Thumbnail preview extension crashing when loading WKWebView

Question

Created Dec ’20

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Developing a thumbnail extension for a custom file type in my iOS app. I am using a WKWebView to render an HTML string and then capturing a snapshot of the WKWebView to use for the thumbnail image. Works great on simulators. However, not completing when run on a real device.

Here is the code:

Code Block     let thumbFileView = WKWebView(frame: frame)
    thumbFileView.navigationDelegate = self
    thumbFileView.pageZoom = scale
    thumbFileView.layoutIfNeeded()
    thumbFileView.loadHTMLString(thumbFile.asHtml, baseURL: nil)

Thumbnail image is perfect on simulator, but on real device there is a crash in the logs:

Code Block 2020-12-08 11:01:30.191156-0700 ThumbFileThumbnail[35519:906998] [] networkd_settings_setup_notify_watch notify_register_dispatch(com.apple.system.networkd.settings) [status 9] failed
2020-12-08 11:01:30.205445-0700 ThumbFileThumbnail[35519:906998] [] networkd_settings_setup_notify_watch notify_register_dispatch(com.apple.system.networkd.settings) [status 9] failed, dumping backtrace:
        [arm64] libnetcore-2288.42.1
    0   libnetwork.dylib                    0x00000001a2ce1658 __nw_create_backtrace_string + 116
    1   libnetwork.dylib                    0x00000001a2c6ffdc C67A2D71-4415-3F82-9399-65C3956520AE + 5832668
    2   libnetwork.dylib                    0x00000001a2c6f6c0 C67A2D71-4415-3F82-9399-65C3956520AE + 5830336
    3   libnetwork.dylib                    0x00000001a2a777d0 C67A2D71-4415-3F82-9399-65C3956520AE + 3766224
    4   libnetwork.dylib                    0x00000001a2c26408 nw_path_create_evaluator_for_endpoint_no_evaluate + 544
    5   libnetwork.dylib                    0x00000001a2c25ee0 nw_path_create_evaluator_for_endpoint + 84
    6   Network                             0x00000001b5a063e0 2FB89D76-EA38-3B43-BCD1-E0C7EE9B9012 + 1180640
    7   Network                             0x00000001b5a058b4 2FB89D76-EA38-3B43-BCD1-E0C7EE9B9012 + 1177780
    8   libdispatch.dylib                   0x00000001a18c0280 6C143C51-288F-3CD0-84DD-17B9A0AAEE62 + 397952
    9   libdispatch.dylib                   0x00000001a18642f4 6C143C51-288F-3CD0-84DD-17B9A0AAEE62 + 21236
    10  Network                             0x00000001b5a05888 2FB89D76-EA38-3B43-BCD1-E0C7EE9B9012 + 1177736
    11  NetworkExtension                    0x00000001b268a4e4 4F673F38-E238-37C5-9B26-2A540CB429B9 + 357604
    12  WebKit                              0x00000001ad9a8334 19789FD9-1098-37B7-B639-9E4F0EB867D6 + 2847540
    13  WebKit                              0x00000001ada0bdc8 19789FD9-1098-37B7-B639-9E4F0EB867D6 + 3255752
    14  WebKit                              0x00000001ada0ba20 19789FD9-1098-37B7-B639-9E4F0EB867D6 + 3254816
    15  WebKit                              0x00000001ad6fda9c 19789FD9-1098-37B7-B639-9E4F0EB867D6 + 51868
    16  ThumbFileThumbnail                  0x00000001044f4ee8 $s18ThumbFileThumbnail0abC9GeneratorC04loadaB4View3for2in5scaleSo05WKWebF0CAA0aB0V_So6CGRectV12CoreGraphics7CGFloatVtF + 704
    17  ThumbFileThumbnail                  0x00000001044f42a4 $s18ThumbFileThumbnail0abC9GeneratorC20provideSnapshotImage3for5scale5frame10completionyAA0aB0V_12CoreGraphics7CGFloatVSo6CGRectVySo7UIImageCSgctFyycfU_ + 204

From setting a runtime issues breakpoint, the offending line of code is:

Code Block     thumbFileView.loadHTMLString(thumbFile.asHtml, baseURL: nil)

Since the html contains an image URL, this seems to point to some limitation that iOS is placing on the thumbnail extension that is blocking it from accessing the network. This is evident from the crash log and from the stack at the time of the issue.
I've studied Apple's documentation of NSExtensionAttributes and can't find anything that would address this permission issue.
Here are the NSExtensionAttributes for the thumbnail extension:

Code Block    <key>NSExtension</key>
    <dict>
        <key>NSExtensionAttributes</key>
        <dict>
            <key>QLSupportedContentTypes</key>
            <array>
                <string>com.raywenderlich.RazeThumb.ThumbFile</string>
            </array>
            <key>QLThumbnailMinimumDimension</key>
            <integer>0</integer>
        </dict>

Why is this crashing on a real device but not on a simulator?

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