AppendStruct() for FixedString does not add Proper Padding

[kuro337]

Issue description

I am using clickhouse-go/v2 and using AppendStruct() to flush rows into a Clickhouse ReplicatedMergeTree table.

When my table has a FixedString(10) type defined for a column , the library panics on AppendStruct().

Solution : I was able to fix this by adding a function to add necessary padding to my strings before passing the pointer to AppendStruct().

The Column Type in Clickhouse is : Col1 LowCardinality FixedString (7) DEFAULT 'unknown',

Example code

type ParquetRow struct {
	Col1       string
}

insert_row := ParquetRow{}
insert_row.Col1 = "Test"

batch, err := conn.PrepareBatch(context.Background(), "INSERT INTO example")
	if err != nil {
		return err
	}

fmt.Println("About to call AppendStruct")

err = batch.AppendStruct(&insert_row)
         if err != nil {
	        log.Fatalf("Failed Appending : ", err)
                return err
	}

Error log

About to call AppendStruct
panic: invalid size
goroutine 1 [running]:
[github.com/ClickHouse/ch-go/proto.(*ColFixedStr).Append(...)](http://github.com/ClickHouse/ch-go/proto.(*ColFixedStr).Append(...))
        /Users//go/pkg/mod/[github.com/!click!house/[email protected]/proto/col_fixed_str.go:64](http://github.com/!click!house/[email protected]/proto/col_fixed_str.go:64)
[github.com/ClickHouse/clickhouse-go/v2/lib/column.(*FixedString).AppendRow(0xc0004bd440](http://github.com/ClickHouse/clickhouse-go/v2/lib/column.(*FixedString).AppendRow(0xc0004bd440), {0x1644920?, 0xc000565ab0})
        /Users//go/pkg/mod/[github.com/!click!house/clickhouse-go/[email protected]/lib/column/fixed_string.go:166](http://github.com/!click!house/clickhouse-go/[email protected]/lib/column/fixed_string.go:166) +0x37e
[github.com/ClickHouse/clickhouse-go/v2/lib/column.(*LowCardinality).AppendRow(0xc0001270e0](http://github.com/ClickHouse/clickhouse-go/v2/lib/column.(*LowCardinality).AppendRow(0xc0001270e0), {0x1644920, 0xc000565ab0})
        /Users//go/pkg/mod/[github.com/!click!house/clickhouse-go/[email protected]/lib/column/lowcardinality.go:161](http://github.com/!click!house/clickhouse-go/[email protected]/lib/column/lowcardinality.go:161) +0x3ad
[github.com/ClickHouse/clickhouse-go/v2/lib/proto.(*Block).Append(0xc00036fd00](http://github.com/ClickHouse/clickhouse-go/v2/lib/proto.(*Block).Append(0xc00036fd00), {0xc000591180?, 0x51, 0x10ce92a?})
        /Users//go/pkg/mod/[github.com/!click!house/clickhouse-go/[email protected]/lib/proto/block.go:62](http://github.com/!click!house/clickhouse-go/[email protected]/lib/proto/block.go:62) +0x1a7
[github.com/ClickHouse/clickhouse-go/v2.(*batch).Append(0xc000622cd0](http://github.com/ClickHouse/clickhouse-go/v2.(*batch).Append(0xc000622cd0), {0xc000591180?, 0xc?, 0xc000590c00?})
        /Users//go/pkg/mod/[github.com/!click!house/clickhouse-go/[email protected]/conn_batch.go:122](http://github.com/!click!house/clickhouse-go/[email protected]/conn_batch.go:122) +0x48
[github.com/ClickHouse/clickhouse-go/v2.(*batch).AppendStruct(0xc000622cd0](http://github.com/ClickHouse/clickhouse-go/v2.(*batch).AppendStruct(0xc000622cd0), {0x1635100?, 0xc0005faa00?})
        /Users//go/pkg/mod/[github.com/!click!house/clickhouse-go/[email protected]/conn_batch.go:138](http://github.com/!click!house/clickhouse-go/[email protected]/conn_batch.go:138) +0x95
main.main()
       insert_clickhouse/main.go:263 +0x1188
exit status 2

[jkaflik]

Thanks, @Chinmay337, for filing this issue. Here is a PR that fixes it: #910
If everything goes well, I will have it released today.