stage-fed-b federation: dns record format

src/psyc/lines/federation.py

@@ -18,6 +18,7 @@ from typing import Tuple
 
 from cryptography.hazmat.primitives import serialization
 from cryptography.hazmat.primitives.asymmetric import ed25519
+from pydantic import BaseModel
 
 from psyc import DATA_DIR, log
 
@@ -28,6 +29,10 @@ FED_DIR = DATA_DIR / "federation"
 PRIVATE_KEY_PATH = FED_DIR / "node.key"
 PUBLIC_KEY_PATH = FED_DIR / "node.pub"
 
+FEED_VERSION = "psyc1"
+FEED_ALG = "ed25519"
+FEED_PATH = "/federation/feed"
+
 
 # ---------- keypair persistence -----------------------------------------
 
@@ -93,3 +98,56 @@ def node_fingerprint() -> str:
     _, pub = node_keypair()
     digest = hashlib.sha256(_raw_pubkey_bytes(pub)).digest()
     return digest[:16].hex()
+
+
+def _fingerprint_for_pubkey_pem(pubkey_pem: str) -> str:
+    pub = serialization.load_pem_public_key(pubkey_pem.encode("ascii"))
+    if not isinstance(pub, ed25519.Ed25519PublicKey):
+        raise ValueError("not an Ed25519 public key")
+    return hashlib.sha256(_raw_pubkey_bytes(pub)).digest()[:16].hex()
+
+
+# ---------- DNS record format -------------------------------------------
+
+class DNSRecord(BaseModel):
+    """The SRV + TXT pair an admin pastes into their zone file."""
+    srv_name: str
+    srv_target: str
+    srv_port: int
+    srv_priority: int = 10
+    srv_weight: int = 10
+    txt_name: str
+    txt_value: str
+    human_instructions: str
+
+
+def dns_record(domain: str, port: int = 443) -> DNSRecord:
+    """Build the DNS-SD-style records that advertise this node at `domain`."""
+    fp = node_fingerprint()
+    srv_name = f"_psyc._tcp.{domain}"
+    srv_target = f"{domain}."
+    txt_name = srv_name
+    txt_value = f"v={FEED_VERSION} fp={fp} alg={FEED_ALG} path={FEED_PATH}"
+    instructions = (
+        f"; psyc federation records for {domain}\n"
+        f"; ----------------------------------------------------------\n"
+        f"; 1) SRV record — locates this psyc node (host + port).\n"
+        f'{srv_name}.  3600  IN  SRV  10 10 {port} {srv_target}\n'
+        f";\n"
+        f"; 2) TXT record — declares protocol version, key fingerprint,\n"
+        f";    signature algorithm, and the feed endpoint path.\n"
+        f'{txt_name}.  3600  IN  TXT  "{txt_value}"\n'
+        f"; ----------------------------------------------------------\n"
+        f"; Once these are live, federation peers can fetch:\n"
+        f";   https://{domain}{FEED_PATH}   (signed feed JSON)\n"
+        f";   https://{domain}/federation/key   (public key PEM)\n"
+        f";   https://{domain}/federation/info  (capabilities)\n"
+    )
+    return DNSRecord(
+        srv_name=srv_name,
+        srv_target=srv_target,
+        srv_port=port,
+        txt_name=txt_name,
+        txt_value=txt_value,
+        human_instructions=instructions,
+    )