From a1addc329643d3b21c458212f754a1a3f4510787 Mon Sep 17 00:00:00 2001
From: Arman Uguray <armansito@chromium.org>
Date: Fri, 25 Jul 2014 15:08:34 -0700
Subject: [PATCH] shared/gatt: Implement bt_gatt_exchange_mtu.

This patch implements the helper function bt_gatt_exchange_mtu, which performs
an ATT "Exchange MTU" request and resizes the internal buffer based on the
result.
---
 src/shared/gatt-helpers.c | 86 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 84 insertions(+), 2 deletions(-)

diff --git a/src/shared/gatt-helpers.c b/src/shared/gatt-helpers.c
index a119de667..96137bf2e 100644
--- a/src/shared/gatt-helpers.c
+++ b/src/shared/gatt-helpers.c
@@ -30,14 +30,96 @@
 #include "src/shared/att.h"
 #include "lib/uuid.h"
 #include "src/shared/gatt-helpers.h"
+#include "src/shared/util.h"
+
+#ifndef MIN
+#define MIN(a, b) ((a) < (b) ? (a) : (b))
+#endif
+
+struct mtu_op {
+	struct bt_att *att;
+	uint16_t client_rx_mtu;
+	bt_gatt_result_callback_t callback;
+	void *user_data;
+	bt_gatt_destroy_func_t destroy;
+};
+
+static void destroy_mtu_op(void *user_data)
+{
+	struct mtu_op *op = user_data;
+
+	if (op->destroy)
+		op->destroy(op->user_data);
+
+	free(op);
+}
+
+static uint8_t process_error(const void *pdu, uint16_t length)
+{
+	if (!pdu || length != 4)
+		return 0;
+
+	return ((uint8_t *) pdu)[3];
+}
+
+static void mtu_cb(uint8_t opcode, const void *pdu, uint16_t length,
+								void *user_data)
+{
+	struct mtu_op *op = user_data;
+	bool success = true;
+	uint8_t att_ecode = 0;
+	uint16_t server_rx_mtu;
+
+	if (opcode == BT_ATT_OP_ERROR_RSP) {
+		success = false;
+		att_ecode = process_error(pdu, length);
+		goto done;
+	}
+
+	if (opcode != BT_ATT_OP_MTU_RSP || !pdu || length != 2) {
+		success = false;
+		goto done;
+	}
+
+	server_rx_mtu = get_le16(pdu);
+	bt_att_set_mtu(op->att, MIN(op->client_rx_mtu, server_rx_mtu));
+
+done:
+	if (op->callback)
+		op->callback(success, att_ecode, op->user_data);
+}
 
 bool bt_gatt_exchange_mtu(struct bt_att *att, uint16_t client_rx_mtu,
 					bt_gatt_result_callback_t callback,
 					void *user_data,
 					bt_gatt_destroy_func_t destroy)
 {
-	/* TODO */
-	return false;
+	struct mtu_op *op;
+	uint8_t pdu[2];
+
+	if (!att || !client_rx_mtu)
+		return false;
+
+	op = new0(struct mtu_op, 1);
+	if (!op)
+		return false;
+
+	op->att = att;
+	op->client_rx_mtu = client_rx_mtu;
+	op->callback = callback;
+	op->user_data = user_data;
+	op->destroy = destroy;
+
+	put_le16(client_rx_mtu, pdu);
+
+	if (!bt_att_send(att, BT_ATT_OP_MTU_REQ, pdu, sizeof(pdu),
+							mtu_cb, op,
+							destroy_mtu_op)) {
+		free(op);
+		return false;
+	}
+
+	return true;
 }
 
 bool bt_gatt_discover_primary_services(struct bt_att *att,
-- 
2.47.3