urbit/pub/doc/arvo/eyre/commentary.md

Eyre: Reference

State

Stored

• ++bolo
• ++cyst
• ++stem

Runtime

• perk
  • perk-auth
• pest
• even

Cores

• ++handle
  • ++parse
    • ++as...
• ++ya
• ++ix

Eyre: Commentary

Let us follow the loading of a simple cli app, as it bounces from browser to server to browser and back.

Initial request[#init]

An http request for http://sampel-sipnym.urbit.org/cli will be redirected to the %eyre on ~sampel-sipnym, and come in as a %this kiss.

From arvo, requests enter ++call, which after some type reification are passed along to ++apex:ye. In the case of a %this kiss, its components are parsed(see ++zest:epur, ++eat-headers) and handed off to ++handle, wrapped in ++emule to produce a ++fail page in case of error. ++apex:handle will ++process the request to a pest or a ++done core, and in the former case ++resolve the pest into an outgoing card.

XX it also seems to affect the current ship, test that serving ship name is consistently correct

The pest is produced by ++process, which will first further ++parse the request, and if this does not make the response immediately obvious, ++process-parsed the resulting perk.

++parse produces the perk, by attempting to interpret the pork(url path) ++as-magic-filename, ++as-beam, and ++as-aux-request. In this case, /cli is parsed by the second case as a %beam query to /=cli=: a path which starts with a valid ship name is expected to be a full clay(well, ford) path, and one starting with a term implies the current serving ship and a case of 0, the current revision.

XX spur: when the desks are merged, /cli shall point to /=main=/pub/cli

The parsed perk generates a %f %boil note, marked as its extension(here defaulting to %urb) and wired with ~ to return unaltered to the client. It goes on to ++resolve by being passed to ++ford-get-beam, which translates the perk it into a %boil ++ford-req, adding an ++fcgi path-segment containing query string and ++fcgi-cred:for-client auth information.

%fords translation of /=cli=/hymn/hook to a self-refreshing %urb html page deserves its own commentary, but we resume in %eyre when the %made sign arrives in ++take, and soon after ++axon:ye. There the wire, or rather the whir it has been verified to be, determines that the response should be served immediately. However, as the mark is not %mime, another trip to %ford is required to encode it, on the same wire; afterwards, the value of the %mime cage is verified to be of the correct type, and finally delivered back up the requesting duct as a succesful %thou HTTP response.

XX %cast %mime used to be in ford-get-beam, is there a reason it was removed?

Back into the breach, or: auxilary requests

Now, it was mentioned that this result is self-refreshing: the %urb translation door injects a ;script@"/~/on/{deps}.js" into every page, deps is a ford-readable hash of the set of resources that page construction depended on.

This triggers another %this request. Its handling is identical to that of /cli up until ++parse, where it is seen not ++as-beam but ++as-aux-request(auxillary requests starting with /~/ or /~~/). /on/[hash] is a long-%poll, which ++process-parsed, for a .js mark, answers with a direct %js. Its contents are the static ++poll:js, which initiates the long-polling loop, run against an injected urb.js of {poll:[hash]}.

A %js pest is resolved as a text/javascript success %this.

When poll.js is recieved by the client, it opens an XMLHttpRequest for /~/on/{window.urb.poll}.json, bringing us back to %poll:process.

In the case of a non-%js /~/on/, %poll:process-parsed turns into a ++new-dependency, which stores the listening duct, and pass-notes a %wasp with the deps-hash back to %ford whence it came. While this occured, the page has loaded.

Some indeterminate amount of time afterwards, with dropped /~/on/{...}.jsons being retried upon expiring and also being stored, a %news sign arrives in ++axon, and the hash in question is retrieved from the wire, and the listening long-polls retrieved by the hash. Each receives a 205 "Reload parent view" HTTP response, which poll.js dutifully executes, and a fixed typo of markdown is rendered.

Authentication.

Now, while this accurately reflects the presentation of e.g. a markdown file, /cli is an application front-end, and one that permits only owner access. Its second script is @"/~~/~/at/main/lib/urb.js", semantically equivalent to /~/as/own/~/at/main/lib/urb.js, and handled as follows.

In ++as-aux-request, %as %own becomes %auth %get our perk, which ++process passes to ++process-parsed passes to ++process-auth. There, a yac "ya" core is built ++for-client: a ++cookie-prefix, which is just the serving ship name, is used to get a ++session-from-cookies, here nil as the client has no cookie set. In lieu of a cookie, a ++new-ya is constructed, with a random token hole and a ++new-cyst which fills out cyst session state from request data.

Returning to ++process-auth, %get checks if the yac is authenticated with the requested credentials(anon requests are always granted), which for the fresh new cyst is not the case (more on success later). Unless authentiacting as a foreign ship, the only thing left is to ++show-login-page, which detects that the requested resource is not %html, and produces a %red pest. For %js, %redirections ++resolve to ++auth-redir:js, a line of javascript which prepends /~~ to the url path.

The owner-authenticated main page request similarly ends in ++show-login-page, which for the empty session is an [%htme ++login-page:xml], resolved to ++give-html with a 401 "unathorized".

The login page shows a simple prompt, and requests /~/at/auth.js to handle the submission. And so we are, once again, attempting to divine if what we're doing makes sense ++as-aux-request.

To understand /~/at, there will first be a brief diversion to ~/auth.json. auth.json, perk [%auth %json], in ++process-auth serves ++stat-json:ya, containing such information as the serving ship, which identities are associated with this session, and oryx, a CSRF token. An oryx must be present on all stateful requests, in this case executing a log in. It also saves the new/old session using abet.

XX explain ixor here and not later?

/~/at is an alternate interface, which injects auth.json data into the requested file. /~/at/auth.js, then, is a request for the built-in auth:js (parsed to and processed from an [%auth %js ~] perk), with session data added as window.urb. And indeed, [`%js /~/at/auth] is parsed to [%auth at [`%js /auth], which in ++process-auth is re-processed to [%js ++auth:js], which is ++resolved after an ++add-json of the relevant data. The yac cookies are also passed to resolve, which ++add-cookies injects into the httr.

It is at this point that there is first occasion for user input, namely the password.

The auth:js script sends a PUT request, also to /~/auth.json. In parse, the first nontrivial ++check-oryx occurs, ++grab-body the request oryx and ensuring it is recorded for the session. The request parsed with ++need-body to a [%auth %try {password}] perk. %get:process-auth checks it against ++load-secret, upon success updates the session with ++logon:ya, and serves a fresh auth.json which reflects the changed user. Upon recieving this, the page is refreshed to retry the original request.

Post-authentication: app communication. [#auth-ok]

Upon refresh, /~~/cli brings us for the third time to %get:process-auth, but this time the cookie is set, and the yac fetched contains the serving ship as authenticated. The ++handle sample is updated to reflect the requesting ship, and the process continues for the rest of the pork, once again serving the ford page.

The /~/on/[deps].json poll starts anew, and /~~/~/at/main/lib/urb.js we now know to serve the window.urb necessary to make requests, and the urb.js standard library which extends it with a number of wrappers to them and other useful functions.

---

One of those functions is urb.bind, which is used to subscribe to application data. Userspace javascript sets urb.appl to /tic, and binds lines to a ;pre; text display, using a callback.

This triggers a PUT to /~/is/{ixor}/cli/lines.json, where ixor is a hash of oryx that identifies the connection. ++as-aux-request, an %is is a %subs subscription update update, which for %put forwards to ++add-subs:ix, the ix core fetched ++for-view by hashing the request ++oryx-to-ixor.

[#ixor] A view has all the state associated with a client that must be remembered between events. In this case, this is what app/path the request duct is associated with; but mainly, ++add-subs:ix will pass-note to %gall so it %shows the data on the path, current and future.

This will immediately(assuming the ship is local) result in a %nice by the /cli app, returning {ok:true} ++nice-json to urb.bind's second callback as {ok:true}. The initial %rush results also arrive, and in ++axon are converted to json using ++back(ford %cast wrapper), and when %made get passed to ++get-rush:ix. There the source application/path are decoded by duct, and then the full event goes to ++get-even; ++add-even inserts it to the queue, and as there is no long poll it simply stays there.

Upon receipt, the client realizes the long-poll isn't actually running, so that is started using urb.poll. At /~/of/{ixor}, perk [%view ixor ~ {sequence-number}], it is processed by ++poll:ix (the cyst is retrieved by ++ire-ix form global state, using the perk ixor): the sequence number is in the past, so the previously recieved %rush is ++give-even. After deleting the previous message in the queue and invoking ++pass-took to signal %gall of this occurrence, the data is annotated with the source app+path ++subs-to-json, and returned to the polling duct.

On the client, the user callback receives the /cli history, and displays it on the page. The /~/of long poll is continued, this time reaching ++poll:ix with the "pending" sequence number, and being stored in the cyst for its troubles.

---

Its next update proceeds idenitcally, but first it must be triggered, which happens when the user enters "(add 2 2)\n", firing an urb.send from the event handler. This sends a POST request to /~/to/cli/json.json, perk %mess, ++processed to a %g %mess. Were the mark not %json, a %ford conversion would occur first, and %made:axon would send the gall message proper. In either case, eventually a %mean or %nice arrives, is encoded as json, and sent to the client callback.

A path not taken: magic filenames [#mage]

The /robots.txt and /favicon.(ico|png) files are static, and served immediately when caught by a ++parse.

XX index.html?

A path not taken: foreign auth [#xeno]

While this example details a login /~/as/own, it is possible to be authenticated as any ship on the network. A request for such seen in %get:process-auth is passed to ++foreign-auth:ya, which sends an %ames /lon message to the ship in question. The foreign ship stores the inquiry, calculates(the local) ++our-host and responds with a /hat, containing the redirection host, which is stored by ++foreign-hat; it is later used to send the client to a /~/am url on the foreign client, which acts as a normal login page but later sends the client back. XX expand, basically the status quo is you're logged in and /~/as/foo is ignored, just setting your urb.user XX

A path not taken: deauthentication

/~/away, perk [%away ~], produces a static ++logout-page:xml, which also uses /~/at/auth.js, to send a DELETE /~/auth.json, perk [%auth %del]. This executes ++logoff:ya for the cookie session, resolving to ++abut to wipe it from memory.

A path not taken: unsubscription

DELETE /~/is/app/path/within works much like PUT /~/is/app/path/within, ++del-subs:ix acting as reverse of ++add-subs by deleting the duct binding and sending %g %nuke.

XX unmentioned arms: abet, add-poll, adit, ames-gram, anon, ares-to-json, bolo, cyst, doze, even, ford-kill, get-mean, gift, give-json, give-thou, gram, hapt, hasp, host-to-ship, ix, ixor, js, kiss, load, mean-json, move, note, pass-note, perk, perk-auth, pest, poke-test, print-subs, render-tang, resp, root-beak, scry, ses-authed, ses-ya, sign, silk, sine, stay, stem, teba, titl, to-oryx, urb, wait-era, wake, whir, wush, xml, ya, ye

Appendix A: DNS [#dns]

The *.urbit.org domain can be used to access destroyers and cruisers. In the common case oh hosted ships, this is done by dynamic DNS directly to the hosting instance. We do not speak of the uncommon case. When ports are blocked and infrastructure crumbles around you, only imported martian networking can be trusted: the %get and %got grams are used to proxy %this requests and %thou responses respectively.