NewsDownloader: add a cache to reduce wasted bandwidth

Closes koreader#13061.

plugins/newsdownloader.koplugin/epubdownloadbackend.lua

@@ -1,3 +1,5 @@
+local CacheSQLite = require("cachesqlite")
+local DataStorage = require("datastorage")
 local Version = require("version")
 local ffiutil = require("ffi/util")
 local http = require("socket.http")
@@ -22,6 +24,12 @@ local EpubDownloadBackend = {
 }
 local max_redirects = 5; --prevent infinite redirects
 
+local FeedCache = CacheSQLite:new{
+    slots = 500,
+    db_path = DataStorage:getDataDir() .. "/cache/newsdownloader.sqlite",
+    size = 1024 * 1024 * 10, -- 10MB
+}
+
 -- filter HTML using CSS selector
 local function filter(text, element)
     local htmlparser = require("htmlparser")
@@ -150,8 +158,8 @@ local function build_cookies(cookies)
 end
 
 -- Get URL content
-local function getUrlContent(url, cookies, timeout, maxtime, redirectCount)
-    logger.dbg("getUrlContent(", url, ",", cookies, ", ", timeout, ",", maxtime, ",", redirectCount, ")")
+local function getUrlContent(url, cookies, timeout, maxtime, redirectCount, add_to_cache)
+    logger.dbg("getUrlContent(", url, ",", cookies, ", ", timeout, ",", maxtime, ",", redirectCount, ",", add_to_cache, ")")
     if not redirectCount then
         redirectCount = 0
     elseif redirectCount == max_redirects then
@@ -209,7 +217,7 @@ local function getUrlContent(url, cookies, timeout, maxtime, redirectCount)
              redirected_url = socket_url.build(parsed_redirect_location)
            end
            logger.dbg("getUrlContent: Redirecting to url: ", redirected_url)
-           return getUrlContent(redirected_url, timeout, maxtime, redirectCount + 1)
+           return getUrlContent(redirected_url, timeout, maxtime, redirectCount + 1, add_to_cache)
         else
            error("EpubDownloadBackend: Don't know how to handle HTTP response status:", status or code)
         end
@@ -223,10 +231,23 @@ local function getUrlContent(url, cookies, timeout, maxtime, redirectCount)
             return false, "Incomplete content received"
         end
     end
+
+    if add_to_cache then
+        logger.dbg("Adding to cache", url)
+        FeedCache:insert(url, {
+            headers = headers,
+            content = content,
+        })
+    end
+
     logger.dbg("Returning content ok")
     return true, content
 end
 
+function EpubDownloadBackend:getCache()
+    return FeedCache
+end
+
 function EpubDownloadBackend:getConnectionCookies(url, credentials)
 
     local body = ""
@@ -258,9 +279,9 @@ function EpubDownloadBackend:getConnectionCookies(url, credentials)
     return cookies
 end
 
-function EpubDownloadBackend:getResponseAsString(url, cookies)
+function EpubDownloadBackend:getResponseAsString(url, cookies, add_to_cache)
     logger.dbg("EpubDownloadBackend:getResponseAsString(", url, ")")
-    local success, content = getUrlContent(url, cookies)
+    local success, content = getUrlContent(url, cookies, nil, nil, nil, add_to_cache)
     if (success) then
         return content
     else

plugins/newsdownloader.koplugin/main.lua

@@ -16,8 +16,11 @@ local NetworkMgr = require("ui/network/manager")
 local Persist = require("persist")
 local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local dateparser = require("lib.dateparser")
+local http = require("socket.http")
 local lfs = require("libs/libkoreader-lfs")
+local ltn12 = require("ltn12")
 local logger = require("logger")
+local socket = require("socket")
 local util = require("util")
 local _ = require("gettext")
 local T = FFIUtil.template
@@ -341,16 +344,52 @@ function NewsDownloader:loadConfigAndProcessFeedsWithUI(touchmenu_instance)
 end
 
 function NewsDownloader:processFeedSource(url, credentials, limit, unsupported_feeds_urls, download_full_article, include_images, message, enable_filter, filter_element)
+    -- Check if we have a cached response first
+    local cache = DownloadBackend:getCache()
+    local cached_response = cache:check(url)
+    local ok, response
 
     local cookies = nil
     if credentials ~= nil then
-        logger.dbg("Auth Cookies from ", cookies)
+        logger.dbg("Auth Cookies from ", credentials.url)
         cookies = DownloadBackend:getConnectionCookies(credentials.url, credentials.auth)
     end
 
-    local ok, response = pcall(function()
-            return DownloadBackend:getResponseAsString(url, cookies)
-    end)
+    if cached_response then
+        logger.dbg("NewsDownloader: Using cached response for ", url)
+        local headers_cached = cached_response.headers
+        logger.dbg("NewsDownloader: Cached response headers", headers_cached)
+
+        -- use last-modified from headers to send a modified since request
+        local last_modified = headers_cached["last-modified"]
+        if last_modified then
+            logger.dbg("NewsDownloader: sending If-Modified-Since", last_modified, url)
+            local response_body = {}
+            local headers = {
+                ["If-Modified-Since"] = last_modified
+            }
+            if cookies then
+                headers["Cookie"] = cookies
+            end
+            local code, response_headers = socket.skip(1, http.request{
+                url = url,
+                headers = headers,
+                sink = ltn12.sink.table(response_body)
+            })
+            ok = (code == 304)
+            logger.dbg("NewsDownloader: If-Modified-Since response", code, response_headers)
+            if ok then
+                response = cached_response.content
+            end
+        end
+    end
+
+    if not response then
+        ok, response = pcall(function()
+            return DownloadBackend:getResponseAsString(url, cookies, true)
+        end)
+    end
+
     local feeds
     -- Check to see if a response is available to deserialize.
     if ok then