libraries/SocketWrapper: Support loading CA certs from the file system.

This patch adds support for automatically loading CA certificates
from the filesystem. The file system certs are loaded on the first
call to connectSSL(), once, and shared between all sockets.

If filesystem support is not enabled, or CA loading fails, the
connection proceeds without error.

Custom CA certificates can still be passed via the 'cert' parameter,
and both filesystem and custom certificates are registered with
using different TLS tags. This allows users to add their own certs
without recreating the whole file.

Signed-off-by: iabdalkader <i.abdalkader@gmail.com>

Author: iabdalkader

libraries/SocketWrapper/SocketWrapper.h

@@ -1,9 +1,13 @@
 #pragma once
 
 #include "zephyr/sys/printk.h"
+#if defined(CONFIG_FILE_SYSTEM)
+#include <zephyr/fs/fs.h>
+#endif
+
 #if defined(CONFIG_NET_SOCKETS_SOCKOPT_TLS)
 #include <zephyr/net/tls_credentials.h>
-#define CA_CERTIFICATE_TAG 1
+#define CA_CERTIFICATE_TAG_BASE 1
 #endif
 
 #include <zephyr/net/socket.h>
@@ -14,6 +18,47 @@ class ZephyrSocketWrapper {
 	bool is_ssl = false;
 	int ssl_sock_temp_char = -1;
 
+#if defined(CONFIG_NET_SOCKETS_SOCKOPT_TLS) && defined(CONFIG_FILE_SYSTEM)
+	inline static char *cadata = nullptr;
+
+	bool loadCADataFromFS(const char *cert_path = "/wlan:/cacert.pem") {
+		struct fs_file_t file;
+		fs_file_t_init(&file);
+
+		if (fs_open(&file, cert_path, FS_O_READ) != 0) {
+			return false;
+		}
+
+		// Get file size
+		struct fs_dirent entry;
+		if (fs_stat(cert_path, &entry) != 0) {
+			fs_close(&file);
+			return false;
+		}
+
+		size_t file_size = entry.size;
+
+		// Allocate buffer for entire file
+		cadata = (char *)k_malloc(file_size);
+		if (!cadata) {
+			fs_close(&file);
+			return false;
+		}
+
+		// Read entire file
+		ssize_t bytes_read = fs_read(&file, cadata, file_size);
+		fs_close(&file);
+
+		if (bytes_read != file_size) {
+			k_free(cadata);
+			cadata = nullptr;
+			return false;
+		}
+
+		return true;
+	}
+#endif
+
 public:
 	ZephyrSocketWrapper() : sock_fd(-1) {
 	}
@@ -102,7 +147,7 @@ class ZephyrSocketWrapper {
 	}
 
 #if defined(CONFIG_NET_SOCKETS_SOCKOPT_TLS)
-	bool connectSSL(const char *host, uint16_t port, const char *ca_certificate_pem = nullptr) {
+	bool connectSSL(const char *host, uint16_t port, const char *cert = nullptr) {
 
 		// Resolve address
 		struct addrinfo hints = {0};
@@ -115,9 +160,9 @@ class ZephyrSocketWrapper {
 		int ret;
 		bool rv = false;
 
-		sec_tag_t sec_tag_opt[] = {
-			CA_CERTIFICATE_TAG,
-		};
+		sec_tag_t sec_tag_opt[2];
+		int tag_count = 0;
+		int tag = CA_CERTIFICATE_TAG_BASE;
 
 		struct timeval timeout_opt = {
 			.tv_sec = 0,
@@ -138,21 +183,39 @@ class ZephyrSocketWrapper {
 			goto exit;
 		}
 
-		if (ca_certificate_pem != nullptr) {
-			ret = tls_credential_add(CA_CERTIFICATE_TAG, TLS_CREDENTIAL_CA_CERTIFICATE,
-									 ca_certificate_pem, strlen(ca_certificate_pem) + 1);
-			if (ret != 0) {
+#if defined(CONFIG_FILE_SYSTEM)
+		// Try to load builtin CA from filesystem (once)
+		if (cadata == nullptr && loadCADataFromFS()) {
+			// Successfully loaded, add with tag (ignore errors)
+			if (tls_credential_add(tag++, TLS_CREDENTIAL_CA_CERTIFICATE, cadata,
+								   strlen(cadata) + 1)) {
 				goto exit;
 			}
 		}
+#endif
+
+		// Add custom CA if provided (uses next available tag)
+		if (cert != nullptr) {
+			if (tls_credential_add(tag++, TLS_CREDENTIAL_CA_CERTIFICATE, cert, strlen(cert) + 1) !=
+				0) {
+				goto exit;
+			}
+		}
+
+		// Build sequential tag list
+		tag_count = tag - CA_CERTIFICATE_TAG_BASE;
+		for (int i = 0; i < tag_count; i++) {
+			sec_tag_opt[i] = CA_CERTIFICATE_TAG_BASE + i;
+		}
 
 		sock_fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TLS_1_2);
 		if (sock_fd < 0) {
 			goto exit;
 		}
 
 		if (setsockopt(sock_fd, SOL_TLS, TLS_HOSTNAME, host, strlen(host)) ||
-			setsockopt(sock_fd, SOL_TLS, TLS_SEC_TAG_LIST, sec_tag_opt, sizeof(sec_tag_opt)) ||
+			setsockopt(sock_fd, SOL_TLS, TLS_SEC_TAG_LIST, sec_tag_opt,
+					   sizeof(sec_tag_t) * tag_count) ||
 			setsockopt(sock_fd, SOL_SOCKET, SO_RCVTIMEO, &timeout_opt, sizeof(timeout_opt))) {
 			goto exit;
 		}