org.msgpack.core.MessageTypeCastException for DECIMAL type

[weasellin]

The org.msgpack.core.MessageTypeCastException would be thrown when the results of the td query contains DECIMAL type.

This exception cause by the following reason.

Since the DECIMAL type "columns" are interpreted as embulks DOUBLE type,
https://github.com/treasure-data/embulk-input-td/blob/v0.2.3/src/main/java/org/embulk/input/td/TdInputPlugin.java#L233

however the DECIMAL type "data fields" are packed and unpacked as MessagePack's String type.

ex.
This query

SELECT * FROM ( VALUES DECIMAL '0.0' ) AS t (dec)

would yeid the msgpack serialized bytes sequence 0x91 0xA3 0x30 0x2E 0x30,
and deserialized as fixstr type (first byte 0xa0 - 0xbf)

And for the ImmutableStringValue, it doesn't support asFloatValue() and will end up with throwing the MessageTypeCastException.

The following is the testing environment I used to reproduce the issue.

• Embulk v0.9.22
• plugin embulk-input-td (0.2.3)
• td-client version: 0.9.0
• config.yml

in:
  type: td
  apikey: [MY_API_KEY]
  database: [MY_DB]
  query: |
    SELECT * FROM ( VALUES DECIMAL '0.0' ) AS t (dec)

out:
  type: stdout

• run embulk preview config.yml

[gccj]

I had the same issue.