How can we cache images in some kind of non-volatile memory in Roku after initially loading images from an AWS S3 bucket?

Issue

Developing screensaver channel and fetching images from AWS S3 bucket.

Environment

SDK 

Answer

You can cache images by using CacheFS. In the same way that a file can be read from “pkg:/filepath/filename,” you can write and read from “cachefs:/filepath/filename."

CacheFS is available to all channels on our platform. 

If you launch Channel A (which is using CacheFS) and later launch Channel B (which is also using CacheFS) on the same device, it is possible that Channel A's images are no longer cached due to CacheFS memory constraints. 

Example of how to check if images is in CacheFS:

 for each image in xml.image
       cl=createobject("roSGNode","ContentNode")
       cl.addField("url","string",false)
       cl.addfield("title","string",false)
       cl.addfield("author","string",false)
 
       xfer.seturl(image.url.gettext())
       'find last slash
         txtstr=image.url.gettext()
         txtstr=mid(txtstr,instr(txtstr,"//")+1)
         while instr(txtstr,"/") > 0
           txtstr=mid(txtstr,instr(txtstr,"/")+1)
         end while
 
         ttimer=createobject("rotimespan")
         ttimer.mark()
         if not fs.exists("cachefs:/"+txtstr) then
 
             print "not in cache, get image"
             xfer.seturl(image.url.gettext())
             xfer.gettofile("cachefs:/"+txtstr)
             print "transfer time";ttimer.totalmilliseconds()
 
         else
             print "found in cache!!!"
             txtstr=image.url.gettext()
         end if
         print "transfer time";ttimer.totalmilliseconds()
 
       cl.setfield("url",txtstr)
       cl.setfield("title",image.title.getText())
       cl.setfield("author",image.author.getText())
       ?image.url.gettext()
       ?image.author.gettext()
       ?image.title.gettext()
       slidenode.appendChild(cl)
       imgcount=imgcount+1
       if imgcount > 20 then exit for
     end for

Additional Resources

Architecture essentials > File system > Cachefs documentation

Is it possible to add roBitmap component to CacheFS?

If you are building a SceneGraph channel, we don't currently have a way to extract a bitmap and save it to a file. 

However, if you are building a game using the 2D API, you can save a .png from an roBitmap by calling GetByteArray.