resty_functions/prod/upload/combine.lua

local uuid      = require "resty.jit-uuid"
local cjson     = require "cjson"
uuid.seed()

local file_dir = ngx.var.tmp_file_dir
ngx.req.read_body()
local req_body = cjson.decode(ngx.req.get_body_data())

local data = req_body["data"]
local combined = file_dir .. "/" .. uuid.generate_v4() .. ".jpeg";
local len = table.getn(data)
local origin = {}
for i = 1, len do
    origin[i] = file_dir .. "/" .. data[i] .. " "
end
-- linux
local magick = "/usr/local/ImageMagick/bin/magick"
local tmp = io.open(magick,"r")
if tmp == nil then
    -- mac os
    magick = "/usr/local/bin/magick"
else
    io.close(tmp)
end

local result, _, code = os.execute(magick .. " convert -append " .. table.concat(origin, " ") .. " " .. combined)
if result and code == 0 then
    local file = io.open(combined)
    local content = file:read("*all")
    file:close()
    os.remove(combined)
    ngx.say(content)
else
    ngx.status = 500
    ngx.say("image combine failed.")
end