Retwis ported to modern Redis data types.

The example (and related documentation at redis.io) was not updated for
5 years. Redis had no sorted sets and hashes when the original code was
written (!). An update was really needed.

We also use a modern PHP client now: Predis. A copy is shipped within
this repository to make life easier to newcomers trying Redis for the
first time via this example.

register.php

@@ -0,0 +1,38 @@
+<?
+include("retwis.php");
+
+# Form sanity checks
+if (!gt("username") || !gt("password") || !gt("password2"))
+    goback("Every field of the registration form is needed!");
+if (gt("password") != gt("password2"))
+    goback("The two password fileds don't match!");
+
+# The form is ok, check if the username is available
+$username = gt("username");
+$password = gt("password");
+$r = redisLink();
+if ($r->hget("users",$username))
+    goback("Sorry the selected username is already in use.");
+
+# Everything is ok, Register the user!
+$userid = $r->incr("next_user_id");
+$authsecret = getrand();
+$r->hset("users",$username,$userid);
+$r->hmset("user:$userid",
+    "username",$username,
+    "password",$password,
+    "auth",$authsecret);
+$r->hset("auths",$authsecret,$userid);
+
+$r->zadd("users_by_time",time(),$username);
+
+# User registered! Login her / him.
+setcookie("auth",$authsecret,time()+3600*24*365);
+
+include("header.php");
+?>
+<h2>Welcome aboard!</h2>
+Hey <?=utf8entities($username)?>, now you have an account, <a href="index.php">a good start is to write your first message!</a>.
+<?
+include("footer.php")
+?>