If the uploaded file is a picture，I want it to be a 2048 by 2048 image with maximum height and width

while true do
	local typ, res, err = form:read()
	if not typ then
		ngx.say("failed to read: ", err)
		return
	end
	if typ == "header" then
		local key = res[1]
		local value = res[2]
		if key == "Content-Disposition" then
		local kvlist = string.split(value, ';')
			for _, kv in ipairs(kvlist) do
				local seg = string.trim(kv)
				if seg:find("filename") then
					local kvfile = string.split(seg, "=")
					local filename = string.sub(kvfile[2], 2, -2)
					if filename then
						ext = getExtension(filename)
						local now = os.date("%Y%m%d%H%M%S", os.time())
						local filename = now.."-"..string.sub(ngx.md5(now..user_cid), 0, 8)..ext
						local image_id = ""
						if string.find(uri, "/upload/photo") then
							uri = string.gsub(ngx.var.uri, '/upload/photo', "/bfs/g/"..filename)
							image_id = "/g/"..filename
						elseif string.find(uri, "/upload/voice") then
							uri = string.gsub(ngx.var.uri, '/upload/voice', "/bfs/v/"..filename)
						else 
							ngx.print(cjson.encode({code=404, message="Not Found"}))
							ngx.exit(404)
						end
						break
					end
				end
			end
		end
	--append body
	elseif typ == "body" then
		if res then
				appender = appender..res
		end
	--one file has been read
	elseif typ == "part_end" then
		if appender ~= '' then
			-- If the uploaded file is a picture，I want it to be a 2048 by 2048 image with maximum height and width
			code = upload2BFS(uri, data)

Start at the /upload/photo branch in the upload loop and trace how the uploaded data reaches upload2BFS(uri, data). Determine how picture files are identified and how the 2048 maximum height and width requirement should be applied. Done should be demonstrated by verified picture-upload behavior, but the issue does not name tests or implementation files.