Nginx LUA script for accessing a Redis request cache

nginx-redis-cache.lua

  local redis = require "resty.redis"
  local red = redis:new()
  red:set_timeout(1000) -- 1 sec

  local ok, err = red:connect("127.0.0.1", 6379)
  if not ok then
    ngx.log(ngx.ERR, "Redis failed to connect")
    return ngx.exit(ngx.HTTP_SERVICE_UNAVAILABLE)
  end

  uri = ngx.var.uri
  meta = uri.."-meta"
  content = uri.."-content"

  -- First get the info hash
  local arr, err = red:hgetall(meta)
  if not arr then
    return ngx.exit(ngx.HTTP_NOT_FOUND)  -- NOT FOUND
  end

  hash = red:array_to_hash(arr)

  local ttl, err = red:ttl(content)
  if ttl > 0 then
    ngx.header.Cache_Control = "max-age="..ttl
  end

  if hash['etag'] then
    if ngx.req.get_headers()["If-None-Match"] == hash['etag'] then
      return ngx.exit(ngx.HTTP_NOT_MODIFIED) -- NOT MODIFIED
    end
    ngx.header.ETag = hash['etag']
  end

  if hash['content_type'] then
    ngx.header.Content_Type = hash['content_type']
  end

  if hash['content_encoding'] then
    ngx.header.Content_Encoding = hash['content_encoding']
  end

  if hash['content_length'] then
    ngx.header.Content_Length = hash['content_length']
  end

  -- Get the actual content now we know the user needs it
  local body, err = red:get(content)
  if not body then
    return ngx.exit(ngx.HTTP_NOT_FOUND) -- 404 to continue to the upstream
  end
  if body == ngx.null then
    return ngx.exit(ngx.HTTP_NOT_FOUND)
  end

  ngx.header.Source = "Redis"
  ngx.print(body)