revert read col & fix reading logic

Author: mzitnik

clickhouse-data/src/main/java/com/clickhouse/data/ClickHouseColumn.java

@@ -249,9 +249,8 @@ private static ClickHouseColumn update(ClickHouseColumn column) {
             case FixedString:
                 if (size > 0) {
                     column.precision = Integer.parseInt(column.parameters.get(0));
-                    column.estimatedByteLength += column.precision;
-                    if (column.nullable) {
-                        column.estimatedByteLength -= 1;
+                    if (!column.nullable) {
+                        column.estimatedByteLength += column.precision;
                     }
                 }
                 column.template = ClickHouseStringValue.ofNull();

client-v2/src/main/java/com/clickhouse/client/api/data_formats/internal/BinaryStreamReader.java

@@ -112,10 +112,11 @@ public <T> T readValue(ClickHouseColumn column, Class<?> typeHint) throws IOExce
             switch (dataType) {
                 // Primitives
                 case FixedString: {
-                    byte[] bytes = estimatedLen > STRING_BUFF.length ?
-                            new byte[estimatedLen] : STRING_BUFF;
-                    readNBytes(input, bytes, 0, estimatedLen);
-                    return (T) new String(bytes, 0, estimatedLen, StandardCharsets.UTF_8);
+                    int estimatedLenTemp = (estimatedLen > precision ? estimatedLen : precision);
+                    byte[] bytes = estimatedLenTemp > STRING_BUFF.length ?
+                            new byte[estimatedLenTemp] : STRING_BUFF;
+                    readNBytes(input, bytes, 0, estimatedLenTemp);
+                    return (T) new String(bytes, 0, estimatedLenTemp, StandardCharsets.UTF_8);
                 }
                 case String: {
                     return (T) readString();