Implements merging of same requests in OlpClient. (#1111)

This commit implements merging of same URL requests
for the async OlpClient::CallApi() method by using
the previously created PendingUrlRequest(s) classes.
The merging is only performed in case the request
does not have any body as this could alter the
response.
Additionaly this commit adds support for HEAD and
PATCH requests, already supported by the Network
layer.
OlpClientTests adapted and extended accordingly
with additional test cases. All other tests using
mocked networked changed to returning the callback
asynchronously.

Relates-To: OLPEDGE-1805

Signed-off-by: Andrei Popescu <[email protected]>

Author: Andrei Popescu

olp-cpp-sdk-core/include/olp/core/client/OlpClient.h

@@ -33,7 +33,8 @@ namespace olp {
 namespace client {
 /**
  * @brief Executes HTTP requests by using the base url and the provided
- * parameters and body.
+ * parameters and body. This class will handle retries based on the
+ * RetrySettings and will merge all similar URL requests into one.
  */
 class CORE_API OlpClient {
  public:
@@ -42,6 +43,7 @@ class CORE_API OlpClient {
   using RequestBodyType = std::shared_ptr<std::vector<std::uint8_t>>;
 
   OlpClient();
+  OlpClient(const OlpClientSettings& settings, std::string base_url);
   virtual ~OlpClient();
 
   // Movable and copyable
@@ -52,8 +54,10 @@ class CORE_API OlpClient {
 
   /**
    * @brief Sets the base URL used for all requests.
-
-   * @param base_url The base URL.
+   *
+   * @note The base URL can change over time and it is thread safe to change it.
+   *
+   * @param base_url The new base URL to be used for all outgoing requests.
    */
   void SetBaseUrl(const std::string& base_url);
 
@@ -67,14 +71,24 @@ class CORE_API OlpClient {
   /**
    * @brief Gets the default headers that are added to each request.
    *
+   * @note Do not change this while requests are ongoing.
+   *
    * @return The default headers.
    */
   ParametersType& GetMutableDefaultHeaders();
 
   /**
    * @brief Sets the client settings.
    *
+   * @note Handle with care and do not change while requests are ongoing.
+   * Ideally the settings would not change during the lifecycle of this
+   * instance.
+   *
    * @param settings The client settings.
+   *
+   * @deprecated This method will be removed by 05.2021. Please use the
+   * constructor instead. The settings should not change during the lifetime of
+   * the instance.
    */
   void SetSettings(const OlpClientSettings& settings);