Better Error Handling and Logging

Summary

Better error handling (less exceptions, more error codes) and logging (for more detailed error handling and configuration issues).

Issue: https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/390

See also the tests in caosdb-cppinttest!2 (merged)

Focus

• The TransactionStatus class represents the current status of a Transaction instance.
• The TransactionCode is a numeric representation of the status and intended for c-compatible error handling.
• Messages and Message classes handle the errors, warnings and info messages that come from the server.
• Logging: The logging can be configured via a json file. Otherwise the default configuration is in place.
• A lot of code was moved in order to comply with -pedantic flag. Don't waste your time

Test Environment

Unit tests should run as described in README_SETUP

Integration tests should run against a linkahead in the f-grpc branch

Check List for the Author

Please, prepare your MR for a review. Be sure to write a summary and a focus and create gitlab comments for the reviewer. They should guide the reviewer through the changes, explain your changes and also point out open questions. For further good practices have a look at our review guidelines

• All automated tests pass
• Reference related Issues
• Up-to-date CHANGELOG.md
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there spezifications? Are they satisfied?

For further good practices have a look at our review guidelines.

include/caosdb/connection.h

@@ -45,6 +45,7 @@ using caosdb::entity::v1alpha1::EntityTransactionService;
 using caosdb::info::VersionInfo;
 using caosdb::info::v1alpha1::GeneralInfoService;
 using caosdb::transaction::Transaction;
+using caosdb::transaction::TransactionStatus;
 using grpc::ChannelCredentials;
 
 class CertificateProvider {
@@ -82,11 +83,7 @@ private:
 public:
   ConnectionConfiguration(const std::string &host, int port);
   virtual ~ConnectionConfiguration() = default;
-  friend auto operator<<(std::ostream &out,
-                         const ConnectionConfiguration &configuration)
-    -> std::ostream &;
 
-  [[nodiscard]] auto virtual ToString() const -> std::string = 0;
   [[nodiscard]] auto GetHost() const -> std::string;
   [[nodiscard]] auto GetPort() const -> int;
   [[nodiscard]] auto virtual GetChannelCredentials() const
@@ -101,7 +98,6 @@ public:
   InsecureConnectionConfiguration(const std::string &host, int port);
   [[nodiscard]] auto GetChannelCredentials() const
     -> std::shared_ptr<ChannelCredentials> override;
-  [[nodiscard]] auto ToString() const -> std::string override;
 };
 
 class TlsConnectionConfiguration : public ConnectionConfiguration {
@@ -120,23 +116,62 @@ public:
                              const Authenticator &authenticator);
   [[nodiscard]] auto GetChannelCredentials() const
     -> std::shared_ptr<ChannelCredentials> override;
-  [[nodiscard]] auto ToString() const -> std::string override;
 };
 
 /**
  * @brief A reusable connection to a CaosDBServer.
  */
 class Connection {
-  std::shared_ptr<grpc::Channel> channel;
-  std::unique_ptr<GeneralInfoService::Stub> general_info_service;
-  std::shared_ptr<EntityTransactionService::Stub> entity_transaction_service;
-
 public:
   explicit Connection(const ConnectionConfiguration &configuration);
-  friend auto operator<<(std::ostream &out, const Connection &connection)
-    -> std::ostream &;
-  [[nodiscard]] auto GetVersionInfo() const -> std::unique_ptr<VersionInfo>;
+
+  /**
+   * Request the server's version and return the status of this request after
+   * termination..
+   *
+   * The version is stored in the connection object and may be retrieved via
+   * GetVersionInfo() if the request was successful.
+   *
+   * This method does not throw any exceptions. Errors are indicated in the
+   * return value instead.
+   */
+  auto RetrieveVersionInfoNoExceptions() const noexcept -> TransactionStatus;
+
+  /**
+   * Request and return the server's version.
+   *
+   * If the request terminated unsuccessfully, a corresponding exception is
+   * being thrown.
+   */
+  auto RetrieveVersionInfo() const -> const VersionInfo &;
+
+  /**
+   * Return the server's version.
+   *
+   * Clients need to call RetrieveVersionInfo() or
+   * RetrieveVersionInfoNoExceptions() before the version info is locally
+   * available. Otherwise an empty instance is being returned.
+   */
+  [[nodiscard]] inline auto GetVersionInfo() const noexcept
+    -> const VersionInfo & {
+    return this->version_info;
+  };
+
   [[nodiscard]] auto CreateTransaction() const -> std::unique_ptr<Transaction>;
+
+private:
+  /// GRPC-Channel (HTTP/2 Connection plus Authentication). We use a shared
+  /// pointer because Transaction instances also own the channel.
+  std::shared_ptr<grpc::Channel> channel;
+  /// Service for retrieving the server's version. We use a unique pointer
+  /// because only this connection owns and uses this service.
+  std::unique_ptr<GeneralInfoService::Stub> general_info_service;
+  /// The server's version. It's mutable because it is rather a cache than a
+  /// data member which is subject to change.
+  mutable VersionInfo version_info;
+  /// Service for entity transactions. We use a shared pointer because
+  /// Transaction instances also own this service stub.
+  std::shared_ptr<EntityTransactionService::Stub> entity_transaction_service;
 };
 
 /**