WebKitGTK2 compile for snap

Hello. I try compile WebKitGTK from sources. My snapcraft.yaml:

name: testsnap-py # you probably want to 'snapcraft register <name>'
version: '0.5.2' # just for humans, typically '1.2+git' or '1.3.2'
summary: Single-line elevator pitch for your amazing snap # 79 char long summary
description: |
  This is my-snap's description. You have a paragraph or two to tell the
  most important story about your snap. Keep it under 100 words though,
  we live in tweetspace and your description wants to look good in the snap

grade: devel # must be 'stable' to release into candidate/stable channels
confinement: strict # use 'strict' once you have the right plugs and slots

        command: desktop-launch python3 $SNAP/usr/bin/testsnap.py
        plugs: [x11, unity7, pulseaudio, home, gsettings, network]
            LD_LIBRARY_PATH: $LD_LIBRARY_PATH:$SNAP/usr/lib/x86_64-linux-gnu/pulseaudio

        # See 'snapcraft plugins'
        plugin: python
        python-version: python3
        source: .
            - libssl-dev
            - libjpeg-dev
            - libtiff-dev
            - libsdl1.2-dev
            - libnotify-dev
            - freeglut3
            - ibus-gtk3
            - zlib1g
            - libsm6
            - libpulse0
            - webkitgtk
            - desktop-gtk3
            - https://extras.wxpython.org/wxPython4/extras/linux/gtk3/ubuntu-16.04/wxPython-4.0.4-cp35-cp35m-linux_x86_64.whl
        override-build: |
            snapcraftctl build
            cp $SNAPCRAFT_PART_SRC/testsnap.py $SNAPCRAFT_PART_INSTALL/usr/bin/
            chmod +x $SNAPCRAFT_PART_INSTALL/usr/bin/testsnap.py

            - gcc
        plugin: cmake
            - -DCMAKE_INSTALL_PREFIX=/
            - -DCMAKE_BUILD_TYPE=Release
            - -DPORT=GTK
            - -DENABLE_WEB_CRYPTO=0
            - -DUSE_OPENJPEG=0
            - -DUSE_WOFF2=0
            - -DUSE_GSTREAMER_GL=0
            - -DENABLE_MEDIA_SOURCE=0
            - -DCMAKE_C_COMPILER=gcc-6
            - -DCMAKE_CXX_COMPILER=g++-6
        source: https://www.webkitgtk.org/releases/webkitgtk-2.24.1.tar.xz
            - ruby
            - libgcrypt20-dev
            - libwebp-dev
            - libxslt1-dev
            - libsecret-1-dev
            - libtasn1-6-dev
            - libenchant-dev
            - libhyphen-dev
            - libjpeg-dev
            - libsoup2.4-dev
            - libxkbcommon-dev
            - libnghttp2-14
            - libpixman-1-dev
            - libsqlite3-dev
            - libgl1-mesa-dev
            - freeglut3-dev 
            - libgirepository1.0-dev
            - libgtk-3-dev
            - libgtk2.0-dev
            - libnotify-dev
            - libgstreamer1.0-dev
            - libgstreamer-plugins-base1.0-dev
            - libc6
            - libstdc++6
            - libgl1
            - libgles2
            - geoclue-2.0
            - gperf
            - gobject-introspection

        plugin: nil
        override-pull: 'true'
        override-build: |
            sudo apt --yes install software-properties-common

            # Install newer GCC from Toolchain test builds PPA
            sudo add-apt-repository --yes ppa:ubuntu-toolchain-r/test
            sudo apt update
            sudo apt --yes install gcc-6 g++-6

        override-stage: 'true'
        override-prime: 'true'

Snap is created successfully. But I have error during application launch:

** (testsnap.py:21609): WARNING **: Failed to start web extension server on unix:tmpdir=/tmp: Error binding to address: Permission denied

** (testsnap.py:21609): ERROR **: Unable to fork a new child process: Failed to execute child process “/usr/libexec/webkit2gtk-4.0/WebKitWebProcess” (No such file or directory)

And application falls.

WebKitWebProcess file exists in /snap/testsnap-py/current/usr/libexec/webkit2gtk-4.0/ directory.

What can I do in this situation?

The error disappeared after adding lines:

            bind: $SNAP/usr/libexec/webkit2gtk-4.0
            bind: $SNAP/usr/lib/webkit2gtk-4.0/injected-bundle

But the warning remains:

Failed to start web extension server on unix:tmpdir=/tmp: Error binding to address: Permission denied

install the snappy-debug snap and run:

sudo snappy-debug.scanlog -r

to see if/what interfaces are missing in your snap (the output will make suggestions).

The log contains the following entries:

= AppArmor =
Time: May 14 07:42:01
Log: apparmor="DENIED" operation="bind" profile="snap.testsnap-py.testsnap-py" pid=28340 comm="python3" family="unix" sock_type="stream" protocol=0 requested_mask="bind" denied_mask="bind" addr="@/tmp/dbus-XLHbtEsI"

I added the plug network-bind, but it did not help.

Your snap is

network-bind gives you the bind syscall, but this is an AppArmor denial. Is your snap trying to start a private dbus session?

I do not use it explicitly, but maybe WebKit uses it for its own purposes.