Fix blocking call in static StartupMessage initializer

We now no longer use ZoneId.systemDefault() to determine the system timezone to avoid blocking I/O and use TimeZone.getDefault() instead. ZoneId attempts to resolve its zone information from TzdbZoneRulesProvider which uses a file (tzdb.dat) that contains timezone information. Since TzdbZoneRulesProvider opens the file in its constructor we have no other way to override the blocking behavior therefore we use the legacy API which does not use files at all.

[resolves #275]

Author: mp911de

src/main/java/io/r2dbc/postgresql/message/frontend/StartupMessage.java

@@ -24,9 +24,9 @@
 import reactor.core.publisher.Mono;
 import reactor.util.annotation.Nullable;
 
-import java.time.ZoneId;
 import java.util.Map;
 import java.util.Objects;
+import java.util.TimeZone;
 
 import static io.netty.util.CharsetUtil.UTF_8;
 import static io.r2dbc.postgresql.message.frontend.FrontendMessageUtils.writeByte;
@@ -55,7 +55,7 @@ public final class StartupMessage implements FrontendMessage {
 
     private static final ByteBuf NUMERAL_2 = Unpooled.copiedBuffer("2", UTF_8).asReadOnly();
 
-    private static final ByteBuf SYSTEM_TIME_ZONE = Unpooled.copiedBuffer(ZoneId.systemDefault().toString(), UTF_8).asReadOnly();
+    private static final ByteBuf SYSTEM_TIME_ZONE = Unpooled.copiedBuffer(TimeZone.getDefault().getID(), UTF_8).asReadOnly();
 
     private static final ByteBuf TIMEZONE = Unpooled.copiedBuffer("TimeZone", UTF_8).asReadOnly();