Start tag expected, '<' not found [4]

[dusadrian]

This issue is (still) a pesky one, and for many years so. I only recently realized it is linked to package xml2, while for a long time thought it was due to one of my own packages (that imports xml2) and I was banging my head to find out why it happens.

In my case, it has nothing to do with Quartz as I don't plot anything, it happens even when I open a help page (by default, html in the R.app):

> library(xml2)
> ?paste
starting httpd help server ... done
Error: Start tag expected, '<' not found [4]

I tried to reopen the previous issue 458, but I don't have enough privileges.

[jeroen]

This is a bug in R.app, it does not happen when using R in the console or Rstudio. It has to do with the custom "browser" which opens the html file, and in the process it seems to be reading a broken xml2 (svg icon?) file.

?paste
Sys.sleep(1)
library(xml2)
browser <- get("aqua.browser", envir = as.environment("tools:RGUI"))
browser("https://www.google.com")

Because the svg fails to read and the error is not handled, it hits our global error handler.

3   xml2.so                       	       0x134749f6c handleStructuredError + 44 (xml2_init.c:31)
4   libxml2.2.dylib               	       0x1a8673494 __xmlRaiseError + 932
5   libxml2.2.dylib               	       0x1a8676c8c xmlFatalErrMsg + 120
6   libxml2.2.dylib               	       0x1a867ff50 xmlParseDocument + 988
7   libxml2.2.dylib               	       0x1a867fb28 xmlDoRead + 116
8   AppKit                        	       0x1a3386568 +[_NSSVGImageRep canInitWithData:] + 96
9   AppKit                        	       0x1a2eb4fb4 +[NSImageRep imageRepClassForData:] + 220
10  AppKit                        	       0x1a2d7d074 -[NSImage initWithData:] + 40
11  WebCore                       	       0x1c4a4ca88 WebCore::ImageAdapter::nsImage() + 76
12  WebKitLegacy                  	       0x1bca74f18 WTF::Detail::CallableWrapper<WebFrameLoaderClient::getLoadDecisionForIcons(WTF::Vector<std::__1::pair<WebCore::LinkIcon&, unsigned long long>, 0ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc> const&)::$_3, void, WebCore::FragmentedSharedBuffer*>::call(WebCore::FragmentedSharedBuffer*) + 276
13  WebCore                       	       0x1c5b4ebf8 WebCore::DocumentLoader::finishedLoadingIcon(WebCore::IconLoader&, WebCore::FragmentedSharedBuffer*) + 96
14  WebCore                       	       0x1c5c4d6f0 WebCore::IconLoader::notifyFinished(WebCore::CachedResource&, WebCore::NetworkLoadMetrics const&, WebCore::LoadWillContinueInAnotherProcess) + 208
15  WebCore                       	       0x1c5c22fc4 WebCore::CachedResource::checkNotify(WebCore::NetworkLoadMetrics const&, WebCore::LoadWillContinueInAnotherProcess) + 156
16  WebCore                       	       0x1c5c1ea9c WebCore::CachedRawResource::finishLoading(WebCore::FragmentedSharedBuffer const*, WebCore::NetworkLoadMetrics const&) + 404
17  WebCore                       	       0x1c5beea74 WebCore::SubresourceLoader::didFinishLoading(WebCore::NetworkLoadMetrics const&) + 1080
18  WebCore                       	       0x1c698ac74 WTF::Detail::CallableWrapper<-[WebCoreResourceHandleAsOperationQueueDelegate connectionDidFinishLoading:]::$_10, void>::call() + 344
19  JavaScriptCore                	       0x1bf6fb1d8 WTF::RunLoop::performWork() + 552
20  JavaScriptCore                	       0x1bf6fcbd0 WTF::RunLoop::performWork(void*) + 36
21  CoreFoundation                	       0x19e1dc9e8 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 28
22  CoreFoundation                	       0x19e1dc97c __CFRunLoopDoSource0 + 172
23  CoreFoundation                	       0x19e1dc6e8 __CFRunLoopDoSources0 + 232
24  CoreFoundation                	       0x19e1db378 __CFRunLoopRun + 820
25  CoreFoundation                	       0x19e29535c _CFRunLoopRunSpecificWithOptions + 532
26  HIToolbox                     	       0x1aac98768 RunCurrentEventLoopInMode + 316
27  HIToolbox                     	       0x1aac9ba90 ReceiveNextEventCommon + 488
28  HIToolbox                     	       0x1aae25308 _BlockUntilNextEventMatchingListInMode + 48
29  AppKit                        	       0x1a2aec3c0 _DPSBlockUntilNextEventMatchingListInMode + 236
30  AppKit                        	       0x1a25e5e34 _DPSNextEvent + 588
31  AppKit                        	       0x1a30b3f44 -[NSApplication(NSEventRouting) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 688
32  AppKit                        	       0x1a30b3c50 -[NSApplication(NSEventRouting) nextEventMatchingMask:untilDate:inMode:dequeue:] + 72
33  R                             	       0x102ef6934 -[RController doProcessEvents:] + 160
34  R                             	       0x102ef2594 -[RController handleReadConsole:] + 80
35  R                             	       0x102ef9428 Re_ReadConsole + 192
36  libR.dylib                    	       0x1038f3264 R_ReplDLLdo1 + 164 (main.c:375)
37  R                             	       0x102f03eec run_REngineRmainloop + 284
38  R                             	       0x102efb904 -[REngine runREPL] + 124
39  R                             	       0x102eeef50 main + 592
40  dyld                          	       0x19dd75d54 start + 7184

[dusadrian]

Thank you Jeroen, should I report it to r-sig-mac then?

[jeroen]

Yes or just to Simon directly, he is the one maintaining R.app.

[s-u]

Again, this is still the same bug in the xml2 package which is well known and has been closed without getting fixed in #458. To recap, xml2 installs a global handler which interferes with other calls to the xml2 library by all other code. This is a serious bug and needs to be fixed in the xml2 package as previously discussed since the package cannot assume it own the library.