Link two nodes without a connection over UDP (093, design 011's first stage)

pure-serve --send OUTPUT=pure://host:port/INPUT sends an output's saved
sends to another node's --link-port with no handshake: the first packet
carries records. Keys come from the two nodes' keys (X25519, HKDF-SHA256,
AES-128-GCM), with a random run in each packet's header so no nonce
repeats across restarts; nothing is stored for them. What lasts is the
apps' own: the sender's outbox and the receiver's heard numbers
(pure_app_heard, new). The sender detects losses as RFC 9002 says, with
NewReno, and trims a send once the receiver says it stored it; the
receiver hands the owner whole records in order, which it applies from
the one after the source's last heard number, stopping at a gap, and
answers how far it stored with every acknowledgment. Stored bytes are
the bytes on the wire: an output and an input of one shape need no JSON.

server_links_udp kills the receiver, the sender, then both (-9) while
four clients buy: every saved order is applied once, with no handshake
(five runs, 10k-11k orders each). server_links_udp_lossy does it again in
a namespace of its own with the link's packets delayed, lost (3 %) and
reordered (10 %) by netem (three runs, 11k-12k orders).

1 files changed, 30 insertions, 0 deletions

diff --git a/serve/crypto.c b/serve/crypto.c
index 8eae6d1..d43de93 100644
--- a/serve/crypto.c
+++ b/serve/crypto.c
@@ -133,3 +133,33 @@ bool pure_unseal(PureOpener *o, uint64_t n, const char *aad, const unsigned char
 }
 
 void pure_opener_free(PureOpener *o) { if (o) crypto->opener_free(o); }
+
+/* ---- Links */
+
+bool pure_link_secret(const PureSealKey *own, const unsigned char peer[PURE_SEAL_KEY], unsigned char out[32]) {
+    const PureCrypto *c = loaded(NULL, 0);
+    return c && own && c->link_secret(own, peer, out);
+}
+
+bool pure_link_derive(const unsigned char secret[32], const unsigned char *info, size_t info_size, unsigned char *out,
+                      size_t out_size) {
+    const PureCrypto *c = loaded(NULL, 0);
+    return c && c->link_derive(secret, info, info_size, out, out_size);
+}
+
+PureAead *pure_aead(const unsigned char key[PURE_AEAD_KEY]) {
+    const PureCrypto *c = loaded(NULL, 0);
+    return c ? c->aead(key) : NULL;
+}
+
+bool pure_aead_seal(PureAead *a, const unsigned char nonce[PURE_AEAD_NONCE], const unsigned char *aad, size_t aad_size,
+                    const unsigned char *plain, size_t size, unsigned char *out) {
+    return crypto->aead_seal(a, nonce, aad, aad_size, plain, size, out);
+}
+
+bool pure_aead_open(PureAead *a, const unsigned char nonce[PURE_AEAD_NONCE], const unsigned char *aad,
+                    size_t aad_size, const unsigned char *sealed, size_t size, unsigned char *plain) {
+    return crypto->aead_open(a, nonce, aad, aad_size, sealed, size, plain);
+}
+
+void pure_aead_free(PureAead *a) { if (a) crypto->aead_free(a); }