add getCoverPageImage api for CreDocument

frontend/document/credocument.lua

@@ -3,11 +3,13 @@ local Document = require("document/document")
 local Configurable = require("configurable")
 local Blitbuffer = require("ffi/blitbuffer")
 local lfs = require("libs/libkoreader-lfs")
+local Image = require("ffi/mupdfimg")
 local Geom = require("ui/geometry")
 local Device = require("ui/device")
 local Screen = require("ui/screen")
 local Font = require("ui/font")
 local DEBUG = require("dbg")
+local ffi = require("ffi")
 
 local CreDocument = Document:new{
     -- this is defined in kpvcrlib/crengine/crengine/include/lvdocview.h
@@ -130,6 +132,16 @@ function CreDocument:getPageCount()
     return self._document:getPages()
 end
 
+function CreDocument:getCoverPageImage()
+    self._document:loadDocument(self.file)
+    local data, size = self._document:getCoverPageImageData()
+    if data and size then
+        local image = Image:fromData(data, size)
+        ffi.C.free(data)
+        return image
+    end
+end
+
 function CreDocument:getWordFromPosition(pos)
     local word_box = self._document:getWordFromPosition(pos.x, pos.y)
     DEBUG("CreDocument: get word box", word_box)

spec/unit/document_spec.lua

@@ -54,6 +54,12 @@ describe("EPUB document module", function()
         doc = DocumentRegistry:openDocument(sample_epub)
         assert.truthy(doc)
     end)
+    it("should get cover image", function()
+        local image = doc:getCoverPageImage()
+        assert.truthy(image)
+        assert.are.same(image:getWidth(), 442)
+        assert.are.same(image:getHeight(), 616)
+    end)
     it("should close document", function()
         doc:close()
     end)