lib: at_shell: Add optional multiline support

Added CONFIG_AT_SHELL_UNESCAPE_LF to enable reception of
multiline AT commands.

Updated the at_shell() function to replace the 2 character
sequence "\n" with <CR><LF> if CONFIG_AT_SHELL_UNESCAPE_LF
is enabled.

Jira: IRIS-6919

Signed-off-by: Pete Skeggs <[email protected]>

Author: plskeggs

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -739,6 +739,11 @@ Modem libraries
     * To use the ``AT+CMMS`` AT command when sending concatenated SMS message.
     * To set "7" as a fallback SMS service center address for type approval SIM cards which do not have it set.
 
+* :ref:`lib_at_shell` library:
+
+  * Added the :kconfig:option:`CONFIG_AT_SHELL_UNESCAPE_LF` Kconfig option to enable reception of multiline AT commands.
+  * Updated the :c:func:`at_shell` function to replace ``\n`` with ``<CR><LF>`` if :kconfig:option:`CONFIG_AT_SHELL_UNESCAPE_LF` is enabled.
+
 Multiprotocol Service Layer libraries
 -------------------------------------
 

lib/at_shell/Kconfig

@@ -20,4 +20,12 @@ config AT_SHELL_CMD_RESPONSE_MAX_LEN
 	int "Maximum AT command response length"
 	default 2700
 
+config AT_SHELL_UNESCAPE_LF
+	bool "Unescape linefeed"
+	help
+	  Replaces \n with <CR><LF>. This enables commands such as AT%CMNG=0 to
+	  properly receive certificates that ordinarily have multiple lines.
+	  The certificate must have been preprocessed to replace EOL sequences
+	  with a literal \ character followed by an n character.
+
 endif # AT_SHELL

lib/at_shell/at_shell.c

@@ -10,6 +10,8 @@
 #include <nrf_modem_at.h>
 #include <modem/at_monitor.h>
 
+#define CREDENTIALS_CMD "AT%CMNG=0"
+
 static struct shell *global_shell;
 static const char at_usage_str[] =
 	"Usage: at <subcommand>\n"
@@ -54,6 +56,22 @@ int at_shell(const struct shell *shell, size_t argc, char **argv)
 		at_monitor_pause(&at_shell_monitor);
 		shell_print(shell, "AT command event handler disabled");
 	} else {
+		if (IS_ENABLED(CONFIG_AT_SHELL_UNESCAPE_LF)) {
+			/* Replace the two character sequence "\n" with <CR><LF> so AT%CMNG=0,
+			 * which accepts multiline input, will work with a properly
+			 * pre-processed cert. Without this, the second and subsequent lines of the
+			 * cert are treated as new shell commands, which of course fail.
+			 */
+			if (strncmp(command, CREDENTIALS_CMD, strlen(CREDENTIALS_CMD)) == 0) {
+				char *c = command;
+
+				while ((c = strstr(c, "\\n")) != NULL) {
+					c[0] = '\r';
+					c[1] = '\n';
+				}
+			}
+		}
+
 		err = nrf_modem_at_cmd(response, sizeof(response), "%s", command);
 		if (err < 0) {
 			shell_print(shell, "Sending AT command failed with error code %d", err);

subsys/net/lib/nrf_cloud/Kconfig

@@ -127,6 +127,7 @@ choice NRF_CLOUD_CREDENTIALS_MGMT
 config NRF_CLOUD_CREDENTIALS_MGMT_MODEM
 	depends on NRF_MODEM_LIB
 	select MODEM_KEY_MGMT
+	imply AT_SHELL_UNESCAPE_LF if AT_SHELL
 	bool "Credentials are managed by the modem"
 
 config NRF_CLOUD_CREDENTIALS_MGMT_TLS_CRED