feat: Adds rate limiting

src/cellular/sf_cloud.cpp

@@ -4,13 +4,15 @@
 #include "product.hpp"
 #include "sys/NVRAM.hpp"
 #include "system.hpp"
+#include "consts.hpp"
 
 #include <stdint.h>
 
 #include "Particle.h"
 
 namespace sf::cloud
 {
+    system_tick_t last_publish_time = 0;
     int wait_connect(int timeout_ms)
     {
         uint16_t n_attempts;
@@ -74,6 +76,12 @@ namespace sf::cloud
 
     int publish_blob(const char* title, const char* blob)
     {
+        system_tick_t time_since_last = millis() - last_publish_time;
+        // SF_OSAL_printf("%u ms since last publish" __NL__, time_since_last);
+        if (time_since_last < SF_UPLOAD_MS_PER_TRANSMIT)
+        {
+            delay(SF_UPLOAD_MS_PER_TRANSMIT - time_since_last);
+        }
         if (strlen(blob) > particle::protocol::MAX_EVENT_DATA_LENGTH)
         {
             return OVERSIZE_DATA;
@@ -90,6 +98,7 @@ namespace sf::cloud
         {
             return PUBLISH_FAIL;
         }
+        last_publish_time = millis();
         return SUCCESS;
     }
 

src/cellular/sf_cloud.hpp

@@ -55,6 +55,7 @@ namespace sf
         /**
          * @brief Publishes the specified message
          * 
+         * This function may block for as much as 20 seconds.
          *
          * @param title Message title.  Must be 1-64 characters and only letters,
          *                              numbers, underscores, dashes, or slashes.