Cellular: Suppress long AT traces

When AT traces are enabled and very long AT commands are traced,
system can easily go to unwanted state. Therefore the length of the AT
traces is limited to DEBUG_MAXLEN (currently 60 characters).

This commit fixes read_hex_string, read_bytes and write to use this
limitter.

features/cellular/framework/AT/ATHandler.cpp

@@ -585,6 +585,12 @@ ssize_t ATHandler::read_bytes(uint8_t *buf, size_t len)
     }
 
     bool debug_on = _debug_on;
+    bool disabled_debug = false;
+    if (len > DEBUG_MAXLEN) {
+        _debug_on = false;
+        disabled_debug = true;
+    }
+
     size_t read_len = 0;
     for (; read_len < len; read_len++) {
         int c = get_char();
@@ -594,10 +600,16 @@ ssize_t ATHandler::read_bytes(uint8_t *buf, size_t len)
             return -1;
         }
         buf[read_len] = c;
-        if (_debug_on && read_len >= DEBUG_MAXLEN) {
-            _debug_on = false;
-        }
     }
+
+#if MBED_CONF_CELLULAR_DEBUG_AT
+    if (debug_on && disabled_debug) {
+        tr_info("read_bytes trace suppressed (total length %d)", read_len);
+    }
+#else
+    (void)disabled_debug; // Remove compiler warning
+#endif
+
     _debug_on = debug_on;
     return read_len;
 }
@@ -690,13 +702,15 @@ ssize_t ATHandler::read_hex_string(char *buf, size_t size)
     char hexbuf[2];
 
     bool debug_on = _debug_on;
+    bool disabled_debug = false;
+    if (size > DEBUG_MAXLEN) {
+        _debug_on = false;
+        disabled_debug = true;
+    }
+
     for (; read_idx < size * 2 + match_pos; read_idx++) {
         int c = get_char();
 
-        if (_debug_on && read_idx >= DEBUG_MAXLEN) {
-            _debug_on = false;
-        }
-
         if (match_pos) {
             buf_idx++;
         } else {
@@ -737,12 +751,21 @@ ssize_t ATHandler::read_hex_string(char *buf, size_t size)
             }
         }
     }
-    _debug_on = debug_on;
 
     if (read_idx && (read_idx == size * 2 + match_pos)) {
         buf_idx++;
     }
 
+#if MBED_CONF_CELLULAR_DEBUG_AT
+    if (debug_on && disabled_debug) {
+        tr_info("read_hex_string trace suppressed (total length %d)", buf_idx);
+    }
+#else
+    (void)disabled_debug; // Remove compiler warning
+#endif
+
+    _debug_on = debug_on;
+
     return buf_idx;
 }
 
@@ -1460,30 +1483,37 @@ size_t ATHandler::write(const void *data, size_t len)
     fhs.fh = _fileHandle;
     fhs.events = POLLOUT;
     size_t write_len = 0;
-    bool debug_on = _debug_on;
+
+#if MBED_CONF_CELLULAR_DEBUG_AT
+    bool suppress_traced = false;
+#endif
+
     for (; write_len < len;) {
         int count = poll(&fhs, 1, poll_timeout());
         if (count <= 0 || !(fhs.revents & POLLOUT)) {
             set_error(NSAPI_ERROR_DEVICE_ERROR);
-            _debug_on = debug_on;
             return 0;
         }
         ssize_t ret = _fileHandle->write((uint8_t *)data + write_len, len - write_len);
         if (ret < 0) {
             set_error(NSAPI_ERROR_DEVICE_ERROR);
-            _debug_on = debug_on;
             return 0;
         }
-        if (_debug_on && write_len < DEBUG_MAXLEN) {
-            if (write_len + ret < DEBUG_MAXLEN) {
-                debug_print((char *)data + write_len, ret, AT_TX);
-            } else {
-                _debug_on = false;
+
+#if MBED_CONF_CELLULAR_DEBUG_AT
+        if (write_len + ret > DEBUG_MAXLEN) {
+            if (_debug_on && !suppress_traced) {
+                debug_print((char *)data + write_len, DEBUG_MAXLEN, AT_TX);
+                tr_debug("write trace suppressed (total length %d)", len);
             }
+            suppress_traced = true;
+        } else {
+            debug_print((char *)data + write_len, ret, AT_TX);
         }
+#endif
+
         write_len += (size_t)ret;
     }
-    _debug_on = debug_on;
 
     return write_len;
 }

features/cellular/mbed_lib.json

@@ -14,7 +14,7 @@
             "value": 0
         },
         "debug-at": {
-            "help": "Enable AT debug prints",
+            "help": "Enable AT debug prints. Note! This can have impact on UART performance and might need increasing of drivers.uart-serial-rxbuf-size",
             "value": false
         },
         "radio-access-technology": {