folder 'lib' was previously ignored, contains espnow.cpp and its header

client/client/lib/README

+
+This directory is intended for project specific (private) libraries.
+PlatformIO will compile them to static libraries and link into executable file.
+
+The source code of each library should be placed in a an own separate directory
+("lib/your_library_name/[here are source files]").****
+
+For example, see a structure of the following two libraries `Foo` and `Bar`:
+
+|--lib
+|  |
+|  |--Bar
+|  |  |--docs
+|  |  |--examples
+|  |  |--src
+|  |     |- Bar.c
+|  |     |- Bar.h
+|  |  |- library.json (optional, custom build options, etc) https://docs.platformio.org/page/librarymanager/config.html
+|  |
+|  |--Foo
+|  |  |- Foo.c
+|  |  |- Foo.h
+|  |
+|  |- README --> THIS FILE
+|
+|- platformio.ini
+|--src
+   |- main.c
+
+and a contents of `src/main.c`:
+```
+#include <Foo.h>
+#include <Bar.h>
+
+int main (void)
+{
+  ...
+}
+
+```
+
+PlatformIO Library Dependency Finder will find automatically dependent
+libraries scanning project source files.
+
+More information about PlatformIO Library Dependency Finder
+- https://docs.platformio.org/page/librarymanager/ldf.html

client/client/lib/espnow/src/espnow.cpp

+#include <esp_now.h>
+#include "WiFi.h"
+#include "espnow.h"
+
+uint8_t BROADCAST_MAC[] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}; //probably shouldn't be defined here, works for now
+esp_now_peer_info_t hostInfo;
+
+void on_data_sent(const uint8_t *mac_addr, esp_now_send_status_t status){
+    // go to sleep
+}
+
+void on_data_recv(const uint8_t *mac, const uint8_t *incomingData, int len){
+    // sync time
+}
+
+int send_data(dataMessage data){
+    esp_err_t result = esp_now_send(BROADCAST_MAC, (uint8_t *) &data, sizeof(data));
+    return result;
+}
+
+int espnow_setup(){
+    WiFi.mode(WIFI_STA);
+    if(esp_now_init() != ESP_OK){
+        //initialization failed
+        return 1;
+    }
+
+    memcpy(hostInfo.peer_addr, BROADCAST_MAC, sizeof(BROADCAST_MAC));
+    hostInfo.channel = 0;
+    hostInfo.encrypt = true; //if we encrypt espnow we can have no more than 10 clients per host
+    esp_err_t peerAddStatus = esp_now_add_peer(&hostInfo); //there are a couple errors that can happen here
+    if(peerAddStatus != ESP_OK){
+        //peer couldn't be added
+        return 2;
+    }
+
+    esp_now_register_recv_cb(on_data_recv);
+    esp_now_register_send_cb(on_data_sent);
+
+    return 0;
+}

client/client/lib/espnow/src/espnow.h

+#define NUM_SENSORS 10
+
+// I originally wanted to define the mac addresses here, but i got a "multiple definition" error?
+typedef struct dataMessage{
+    int identifiers[NUM_SENSORS];
+    float values[NUM_SENSORS];
+}dataMessage;
+
+int send_data(dataMessage data);
+
+int espnow_setup();
+