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From "Uwe Schindler (Commented) (JIRA)" <>
Subject [jira] [Commented] (SOLR-2878) Regression in concerning the getOutputStream vs getWriter
Date Sat, 05 Nov 2011 10:40:51 GMT


Uwe Schindler commented on SOLR-2878:

Just to add another note:
The API of ServletResponse supplying getWriter() APIs is a mis-conception in relation to the
HTTP protocol. The HTTP protocol is defined to transfer binary output. The use of a char stream
as Java supplies by getWriter() is only for convenience, but a filter should never rely on
the fact that a Servlet uses a Writer. Unfortunately Sun never changed this for backwards
compatibility reasons, but the correct API design of the Servlet API would be to make the
getWriter() method final in the ServletResponse.

About your last example code that works around your issue: The code of your filter is simply
wrong - it assumes that all chars are represented by exactly one byte with the same binary
code-point in the output, which is only true for US-ASCII. It completely ignores the charset.
Solr by default always uses UTF-8 so you would make the output unreadable once a code poiunt
> 127 would appear in the output. To correctly buffer your output use a ByteArrayOutputStream.
To check the contents of the buffered code as a string, you have to use: new String(ByteArrayOutputStream.getBytes(),
> Regression in concerning the getOutputStream vs getWriter
> ---------------------------------------------------------------------------------
>                 Key: SOLR-2878
>                 URL:
>             Project: Solr
>          Issue Type: Bug
>          Components: Build, Response Writers
>    Affects Versions: 3.4
>         Environment: Any unix system, it's a  global problem
>            Reporter: Nick Veenhof
>              Labels: filter, getOutputStream, getWriter, regression
>             Fix For: 3.5, 4.0
> In solr 1.4 we used getWriter in the writeResponse for solrDispatchFilter::doFilter which
invoked writeResponse.
> This code looked in summary like this :
> {|borderStyle=solid}
> private void writeResponse(SolrQueryResponse solrRsp, ServletResponse response, 
>    QueryResponseWriter responseWriter, SolrQueryRequest solrReq, Method reqMethod) 
>    throws IOException {
> ...
>  PrintWriter out = response.getWriter();
>  responseWriter.write(out, solrReq, solrRsp);
> ...
> {code}
> In solr 3.x this has changed to something like this 
> {|borderStyle=solid}
> private void writeResponse(SolrQueryResponse solrRsp, ServletResponse response,
>   QueryResponseWriter responseWriter, SolrQueryRequest solrReq, Method reqMethod) 
>   throws IOException {
> ...
> String charset = ContentStreamBase.getCharsetFromContentType(ct);
> Writer out = (charset == null || charset.equalsIgnoreCase("UTF-8"))
>   ? new OutputStreamWriter(response.getOutputStream(), UTF8)
>   : new OutputStreamWriter(response.getOutputStream(), charset);
> out = new FastWriter(out);
> responseWriter.write(out, solrReq, solrRsp);
> out.flush();
> ...
> {code}
> Now, when we add another filter that tries to modify the output it is being blocked by
the out.flush(). 
> flush() is telling our outputstream that it can write directly to the destination (similar
to the out.close()), since this normally happens automatically there shouldn't be a need to
execute this flush.
> In our case this secondary filter is trying to add headers to the response object. When
we were using getwriter() it was not closing the writer so we could still modify this output.
Since the flush happens now we are no longer able to modify the headers accordingly. 
> It would be an easy fix if the flush could be commented out and everything would work
but that is not the case. The headers are working when this happens but there is no more output.
> When I modify both classes to use getWriter() everything is working as expected.
> This is a severe regression for our use of solr.
> Our code that is used in the filter
> {|borderStyle=solid}
> public void doFilter(ServletRequest req, ServletResponse res,FilterChain chain) 
>   throws IOException, ServletException {
> ...
> Writer out = new OutputStreamWriter(response.getOutputStream(), "UTF8"); //auto flush
> out = new FastWriter(out);
> // convert to a chartext
> CharResponseWrapper wrapper = new CharResponseWrapper((HttpServletResponse) response);
> chain.doFilter(request, wrapper);
> String responseBody = wrapper.toString();
> //write the outgoing header. Only succeeds when flush of solrDispatchFilter is commented
> response.addHeader("pragma", "somevalue;");
> out.write(responseBody);
> ...
> {code}
> Sources :
> {quote}
> SRV.5.5 Closure of Response Object
> When a response is closed, the container must immediately flush all remaining content
in the response buffer to the client. The following events indicate that the servlet has satisfied
the request and that the response object is to be closed:
> • The termination of the service method of the servlet. 
> • The amount of content specified in the setContentLength method of the response has
been written to the response. 
> • The sendError method is called. 
> • The sendRedirect method is called.
> {quote}
> Solr 1.4
> Solr 3.4

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