[jira] [Created] (THRIFT-3752) nil collections are serialized as empty collections

[John Sirois (JIRA)]

John Sirois created THRIFT-3752:
-----------------------------------

             Summary: nil collections are serialized as empty collections
                 Key: THRIFT-3752
                 URL: https://issues.apache.org/jira/browse/THRIFT-3752
             Project: Thrift
          Issue Type: Bug
          Components: Go - Compiler
            Reporter: John Sirois


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

In short, for this struct:
{noformat}
struct TaskQuery {
    4: optional set<string> taskIds
}
{noformat}

The following go struct is generated:
{noformat}
type TaskQuery struct {
        TaskIds  map[string]bool         `thrift:"taskIds,4" json:"taskIds"`
}
{noformat}

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:
{noformat}
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
}
{noformat}

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.



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