AP_Logger: add message validation check against duplicate labels

libraries/AP_Logger/AP_Logger.cpp

@@ -298,6 +298,44 @@ void AP_Logger::dump_structures(const struct LogStructure *logstructures, const
 #endif
 }
 
+bool AP_Logger::labels_string_is_good(const char *labels) const
+{
+    // This goes through and slices labels up into substrings by
+    // changing commas to nulls - keeping references to each string in
+    // label_offsets.
+    bool passed = true;
+    char *label_offsets[LS_LABELS_SIZE];
+    uint8_t label_offsets_offset = 0;
+    char labels_copy[LS_LABELS_SIZE];
+    strncpy(labels_copy, labels, ARRAY_SIZE(labels_copy));
+    if (labels_copy[0] == ',') {
+        Debug("Leading comma in (%s)", labels);
+        passed = false;
+    }
+    label_offsets[label_offsets_offset++] = labels_copy;
+    const uint8_t len = strnlen(labels_copy, ARRAY_SIZE(labels_copy));
+    for (uint8_t i=0; i<len; i++) {
+        if (labels_copy[i] == ',') {
+            if (labels_copy[i+1] == '\0') {
+                Debug("Trailing comma in (%s)", labels);
+                passed = false;
+                continue;
+            }
+            labels_copy[i] = '\0';
+            label_offsets[label_offsets_offset++] = &labels_copy[i+1];
+        }
+    }
+    for (uint8_t i=0; i<label_offsets_offset-1; i++) {
+        for (uint8_t j=i+1; j<label_offsets_offset; j++) {
+            if (!strcmp(label_offsets[i], label_offsets[j])) {
+                Debug("Duplicate label (%s) in (%s)", label_offsets[i], labels);
+                passed = false;
+            }
+        }
+    }
+    return passed;
+}
+
 bool AP_Logger::validate_structure(const struct LogStructure *logstructure, const int16_t offset)
 {
     bool passed = true;
@@ -337,6 +375,10 @@ bool AP_Logger::validate_structure(const struct LogStructure *logstructure, cons
         passed = false;
     }
 
+    if (!labels_string_is_good(logstructure->labels)) {
+        passed = false;
+    }
+
     // check that the structure is of an appropriate length to take fields
     const int16_t msg_len = Write_calc_msg_len(logstructure->format);
     if (msg_len != logstructure->msg_len) {

libraries/AP_Logger/AP_Logger.h

@@ -470,6 +470,7 @@ private:
     const char* unit_name(const uint8_t unit_id);
     double multiplier_name(const uint8_t multiplier_id);
     bool seen_ids[256] = { };
+    bool labels_string_is_good(const char *labels) const;
 #endif
 
     // possibly expensive calls to start log system: