ESP32: extend sh2lib with distinct recv and send funcs

sh2lib_execute() processes send, then recv. This is fine
for a general purpose server, however, it can lead to code like:

loop:
  1) sh2lib_execute()
  2) based on handler called in (1), sh2lib_do_get/post()
  3) do other system task

^^This means that any requests queued in (2) cannot be sent
until the next sh2lib_execute(). Instead, this commit
splits sh2lib_execute() into distinct _send() and _recv()
phases, so client use this pattern, which reduces latency
between request generation in (2) and request sending in(3):

loop:
  1) sh2lib_execute_recv()
  2) based on handler called in (1), sh2lib_do_get/post()
  3) sh2lib_execute_send()
  4) do other system task

Author: bryghtlabs-richard

sh2lib/sh2lib.c

@@ -328,21 +328,39 @@ void sh2lib_free(struct sh2lib_handle *hd)
 int sh2lib_execute(struct sh2lib_handle *hd)
 {
     int ret;
-    ret = nghttp2_session_send(hd->http2_sess);
+    ret = sh2lib_execute_send(hd);
     if (ret != 0) {
-        ESP_LOGE(TAG, "[sh2-execute] HTTP2 session send failed %d", ret);
         return ret;
     }
 
-    ret = nghttp2_session_recv(hd->http2_sess);
+    ret = sh2lib_execute_recv(hd);
     if (ret != 0) {
-        ESP_LOGE(TAG, "[sh2-execute] HTTP2 session recv failed %d", ret);
         return ret;
     }
 
     return 0;
 }
 
+int sh2lib_execute_recv(struct sh2lib_handle *hd)
+{
+    int ret = nghttp2_session_recv(hd->http2_sess);
+    if (ret != 0) {
+        ESP_LOGE(TAG, "[sh2-execute] HTTP2 session recv failed %d", ret);
+    }
+
+    return ret;
+}
+
+int sh2lib_execute_send(struct sh2lib_handle *hd)
+{
+    int ret = nghttp2_session_send(hd->http2_sess);
+    if (ret != 0) {
+        ESP_LOGE(TAG, "[sh2-execute] HTTP2 session send failed %d", ret);
+    }
+
+    return ret;
+}
+
 int sh2lib_do_get_with_nv(struct sh2lib_handle *hd, const nghttp2_nv *nva, size_t nvlen, sh2lib_frame_data_recv_cb_t recv_cb)
 {
     int ret = nghttp2_submit_request(hd->http2_sess, NULL, nva, nvlen, NULL, recv_cb);

sh2lib/sh2lib.h

@@ -201,6 +201,38 @@ int sh2lib_do_put(struct sh2lib_handle *hd, const char *path,
  */
 int sh2lib_execute(struct sh2lib_handle *hd);
 
+/**
+ * @brief Execute receive on an HTTP/2 connection
+ *
+ * While the API sh2lib_do_get(), sh2lib_do_post() setup the requests to be
+ * initiated with the server, this API performs the actual data send/receive
+ * operations on the HTTP/2 connection. The callback functions are accordingly
+ * called during the processing of these requests.
+ *
+ * @param[in] hd      Pointer to a variable of the type 'struct sh2lib_handle'
+ *
+ * @return
+ *             - 0 if it succeeds
+ *             - Negative error code from nghttp2 on failure
+ */
+int sh2lib_execute_recv(struct sh2lib_handle *hd);
+
+/**
+ * @brief Execute send on an HTTP/2 connection
+ *
+ * While the API sh2lib_do_get(), sh2lib_do_post() setup the requests to be
+ * initiated with the server, this API performs the actual data send/receive
+ * operations on the HTTP/2 connection. The callback functions are accordingly
+ * called during the processing of these requests.
+ *
+ * @param[in] hd      Pointer to a variable of the type 'struct sh2lib_handle'
+ *
+ * @return
+ *             - 0 if it succeeds
+ *             - Negative error code from nghttp2 on failure
+ */
+int sh2lib_execute_send(struct sh2lib_handle *hd);
+
 #define SH2LIB_MAKE_NV(NAME, VALUE)                                    \
   {                                                                    \
     (uint8_t *)NAME, (uint8_t *)VALUE, strlen(NAME), strlen(VALUE),    \