A very ugly first version of a URL shortening service written in VCL inline C. There's a whole lot still to be done, but this thing works quite well already.

shortener.vcl

C{
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <hiredis/hiredis.h>
}C

sub vcl_recv {
    if (req.http.host ~ "(?i)^a.luit.it$") {
        if (req.url ~ "(?i)^/l/.*[A-Za-z0-9\-_]{4,}\+?$") {
            set req.url = regsub(req.url, 
                "(?i)(.*/)+([A-Za-z0-9\-_]{4}[A-Za-z0-9\-_]*)\+?$", "\2");
            C{
                redisContext *c;
                redisReply *reply;
                //c = redisConnectUnix("/var/run/redis/redis.sock");
                c = redisConnect("127.0.0.1", 6379);
                
                if (c->err) {
                    VRT_error(sp, 751, c->errstr);
                } else {
                    char key[32]; // SHA1 hash in b64 plus some extra
                    char keykey[3];
                    strncpy(key, VRT_r_req_url(sp), 31);
                    key[31] = '\0';
                    strncpy(keykey, key, 2);
                    keykey[2] = '\0';
                    reply = redisCommand(c, "HGET shortener-%s %s", keykey, key + 2);
                    if (reply->type == REDIS_REPLY_STRING) {
                    	VRT_error(sp, 750, reply->str);
                    } else if (reply->type == REDIS_REPLY_NIL) {
                        VRT_error(sp, 754, key);
                    } else {
                        VRT_error(sp, 752, reply->str);
                    }
                    
                    freeReplyObject(reply);
                    redisFree(c);
                }
            }C
            return (error);
        }
        error 404;
    }
}

sub vcl_error {
    if (obj.status == 754) {
        set obj.status = 404;
        set obj.response = "Not Found";
        synthetic {"Short URL code "} + req.url + {" not found"};
        return (deliver);
    }
    if (obj.status == 751 || obj.status == 752) {
        set obj.status = 500;
        synthetic {"Having trouble with Redis: "} + obj.response;
        set obj.http.X-Redis-Error = obj.response;
        set obj.response = "Internal Server Error";
        return (deliver);
    }
    if (obj.status == 750) {
        set obj.http.Location = obj.response;
        
        # Probably should make this 301 Moved Permanently in the end
        set obj.status = 302;
        set obj.response = "Found";
        return (deliver);
    }
}