mysql: Parse incoming optimized TIME binary format

When sending a `TIME` value over the binary protocol (a prepared
statement), if the value is '00:00:00', the client may send an
optimized value by setting the byte length to 0 and sending no bytes.
See the mysql developer docs [0], section
`ProtocolBinary::MYSQL_TYPE_TIME`.

We weren't handling this optimization case and would fail because we
expected bytes in the buffer, but there were none.

[0] https://dev.mysql.com/doc/dev/mysql-server/latest/
  page_protocol_binary_resultset.html

Fixes: REA-5962
Release-Note-Core: Correctly handle incoming optimized `TIME` binary
  format values when the value is '00:00:00'.
Change-Id: I8c6c7b33de540e6360a0ae5988c06f25e517be4d
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/10333
Reviewed-by: Michael Zink <michael.z@readyset.io>
Tested-by: Buildkite CI

Author: jasobrown-rs

mysql-srv/src/value/decode.rs

@@ -277,6 +277,13 @@ impl<'a> TryFrom<Value<'a>> for MySqlTime {
     type Error = MsqlSrvError;
     fn try_from(val: Value<'a>) -> Result<MySqlTime, Self::Error> {
         if let ValueInner::Time(mut v) = val.0 {
+            // if there's no bytes, it means the client sent an "optimized"
+            // time value of '00:00:00'.
+            // see https://dev.mysql.com/doc/dev/mysql-server/latest/page_protocol_binary_resultset.html
+            if v.is_empty() {
+                return Ok(Default::default());
+            }
+
             let is_positive = v.read_u8()? == 0; // sign: 1 negative, 0 positive
             let d = v.read_u32::<LittleEndian>()? as u16;
             let h = v.read_u8()? as u16;