bblfish
commented
9 years ago thanks. Can you narrow down on the problem? That will help for documentation of the bug, and help me read quickly what the problem is.
Closed reederz closed 9 years ago
bblfish
commented
9 years ago thanks. Can you narrow down on the problem? That will help for documentation of the bug, and help me read quickly what the problem is.
reederz
commented
9 years ago OK. So the fix which you did for https://github.com/w3c/banana-rdf/issues/239 worked. Now, when we serialize graph to application/n-triples format, we get absolute URLs instead of relative URLs. The thing is, that the serializer takes in the wrong base. Above, you can see that we get http://localhost:8888/#mycouch (wrong) instead of https://localhost:8443/2013/couch#mycouch (right).
It seemed to me that http://localhost:8888/ is some sort of default base URL. I have dug a bit deeper and found that it comes from https://github.com/read-write-web/rww-play/blob/dev/app/rww/play/PlayWriterBuilder.scala#L67-73:
/**
* turn a blocking writer into an enumerator
* todo: perhaps save some memory by not doing this operation in one chunk
* todo: the base url
*
* @param writer
* @tparam Obj
* @return
*/
def toEnum[Obj](writer: Writer[Obj,Try,_]) =
(obj: Obj) => {
utils.FileUtils.using(new ByteArrayOutputStream()) { out =>
val tw = writer.write(obj, out, "http://localhost:8888/") // TODO ???????
Enumerator(out.toByteArray)
}
}
I have then tried to figure out why, when requesting an n-triples resource through CORS proxy I always get the correct base URL and when I request the same resource normally, the default base URL (http://localhost:8888/) is used. What I have found is that CORS proxy is using absolute graph to write responses and when we request a resource normally, relative graph is used.
https://github.com/read-write-web/rww-play/blob/dev/app/rww/play/CORSProxy.scala#L118-129 :
private def createResultForLDPR(ldpr: LDPR[Rdf], writer: Writer[Rdf#Graph, Try, Any])
(implicit request: PlayRequest[AnyContent]): Result = {
// TODO maybe it's not a good idea to put AllowCredentialsHeader here? needs to be checked
val hdrs = request.headers.toSimpleMap - "ContentType" + AllowCredentialsHeader
//todo: this needs to be refined a lot, and thought through quite a lot more carefully
val corsHeaders = if (!hdrs.contains("Access-Control-Allow-Origin")) {
hdrs + AllowOriginHeader(request)
} else {
hdrs
}
//HERE
result(203, writer)(ldpr.graph).withHeaders(corsHeaders.toSeq: _*)
}
private def writeGetResult(authResult: AuthResult[NamedResource[Rdf]])
(implicit request: PlayApi.mvc.Request[AnyContent]): Result = {
def commonHeaders: List[(String, String)] =
allowHeaders(authResult) :::
etagHeader(authResult) :::
updatedHeader(authResult) :::
userHeader(authResult.authInfo.user).toList
authResult.result match {
case ldpr: LDPR[Rdf] => {
writerFor[Rdf#Graph](request).map { wr =>
val headers =
"Access-Control-Allow-Origin" -> "*" ::
"Accept-Patch" -> Syntax.SparqlUpdate.mimeTypes.head.mime :: //todo: something that is more flexible
linkHeaders(ldpr) ::
commonHeaders
//HERE
result(200, wr, Map(headers: _*))(ldpr.relativeGraph)
} getOrElse {
play.api.mvc.Results.UnsupportedMediaType("could not find serialiser for Accept types " +
request.headers.get(play.api.http.HeaderNames.ACCEPT))
}
}
case bin: BinaryResource[Rdf] => {
val contentType = bin.mime.mime
val headers = "Content-Type" -> contentType :: linkHeaders(bin)::commonHeaders
Result(
header = ResponseHeader(200, Map(headers:_*)),
body = bin.readerEnumerator(1024 * 8)
)
}
}
}
My proposed solution is to use absolute graph in normal mode as well. I have tried it and it works.
bblfish
commented
9 years ago ok, yes. Relative graphs should be used rarely.
Here's the line in question: https://github.com/read-write-web/rww-play/blob/dev/app/controllers/ldp/ReadWriteWebControllerGeneric.scala#L210 And here's how CORS proxy writes responses: https://github.com/read-write-web/rww-play/blob/dev/app/rww/play/CORSProxy.scala#L128
Notice that CORS proxy uses absolute graph from ldpr whereas the ReadWriteWebControllerController uses relative graph.
I don't know if changing ReadWriteWebController to use absolute graph instead of relative graph would have some unintended consequences, but it fixes my issue with messed up subjects/objects when requesting resources with "Accept: application/n-triples" header.
Using relative graph in ReadWriteWebControllerGeneric (messed up response):
Using relative graph in ReadWriteWebControllerGeneric (good response):
I can make a PR for this but I don't know if I wouldn't be breaking something else with it.