cmd/anubis: configurable difficulty per-bot rule (#53)

Closes #30

Introduces the "challenge" field in bot rule definitions:

```json
{
  "name": "generic-bot-catchall",
  "user_agent_regex": "(?i:bot|crawler)",
  "action": "CHALLENGE",
  "challenge": {
    "difficulty": 16,
    "report_as": 4,
    "algorithm": "slow"
  }
}
```

This makes Anubis return a challenge page for every user agent with
"bot" or "crawler" in it (case-insensitively) with difficulty 16 using
the old "slow" algorithm but reporting in the client as difficulty 4.

This is useful when you want to make certain clients in particular
suffer.

Additional validation and testing logic has been added to make sure
that users do not define "impossible" challenge settings.

If no algorithm is specified, Anubis defaults to the "fast" algorithm.

Signed-off-by: Xe Iaso <me@xeiaso.net>

cmd/anubis/static/js/main.mjs

@@ -1,2 +1,2 @@
-(()=>{function m(n,s=5,e=(navigator.hardwareConcurrency||1)){return new Promise((t,l)=>{let a=URL.createObjectURL(new Blob(["(",g(),")()"],{type:"application/javascript"})),r=[];for(let d=0;d<e;d++){let i=new Worker(a);i.onmessage=c=>{r.forEach(u=>u.terminate()),i.terminate(),t(c.data)},i.onerror=c=>{i.terminate(),l()},i.postMessage({data:n,difficulty:s,nonce:d,threads:e}),r.push(i)}URL.revokeObjectURL(a)})}function g(){return function(){let n=e=>{let t=new TextEncoder().encode(e);return crypto.subtle.digest("SHA-256",t.buffer)};function s(e){return Array.from(e).map(t=>t.toString(16).padStart(2,"0")).join("")}addEventListener("message",async e=>{let t=e.data.data,l=e.data.difficulty,a,r=e.data.nonce,d=e.data.threads;for(;;){let i=await n(t+r),c=new Uint8Array(i),u=!0;for(let o=0;o<l;o++){let f=Math.floor(o/2),p=o%2;if((c[f]>>(p===0?4:0)&15)!==0){u=!1;break}}if(u){a=s(c),console.log(a);break}r+=d}postMessage({hash:a,data:t,difficulty:l,nonce:r})})}.toString()}var w=(n="",s={})=>{let e=new URL(n,window.location.href);return Object.entries(s).forEach(t=>{let[l,a]=t;e.searchParams.set(l,a)}),e.toString()},h=(n,s)=>w(`/.within.website/x/cmd/anubis/static/img/${n}.webp`,{cacheBuster:s});(async()=>{let n=document.getElementById("status"),s=document.getElementById("image"),e=document.getElementById("title"),t=document.getElementById("spinner"),l=JSON.parse(document.getElementById("anubis_version").textContent);n.innerHTML="Calculating...";let{challenge:a,difficulty:r}=await fetch("/.within.website/x/cmd/anubis/api/make-challenge",{method:"POST"}).then(o=>{if(!o.ok)throw new Error("Failed to fetch config");return o.json()}).catch(o=>{throw e.innerHTML="Oh no!",n.innerHTML=`Failed to fetch config: ${o.message}`,s.src=h("sad"),t.innerHTML="",t.style.display="none",o});n.innerHTML=`Calculating...<br/>Difficulty: ${r}`;let d=Date.now(),{hash:i,nonce:c}=await m(a,r),u=Date.now();console.log({hash:i,nonce:c}),e.innerHTML="Success!",n.innerHTML=`Done! Took ${u-d}ms, ${c} iterations`,s.src=h("happy",l),t.innerHTML="",t.style.display="none",setTimeout(()=>{let o=window.location.href;window.location.href=w("/.within.website/x/cmd/anubis/api/pass-challenge",{response:i,nonce:c,redir:o,elapsedTime:u-d})},250)})();})();
+(()=>{function p(r,n=5,t=navigator.hardwareConcurrency||1){return console.debug("fast algo"),new Promise((e,o)=>{let s=URL.createObjectURL(new Blob(["(",y(),")()"],{type:"application/javascript"})),a=[];for(let i=0;i<t;i++){let c=new Worker(s);c.onmessage=d=>{a.forEach(u=>u.terminate()),c.terminate(),e(d.data)},c.onerror=d=>{c.terminate(),o()},c.postMessage({data:r,difficulty:n,nonce:i,threads:t}),a.push(c)}URL.revokeObjectURL(s)})}function y(){return function(){let r=t=>{let e=new TextEncoder().encode(t);return crypto.subtle.digest("SHA-256",e.buffer)};function n(t){return Array.from(t).map(e=>e.toString(16).padStart(2,"0")).join("")}addEventListener("message",async t=>{let e=t.data.data,o=t.data.difficulty,s,a=t.data.nonce,i=t.data.threads;for(;;){let c=await r(e+a),d=new Uint8Array(c),u=!0;for(let m=0;m<o;m++){let l=Math.floor(m/2),g=m%2;if((d[l]>>(g===0?4:0)&15)!==0){u=!1;break}}if(u){s=n(d),console.log(s);break}a+=i}postMessage({hash:s,data:e,difficulty:o,nonce:a})})}.toString()}function f(r,n=5,t=1){return console.debug("slow algo"),new Promise((e,o)=>{let s=URL.createObjectURL(new Blob(["(",b(),")()"],{type:"application/javascript"})),a=new Worker(s);a.onmessage=i=>{a.terminate(),e(i.data)},a.onerror=i=>{a.terminate(),o()},a.postMessage({data:r,difficulty:n}),URL.revokeObjectURL(s)})}function b(){return function(){let r=n=>{let t=new TextEncoder().encode(n);return crypto.subtle.digest("SHA-256",t.buffer).then(e=>Array.from(new Uint8Array(e)).map(o=>o.toString(16).padStart(2,"0")).join(""))};addEventListener("message",async n=>{let t=n.data.data,e=n.data.difficulty,o,s=0;do o=await r(t+s++);while(o.substring(0,e)!==Array(e+1).join("0"));s-=1,postMessage({hash:o,data:t,difficulty:e,nonce:s})})}.toString()}var L={fast:p,slow:f},w=(r="",n={})=>{let t=new URL(r,window.location.href);return Object.entries(n).forEach(e=>{let[o,s]=e;t.searchParams.set(o,s)}),t.toString()},h=(r,n)=>w(`/.within.website/x/cmd/anubis/static/img/${r}.webp`,{cacheBuster:n});(async()=>{let r=document.getElementById("status"),n=document.getElementById("image"),t=document.getElementById("title"),e=document.getElementById("spinner"),o=JSON.parse(document.getElementById("anubis_version").textContent);r.innerHTML="Calculating...";let{challenge:s,rules:a}=await fetch("/.within.website/x/cmd/anubis/api/make-challenge",{method:"POST"}).then(l=>{if(!l.ok)throw new Error("Failed to fetch config");return l.json()}).catch(l=>{throw t.innerHTML="Oh no!",r.innerHTML=`Failed to fetch config: ${l.message}`,n.src=h("sad",o),e.innerHTML="",e.style.display="none",l}),i=L[a.algorithm];if(!i){t.innerHTML="Oh no!",r.innerHTML="Failed to resolve check algorithm. You may want to reload the page.",n.src=h("sad",o),e.innerHTML="",e.style.display="none";return}r.innerHTML=`Calculating...<br/>Difficulty: ${a.report_as}`;let c=Date.now(),{hash:d,nonce:u}=await i(s,a.difficulty),m=Date.now();console.log({hash:d,nonce:u}),t.innerHTML="Success!",r.innerHTML=`Done! Took ${m-c}ms, ${u} iterations`,n.src=h("happy",o),e.innerHTML="",e.style.display="none",setTimeout(()=>{let l=window.location.href;window.location.href=w("/.within.website/x/cmd/anubis/api/pass-challenge",{response:d,nonce:u,redir:l,elapsedTime:m-c})},250)})();})();
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