Hello! On Wed, Jul 13, 2022 at 08:12:06PM +0400, Roman Arutyunyan wrote:
> Hi, > > On Sun, Jul 10, 2022 at 11:35:48AM +0300, Maxim Dounin wrote: > > Hello! > > > > On Fri, Jul 08, 2022 at 07:13:33PM +0000, Lucas Rolff wrote: > > > > > I’m having an nginx instance where I utilise the nginx slice > > > module to slice upstream mp4 files when using proxy_cache. > > > > > > However, I have an interesting origin where if sending a range > > > request (which happens when the slice module is enabled), to a > > > file that’s less than the slice range, the origin returns a 200 > > > OK, but with the range related headers such as content-range, > > > but obviously the full file is returned since it’s within the > > > requested range. > > > > > > When playing the MP4s through Google Chrome and Firefox it works > > > fine when going through the nginx proxy instance, however, it > > > somehow breaks Safari (both on MacOS, and iOS) - I guess Safari > > > is more strict. > > > When playing directly through the origin it works fine in all > > > browsers. > > > > > > The md5 of response from the origin remains the same, so it’s > > > not that the response itself is an invalid MP4 file, and even if > > > you compare the cache files on disk with a “working” origin and > > > the “broken” origin (one sends a 206 Partial Content, another > > > sends 200 OK) - the content of the cache files remain the same, > > > except obviously the header section of the cache file. > > > > > > The origin returns a 206 status code, only if the file exceeds > > > the slice size, so if I configure a slice size of 5 megabyte, > > > only files above 5 megabytes will give 206s. Anything under 5 > > > megabytes will result in a 200 OK with content-range and the > > > correct content-length, > > > > > > Looking in the slice module itself I see: > > > https://github.com/nginx/nginx/blob/master/src/http/modules/ngx_http_slice_filter_module.c#L116-L126 > > > > > > > > > if (r->headers_out.status != NGX_HTTP_PARTIAL_CONTENT) { > > > if (r == r->main) { > > > ngx_http_set_ctx(r, NULL, ngx_http_slice_filter_module); > > > return ngx_http_next_header_filter(r); > > > } > > > > > > ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, > > > "unexpected status code %ui in slice response", > > > r->headers_out.status); > > > return NGX_ERROR; > > > } > > > > > > This seems like the slice module expects a 206 status code to be > > > returned, > > > > For the main request, the code accepts two basic valid variants: > > > > - 206, so the slice module will combine multiple responses to > > range requests as needed; > > > > - anything else, so the slice module will give up and simply > > return the response to the client. > > > > If the module sees a non-206 response to a subrequest, this is an > > error, as the slice module expects underlying resources to be > > immutable, and does not expect that some ranges can be requested, > > while some other aren't. This isn't something related to your > > case though. > > > > > however, later in the same function > > > https://github.com/nginx/nginx/blob/master/src/http/modules/ngx_http_slice_filter_module.c#L200-L211 > > > > > > > > > if (r->headers_out.status == NGX_HTTP_PARTIAL_CONTENT) { > > > if (ctx->start + (off_t) slcf->size <= > > > r->headers_out.content_offset) { > > > ctx->start = slcf->size > > > * (r->headers_out.content_offset / slcf->size); > > > } > > > > > > ctx->end = r->headers_out.content_offset > > > + r->headers_out.content_length_n; > > > > > > } else { > > > ctx->end = cr.complete_length; > > > } > > > > > > There it will do an else statement if the status code isn’t 206. > > > So would this piece of code ever be reached, since there’s the initial > > > error? > > > > Following the initial check, r->headers_out.status is explicitly > > changed to NGX_HTTP_OK. Later on the > > ngx_http_next_header_filter() call might again change > > r->headers_out.status as long as the client used a range request, > > and this is what checked here. > > > > > Additionally I don’t see in RFC7233 that 206 responses are an > > > absolute requirement, additionally I don’t see content-range > > > being prohibited/forbidden to be used for 200 OK responses. > > > Now, if one have a secondary proxy that modifies the response > > > headers in between the origin returning 200 OK with the > > > Content-Range header, and then strip out the Content-Range > > > header, the nginx slice module seems to handle it fine, so > > > somehow the combination of 200 OK and a Content-Range header > > > being present seems to break the slice module from functioning. > > > > > > I’m just curious why this happens within the slice module, and > > > if there’s any possible solution for it (like allowing the > > > combination of 200 OK and Content-Range, since those two would > > > still indicate that the origin/upstream supports range requests) > > > - obviously it would be nice to fix the upstream server but > > > sometimes that’s sadly not possible. > > > > >From the above explanation it is probably already clear that > > "disabling slice when an origin returns 200 OK" is what actually > > happens. > > > > The issue does not appear without the slice module in your testing > > because the Content-Range header seems to be only present in your > > backend 200 responses when there was a Range header in the > > request, and this is what happens only with the slice module. > > > > I've done some limited testing with Safari and manually added > > Content-Range header, and there seem to be at least two issues: > > > > - Range filter in nginx does not expect the Content-Range header > > to be already present in 200 responses and simply adds another > > one. This results in incorrect range responses with multiple > > Content-Range headers, and this breaks Safari. > > > > - Safari also breaks if its test request with "Range: bytes=0-1" > > results in 200 with the Content-Range header. > > > > My initial fix was to simply disable handling of 200 responses > > with Content-Range headers in the range filter, so such responses > > wouldn't be touched at all. This is perfectly correct and > > probably the most secure thing to do, but does not work with > > Safari due to the second issue outlined above. > > > > Another approach would be to clear pre-existing Content-Range > > headers in the range filter. This seems to work, at least in my > > testing. See below for the patch. > > > > > I know the parts of the slice module haven’t been touched for > > > years, so obviously it works for most people, just dipping my > > > toes here to see if there’s a possible solution other than > > > disabling slice when an origin returns 200 OK for files smaller > > > than the slice size. > > > > Note that that slice module is generally unsafe to use for > > arbitrary upstream servers: it relies on expectations which are > > beyond the HTTP standard requirements. In particular: > > > > - It requires resources to be immutable, so different range > > responses can be combined together. > > > > - It does not try to handle edge cases, such as 416 returned by > > the upstream on empty files (which is correct per RFC, but > > requires complicated additional handling to convert 416 to 200, so > > it is better to just return 200 OK). > > > > In general, the slice module is to be used only in your own > > infrastructure when you control the backend and can be sure that > > the slice module expectations are met. As such, disabling it for > > backends which do something unexpected might actually be a good > > idea. On the other hand, in this particular case the nginx > > behaviour can be adjusted to handle things gracefully. > > > > Below is a patch to clear pre-existing Content-Range headers > > in the range filter. Please test if it works for you. > > > > # HG changeset patch > > # User Maxim Dounin <mdou...@mdounin.ru> > > # Date 1657439390 -10800 > > # Sun Jul 10 10:49:50 2022 +0300 > > # Node ID 219217ea49a8d648f5cadd046f1b1294ef05693c > > # Parent 9d98d524bd02a562d9cd83f4e369c7e992c5753b > > Range filter: clearing of pre-existing Content-Range headers. > > > > Some servers might emit Conten-Range header on 200 responses, and this > > Missing "t" in "Conten-Range". Fixed, thnx. > > does not seem to contradict RFC 9110: as per RFC 9110, the Content-Range > > header have no meaning for status codes other than 206 and 417. Previously > > have -> has > 417 -> 416 Fixed, thnx. > > this resulted in duplicate Content-Range headers in nginx responses handled > > by the range filter. Fix is to clear pre-existing headers. > > > > diff --git a/src/http/modules/ngx_http_range_filter_module.c > > b/src/http/modules/ngx_http_range_filter_module.c > > --- a/src/http/modules/ngx_http_range_filter_module.c > > +++ b/src/http/modules/ngx_http_range_filter_module.c > > @@ -425,6 +425,10 @@ ngx_http_range_singlepart_header(ngx_htt > > return NGX_ERROR; > > } > > > > + if (r->headers_out.content_range) { > > + r->headers_out.content_range->hash = 0; > > + } > > + > > r->headers_out.content_range = content_range; > > > > content_range->hash = 1; > > @@ -582,6 +586,11 @@ ngx_http_range_multipart_header(ngx_http > > r->headers_out.content_length = NULL; > > } > > > > + if (r->headers_out.content_range) { > > + r->headers_out.content_range->hash = 0; > > + r->headers_out.content_range = NULL; > > + } > > + > > return ngx_http_next_header_filter(r); > > } > > > > @@ -598,6 +607,10 @@ ngx_http_range_not_satisfiable(ngx_http_ > > return NGX_ERROR; > > } > > > > + if (r->headers_out.content_range) { > > + r->headers_out.content_range->hash = 0; > > + } > > + > > r->headers_out.content_range = content_range; > > > > content_range->hash = 1; > > The patch looks ok to me > > Tested with proxy_force_ranges. Pushed to http://mdounin.ru/hg/nginx/. -- Maxim Dounin http://mdounin.ru/ _______________________________________________ nginx mailing list -- nginx@nginx.org To unsubscribe send an email to nginx-le...@nginx.org
