Adding UDP logger plugin

[sshniro]

The UDP logger sends the logs to a UDP server.
Fix for #1069

[membphis]

There are performance issues with the per-request log message mode.

It is better to put log messages in the queue first, and then send them in batches.

[moonming]

There are performance issues with the per-request log message mode.

It is better to put log messages in the queue first, and then send them in batches.

Done is better then perfect. I think we can use another PR to fix performance issues.

[membphis]

t/admin/plugins.t ...................... 1/? 
#   Failed test 'TEST 1: get plugins' name - response_body_like - response is expected (["limit-req","limit-count","limit-conn","key-auth","basic-auth","prometheus","node-status","jwt-auth","zipkin","ip-restriction","grpc-transcode","serverless-pre-function","serverless-post-function","openid-connect","proxy-rewrite","redirect","response-rewrite","fault-injection","udp-logger"])'
#   at /home/travis/build/apache/incubator-apisix/test-nginx/lib/Test/Nginx/Socket.pm line 1635.
#                   '["limit-req","limit-count","limit-conn","key-auth","basic-auth","prometheus","node-status","jwt-auth","zipkin","ip-restriction","grpc-transcode","serverless-pre-function","serverless-post-function","openid-connect","proxy-rewrite","redirect","response-rewrite","fault-injection","udp-logger"]
# '
#     doesn't match '(?^:\["limit-req","limit-count","limit-conn","key-auth","prometheus","node-status","jwt-auth","zipkin","ip-restriction","grpc-transcode","serverless-pre-function","serverless-post-function","openid-connect","proxy-rewrite","redirect","response-rewrite","udp-logger"\])'
t/admin/plugins.t ...................... 3/? # Looks like you failed 1 test of 3.

[sshniro]

@membphis The following is the final log sent to the server.

{
  "upstream": "127.0.0.1:80",
  "start_time": 1579231324391,
  "client_ip": "127.0.0.1",
  "service_id": "10",
  "route_id": "5",
  "request": {
    "querystring": {
      "param1": "value"
    },
    "size": 118,
    "uri": "/?param1=value",
    "url": "http://127.0.0.1:9080/?param1=value",
    "headers": {
      "host": "127.0.0.1:9080",
      "apikey": "superSecretAPIKey",
      "accept": "*/*",
      "user-agent": "curl/7.58.0"
    },
    "method": "GET"
  },
  "response": {
    "headers": {
      "accept-ranges": "bytes",
      "content-type": "text/html",
      "date": "Fri, 17 Jan 2020 03:22:04 GMT",
      "server": "APISIX web server",
      "connection": "close",
      "last-modified": "Thu, 29 Aug 2019 23:49:13 GMT",
      "etag": "\"5d686479-289\"",
      "content-length": "649"
    },
    "status": 200,
    "size": 892
  },
  "latency": 0.99992752075195
}

should I round the number for latency?

[membphis]

should I round the number for latency?

Recommended to milliseconds.

[sshniro]

@membphis the review comments have been resolved, thanks for the pointers.

[membphis]

Look good to me