Add updater script using the HTTP API (#27)

Check for core feature `httpfetch_binary_data` to run the updater properly.
This requires Minetest cb00632 or newer.
README.md: Add documentation for the updater

skins_updater.lua

@@ -0,0 +1,115 @@
+-- Skins update script
+-- Load it in init.lua or write a frontend GUI/chatcommand for it. Good luck.
+
+local _ID_ = "Lua Skins Updater"
+local _SKIN_PAGE_START_ = 1   -- Starting page to fetch the skins
+local _SKIN_PAGE_END_   = nil -- End page number (nil = all skins)
+
+if not core.features.httpfetch_binary_data then
+	error(_ID_ .. " requires the feature 'httpfetch_binary_data'. Update Minetest.")
+end
+
+local ie, http = skins.ie, skins.http
+if not ie or not http then
+	error(_ID_ .. " requires the insecure environment. " ..
+		"Please add skinsdb to `secure.trusted_mods` in minetest.conf")
+end
+
+-- http://minetest.fensta.bplaced.net/api/apidoku.md
+local root_url = "http://minetest.fensta.bplaced.net"
+local page_url = root_url .. "/api/v2/get.json.php?getlist&page=%i&outformat=base64" -- [1] = Page#
+local preview_url = root_url .. "/skins/1/%i.png" -- [1] = ID
+
+local mod_path = skins.modpath
+local meta_path = mod_path .. "/meta/"
+local skins_path = mod_path .. "/textures/"
+
+-- Fancy debug wrapper to download an URL
+local function fetch_url(url, callback)
+	http.fetch({
+		url = url,
+		user_agent = _ID_
+	}, function(result)
+		if result.succeeded then
+			if result.code ~= 200 then
+				core.log("warning", ("%s: STATUS=%i URL=%s"):format(
+					_ID_, result.code, url))
+			end
+			return callback(result.data)
+		end
+		core.log("warning", ("%s: Failed to download URL=%s"):format(
+			_ID_, url))
+	end)
+end
+
+-- Insecure workaround since meta/ and textures/ cannot be written to
+local function unsafe_file_write(path, contents)
+	local f = ie.io.open(path, "w")
+	f:write(contents)
+	f:close()
+end
+
+-- Takes a valid skin table from the Skins Database and saves it
+local function safe_single_skin(skin)
+	local meta = {
+		skin.name,
+		skin.author,
+		skin.license
+	}
+
+	local name =  "character_" .. skin.id
+
+	-- core.safe_file_write does not work here
+	unsafe_file_write(
+		meta_path .. name .. ".txt",
+		table.concat(meta, "\n")
+	)
+
+	unsafe_file_write(
+		skins_path .. name .. ".png",
+		core.decode_base64(skin.img)
+	)
+	fetch_url(preview_url:format(skin.id), function(preview)
+		unsafe_file_write(skins_path .. name .. "_preview.png", preview)
+	end)
+	core.log("action", ("%s: Completed skin %s"):format(_ID_, name))
+end
+
+-- Get total pages since it'll just return the last page all over again
+local function get_pages_count(callback)
+	fetch_url(page_url:format(1) .. "&per_page=5", function(data)
+		local list = core.parse_json(data)
+		print(dump(list))
+		callback(list.pages)
+	end)
+end
+	
+-- Just fetch them all. YOLO
+get_pages_count(function(pages_total)
+	local start_page = _SKIN_PAGE_START_ or 1
+	local end_page = math.min(pages_total, _SKIN_PAGE_END_ or pages_total)
+
+	for page_n = 1, end_page do
+		local page_cpy = page_n
+		fetch_url(page_url:format(page_n), function(data)
+			core.log("action", ("%s: Page %i"):format(_ID_, page_cpy))
+
+			local list = core.parse_json(data)
+			for i, skin in pairs(list.skins) do
+				assert(skin.type == "image/png")
+				assert(skin.id ~= "")
+
+				if skin.id ~= 1 then -- Skin 1 is bundled with skinsdb
+					safe_single_skin(skin)
+				end
+			end
+
+			if page_cpy == end_page then
+				core.log("action", _ID_ .. " finished downloading all skins. " ..
+					"Please comment out this script to reduce server traffic.")
+				core.request_shutdown("Reloading skinsdb media cache after download",
+					true, 3 --[[give some time for pending requests]])
+			end
+		end)
+	end
+end)