feat(sender): add outgoing Webmention pipeline

Scan generated h-entry documents for Webmention targets and track source
revisions and delivery state in the database.

Discover target endpoints, send Webmentions asynchronously, and reconcile
updated, removed, restored, and deleted sources across scans.

Add authenticated views for inspecting sent Webmentions and make the scanner
schedule configurable.

1 files changed, 15 insertions, 13 deletions

diff --git a/webmentions_ssg/url_security.py b/webmentions_ssg/url_security.py
index ce5d700..51c037a 100644
--- a/webmentions_ssg/url_security.py
+++ b/webmentions_ssg/url_security.py
@@ -9,15 +9,11 @@ class AddressResolutionError(Exception):
     pass
 
 
-class NonPublicAddressError(Exception):
-    pass
-
-
-def ensure_public_url(url: str) -> None:
+def is_public_url(url: str) -> bool:
     hostname = urlsplit(url).hostname
 
     if hostname is None:
-        raise NonPublicAddressError("URL has no hostname")
+        raise ValueError("No hostname was specified")
 
     try:
         answers = dns.resolver.resolve_name(hostname)
@@ -25,13 +21,19 @@ def ensure_public_url(url: str) -> None:
         raise AddressResolutionError(
             f"Could not resolve hostname {hostname!r}"
         ) from exc
+    else:
+        for address in answers.addresses():
+            if not ipaddress.ip_address(address).is_global:
+                return False
 
-    addresses = {ipaddress.ip_address(address) for address in answers.addresses()}
+        return True
 
-    if not addresses:
-        raise AddressResolutionError(f"Hostname {hostname!r} did not resolve")
 
-    if any(not address.is_global for address in addresses):
-        raise NonPublicAddressError(
-            f"Hostname {hostname!r} resolves to a non-public address"
-        )
+def is_http_url(url: str) -> bool:
+    """Return whether a URL is an absolute HTTP or HTTPS URL."""
+    try:
+        parsed = urlsplit(url)
+    except ValueError:
+        return False
+
+    return parsed.scheme.lower() in {"http", "https"} and parsed.hostname is not None