Many C Driver functions report errors by returning false or -1 and filling out a bson_error_t structure with an error domain, error code, and message. Use domain to determine which subsystem generated the error, and code for the specific error. message is a human-readable error description.
See also: Handling Errors in libbson.
MONGOC_ERROR_CLIENT MONGOC_ERROR_CLIENT_TOO_BIG You tried to send a message larger than the server's max message size.
MONGOC_ERROR_CLIENT_AUTHENTICATE Wrong credentials, or failure sending or receiving authentication messages.
MONGOC_ERROR_CLIENT_NO_ACCEPTABLE_PEER You tried an SSL connection but the driver was not built with SSL.
MONGOC_ERROR_CLIENT_IN_EXHAUST You began iterating an exhaust cursor, then tried to begin another operation with the same mongoc_client_t.
MONGOC_ERROR_CLIENT_SESSION_FAILURE Failure related to creating or using a logical session.
MONGOC_ERROR_STREAM_SOCKET Timeout communicating with server, or connection closed.
MONGOC_ERROR_STREAM_CONNECT Failed to connect to server.
MONGOC_ERROR_PROTOCOL MONGOC_ERROR_PROTOCOL_INVALID_REPLY Corrupt response from server.
MONGOC_ERROR_PROTOCOL_BAD_WIRE_VERSION The server version is too old or too new to communicate with the driver.
MONGOC_ERROR_CURSOR MONGOC_ERROR_CURSOR_INVALID_CURSOR You passed bad arguments to mongoc_collection_find_with_opts(), or you called mongoc_cursor_next() on a completed or failed cursor, or the cursor timed out on the server.
MONGOC_ERROR_QUERY MONGOC_ERROR_QUERY_FAILURE Error API Version 1: Server error from command or query. The server error message is in message.
MONGOC_ERROR_SERVER MONGOC_ERROR_QUERY_FAILURE Error API Version 2: Server error from command or query. The server error message is in message.
MONGOC_ERROR_SASL A SASL error code. man sasl_errors for a list of codes.
MONGOC_ERROR_BSON MONGOC_ERROR_BSON_INVALID You passed an invalid or oversized BSON document as a parameter, or called mongoc_collection_create_index() with invalid keys, or the server reply was corrupt.
MONGOC_ERROR_NAMESPACE MONGOC_ERROR_NAMESPACE_INVALID You tried to create a collection with an invalid name.
MONGOC_ERROR_COMMAND MONGOC_ERROR_COMMAND_INVALID_ARG Many functions set this error code when passed bad parameters. Print the error message for details.
MONGOC_ERROR_PROTOCOL_BAD_WIRE_VERSION You tried to use a command option the server does not support.
MONGOC_ERROR_DUPLICATE_KEY An insert or update failed because because of a duplicate _id or other unique-index violation.
MONGOC_ERROR_COMMAND Error code from server. Error API Version 1: Server error from a command. The server error message is in message.
MONGOC_ERROR_SERVER Error code from server. Error API Version 2: Server error from a command. The server error message is in message.
MONGOC_ERROR_COLLECTION MONGOC_ERROR_COLLECTION_INSERT_FAILED, MONGOC_ERROR_COLLECTION_UPDATE_FAILED, MONGOC_ERROR_COLLECTION_DELETE_FAILED. Invalid or empty input to mongoc_collection_insert_one(), mongoc_collection_insert_bulk(), mongoc_collection_update_one(), mongoc_collection_update_many(), mongoc_collection_replace_one(), mongoc_collection_delete_one(), or mongoc_collection_delete_many().
MONGOC_ERROR_COLLECTION Error code from server. Error API Version 1: Server error from mongoc_collection_insert_one(), mongoc_collection_insert_bulk(), mongoc_collection_update_one(), mongoc_collection_update_many(), mongoc_collection_replace_one(), mongoc_collection_delete_one(), or mongoc_collection_delete_many().
MONGOC_ERROR_SERVER Error code from server. Error API Version 2: Server error from mongoc_collection_insert_one(), mongoc_collection_insert_bulk(), mongoc_collection_update_one(), mongoc_collection_update_many(), mongoc_collection_replace_one(), mongoc_collection_delete_one(), or mongoc_collection_delete_many().
MONGOC_ERROR_GRIDFS MONGOC_ERROR_GRIDFS_CHUNK_MISSING The GridFS file is missing a document in its chunks collection.
MONGOC_ERROR_GRIDFS_CORRUPT A data inconsistency was detected in GridFS.
MONGOC_ERROR_GRIDFS_INVALID_FILENAME You passed a NULL filename to mongoc_gridfs_remove_by_filename().
MONGOC_ERROR_GRIDFS_PROTOCOL_ERROR You called mongoc_gridfs_file_set_id() after mongoc_gridfs_file_save(), or tried to write on a closed GridFS stream.
MONGOC_ERROR_GRIDFS_BUCKET_FILE_NOT_FOUND A GridFS file is missing from files collection.
MONGOC_ERROR_GRIDFS_BUCKET_STREAM An error occurred on a stream created from a GridFS operation like mongoc_gridfs_bucket_upload_from_stream().
MONGOC_ERROR_SCRAM MONGOC_ERROR_SCRAM_PROTOCOL_ERROR Failure in SCRAM-SHA-1 authentication.
MONGOC_ERROR_SERVER_SELECTION MONGOC_ERROR_SERVER_SELECTION_FAILURE No replica set member or mongos is available, or none matches your read preference, or you supplied an invalid mongoc_read_prefs_t.
MONGOC_ERROR_WRITE_CONCERN Error code from server. There was a write concern error or timeout from the server.
MONGOC_ERROR_TRANSACTION MONGOC_ERROR_TRANSACTION_INVALID You attempted to start a transaction when one is already in progress, or commit or abort when there is no transaction.
In some cases your application must make decisions based on what category of error the driver has returned, but these categories do not correspond perfectly to an error domain or code. In such cases, error labels provide a reliable way to determine how your application should respond to an error.
Use mongoc_error_has_label() to test if a reply contains a specific label. See mongoc_client_session_start_transaction() for example code that demonstrates the use of error labels in application logic.
The following error labels are currently defined. Future versions of MongoDB may introduce new labels.
Within a multi-document transaction, certain errors can leave the transaction in an unknown or aborted state. These include write conflicts, primary stepdowns, and network errors. In response, the application should abort the transaction and try the same sequence of operations again in a new transaction.
When mongoc_client_session_commit_transaction() encounters a network error or certain server errors, it is not known whether the transaction was committed. Applications should attempt to commit the transaction again until: the commit succeeds, the commit fails with an error not labeled "UnknownTransactionCommitResult", or the application chooses to give up.
The driver's error reporting began with a design flaw: when the error domain is MONGOC_ERROR_COLLECTION, MONGOC_ERROR_QUERY, or MONGOC_ERROR_COMMAND, the error code might originate from the server or the driver. An application cannot always know where an error originated, and therefore cannot tell what the code means.
For example, if mongoc_collection_update_one() sets the error's domain to MONGOC_ERROR_COLLECTION and its code to 24, the application cannot know whether 24 is the generic driver error code MONGOC_ERROR_COLLECTION_UPDATE_FAILED or the specific server error code "LockTimeout".
To fix this flaw while preserving backward compatibility, the C Driver 1.4 introduces "Error API Versions". Version 1, the default Error API Version, maintains the flawed behavior. Version 2 adds a new error domain, MONGOC_ERROR_SERVER. In Version 2, error codes originating on the server always have error domain MONGOC_ERROR_SERVER or MONGOC_ERROR_WRITE_CONCERN. When the driver uses Version 2 the application can always determine the origin and meaning of error codes. New applications should use Version 2, and existing applications should be updated to use Version 2 as well.
The Error API Versions are defined with MONGOC_ERROR_API_VERSION_LEGACY and MONGOC_ERROR_API_VERSION_2. Set the version with mongoc_client_set_error_api() or mongoc_client_pool_set_error_api().