Resume failed update feature (#1226)

* [PATCH 1/2] Resume failed download

* [PATCH 2/2] Get proper local directory

* [PATCH 1/2] Fix flashing command prompt during update check

-use GetScriptPath and GetRuntimePath to assign vas in UpdateCheck.lua
-fixes flashing command prompt caused by io.popen
-fall back to "." if unable to determine paths

* [PATCH 2/2] Define scriptPath and runtimePath as local

-preserves original definition, prevents global namespace pollution

* Use local script path

---------

Co-authored-by: Craig Citro <craig@citro.net>

Author: Wires77

src/UpdateCheck.lua

@@ -78,6 +78,7 @@ end
 
 ConPrintf("Checking for update...")
 
+-- Use built-in helpers to obtain absolute paths without spawning a shell.
 local scriptPath = "."
 local runtimePath = "."
 
@@ -214,7 +215,6 @@ for index, data in ipairs(updateFiles) do
 	source = source:gsub("{branch}", localBranch)
 	local fileName = scriptPath.."/Update/"..data.name:gsub("[\\/]","{slash}")
 	data.updateFileName = fileName
-	local content
 	local zipName = source:match("/([^/]+%.zip)$")
 	if zipName then
 		if not zipFiles[zipName] then
@@ -238,8 +238,20 @@ for index, data in ipairs(updateFiles) do
 			ConPrintf("Couldn't extract '%s' from '%s' (zip open failed)", data.name, zipName)
 		end
 	else
-		ConPrintf("Downloading %s... (%d of %d)", data.name, index, #updateFiles)
-		downloadFile(source, data.name, fileName)
+		local skipDownload
+		local file = io.open(fileName, "rb")
+		if file then
+			local content = file:read("*all")
+			if data.sha1 == sha1(content) or data.sha1 == sha1(content:gsub("\n", "\r\n")) then
+				ConPrintf("Using file from previous update attempt '%s'", fileName)
+				skipDownload = true
+			end
+			file:close()
+		end
+		if not skipDownload then
+			ConPrintf("Downloading %s... (%d of %d)", data.name, index, #updateFiles)
+			downloadFile(source, data.name, fileName)
+		end
 	end
 	local file = io.open(fileName, "rb")
 	if not file then