daemon/session2: protocol layer refactors + docs

This makes some readability enhancements to the `protolayer_` API as
well as clarifies some of the documentation.

There is also a change where the definitions of protocol layer sequences
does not require a `_NULL` layer to be present at the end anymore, as
the number of layers in a sequence is determined at compile time. This
makes defining new sequences less error-prone.

daemon/http.c

@@ -390,8 +390,8 @@ static ssize_t send_callback(nghttp2_session *h2, const uint8_t *data, size_t le
 
 	kr_log_debug(DOH, "[%p] send_callback: %p\n", (void *)h2, (void *)send_ctx->data);
 	session2_wrap_after(http->h.session, PROTOLAYER_TYPE_HTTP,
-			protolayer_buffer(send_ctx->data, length, false), NULL,
-			callback_finished_free_baton, send_ctx);
+			protolayer_payload_buffer(send_ctx->data, length, false),
+			NULL, callback_finished_free_baton, send_ctx);
 
 	return length;
 }
@@ -506,7 +506,7 @@ static int send_data_callback(nghttp2_session *h2, nghttp2_frame *frame, const u
 
 	kr_assert(cur == iovcnt);
 	int ret = session2_wrap_after(http->h.session, PROTOLAYER_TYPE_HTTP,
-			protolayer_iovec(dest_iov, cur, false),
+			protolayer_payload_iovec(dest_iov, cur, false),
 			NULL, callback_finished_free_baton, sdctx);
 
 	if (ret < 0)
@@ -733,7 +733,8 @@ static int submit_to_wirebuffer(struct pl_http_sess_data *ctx)
 
 	ret = 0;
 	session2_unwrap_after(ctx->h.session, PROTOLAYER_TYPE_HTTP,
-			protolayer_wire_buf(wb, false), NULL, NULL, NULL);
+			protolayer_payload_wire_buf(wb, false),
+			NULL, NULL, NULL);
 cleanup:
 	http_cleanup_stream(ctx);
 	return ret;
@@ -938,7 +939,7 @@ static enum protolayer_iter_cb_result pl_http_unwrap(
 
 	struct protolayer_payload pld = ctx->payload;
 	if (pld.type == PROTOLAYER_PAYLOAD_WIRE_BUF) {
-		pld = protolayer_as_buffer(&pld);
+		pld = protolayer_payload_as_buffer(&pld);
 	}
 
 	if (pld.type == PROTOLAYER_PAYLOAD_BUFFER) {

daemon/io.c

@@ -98,7 +98,7 @@ void udp_recv(uv_udp_t *handle, ssize_t nread, const uv_buf_t *buf,
 		.comm_addr = comm_addr,
 		.src_addr = comm_addr
 	};
-	session2_unwrap(s, protolayer_wire_buf(&s->layers->wire_buf, false),
+	session2_unwrap(s, protolayer_payload_wire_buf(&s->layers->wire_buf, false),
 			&in_comm, udp_on_unwrapped, NULL);
 }
 
@@ -146,7 +146,7 @@ struct pl_udp_iter_data {
 static enum protolayer_iter_cb_result pl_udp_unwrap(
 		void *sess_data, void *iter_data, struct protolayer_iter_ctx *ctx)
 {
-	ctx->payload = protolayer_as_buffer(&ctx->payload);
+	ctx->payload = protolayer_payload_as_buffer(&ctx->payload);
 	if (kr_fails_assert(ctx->payload.type == PROTOLAYER_PAYLOAD_BUFFER)) {
 		/* unsupported payload */
 		return protolayer_break(ctx, kr_error(EINVAL));
@@ -197,7 +197,7 @@ static enum protolayer_iter_cb_result pl_udp_unwrap(
 			}
 		}
 
-		ctx->payload = protolayer_buffer(
+		ctx->payload = protolayer_payload_buffer(
 				data + trimmed, data_len - trimmed, false);
 	}
 
@@ -278,7 +278,7 @@ static enum protolayer_iter_cb_result pl_tcp_unwrap(
 
 		memcpy(wire_buf_free_space(&tcp->wire_buf), buf, len);
 		wire_buf_consume(&tcp->wire_buf, ctx->payload.buffer.len);
-		ctx->payload = protolayer_wire_buf(&tcp->wire_buf, false);
+		ctx->payload = protolayer_payload_wire_buf(&tcp->wire_buf, false);
 	}
 
 	if (kr_fails_assert(ctx->payload.type == PROTOLAYER_PAYLOAD_WIRE_BUF)) {
@@ -511,7 +511,7 @@ static void tcp_recv(uv_stream_t *handle, ssize_t nread, const uv_buf_t *buf)
 		return;
 	}
 
-	session2_unwrap(s, protolayer_wire_buf(&s->layers->wire_buf, false),
+	session2_unwrap(s, protolayer_payload_wire_buf(&s->layers->wire_buf, false),
 			NULL, NULL, NULL);
 }
 
@@ -950,7 +950,7 @@ static void xdp_rx(uv_poll_t* handle, int status, int events)
 		memcpy(comm.eth_from, msg->eth_from, sizeof(comm.eth_from));
 		memcpy(comm.eth_to, msg->eth_to, sizeof(comm.eth_to));
 		session2_unwrap(xhd->session,
-				protolayer_buffer(
+				protolayer_payload_buffer(
 					msg->payload.iov_base,
 					msg->payload.iov_len, false),
 				&comm, NULL, NULL);