resty_functions/file_upload/upload_image.lua

local upload    = require "upload"
local uuid      = require "uuid"

local chunk_size = 5 -- should be set to 4096 or 8192
                     -- for real-world settings

local form, err = upload:new(chunk_size)

local output_image_filename_uuid = uuid.generate();

if not form then
    ngx.log(ngx.ERR, "failed to new upload: ", err)
    ngx.say("failed to new upload: ", err)
    ngx.exit(500)
end

form:set_timeout(1000) -- 1 sec

-- String split
string.split = function(s, p)
    local rt= {}
    string.gsub(s, '[^'..p..']+', function(w) table.insert(rt, w) end )
    return rt
end

-- Get file trim
string.trim = function(s)
    return (s:gsub("^%s*(.-)%s*$", "%1"))
end

-- Upload file save path config in nginx.conf
local saveRootPath = ngx.var.store_dir

local fileToSave
local ret_save = false
local upload_image_filename
local save_image_filename

local upload_image_table = {}
local upload_image_index = 1

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
        -- 开始读取 http header
        -- 解析出本次上传的文件名
        local key = res[1]
        local value = res[2]
        if key == "Content-Disposition" then
            -- 解析出本次上传的文件名
            -- form-data; name="testFileName"; filename="testfile.txt"
            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, "=")
                    upload_image_filename = string.sub(kvfile[2], 2, -2)

                    ngx.say(" -->> POST : Upload origin image is ", upload_image_filename)
                    ngx.say("\n")

                    if upload_image_filename then
                        -- Save file name with generate uuid
                        save_image_filename = uuid:generate()
                        save_image_filename = save_image_filename .. '.' .. upload_image_filename:match(".+%.(%w+)$")
                        fileToSave = io.open(saveRootPath .. save_image_filename, "w+")
                        if not fileToSave then
                            ngx.say(" Error: Failed to open file ", save_image_filename)
                            return
                        else
                            ngx.say("Open file ok ", save_image_filename)
                            ngx.say("\n")

                            upload_image_table[upload_image_index] = saveRootPath .. save_image_filename .. " "
                            ngx.say("Insert upload image table "..upload_image_index.." with "..upload_image_table[upload_image_index])
                            ngx.say("\n")

                            upload_image_index = upload_image_index + 1
                        end
                        break
                    end
                end
            end
        end
    elseif typ == "body" then
        -- 开始读取 http body
        if fileToSave then
            fileToSave:write(res)
        end
    elseif typ == "part_end" then
        -- 文件写结束，关闭文件
        if fileToSave then
            fileToSave:close()
            fileToSave = nil
        end

        ret_save = true
    elseif typ == "eof" then
        -- 文件读取结束
        break
    else
        ngx.log(ngx.INFO, "do other things")
    end
end
if ret_save then
    ngx.say("Show all upload files\n")

    -- Show all upload files
    upload_image_index = upload_image_index -1
    for i = 1, upload_image_index do
        ngx.say("Save upload file is : " .. upload_image_table[i])
        ngx.say("\n")
    end

    image_append_coroutine = coroutine.create(
        function ()
            -- Append images
            -- ngx.say("Upload image number is : " , upload_image_index )
            local append_images_path
            append_images_path = table.concat(upload_image_table)
            ngx.say("Input images list  : " , append_images_path)
            ngx.say("\n")

--             local append_output_image = saveRootPath .. uuid.generate()..".jpg ";
            local append_output_image = saveRootPath .. output_image_filename_uuid..".jpg ";
            ngx.say("Output image is : "..append_output_image)
            ngx.say("\n")

            -- Debug
            ngx.say('/usr/local/ImageMagick/bin/magick convert -append '..append_images_path..' '..append_output_image)
            ngx.say("\n")

            local call_imagemagick_cmd = io.popen('/usr/local/ImageMagick/bin/magick convert -append '..append_images_path..' '..append_output_image)
            local imagemagick_cmd_replay = call_imagemagick_cmd:read("*all")
            ngx.say(imagemagick_cmd_replay)


        end
    )

    coroutine.resume(image_append_coroutine)

end