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

["Connor Gorman (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/THRIFT-3752?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15324969#comment-15324969 ] 

Connor Gorman commented on THRIFT-3752:
---------------------------------------

Hey [~jsirois],

How is this going? I can jump in and help if you'd like. Considering this is for Aurora, watch out for https://issues.apache.org/jira/browse/THRIFT-3851. Making a patch for it now

> 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
>            Assignee: 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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