refactor: split the library into fumi-core and make it embeddable

core/shim/smolmail_rns.h

@@ -0,0 +1,59 @@
+/*
+ * C ABI between fumi (Rust) and the microReticulum client shim.
+ *
+ * All calls block the caller; the shim owns the Reticulum loop thread and
+ * every callback fires on that thread. link_id and destination_hash are
+ * always 16 bytes. No client Reticulum identity is created or loaded anywhere
+ * (upstream spec sec 13.8): a server MUST NOT require identification, and a
+ * durable client handle is exactly what the wire format withholds.
+ */
+#ifndef SMOLMAIL_RNS_H
+#define SMOLMAIL_RNS_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Implemented in smolmail_rns.cpp, called from src/rns/ffi.rs.
+ * udp_forward_host may be NULL: with no forward target the interface sends
+ * to the source address of the last datagram received, which a client that
+ * only listens cannot use -- a client speaks first, so the forward target
+ * should point at the server's UDP interface.
+ * Returns 0 on success, negative on failure. */
+int smolmail_rns_start(const char *storage_dir,
+                       const char *udp_listen_host, uint16_t udp_listen_port,
+                       const char *udp_forward_host, uint16_t udp_forward_port);
+
+/* Requests a path if none is known and waits for it (upstream spec sec
+ * 13.3), recalls the identity, builds the OUT/SINGLE smolmail.server
+ * destination, opens the link and waits for ACTIVE. Returns the 16-byte
+ * link id, which the caller's AUTH and REGISTER bind values are derived
+ * from (upstream spec sec 13.6).
+ * Returns 0 on success, negative on failure. */
+int smolmail_rns_connect(const uint8_t *destination_hash, uint32_t timeout_ms,
+                         uint8_t *link_id_out);
+
+/* request is `op u8 || body`, the response `status u8 || payload`
+ * (upstream spec sec 13.5). A CLI has one request in flight at a time, so
+ * the shim keeps a single response slot rather than a map.
+ * Returns 0 on success and writes the response length to *out_len;
+ * negative on failure: no link (-1), send failure (-2), timeout or closed
+ * link (-3), failed transfer (-4), malformed response (-5), response larger
+ * than cap (-6). These are local errors and MUST NOT be reported as status
+ * codes (upstream spec sec 13.5). */
+int smolmail_rns_request(const uint8_t *request, size_t request_len,
+                         uint32_t timeout_ms, uint8_t *out, size_t cap,
+                         size_t *out_len);
+
+/* Tears the link down rather than leave it on keepalives, which run for
+ * minutes (upstream spec sec 13.10). */
+void smolmail_rns_close(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* SMOLMAIL_RNS_H */