feat(modem): Added support for at_raw() command

at_raw() sends raw string and supports custom pass/fail phrases for the
API to return OK/FAIL. It also returns raw, unprocessed string as
output.
This allows sending custom requests, such as:
* dce->at_raw("", resp, "RDY", "...", 20000) -- waiting for reset
* esp_modem_at_raw(dce, "+++", resp, "DISCONNECTED", "ERROR", 5000) --
exits PPP mode

Closes #471
Partially addresses #468

components/esp_modem/include/generate/esp_modem_command_declare.inc

@@ -44,6 +44,18 @@ ESP_MODEM_DECLARE_DCE_COMMAND(store_profile, command_result, 0) \
  */\
 ESP_MODEM_DECLARE_DCE_COMMAND(set_pin, command_result, 1, STRING_IN(p1, pin)) \
     \
+/**
+ * @brief Execute the supplied AT command in raw mode (doesn't append '\r' to command, returns everything)
+ * @param[in] cmd String command that's send to DTE
+ * @param[out] out Raw output from DTE
+ * @param[in] pass Pattern in response for the API to return OK
+ * @param[in] fail Pattern in response for the API to return FAIL
+ * @param[in] cmd String command that's send to DTE
+ * @param[in] timeout AT command timeout in milliseconds
+ * @return OK, FAIL or TIMEOUT
+ */\
+ESP_MODEM_DECLARE_DCE_COMMAND(at_raw, command_result, 5, STRING_IN(p1, cmd), STRING_OUT(p2, out), STRING_IN(p3, pass), STRING_IN(p4, fail), INT_IN(p5, timeout)) \
+    \
 /**
  * @brief Execute the supplied AT command
  * @param[in] cmd AT command

components/esp_modem/src/esp_modem_c_api.cpp

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2021-2023 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2021-2024 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -17,7 +17,7 @@
 #include "esp_private/c_api_wrapper.hpp"
 
 #ifndef ESP_MODEM_C_API_STR_MAX
-#define ESP_MODEM_C_API_STR_MAX 64
+#define ESP_MODEM_C_API_STR_MAX 128
 #endif
 
 #ifndef HAVE_STRLCPY
@@ -206,6 +206,20 @@ extern "C" esp_err_t esp_modem_get_imsi(esp_modem_dce_t *dce_wrap, char *p_imsi)
     return ret;
 }
 
+extern "C" esp_err_t esp_modem_at_raw(esp_modem_dce_t *dce_wrap, const char *cmd, char *p_out, const char *pass, const char *fail, int timeout)
+{
+    if (dce_wrap == nullptr || dce_wrap->dce == nullptr) {
+        return ESP_ERR_INVALID_ARG;
+    }
+    std::string out;
+    auto ret = command_response_to_esp_err(dce_wrap->dce->at_raw(cmd, out, pass, fail, timeout));
+    if ((p_out != NULL) && (!out.empty())) {
+        strlcpy(p_out, out.c_str(), ESP_MODEM_C_API_STR_MAX);
+    }
+    return ret;
+}
+
+
 extern "C" esp_err_t esp_modem_set_flow_control(esp_modem_dce_t *dce_wrap, int dce_flow, int dte_flow)
 {
     if (dce_wrap == nullptr || dce_wrap->dce == nullptr) {

components/esp_modem/src/esp_modem_command_library.cpp

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2021-2023 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2021-2024 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -394,6 +394,22 @@ command_result at(CommandableIf *t, const std::string &cmd, std::string &out, in
     return generic_get_string(t, at_command, out, timeout);
 }
 
+command_result at_raw(CommandableIf *t, const std::string &cmd, std::string &out, const std::string &pass, const std::string &fail, int timeout = 500)
+{
+    ESP_LOGV(TAG, "%s", __func__ );
+    return t->command(cmd, [&](uint8_t *data, size_t len) {
+        out.assign(reinterpret_cast<char *>(data), len);
+
+        if (out.find(pass) != std::string::npos) {
+            return command_result::OK;
+        } else if (out.find(fail) != std::string::npos) {
+            return command_result::FAIL;
+        }
+
+        return command_result::TIMEOUT;
+    }, timeout);
+}
+
 command_result get_signal_quality(CommandableIf *t, int &rssi, int &ber)
 {
     ESP_LOGV(TAG, "%s", __func__ );