[plugin] Add a caching mechanism for CoverImage (#7510)

frontend/device/android/device.lua

@@ -392,7 +392,20 @@ function Device:canExecuteScript(file)
 end
 
 function Device:isValidPath(path)
-    return android.isPathInsideSandbox(path)
+    -- the fast check
+    if android.isPathInsideSandbox(path) then
+        return true
+    end
+
+    -- the thorough check
+    local real_ext_storage = FFIUtil.realpath(android.getExternalStoragePath())
+    local real_path = FFIUtil.realpath(path)
+
+    if real_path then
+        return real_path:sub(1, #real_ext_storage) == real_ext_storage
+    else
+        return false
+    end
 end
 
 function Device:showLightDialog()
@@ -432,6 +445,15 @@ function Device:untar(archive, extract_to)
     return android.untar(archive, extract_to)
 end
 
+-- todo: Wouldn't we like an android.deviceIdentifier() method, so we can use better default paths?
+function Device:getDefaultCoverPath()
+    if android.prop.product == "ntx_6sl" then -- Tolino HD4 and other
+        return android.getExternalStoragePath() .. "/suspend_others.jpg"
+    else
+        return android.getExternalStoragePath() .. "/cover.jpg"
+    end
+end
+
 android.LOGI(string.format("Android %s - %s (API %d) - flavor: %s",
     android.prop.version, getCodename(), Device.firmware_rev, android.prop.flavor))
 

frontend/device/generic/device.lua

@@ -4,6 +4,7 @@ Generic device abstraction.
 This module defines stubs for common methods.
 --]]
 
+local DataStorage = require("datastorage")
 local logger = require("logger")
 local util = require("util")
 local _ = require("gettext")
@@ -503,6 +504,10 @@ function Device:isStartupScriptUpToDate()
     return true
 end
 
+function Device:getDefaultCoverPath()
+    return DataStorage:getDataDir() .. "/cover.jpg"
+end
+
 --- Unpack an archive.
 -- Extract the contents of an archive, detecting its format by
 -- filename extension. Inspired by luarocks archive_unpack()

frontend/device/pocketbook/device.lua

@@ -363,6 +363,10 @@ function PocketBook:getDeviceModel()
     return ffi.string(inkview.GetDeviceModel())
 end
 
+function PocketBook:getDefaultCoverPath()
+    return "/mnt/ext1/system/logo/offlogo/cover.bmp"
+end
+
 -- Pocketbook HW rotation modes start from landsape, CCW
 local function landscape_ccw() return {
     1, 0, 3, 2,         -- PORTRAIT, LANDSCAPE, PORTRAIT_180, LANDSCAPE_180

frontend/device/remarkable/device.lua

@@ -200,6 +200,10 @@ end
 
 logger.info(string.format("Starting %s", rm_model))
 
+function Remarkable:getDefaultCoverPath()
+    return "/usr/share/remarkable/poweroff.png"
+end
+
 if isRm2 then
     if not os.getenv("RM2FB_SHIM") then
         error("reMarkable2 requires RM2FB to work (https://github.com/ddvk/remarkable2-framebuffer)")