Minimal c interface

Summary

See https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/404

• Minimal C Interface
• Configuration via json files
• Renaming of many classes and functions (In order to comply with best-practices as formulated by https://google.github.io/styleguide/cppguide.html)

Integration tests are in caosdb-cppinttest!1 (merged)

Focus

• Please take a look at the c-interface functions:
  • I the naming consistent?
  • I see one problem regarding the destructors: When a client uses caosdb_connection_connection_manager_get_default_connection to get the default connection, the destructor caosdb_connection_delete_connection should not be called, because the connection object is actually owned by the ConnectionManager. Maybe, we should prevent the deletion of the wrapped connection somehow, when the connection is owned by the ConnectionManager?
• ConfigurationManager and ConnectionManager:
  • These two singletons are tightly coupled. When the ConfigurationManager is being reset, also the ConnectionManager resets. Is this a good behavior?
• There is currently no error/exception handling in the c-interface. I will add this in https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/390

Test Environment

Please try and setup a client (e.g. the ccaosdbcli) with a json configuration file.

Check List for the Author

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• 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/ccaosdb.h

@@ -91,12 +91,17 @@ const char *caosdb_utility_get_env_var(const char *name, const char *fall_back);
  * Use the destructor function
  * `caosdb_connection_delete_certificate_provider` to free the wrapped
  * provider.
+ *
+ * EXPERT USE ONLY.  Memory management with this function is a bit tricky.
+ * Only use it when you know what you are doing.
  */
 int caosdb_connection_create_pem_file_certificate_provider(
   caosdb_connection_certificate_provider *out, const char *path);
 
 /**
  * Destructor function for a certificate provider.
+ *
+ * EXPERT USE ONLY.  Only use it when you know what you are doing.
  */
 int caosdb_connection_delete_certificate_provider(
   caosdb_connection_certificate_provider *provider);
@@ -109,6 +114,9 @@ int caosdb_connection_delete_certificate_provider(
  * Use the destructor function
  * `caosdb_connection_delete_connection_configuration` to free the wrapped
  * configuration.
+ *
+ * EXPERT USE ONLY.  Memory management with this function is a bit tricky.
+ * Only use it when you know what you are doing.
  */
 int caosdb_connection_create_tls_connection_configuration(
   caosdb_connection_connection_configuration *out, const char *host,
@@ -126,6 +134,9 @@ int caosdb_connection_create_tls_connection_configuration(
  * Use the destructor function
  * `caosdb_connection_delete_connection_configuration` to free the wrapped
  * configuration.
+ *
+ * EXPERT USE ONLY.  Memory management with this function is a bit tricky.
+ * Only use it when you know what you are doing.
  */
 int caosdb_connection_create_insecure_connection_configuration(
   caosdb_connection_connection_configuration *out, const char *host,
@@ -134,6 +145,8 @@ int caosdb_connection_create_insecure_connection_configuration(
 /**
  * Destructor function for the caosdb_connection_connection_configuration
  * struct.
+ *
+ * EXPERT USE ONLY.  Only use it when you know what you are doing.
  */
 int caosdb_connection_delete_connection_configuration(
   caosdb_connection_connection_configuration *configuration);
@@ -154,6 +167,9 @@ int caosdb_connection_configuration_add_cacert(
  * Use the destructor function
  * `caosdb_authentication_delete_authenticator` to free the wrapped
  * authenticator.
+ *
+ * EXPERT USE ONLY.  Memory management with this function is a bit tricky.
+ * Only use it when you know what you are doing.
  */
 int caosdb_authentication_create_plain_password_authenticator(
   caosdb_authentication_authenticator *out, const char *username,
@@ -161,6 +177,8 @@ int caosdb_authentication_create_plain_password_authenticator(
 
 /**
  * Destructor function for the caosdb_authentication_authenticator struct.
+ *
+ * EXPERT USE ONLY.  Only use it when you know what you are doing.
  */
 int caosdb_authentication_delete_authenticator(
   caosdb_authentication_authenticator *authenticator);
@@ -174,6 +192,9 @@ int caosdb_authentication_delete_authenticator(
  * Use the destructor function
  * `caosdb_connection_delete_connection` to free the wrapped
  * connection.
+ *
+ * EXPERT USE ONLY.  Memory management with this function is a bit tricky.
+ * Only use it when you know what you are doing.
  */
 int caosdb_connection_create_connection(
   caosdb_connection_connection *out,
@@ -181,6 +202,8 @@ int caosdb_connection_create_connection(
 
 /**
  * Destructor function for the caosdb_connection_connection struct.
+ *
+ * EXPERT USE ONLY.  Only use it when you know what you are doing.
  */
 int caosdb_connection_delete_connection(
   caosdb_connection_connection *connection);