{"id":2041,"date":"2015-01-24T22:56:01","date_gmt":"2015-01-24T22:56:01","guid":{"rendered":"http:\/\/41j.com\/blog\/?p=2041"},"modified":"2015-01-24T22:56:01","modified_gmt":"2015-01-24T22:56:01","slug":"simple-js-dns-proxy-golang-server-side","status":"publish","type":"post","link":"https:\/\/41j.com\/blog\/2015\/01\/simple-js-dns-proxy-golang-server-side\/","title":{"rendered":"Simple JS->DNS Proxy with golang server side"},"content":{"rendered":"

\"jsdnsproxy\"<\/a><\/p>\n

I wanted the ability to resolve DNS addresses in client side Javascript. Unfortunately you can’t do DNS lookups in browser. As a hack I wrote a quick DNS proxy in golang which allows the JS to perform GET requests to a golang server which will lookup and DNS entry and return IP addresses.<\/p>\n

The HTML and golang code is below, there’s also a tarball here<\/a>. You can run the go code with “go run”. If the html file is stored in the same directory you will be able to access it from localhost at http:\/\/localhost:8080\/web.html.<\/p>\n

\r\n<html>\r\n<head>\r\n<meta charset="UTF-8" \/>\r\n\r\n<script>\r\n  \r\n  function gethostbyname(hostname) {\r\n    var xmlHttp = new XMLHttpRequest();\r\n    xmlHttp.open("GET", "http:\/\/localhost:8080\/dns?hostname=" + hostname, false);\r\n    xmlHttp.send(null);\r\n    return xmlHttp.responseText;\r\n  }\r\n\r\n  function press() {\r\n    var hostname = document.getElementById('hostname').value;\r\n    document.getElementById('comms').innerHTML += hostname + "=" + gethostbyname(hostname)  + "<br>";\r\n  }\r\n\r\n<\/script>\r\n\r\n<\/head>\r\n<body>\r\n  ServerIP: <input id="hostname" type="text" \/><br>\r\n  <input type="button" id="lookup" value="lookup" onclick="press()"><\/input><br><br>\r\n  <div id='comms'><\/div>\r\n<\/body>\r\n<\/html>\r\n<\/pre>\n
\r\npackage main\r\n \r\nimport (\r\n    "net\/http"\r\n    "net"\r\n    "fmt"\r\n)\r\n\r\nfunc DNSProxyHandler(w http.ResponseWriter, r *http.Request) {\r\n \r\n  r.ParseForm()\r\n  hostname := r.Form.Get("hostname")\r\n\r\n  fmt.Printf("hostname: %s\\n",hostname)\r\n  \r\n  addrs, err := net.LookupIP(hostname)\r\n\r\n  var sendbytes string;\r\n  if err == nil {\r\n    sendbytes = addrs[0].String()\r\n    fmt.Printf("sending: %s",sendbytes)\r\n  } else {\r\n    fmt.Printf("fail in dnsroxy\\n")\r\n  }\r\n\r\n  fmt.Fprintf(w, "%s",sendbytes);\r\n\r\n}\r\n \r\nfunc main() {\r\n  http.HandleFunc("\/dns" , DNSProxyHandler)\r\n  http.Handle("\/", http.FileServer(http.Dir(".")))\r\n  err := http.ListenAndServe(":8080", nil)\r\n  if err != nil {\r\n    panic("Error: " + err.Error())\r\n  }\r\n}\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
I wanted the ability to resolve DNS addresses in client side Javascript. Unfortunately you can’t do DNS lookups in browser. As a hack I wrote a quick DNS proxy in golang which allows the JS to perform GET requests to a golang server which will lookup and DNS entry and return IP addresses. The HTML […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1],"tags":[],"class_list":["post-2041","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p1RRoU-wV","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/2041","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/comments?post=2041"}],"version-history":[{"count":2,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/2041\/revisions"}],"predecessor-version":[{"id":2045,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/2041\/revisions\/2045"}],"wp:attachment":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/media?parent=2041"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/categories?post=2041"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/tags?post=2041"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}