General

The general contract is that a plugin is made up of five kinds of files:

The metadata.xml file [mandatory].
The dynamic library(.so/.dll/.dylib) [mandatory].
Optional helper binaries.
Data files
Translations

The tarball is the output from make install where these files are located in the System Install Dir. In other words, the plugin should work as expected if the tarball is extracted on the system.

The plugin installer works by translating these typically read-only paths to the rw User Install path. For example, on linux:

  /usr/share/opencpn   =>  ~/.local/share/opencpn
  /usr/bin             =>  ~/.local/bin
  /usr/lib/opencpn     =>  ~/.local/lib/opencpn

The corresponding substitutions are made on other platforms. For this to work the tarball needs to have a specific layout like in examples below. The example plugins contains:

A mandatory dynamic library oesenc (with platform dependent mutations.)
A helper binary oeserverd
Data files: SymbolPatch5.xml and license.txt
Translations

Here is just a few file(s) of each kind mentioned; there are more of them in the actual plugin.

Example macos layout

  oesenc_pi-1.2.0-2
      ├── metadata.xml
      └──  OpenCPN.app
            └── Contents
                 ├── PlugIns
                 │   ├── liboesenc_pi.dylib
                 │   └── oeserverd
                 ├── Resources
                 │   ├── ar_SA.lproj
                 │   │    └── opencpn-oesenc_pi.mo
                 │   └── bg_BG.lproj
                 │        └── opencpn-oesenc_pi.mo
                 │
                 └── SharedSupport
                     └── plugins
                         └── oesenc_pi
                             └── data
                                 ├── license.txt
                                 └── SymbolPatch5.xml

Example flatpak layout

  oesenc_pi-flatpak-1.2.0/
      ├── metadata.xml
      ├── bin
      │   ├── oeserver
      │   └── oeserverd.prog
      ├── lib
      │   └── opencpn
      │       └── liboesenc_pi.so
      ├── manifest.json
      └── share
          ├── locale
          │   ├── ar_SA
          │   │   └── LC_MESSAGES
          │   │       └── opencpn-oesenc_pi.mo
          │   └── ca_ES
          │       └── LC_MESSAGES
          │           └── opencpn-oesenc_pi.mo
          └── opencpn
              └── plugins
                  └── oesenc_pi
                      └── data
                           ├── license.txt
                           └── SymbolPatch5.xml

Example Ubuntu layout

  oesenc_pi-1.2.0-2_ubuntu-16.04
      │
      ├── metadata.xml
      ├── bin
      │   └── oeserverd
      ├── lib
      │   └── opencpn
      │       ├── liboesenc_pi.so
      │       └── libsgllnx64-2.29.02.so
      └── share
          ├── locale
          │   ├── ar_SA
          │   │   └── LC_MESSAGES
          │   │       └── opencpn-oesenc_pi.mo
          │   └── bg_BG
          │       └── LC_MESSAGES
          │           └── opencpn-oesenc_pi.mo
          └── opencpn
              └── plugins
                  └── oesenc_pi
                      └── data
                          ├── license.txt
                          └── SymbolPatch5.xml

The example shows the directories bin, lib and share in the top directory. Having them as /usr/\{bin, lib, share} or /usr/local/\{bin, lib, share} is also ok.

Example windows layout

  oesenc_pi-1.2.0-2_msvc-10.0.14393
   ├── metadata.xml
   ├── plugins
   │   ├── oesenc_pi
   │   │   ├── data
   │   │   │   ├── license.txt
   │   │   │   └── SymbolPatch5.xml
   │   │   ├── msvcp140.dll
   │   │   ├── oeserverd.exe
   │   │   └── vcruntime140.dll
   │   └── oesenc_pi.dll
   └── share
         └── locale
               ├── ar_SA
               │   └── LC_MESSAGES
               │        └── opencpn-oesenc_pi.mo
               └── bg_BG
                   └── LC_MESSAGES
                        └── opencpn-oesenc_pi.mo

Tarball names

The filename need to be unique and are formed like

  <plugin name>-<version>[-release]_<target os>-<target os version>[-arch].tar.gz

for example oesenc_pi-1.2.0-3_ubuntu-18.04-armhf.tar.gz. The release and arch parts are optional and can be omitted.