Improv - BLE WiFi provisioning (#1807)

Co-authored-by: Paulus Schoutsen <balloob@gmail.com>

esphome/components/improv/improv.cpp

@@ -0,0 +1,66 @@
+#include "improv.h"
+
+namespace improv {
+
+ImprovCommand parse_improv_data(std::vector<uint8_t> &data) { return parse_improv_data(data.data(), data.size()); }
+
+ImprovCommand parse_improv_data(const uint8_t *data, size_t length) {
+  Command command = (Command) data[0];
+  uint8_t data_length = data[1];
+
+  if (data_length != length - 3) {
+    return {.command = UNKNOWN};
+  }
+
+  uint8_t checksum = data[length - 1];
+
+  uint32_t calculated_checksum = 0;
+  for (uint8_t i = 0; i < length - 1; i++) {
+    calculated_checksum += data[i];
+  }
+
+  if ((uint8_t) calculated_checksum != checksum) {
+    return {.command = BAD_CHECKSUM};
+  }
+
+  if (command == WIFI_SETTINGS) {
+    uint8_t ssid_length = data[2];
+    uint8_t ssid_start = 3;
+    size_t ssid_end = ssid_start + ssid_length;
+
+    uint8_t pass_length = data[ssid_end];
+    size_t pass_start = ssid_end + 1;
+    size_t pass_end = pass_start + pass_length;
+
+    std::string ssid(data + ssid_start, data + ssid_end);
+    std::string password(data + pass_start, data + pass_end);
+    return {.command = command, .ssid = ssid, .password = password};
+  }
+
+  return {
+      .command = command,
+  };
+}
+
+std::vector<uint8_t> build_rpc_response(Command command, std::vector<std::string> datum) {
+  std::vector<uint8_t> out;
+  uint32_t length = 0;
+  out.push_back(command);
+  for (auto str : datum) {
+    uint8_t len = str.length();
+    length += len;
+    out.push_back(len);
+    out.insert(out.end(), str.begin(), str.end());
+  }
+  out.insert(out.begin() + 1, length);
+
+  uint32_t calculated_checksum = 0;
+
+  for (uint8_t byte : out) {
+    calculated_checksum += byte;
+  }
+  out.push_back(calculated_checksum);
+  return out;
+}
+
+}  // namespace improv