commit 20ea5d46ee506cc03a5653aa099c53d9b95d2eb8
Author: Jaidyn Ann <10477760+JadedCtrl@users.noreply.github.com>
Date:   Thu May 25 08:59:17 2023 -0500

    Init

diff --git a/activitypub-server.lisp b/activitypub-server.lisp
new file mode 100644
index 0000000..c249eec
--- /dev/null
+++ b/activitypub-server.lisp
@@ -0,0 +1,105 @@
+;;
+;; Copyright 2023, Jaidyn Levesque <jadedctrl@posteo.at>
+;;
+;; This program is free software: you can redistribute it and/or
+;; modify it under the terms of the GNU General Public License as
+;; published by the Free Software Foundation, either version 3 of
+;; the License, or (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+;; GNU General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program. If not, see <https://www.gnu.org/licenses/>.
+;;
+
+(ql:quickload '(clack str yason))
+
+
+;; List of the server's usernames.
+(defun users () '("rod" "mum"))
+
+;; Alist of the server's paths and their response functions.
+(defun directories () '(("u/" . http-user-dir)))
+
+
+;; The default 404 response.
+(defun http-404 (env path-items params)
+  '(404 (:content-type "text/plain")
+    ("uh-oh, I did a war crime!")))
+
+
+;; Respond to requests within the /u/* directory.
+(defun http-user-dir (env path-items params)
+  (let ((user (car path-items)))
+    ;; In case of request for the user's actor.
+    (if (member user (users) :test 'string=)
+        `(200 (:content-type "application/ld+json")
+              (,(user-actor user))))))
+
+
+;; Returns the response data for Clack, given the request data `env`.
+(defun server (env)
+  (let* ((path-split-? (str:split #\? (getf env :request-uri)))
+         (path (car path-split-?))
+         (params (cadr path-split-?))
+         (response-function
+           (or (assoc-by-path *directories* (pathname-components path))
+               '("" . http-404)))
+         ;; So that response functions only deal with relative paths…
+         (path-sans-response-root
+           (pathname-components
+            (str:replace-first (car response-function) "" path))))
+    (or (funcall (cdr response-function) env path-sans-response-root params)
+        (funcall 'http-404 env path-sans-response-root params))))
+
+
+;; Start the server.
+(defparameter *handler*
+  (clack:clackup (lambda (env)
+                   (funcall 'server env))
+                 :server 'woo))
+
+
+;; The JSON of a user's actor.
+(defun user-actor (username)
+  (let* ((host "http://localhost")
+         (user-root (str:concat host "/u/" username)))
+    (yason:with-output-to-string* ()
+      (yason:encode-alist
+       `(("@context" . ("https://www.w3.org/ns/activitystreams"
+                        "https://w3id.org/security/v1"))
+         ("id" . ,user-root)
+         ("type" . "Person")
+         ("preferredUsername" . ,username)
+         ("inbox" . ,(str:concat user-root "/inbox.json"))
+         ("outbox" . ,(str:concat user-root  "/outbox.json")))))))
+
+
+;; Given an associative list and a path decomposed into a list of
+;; its components, return the item with the closest according
+;; pathname as key. If the exact path isn't a valid key, it will
+;; try all parent directories.
+;; E.g., "/bear/apple/momma/" could match either "/bear/apple/momma"
+;; or "/bear/apple/" or "/bear/", but not "/bear" (not a directory).
+(defun assoc-by-path (alist path-items &optional (depth 0))
+  (let ((path (str:join #\/ path-items)))
+    (if (eq path-items nil)
+        (assoc "" alist :test 'string=)
+        (or (and (eq depth 0)
+                 (assoc path alist :test 'string=))
+            (assoc (str:concat path "/")
+                   alist :test 'string=)
+          (assoc-by-path
+           alist (reverse
+                  (cdr (reverse path-items)))
+           (+ depth 1))))))
+
+
+;; Split a pathname into a list of its components.
+;; "/u/bear/apple.txt" → '("u" "bear" "apple.txt")
+(defun pathname-components (pathname)
+  (str:split #\/ pathname :omit-nulls 't))
+