* first draft of new ConfigSerializer. (simple embedded JSON prefs)

examples/simple_repeater/MyMesh.cpp

@@ -872,7 +872,6 @@ MyMesh::MyMesh(mesh::MainBoard &board, mesh::Radio &radio, mesh::MillisecondCloc
 #endif
 
   // defaults
-  memset(&_prefs, 0, sizeof(_prefs));
   _prefs.airtime_factor = 1.0;
   _prefs.rx_delay_base = 0.0f;   // turn off by default, was 10.0;
   _prefs.tx_delay_factor = 0.5f; // was 0.25f

examples/simple_room_server/MyMesh.cpp

@@ -628,7 +628,6 @@ MyMesh::MyMesh(mesh::MainBoard &board, mesh::Radio &radio, mesh::MillisecondCloc
   recv_pkt_region = NULL;
 
   // defaults
-  memset(&_prefs, 0, sizeof(_prefs));
   _prefs.airtime_factor = 1.0;
   _prefs.rx_delay_base = 0.0f;   // off by default, was 10.0
   _prefs.tx_delay_factor = 0.5f; // was 0.25f;

examples/simple_sensor/SensorMesh.cpp

@@ -710,7 +710,6 @@ SensorMesh::SensorMesh(mesh::MainBoard& board, mesh::Radio& radio, mesh::Millise
   set_radio_at = revert_radio_at = 0;
 
   // defaults
-  memset(&_prefs, 0, sizeof(_prefs));
   _prefs.airtime_factor = 1.0;
   _prefs.rx_delay_base =   0.0f;  // turn off by default, was 10.0;
   _prefs.tx_delay_factor = 0.5f;   // was 0.25f

src/helpers/CommonCLI.cpp

@@ -28,16 +28,21 @@ static bool isValidName(const char *n) {
 }
 
 void CommonCLI::loadPrefs(FILESYSTEM* fs) {
-  if (fs->exists("/com_prefs")) {
+  if (fs->exists("/ser_prefs")) {
-    loadPrefsInt(fs, "/com_prefs");   // new filename
+    File file = fs->open("/ser_prefs");
-  } else if (fs->exists("/node_prefs")) {
+    if (file) {
-    loadPrefsInt(fs, "/node_prefs");
+      _prefs->loadSerial(file);   // new Serial prefs
-    savePrefs(fs);  // save to new filename
+      file.close();
-    fs->remove("/node_prefs");  // remove old
+    }
+  } else if (fs->exists("/com_prefs")) {
+    loadPrefsInt(fs, "/com_prefs");
+    if (savePrefs(fs)) {  // save to new Serial prefs
+  //    fs->remove("/com_prefs");  // remove old
+    }
   }
 }
 
-void CommonCLI::loadPrefsInt(FILESYSTEM* fs, const char* filename) {
+void CommonCLI::loadPrefsInt(FILESYSTEM* fs, const char* filename) {  // Legacy prefs loader
 #if defined(RP2040_PLATFORM)
   File file = fs->open(filename, "r");
 #else
@@ -130,70 +135,21 @@ void CommonCLI::loadPrefsInt(FILESYSTEM* fs, const char* filename) {
   }
 }
 
-void CommonCLI::savePrefs(FILESYSTEM* fs) {
+bool CommonCLI::savePrefs(FILESYSTEM* fs) {
 #if defined(NRF52_PLATFORM) || defined(STM32_PLATFORM)
-  fs->remove("/com_prefs");
+  fs->remove("/ser_prefs");
-  File file = fs->open("/com_prefs", FILE_O_WRITE);
+  File file = fs->open("/ser_prefs", FILE_O_WRITE);
 #elif defined(RP2040_PLATFORM)
-  File file = fs->open("/com_prefs", "w");
+  File file = fs->open("/ser_prefs", "w");
 #else
-  File file = fs->open("/com_prefs", "w", true);
+  File file = fs->open("/ser_prefs", "w", true);
 #endif
   if (file) {
-    uint8_t pad[8];
+    bool success = _prefs->saveSerial(file);
-    memset(pad, 0, sizeof(pad));
-
-    file.write((uint8_t *)&_prefs->airtime_factor, sizeof(_prefs->airtime_factor));    // 0
-    file.write((uint8_t *)&_prefs->node_name, sizeof(_prefs->node_name));              // 4
-    file.write(pad, 4);                                                                // 36
-    file.write((uint8_t *)&_prefs->node_lat, sizeof(_prefs->node_lat));                // 40
-    file.write((uint8_t *)&_prefs->node_lon, sizeof(_prefs->node_lon));                // 48
-    file.write((uint8_t *)&_prefs->password[0], sizeof(_prefs->password));             // 56
-    file.write((uint8_t *)&_prefs->freq, sizeof(_prefs->freq));                        // 72
-    file.write((uint8_t *)&_prefs->tx_power_dbm, sizeof(_prefs->tx_power_dbm));        // 76
-    file.write((uint8_t *)&_prefs->disable_fwd, sizeof(_prefs->disable_fwd));          // 77
-    file.write((uint8_t *)&_prefs->advert_interval, sizeof(_prefs->advert_interval));  // 78
-    file.write(pad, 1);                                                                // 79 : 1 byte unused (rx_boosted_gain moved to end)
-    file.write((uint8_t *)&_prefs->rx_delay_base, sizeof(_prefs->rx_delay_base));      // 80
-    file.write((uint8_t *)&_prefs->tx_delay_factor, sizeof(_prefs->tx_delay_factor));  // 84
-    file.write((uint8_t *)&_prefs->guest_password[0], sizeof(_prefs->guest_password)); // 88
-    file.write((uint8_t *)&_prefs->direct_tx_delay_factor, sizeof(_prefs->direct_tx_delay_factor)); // 104
-    file.write(pad, 4); // 108 : 4 byte unused
-    file.write((uint8_t *)&_prefs->sf, sizeof(_prefs->sf));                                         // 112
-    file.write((uint8_t *)&_prefs->cr, sizeof(_prefs->cr));                                         // 113
-    file.write((uint8_t *)&_prefs->allow_read_only, sizeof(_prefs->allow_read_only));               // 114
-    file.write((uint8_t *)&_prefs->multi_acks, sizeof(_prefs->multi_acks));                         // 115
-    file.write((uint8_t *)&_prefs->bw, sizeof(_prefs->bw));                                         // 116
-    file.write((uint8_t *)&_prefs->agc_reset_interval, sizeof(_prefs->agc_reset_interval));         // 120
-    file.write((uint8_t *)&_prefs->path_hash_mode, sizeof(_prefs->path_hash_mode));                 // 121
-    file.write((uint8_t *)&_prefs->loop_detect, sizeof(_prefs->loop_detect));                       // 122
-    file.write(pad, 1);                                                                             // 123
-    file.write((uint8_t *)&_prefs->flood_max, sizeof(_prefs->flood_max));                           // 124
-    file.write((uint8_t *)&_prefs->flood_advert_interval, sizeof(_prefs->flood_advert_interval));   // 125
-    file.write((uint8_t *)&_prefs->interference_threshold, sizeof(_prefs->interference_threshold)); // 126
-    file.write((uint8_t *)&_prefs->bridge_enabled, sizeof(_prefs->bridge_enabled));                 // 127
-    file.write((uint8_t *)&_prefs->bridge_delay, sizeof(_prefs->bridge_delay));                     // 128
-    file.write((uint8_t *)&_prefs->bridge_pkt_src, sizeof(_prefs->bridge_pkt_src));                 // 130
-    file.write((uint8_t *)&_prefs->bridge_baud, sizeof(_prefs->bridge_baud));                       // 131
-    file.write((uint8_t *)&_prefs->bridge_channel, sizeof(_prefs->bridge_channel));                 // 135
-    file.write((uint8_t *)&_prefs->bridge_secret, sizeof(_prefs->bridge_secret));                   // 136
-    file.write((uint8_t *)&_prefs->powersaving_enabled, sizeof(_prefs->powersaving_enabled));       // 152
-    file.write(pad, 3);                                                                             // 153
-    file.write((uint8_t *)&_prefs->gps_enabled, sizeof(_prefs->gps_enabled));                       // 156
-    file.write((uint8_t *)&_prefs->gps_interval, sizeof(_prefs->gps_interval));                     // 157
-    file.write((uint8_t *)&_prefs->advert_loc_policy, sizeof(_prefs->advert_loc_policy));           // 161
-    file.write((uint8_t *)&_prefs->discovery_mod_timestamp, sizeof(_prefs->discovery_mod_timestamp)); // 162
-    file.write((uint8_t *)&_prefs->adc_multiplier, sizeof(_prefs->adc_multiplier));                 // 166
-    file.write((uint8_t *)_prefs->owner_info, sizeof(_prefs->owner_info));                          // 170
-    file.write((uint8_t *)&_prefs->rx_boosted_gain, sizeof(_prefs->rx_boosted_gain));               // 290
-    file.write((uint8_t *)&_prefs->flood_max_unscoped, sizeof(_prefs->flood_max_unscoped));         // 291
-    file.write((uint8_t *)&_prefs->flood_max_advert, sizeof(_prefs->flood_max_advert));             // 292
-    file.write((uint8_t *)&_prefs->radio_fem_rxgain, sizeof(_prefs->radio_fem_rxgain));             // 293
-    file.write((uint8_t *)&_prefs->cad_enabled, sizeof(_prefs->cad_enabled));                       // 294
-    // next: 295
-
     file.close();
+    return success;
   }
+  return false;
 }
 
 #define MIN_LOCAL_ADVERT_INTERVAL   60

src/helpers/CommonCLI.h

@@ -5,6 +5,7 @@
 #include <helpers/SensorManager.h>
 #include <helpers/ClientACL.h>
 #include <helpers/RegionMap.h>
+#include <helpers/ConfigSerializer.h>
 
 #if defined(WITH_RS232_BRIDGE) || defined(WITH_ESPNOW_BRIDGE)
 #define WITH_BRIDGE
@@ -19,7 +20,9 @@
 #define LOOP_DETECT_MODERATE  2
 #define LOOP_DETECT_STRICT    3
 
-struct NodePrefs { // persisted to file
+class NodePrefs : public ConfigSerializer {
+public:
+  // in-memory backing data
   float airtime_factor;
   char node_name[32];
   double node_lat, node_lon;
@@ -65,6 +68,121 @@ struct NodePrefs { // persisted to file
   uint8_t path_hash_mode;   // which path mode to use when sending
   uint8_t loop_detect;
   uint8_t cad_enabled;      // hardware Channel Activity Detection before TX (boolean)
+
+private:
+  class RadioPrefs : public ConfigSerializer {
+    NodePrefs* _parent;
+  protected:
+    void structure() override {
+      def("freq", _parent->freq);
+      def("bw", _parent->bw);
+      def("sf", _parent->sf);
+      def("cr", _parent->cr);
+      def("cad", _parent->cad_enabled);
+      def("int_thr", _parent->interference_threshold);
+      def("rxgain", _parent->rx_boosted_gain);
+      def("fem_rxgain", _parent->rx_boosted_gain);
+      def("tx", _parent->tx_power_dbm);
+      def("af", _parent->airtime_factor);
+      def("rxdelay", _parent->rx_delay_base);
+      def("f_txdelay", _parent->tx_delay_factor);
+      def("d_txdelay", _parent->direct_tx_delay_factor);
+      def("agc_int", _parent->agc_reset_interval);
+      def("hash_mode", _parent->path_hash_mode);
+      def("multi_ack", _parent->multi_acks);
+    }
+  public:
+    RadioPrefs(NodePrefs* parent) : _parent(parent) { }
+  };
+  RadioPrefs radio;
+
+  class BridgePrefs : public ConfigSerializer {
+    NodePrefs* _parent;
+  protected:
+    void structure() override {
+      def("en", _parent->bridge_enabled); // boolean
+      def("delay", _parent->bridge_delay);  // milliseconds (default 500 ms)
+      def("src", _parent->bridge_pkt_src); // 0 = logTx, 1 = logRx (default logTx)
+      def("baud", _parent->bridge_baud);   // 9600, 19200, 38400, 57600, 115200 (default 115200)
+      def("ch", _parent->bridge_channel); // 1-14 (ESP-NOW only)
+      def("secret", _parent->bridge_secret, sizeof(_parent->bridge_secret)); // for XOR encryption of bridge packets (ESP-NOW only)
+    }
+  public:
+    BridgePrefs(NodePrefs* parent) : _parent(parent) { }
+  };
+  BridgePrefs bridge;
+
+  class GPSPrefs : public ConfigSerializer {
+    NodePrefs* _parent;
+  protected:
+    void structure() override {
+      def("en", _parent->gps_enabled); // boolean
+      def("int", _parent->gps_interval);   // interval in seconds
+      def("adv_loc", _parent->advert_loc_policy);
+    }
+  public:
+    GPSPrefs(NodePrefs* parent) : _parent(parent) { }
+  };
+  GPSPrefs gps;
+
+  class PowerPrefs : public ConfigSerializer {
+    NodePrefs* _parent;
+  protected:
+    void structure() override {
+      def("adc_mult", _parent->adc_multiplier);
+      def("pwr_sav_en", _parent->powersaving_enabled);
+    }
+  public:
+    PowerPrefs(NodePrefs* parent) : _parent(parent) { }
+  };
+  PowerPrefs power;
+
+  class RepeatPrefs : public ConfigSerializer {
+    NodePrefs* _parent;
+  protected:
+    void structure() override {
+      def("disable", _parent->disable_fwd);
+      def("f_max", _parent->flood_max);
+      def("f_max_uns", _parent->flood_max_unscoped);
+      def("f_max_adv", _parent->flood_max_advert);
+      def("loop", _parent->loop_detect);
+    }
+  public:
+    RepeatPrefs(NodePrefs* parent) : _parent(parent) { }
+  };
+  RepeatPrefs repeat;
+
+  class RoomPrefs : public ConfigSerializer {
+    NodePrefs* _parent;
+  protected:
+    void structure() override {
+      def("rd_only", _parent->allow_read_only);
+    }
+  public:
+    RoomPrefs(NodePrefs* parent) : _parent(parent) { }
+  };
+  RoomPrefs room;
+
+protected:
+  void structure() override {
+    def("name", node_name, sizeof(node_name));
+    def("pass", password, sizeof(password));
+    def("guest", guest_password, sizeof(guest_password));
+    def("owner", owner_info, sizeof(owner_info));
+    def("adv_int", advert_interval);
+    def("f_adv_int", flood_advert_interval);
+    def("lat", node_lat);
+    def("lon", node_lon);
+    def("radio", radio);
+    def("bridge", bridge);
+    def("gps", gps);
+    def("repeat", repeat);
+    def("room", room);
+    def("power", power);
+  }
+
+public:
+  NodePrefs() : ConfigSerializer(), bridge(this), gps(this), radio(this), power(this), repeat(this), room(this) { }
 };
 
 class CommonCLICallbacks {
@@ -139,7 +257,7 @@ public:
       : _board(&board), _rtc(&rtc), _sensors(&sensors), _region_map(&region_map), _acl(&acl), _prefs(prefs), _callbacks(callbacks) { }
 
   void loadPrefs(FILESYSTEM* _fs);
-  void savePrefs(FILESYSTEM* _fs);
+  bool savePrefs(FILESYSTEM* _fs);
   void handleCommand(uint32_t sender_timestamp, char* command, char* reply);
   uint8_t buildAdvertData(uint8_t node_type, uint8_t* app_data);
 };

src/helpers/ConfigSerializer.cpp

@@ -0,0 +1,278 @@
+#include "ConfigSerializer.h"
+
+bool ConfigSerializer::saveSerial(Stream& s) {
+  Context context(&s, OP::WRITE);
+  _context = &context;  // set the context for structure() call
+  s.print("{");   // root object
+  _first = true;
+  structure();
+  if (s.print("}") != 1) context.success = false;  // failure detect
+  _context = NULL;
+  return context.success;
+}
+
+#define TOK_ERROR     -1
+#define TOK_EOF        0
+#define TOK_KEY        1
+#define TOK_VALUE      2
+#define TOK_START_OBJ  3
+#define TOK_END_OBJ    4
+#define TOK_WHITESPACE 5
+
+static bool is_whitespace(char c) {
+  return c == ' ' || c == '\t' || c == '\r' || c == '\n';
+}
+static bool is_key_char(char c) {
+  return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || c == '_';
+}
+static bool is_value_char(char c) {
+  return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || c == '-' || c == '.';
+}
+
+#define EXPECT_OPEN_BRACE   0
+#define EXPECT_KEY          1
+#define EXPECT_VAL_OR_OBJ   2
+#define EXPECT_STRING_VAL   3
+#define EXPECT_STRING_ESCAPE   4
+#define EXPECT_COMMA_OR_CLOSE  5
+#define EXPECT_COMMA_OR_KEY    6
+#define EXPECT_COMMA_OR_KEY_OR_CLOSE  7
+
+int ConfigSerializer::Context::readNext() {
+  char c;
+  if (pending) {
+    c = pending;
+    pending = 0;
+  } else {
+    if (_f->available() == 0) return TOK_EOF;
+
+    int n = _f->read();
+    if (n < 0) return TOK_EOF;
+    c = (char)n;
+  }
+
+  switch (rd_mode) {
+    case EXPECT_OPEN_BRACE:
+      if (c == '{') { rd_mode = EXPECT_KEY; return TOK_START_OBJ; }
+      if (is_whitespace(c)) return TOK_WHITESPACE;
+      return TOK_ERROR;
+
+    case EXPECT_COMMA_OR_KEY_OR_CLOSE:
+      if (c == '}') { rd_mode = EXPECT_COMMA_OR_KEY_OR_CLOSE; return TOK_END_OBJ; }
+    case EXPECT_COMMA_OR_KEY:
+      if (c == ',') { rd_mode = EXPECT_KEY; return TOK_WHITESPACE; }
+    case EXPECT_KEY:
+      if (rd_len > 0 && c == ':') { rd_buf[rd_len] = 0; rd_len = 0; rd_mode = EXPECT_VAL_OR_OBJ; return TOK_KEY; }
+      if (rd_len == 0 && is_whitespace(c)) return TOK_WHITESPACE;
+      if (rd_len < CONFIG_MAX_KEYLEN-1 && is_key_char(c)) { rd_buf[rd_len++] = c; return TOK_WHITESPACE; }
+      return TOK_ERROR;
+
+    case EXPECT_VAL_OR_OBJ:
+      if (rd_len == 0 && is_whitespace(c)) return TOK_WHITESPACE;
+      if (rd_len == 0 && c == '"') { rd_mode = EXPECT_STRING_VAL; return TOK_WHITESPACE; }
+      if (rd_len == 0 && c == '{') { rd_mode = EXPECT_KEY; return TOK_START_OBJ; }
+      if (is_value_char(c) && rd_len < CONFIG_MAX_TOKEN_LEN-1) { rd_buf[rd_len++] = c; return TOK_WHITESPACE; }
+      if (rd_len > 0 && (c == ',' || c == '}' || is_whitespace(c))) { pending = c; rd_buf[rd_len] = 0; rd_len = 0; rd_mode = EXPECT_COMMA_OR_CLOSE; return TOK_VALUE;  }
+      return TOK_ERROR;
+
+    case EXPECT_STRING_ESCAPE:
+      if ((c == '"' || c == '\\' || c == '/') && rd_len < CONFIG_MAX_TOKEN_LEN-1) { rd_buf[rd_len++] = c; rd_mode = EXPECT_STRING_VAL; return TOK_WHITESPACE; }
+      return TOK_ERROR;  // unsupport escape
+
+    case EXPECT_STRING_VAL:
+      if (c == '"') { rd_buf[rd_len] = 0; rd_len = 0; rd_mode = EXPECT_COMMA_OR_CLOSE; return TOK_VALUE; }
+      if (c == '\\') { rd_mode = EXPECT_STRING_ESCAPE; return TOK_WHITESPACE; }
+      if (rd_len < CONFIG_MAX_TOKEN_LEN-1) { rd_buf[rd_len++] = c; return TOK_WHITESPACE; }
+      return TOK_ERROR;
+
+    case EXPECT_COMMA_OR_CLOSE:
+      if (c == ',') { rd_mode = EXPECT_KEY; return TOK_WHITESPACE; }
+      if (c == '}') { rd_mode = EXPECT_COMMA_OR_KEY_OR_CLOSE; return TOK_END_OBJ; }
+      if (is_whitespace(c)) return TOK_WHITESPACE;
+      return TOK_ERROR;
+  }
+  return TOK_ERROR;   // unknown mode
+}
+
+bool ConfigSerializer::loadSerial(Stream& s) {
+  Context context(&s, OP::READ);
+  _context = &context;  // set the context for structure() call
+  // parse the Json file
+  uint8_t sp = 0;
+  int next_tok;
+
+  while ((next_tok = context.readNext()) > TOK_EOF) {
+    if (next_tok == TOK_KEY) {
+      context.setKey(sp, context.getToken());
+    } else if (next_tok == TOK_VALUE) {
+      _depth = 1;  // re-run the structure() hierarchy again (looking for specific key, at specific depth)
+      structure();
+    } else if (next_tok == TOK_START_OBJ) {
+      if (sp < CONFIF_MAX_DEPTH - 1) {
+        sp++;
+      } else {
+        Serial.printf("Error: max nesting reached"); // TODO: debug logging
+        context.success = false;
+        break;
+      }
+    } else if (next_tok == TOK_END_OBJ) {
+      if (sp > 0) {
+        sp--;
+      } else {
+        Serial.printf("Error: too many closing '}'"); // TODO: debug logging
+        context.success = false;
+        break;
+      }
+    }
+  }
+  if (sp != 0 || next_tok == TOK_ERROR) {
+    context.success = false;   // unmatched { }, or other parse error
+  }
+  _context = NULL;
+  return context.success;
+}
+
+void ConfigSerializer::writeComma() {
+  if (_first) {
+    _first = false;
+  } else {
+    _context->file()->print(",");  // comma separated properties
+  }
+}
+
+void ConfigSerializer::def(const char* key, char* value, size_t max_len) {
+  if (_context->op() == OP::WRITE) {
+    writeComma();
+    _context->file()->print(key);
+    _context->file()->print(":\"");
+    _context->file()->print(value);   // TODO: escape quotes
+    _context->file()->print("\"");
+  } else {
+    if (_context->keyMatch(_depth, key)) {
+      strncpy(value, _context->getToken(), max_len - 1);
+      value[max_len - 1] = 0;
+    }
+  }
+}
+
+void ConfigSerializer::def(const char* key, int32_t& value) {
+  if (_context->op() == OP::WRITE) {
+    writeComma();
+    _context->file()->print(key);
+    _context->file()->print(":");
+    _context->file()->print(value);
+  } else {
+    if (_context->keyMatch(_depth, key)) {
+      value = atol(_context->getToken());
+    }
+  }
+}
+
+void ConfigSerializer::def(const char* key, uint32_t& value) {
+  if (_context->op() == OP::WRITE) {
+    writeComma();
+    _context->file()->print(key);
+    _context->file()->print(":");
+    _context->file()->print(value);
+  } else {
+    if (_context->keyMatch(_depth, key)) {
+      value = atol(_context->getToken());
+    }
+  }
+}
+
+void ConfigSerializer::def(const char* key, int16_t& value) {
+  if (_context->op() == OP::WRITE) {
+    writeComma();
+    _context->file()->print(key);
+    _context->file()->print(":");
+    _context->file()->print((int32_t) value, 10);
+  } else {
+    if (_context->keyMatch(_depth, key)) {
+      value = atol(_context->getToken());
+    }
+  }
+}
+
+void ConfigSerializer::def(const char* key, uint16_t& value) {
+  if (_context->op() == OP::WRITE) {
+    writeComma();
+    _context->file()->print(key);
+    _context->file()->print(":");
+    _context->file()->print((uint32_t) value, 10);
+  } else {
+    if (_context->keyMatch(_depth, key)) {
+      value = atoi(_context->getToken());
+    }
+  }
+}
+
+void ConfigSerializer::def(const char* key, uint8_t& value) {
+  if (_context->op() == OP::WRITE) {
+    writeComma();
+    _context->file()->print(key);
+    _context->file()->print(":");
+    _context->file()->print((uint32_t) value, 10);
+  } else {
+    if (_context->keyMatch(_depth, key)) {
+      value = atoi(_context->getToken());
+    }
+  }
+}
+
+void ConfigSerializer::def(const char* key, int8_t& value) {
+  if (_context->op() == OP::WRITE) {
+    writeComma();
+    _context->file()->print(key);
+    _context->file()->print(":");
+    _context->file()->print((int32_t) value, 10);
+  } else {
+    if (_context->keyMatch(_depth, key)) {
+      value = atoi(_context->getToken());
+    }
+  }
+}
+
+void ConfigSerializer::def(const char* key, double& value) {
+  if (_context->op() == OP::WRITE) {
+    writeComma();
+    _context->file()->print(key);
+    _context->file()->print(":");
+    _context->file()->print(value, 6);  // REVISIT: how many dec places?
+  } else {
+    if (_context->keyMatch(_depth, key)) {
+      value = atof(_context->getToken());
+    }
+  }
+}
+
+void ConfigSerializer::def(const char* key, float& value) {
+  if (_context->op() == OP::WRITE) {
+    writeComma();
+    _context->file()->print(key);
+    _context->file()->print(":");
+    _context->file()->print(value, 4);  // REVISIT: how many dec places?
+  } else {
+    if (_context->keyMatch(_depth, key)) {
+      value = (float) atof(_context->getToken());
+    }
+  }
+}
+
+void ConfigSerializer::def(const char* key, ConfigSerializer& sub_obj) {
+  if (_context->op() == OP::WRITE) {
+    writeComma();
+    _context->file()->print(key);
+    _context->file()->print(":{");
+    sub_obj._context = _context;  // inherit the Context
+    sub_obj._first = true;
+    sub_obj.structure();   // recurse into sub object
+    if (_context->file()->print("}") != 1) _context->success = false;  // failure detect
+  } else {
+    if (_context->keyMatch(_depth, key)) {
+      sub_obj._context = _context;  // inherit the Context
+      sub_obj._depth = _depth + 1;
+      sub_obj.structure();   // recurse into sub object
+    }
+  }
+}

src/helpers/ConfigSerializer.h

@@ -0,0 +1,67 @@
+#pragma once
+
+#include <Arduino.h>
+
+#ifndef CONFIF_MAX_DEPTH
+  #define CONFIF_MAX_DEPTH   8
+#endif
+
+#ifndef CONFIG_MAX_KEYLEN
+  #define CONFIG_MAX_KEYLEN  16
+#endif
+
+#ifndef CONFIG_MAX_TOKEN_LEN
+  #define CONFIG_MAX_TOKEN_LEN   128
+#endif
+
+class ConfigSerializer {
+  bool _first;
+  int8_t _depth;
+
+  enum OP { READ, WRITE };
+
+  class Context {
+    Stream* _f;
+    OP _op;
+    uint8_t rd_len;
+    uint8_t rd_mode;
+    char pending;
+    char rd_buf[CONFIG_MAX_TOKEN_LEN];
+    char _keys[CONFIF_MAX_DEPTH][CONFIG_MAX_KEYLEN];
+
+  public:
+    bool success = true;
+    Context(Stream* f, OP op) : _f(f), _op(op) { rd_buf[rd_len = 0] = 0; rd_mode = 0; pending = 0; }
+    OP op() const { return _op; }
+    Stream* file() const { return _f; }
+    int readNext();
+    const char* getToken() const { return rd_buf; }
+    bool keyMatch(int8_t depth, const char* key) { return strcmp(key, _keys[depth]) == 0; }
+    void setKey(uint8_t depth, const char* key) { strcpy(_keys[depth], key);  }
+  };
+
+  Context* _context = NULL;
+
+  void writeComma();
+
+protected:
+  ConfigSerializer() { }
+
+  void def(const char* key, char* value, size_t max_len);  // max_len inclusive of null
+  void def(const char* key, int32_t& value);
+  void def(const char* key, int16_t& value);
+  void def(const char* key, int8_t& value);
+  void def(const char* key, uint32_t& value);
+  void def(const char* key, uint16_t& value);
+  void def(const char* key, uint8_t& value);
+  void def(const char* key, float& value);
+  void def(const char* key, double& value);
+  void def(const char* key, bool& value);
+  void def(const char* key, ConfigSerializer& sub_obj);
+
+  virtual void structure() = 0;
+
+public:
+  bool loadSerial(Stream& s);
+  bool saveSerial(Stream& s);
+};