Align UDT handling in trino-go-client with Java client’s Base64-encoding default

[moraistejerina]

Summary

Today the two official Trino clients diverge in how they handle User-Defined Types (UDTs):

• trino-java-client
  Defaults to serializing UDT values via a Base64 encoder, allowing arbitrary binary payloads to round-trip without error.
• trino-go-client
  Treats any UDT as an unsupported type and immediately raises an exception when encountering one.

This mismatch causes cross-language interoperability issues and surprises Go users who expect the same “just works” behavior as in Java. We should align the Go client’s behavior to match the Java client: default to Base64-encoding UDT values, and only error if encoding itself fails.

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Current Behavior

trino-go-client

• Unsupported by default
  In (*stmt).NextColumnType, encountering a column with type.kind == “user_defined” will cause NextColumnType (or downstream type mapping) to return an error:

  return nil, fmt.Errorf("unsupported column type: %s", tc.String())

trino-java-client

• Base64 encoder default
  In io.trino.client.StatementClient, UDT payloads are represented as opaque byte[] values, which the client maps to Base64 strings in JSON. When rows are fetched, those JSON Base64 values are decoded into Java’s byte[] and can be consumed via ResultSet.getBytes().
• No error path
  Unless the Base64 itself is malformed, the Java client will never raise a “unsupported type” error for UDT columns.

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Proposal

1. Add a Base64 default converter for UDT columns in trino-go-client

   • In the column-type detection logic (e.g. in ColumnConverterForType), detect type.kind == user_defined and return a converter that:

     1. Reads the raw payload bytes
     2. Calls encoding/base64.StdEncoding.EncodeToString([]bytePayload)
     3. Returns the resulting string to the caller

[moraistejerina]

Would a PR be accepted into the repo with the proposed changes?

[nineinchnick]

Yes, the closer we get to reaching feature parity with the JDBC driver, the better.