From 63441eeecf658a9b76ba29fee7ebca54959e8492 Mon Sep 17 00:00:00 2001
From: Maximilian Deubel <maximilian.deubel@nordicsemi.no>
Date: Wed, 11 Dec 2024 15:22:23 +0100
Subject: [PATCH] lib: nrf_cloud: use BLOCK2 for resumption offset

Fix an issue where resumption wasn't requesting the correct offset
of the FOTA file to download using COAP.
This patch uses the standard offset option instead of a custom one.

Signed-off-by: Maximilian Deubel <maximilian.deubel@nordicsemi.no>
---
 .../lib/nrf_cloud/src/nrf_cloud_download.c    | 58 ++++++++++++++-----
 1 file changed, 45 insertions(+), 13 deletions(-)

diff --git a/subsys/net/lib/nrf_cloud/src/nrf_cloud_download.c b/subsys/net/lib/nrf_cloud/src/nrf_cloud_download.c
index 35e34c350714..304f7aa0342d 100644
--- a/subsys/net/lib/nrf_cloud/src/nrf_cloud_download.c
+++ b/subsys/net/lib/nrf_cloud/src/nrf_cloud_download.c
@@ -36,7 +36,8 @@ static struct nrf_cloud_download_data active_dl = { .type = NRF_CLOUD_DL_TYPE_NO
 #if defined(CONFIG_NRF_CLOUD_COAP_DOWNLOADS)
 #define ACPT_IDX 0
 #define PRXY_IDX 1
-#define OPT_CNT  2
+#define BLOCK2_IDX 2
+#define OPT_CNT  3
 /* CoAP option array */
 static struct coap_client_option cc_opts[OPT_CNT] = {0};
 /* CoAP client to be used for file downloads */
@@ -197,15 +198,43 @@ static void coap_dl_cb(int16_t result_code, size_t offset, const uint8_t *payloa
 }
 
 #define MAX_RETRIES 5
-#define PROXY_RSC_OFFSET_TMPLT		NRF_CLOUD_COAP_PROXY_RSC "?offset=%u"
-#define PROXY_RSC_BUF_SZ		sizeof(PROXY_RSC_OFFSET_TMPLT) + 10
-static int coap_dl_start(struct nrf_cloud_download_data *const dl, const size_t offset)
+/* COAP_OPTION_BLOCK2: set block size */
+#define SET_BLOCK_SIZE(v, b) (v |= ((b) & 0x07))
+/* COAP_OPTION_BLOCK2: set block number */
+#define SET_NUM(v, n) ((v) |= ((n) << 4))
+
+/* convert integer into CoAP option */
+static uint8_t coap_option_write_int_val(uint8_t *data, unsigned int val)
 {
-	static char rsc_path_offset[PROXY_RSC_BUF_SZ];
+	uint8_t len;
+
+	if (val == 0U) {
+		data[0] = 0U;
+		len = 0U;
+	} else if (val < 0xFF) {
+		data[0] = (uint8_t) val;
+		len = 1U;
+	} else if (val < 0xFFFF) {
+		sys_put_be16(val, data);
+		len = 2U;
+	} else if (val < 0xFFFFFF) {
+		sys_put_be16(val, &data[1]);
+		data[0] = val >> 16;
+		len = 3U;
+	} else {
+		sys_put_be32(val, data);
+		len = 4U;
+	}
+
+	return len;
+}
 
+static int coap_dl_start(struct nrf_cloud_download_data *const dl, const size_t offset)
+{
 	int err;
 	int retry = 0;
 	struct coap_client *cc = &coap_client.cc;
+	unsigned int block2_val = 0;
 
 	struct coap_client_request request = {
 		.method = COAP_METHOD_GET,
@@ -221,14 +250,11 @@ static int coap_dl_start(struct nrf_cloud_download_data *const dl, const size_t
 	};
 
 	if (offset > 0) {
-		/* Use the offset parameter in the resource path */
-		err = snprintk(rsc_path_offset, sizeof(rsc_path_offset),
-			       PROXY_RSC_OFFSET_TMPLT, offset);
-		if ((err < 0) || (err >= sizeof(rsc_path_offset))) {
-			LOG_ERR("Could not format CoAP proxy download resource");
-			return -EIO;
-		}
-		request.path = rsc_path_offset;
+		SET_NUM(block2_val, (offset/1024));
+		SET_BLOCK_SIZE(block2_val, COAP_BLOCK_1024);
+		cc_opts[BLOCK2_IDX].code = COAP_OPTION_BLOCK2;
+		cc_opts[BLOCK2_IDX].len =
+			coap_option_write_int_val(cc_opts[BLOCK2_IDX].value, block2_val);
 	}
 
 	while ((err = coap_client_req(cc, cc->fd, NULL, &request, NULL)) == -EAGAIN) {
@@ -287,6 +313,12 @@ static int coap_dl(struct nrf_cloud_download_data *const dl)
 	ret = nrf_cloud_coap_transport_proxy_dl_opts_get(&cc_opts[ACPT_IDX],
 							 &cc_opts[PRXY_IDX],
 							 dl->host, file_path);
+	cc_opts[BLOCK2_IDX].code = COAP_OPTION_BLOCK2;
+	cc_opts[BLOCK2_IDX].len = 1;
+	cc_opts[BLOCK2_IDX].value[0] = 0;
+	SET_BLOCK_SIZE(cc_opts[BLOCK2_IDX].value[0], COAP_BLOCK_1024);
+	SET_NUM(cc_opts[BLOCK2_IDX].value[0], 0);
+
 	if (ret) {
 		LOG_ERR("Failed to set CoAP options, error: %d", ret);
 		return ret;