "InternalQuery": "", "ConstraintName": "", "InternalPosition": 0, "SeverityUnlocalized": "ERROR"}}

If it fails during parameter parsing:

if err = json.Unmarshal([]byte(val), &params); err != nil {
    return
}

message_data.error will contain struct with no actual error message:

{"task": 1, "vxid": 1, "chain": 1, "error": {"Type": {}, "Field": "", "Value": "string", "Offset": 9, "Struct": ""}}

And if ExecuteSQLCommand returns joined errors, message_data.error becomes empty:

{"task": 1, "vxid": 1, "chain": 1, "error": {}}

After fix examples:

• single postgres error:

{"task": 1, "vxid": 1, "chain": 1, "error": "ERROR: there is no parameter $1 (SQLSTATE 42P02)"}

• parameter parse error:

{"task": 1, "vxid": 1, "chain": 1, "error": "failed to parse parameter \"1 month\": json: cannot unmarshal string into Go value of type []interface {}"}

• joined errors (task with two parameters: correct and incorrect):

{"task": 1, "vxid": 1, "chain": 1, "error": "ERROR: procedure F_CreatePartitions(date, date) does not exist (SQLSTATE 42883)\nfailed to parse parameter \"1 month\": json: cannot unmarshal string into Go value of type []interface {}"}

[coveralls]

Pull Request Test Coverage Report for Build 21996320244

Details

• 3 of 7 (42.86%) changed or added relevant lines in 2 files are covered.
• 4 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.3%) to 86.97%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/pgengine/log_hook.go	0	4	0.0%

Files with Coverage Reduction	New Missed Lines	%
internal/pgengine/log_hook.go	4	82.88%

Totals
Change from base Build 21996108468:	-0.3%
Covered Lines:	1722
Relevant Lines:	1980

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💛 - Coveralls