Improved disk login logic safety.

atm.lua

@@ -18,35 +18,47 @@ local function drawFrame()
     g.drawText(term, 2, 1, "ATM", colors.white, colors.black)
 end
 
+local function tryReadDiskCredentials(name)
+    if disk.hasData(name) then
+        local dataFile = fs.combine(disk.getMountPath(name), "bank-credentials.json")
+        if fs.exists(dataFile) then
+            local f = io.open(dataFile, "r")
+            local content = textutils.unserializeJSON(f:read("*a"))
+            f:close()
+            if (
+                content ~= nil and
+                content.username and
+                type(content.username) == "string" and
+                content.password and
+                type(content.password) == "string"
+            ) then
+                return content
+            end
+        end
+    end
+    return nil
+end
+
 local function showLoginUI()
     drawFrame()
     g.drawTextCenter(term, W/2, 3, "Welcome to HandieBank ATM!", colors.green, colors.white)
     g.drawTextCenter(term, W/2, 5, "Insert your card below, or click to login.", colors.black, colors.white)
-    g.fillRect(term, W/2 - 3, 7, 9, 3, colors.green)
+    g.fillRect(term, 22, 7, 9, 3, colors.green)
     g.drawTextCenter(term, W/2, 8, "Login", colors.white, colors.green)
     while true do
         local event, p1, p2, p3 = os.pullEvent()
         if event == "disk" then
-            local side = p1
-            if disk.hasData(side) then
-                local mountPath = disk.getMountPath(side)
-                local dataFile = fs.combine(disk.getMountPath(side), "bank-credentials.json")
-                if fs.exists(dataFile) then
-                    local f = io.open(dataFile, "r")
-                    local content = f:read("*a")
-                    f:close()
-                    return textutils.unserializeJSON(content)
-                else
-                    disk.eject(side)
-                end
+            local credentials = tryReadDiskCredentials(p1)
+            if credentials then
+                return credentials
             else
-                disk.eject(side)
+                disk.eject(p1)
             end
         elseif event == "mouse_click" then
             local button = p1
             local x = p2
             local y = p3
-            if button == 1 and x >= (W/2 - 3) and x <= (W/2 + 4) and y >= 7 and y <= 9 then
+            if button == 1 and x >= 22 and x <= 30 and y >= 7 and y <= 9 then
                 -- TODO: Show login input elements.
                 return {username = "bleh", password = "bleh"}
             end
@@ -57,5 +69,6 @@ end
 while true do
     local credentials = showLoginUI()
     g.clear(term, colors.black)
+    print("Credentials: " .. textutils.serialize(credentials))
     return
 end