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From "Frank Wesemann (JIRA)" <>
Subject [jira] Commented: (SOLR-141) Errors/Exceptions should be formated by ResponseWriter
Date Wed, 07 Apr 2010 20:30:33 GMT


Frank Wesemann commented on SOLR-141:

1) more smarts in SolrCore.getErrorResponseWriter to be able to deal with the possibility
that the ResponseWriter is also an ErrorResponseWriter - that way people wouldn't have to
register a dual purpose impl twice
wouldn't it be sufficient to extend the interface QueryResponseWriter with a writeError(Writer,
HttpServletResponse, SolrResponse, SolrRequest) Method?

The DispatchFilter may set the last caught exception on SolrResponse and call it in the sendError()
The ResponseWriter impl may than do something like:
public void  writeError(Writer out, HttpServletResponse res, SolrResponse solrRes, SolrRequest
solrReq) {
  Throwable th = solrRes.getException();
  res.setContentType( getContentType() );
  myTextResponseWriterImpl.writeInt( code );
  myTextResponseWriterImpl.writeStr( th.getMessage );
  if ( ! th instanceof QueryResponseWritingExecption ) {
    try {
    } catch ( Exception e) {
       myTextResonseWriterIml.writeStr("an additionalError in writing the result occured:
" + e.getMessage() );
 //... do what else you need to.


> Errors/Exceptions should be formated by ResponseWriter
> ------------------------------------------------------
>                 Key: SOLR-141
>                 URL:
>             Project: Solr
>          Issue Type: Wish
>            Reporter: Hoss Man
>             Fix For: 1.5
>         Attachments: solr-exception-writer-solr-1.2.diff, solr-exception-writer-v2.diff,
> Whenever possible, the Solr Dispatcher should to let the ResponseWriter format Exceptions
using the format the user expects -- this should in no way change the fact that Exceptions
currently generate non 200 HTTP status codes, nor should it prevent the Dispatcher from using
the exception message as the HTTP status message -- but clients that want the full details
of the error should be able to parse them in the format they expected based on the request.
> this would also give RequestHandlers the oportunity to return "partial" results - by
adding both whatever results they have to the Response as well as the Exception they encountered.
> situations where this can't happen are obviously:
>   * Exception thrown by ResponseWriter
>   * Exception thrown so early in the request thta the DIspather doesn't know which ResposneWriter
the client wanted.
> those cases, plain text is a wise choice.
> thing that would probably need to be done to make this work:
> 1) if the Dispatcher catches an exception, it should call SolrQueryResponse.setException,
set the HTTP status code/message as it currently does, but then hand off to the ResponseWriter.
> 2) Dispatcher needs to check SolrQueryResponse.getException and set the HTTP status code/message
just like if it caught the exception itself.
> 3) all of the ResponseWriters should start looking at SolrQueryResponse.getException
if they aren't already, and formatting it in a usefull way.
> 4) if the ResponseWriter throws an exception, Dispatcher needs to return a nice plain
text error page
> extension to this idea... add a new method to ResponseWriter to generate a generic error
message in the appropriate format that Dispatcher can use if the ResponseWriter throws an
exception (as a backup before resorting to plain text)

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