[THRIFT-3752] nil collections are serialized as empty collections

• Type: Bug
• Status: In Progress
• Priority: Major
• Resolution: Unresolved
• Component/s: Go - Compiler
• Assignee: John Sirois
• Reporter: John Sirois
• Created: 23/Mar/16 14:35
• Updated: 22/Feb/17 21:05

Description

See discussion here: https://reviews.apache.org/r/45193/
This is likely related to THRIFT-3700.

In short, for this struct:

struct TaskQuery {
    4: optional set<string> taskIds
}

The following go struct is generated:

type TaskQuery struct {
	TaskIds  map[string]bool         `thrift:"taskIds,4" json:"taskIds"`
}

This is all well and good, since TaskQuery{}.TaskIds == nil; ie the TaskIds collection field is - by default - unset.

The problem is in the serialization for the field, which wipes out the unset (nil) vs empty collection distinction at the wire level:

func (p *TaskQuery) writeField4(oprot thrift.TProtocol) (err error) {
	if err := oprot.WriteFieldBegin("taskIds", thrift.SET, 4); err != nil {
		return thrift.PrependError(fmt.Sprintf("%T write field begin error 4:taskIds: ", p), err)
	}
	if err := oprot.WriteSetBegin(thrift.STRING, len(p.TaskIds)); err != nil {
		return thrift.PrependError("error writing set begin: ", err)
	}
	for v, _ := range p.TaskIds {
		if err := oprot.WriteString(string(v)); err != nil {
			return thrift.PrependError(fmt.Sprintf("%T. (0) field write error: ", p), err)
		}
	}
	if err := oprot.WriteSetEnd(); err != nil {
		return thrift.PrependError("error writing set end: ", err)
	}
	if err := oprot.WriteFieldEnd(); err != nil {
		return thrift.PrependError(fmt.Sprintf("%T write field end error 4:taskIds: ", p), err)
	}
	return err
}

So on the receiving end of the wire, a nil collection is turned into an empty collection and so unset-ness cannot be distinguished from set but empty.

Issue Links

• relates to: THRIFT-3700 Go Map has wrong default value when optional
• relates to: THRIFT-3756 Improve requiredness documentation