libhsmd: Add status functions to report to whoever is listening

These are currently just shims that replicate the old behavior, but
when compiling as a library we can relink the status_* functions to
something that makes sense in the context of the user, and not assume
we're running as a subdaemon.

hsmd/hsmd.c

@@ -34,6 +34,8 @@
 #include <common/memleak.h>
 #include <common/node_id.h>
 #include <common/status.h>
+#include <common/status_wire.h>
+#include <common/status_wiregen.h>
 #include <common/subdaemon.h>
 #include <common/type_to_string.h>
 #include <common/utils.h>
@@ -1925,6 +1927,44 @@ static struct io_plan *handle_memleak(struct io_conn *conn,
 }
 #endif /* DEVELOPER */
 
+u8 *hsmd_status_bad_request(struct hsmd_client *client, const u8 *msg, const char *error)
+{
+	/* Extract the pointer to the hsmd representation of the
+	 * client which has access to the underlying connection. */
+	struct client *c = (struct client*)client->extra;
+	bad_req_fmt(c->conn, c, msg, "%s", error);
+
+	/* We often use `return hsmd_status_bad_request` to drop out, and NULL
+	 * means we encountered an error. */
+	return NULL;
+}
+
+void hsmd_status_fmt(enum log_level level, const struct node_id *peer,
+		     const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	status_vfmt(level, peer, fmt, ap);
+	va_end(ap);
+}
+
+void hsmd_status_failed(enum status_failreason reason, const char *fmt, ...)
+{
+	va_list ap;
+	char *str;
+
+	va_start(ap, fmt);
+	str = tal_vfmt(NULL, fmt, ap);
+	va_end(ap);
+
+	/* Give a nice backtrace when this happens! */
+	if (reason == STATUS_FAIL_INTERNAL_ERROR)
+		send_backtrace(str);
+
+	status_send_fatal(take(towire_status_fail(NULL, reason, str)));
+}
+
 /*~ This is the core of the HSM daemon: handling requests. */
 static struct io_plan *handle_client(struct io_conn *conn, struct client *c)
 {

hsmd/libhsmd.c

@@ -120,6 +120,28 @@ bool check_client_capabilities(struct hsmd_client *client, enum hsmd_wire t)
 	return false;
 }
 
+/*~ ccan/compiler.h defines PRINTF_FMT as the gcc compiler hint so it will
+ * check that fmt and other trailing arguments really are the correct type.
+ */
+/* This function is used to format an error message before passing it
+ * to the library user specified hsmd_status_bad_request */
+/* Temporarily pre-declare until we use the function, then we can make
+ * it static again. */
+u8 *hsmd_status_bad_request_fmt(struct hsmd_client *client, const u8 *msg,
+				const char *fmt, ...) PRINTF_FMT(3, 4);
+
+u8 *hsmd_status_bad_request_fmt(struct hsmd_client *client, const u8 *msg,
+				const char *fmt, ...)
+{
+	va_list ap;
+	char *str;
+
+	va_start(ap, fmt);
+	str = tal_fmt(tmpctx, fmt, ap);
+	va_end(ap);
+	return hsmd_status_bad_request(client, msg, str);
+}
+
 u8 *hsmd_handle_client_message(const tal_t *ctx, struct hsmd_client *client,
 			       const u8 *msg)
 {

hsmd/libhsmd.h

@@ -57,6 +57,23 @@ struct hsmd_client *hsmd_client_new_peer(const tal_t *ctx, u64 capabilities,
 u8 *hsmd_handle_client_message(const tal_t *ctx, struct hsmd_client *client,
 			       const u8 *msg);
 
+/* Functions to report debugging information or errors. These must be
+ * implemented by the user of the library. */
+u8 *hsmd_status_bad_request(struct hsmd_client *client, const u8 *msg,
+			    const char *error);
+
+/* Send a printf-style debugging trace. */
+void hsmd_status_fmt(enum log_level level,
+		const struct node_id *peer,
+		const char *fmt, ...)
+	PRINTF_FMT(3,4);
+
+#define hsmd_status_debug(...)				\
+	hsmd_status_fmt(LOG_DBG, NULL, __VA_ARGS__)
+
+void hsmd_status_failed(enum status_failreason code,
+			const char *fmt, ...) PRINTF_FMT(2,3);
+
 /* The following declarations are here only temporarily while we migrate logic from hsmd.c to libhsmd.c */
 
 /*~ Nobody will ever find it here!  hsm_secret is our root secret, the bip32