ntext_len</code></p><p>Decrypts a message using the session. The input message buffer is destroyed. Returns the length of the plain-text on success. Returns olm_error() on failure. If the plain-text buffer is smaller than olm_decrypt_max_plaintext_length() then olm_session_last_error() will be &quot;OUTPUT_BUFFER_TOO_SMALL&quot;. If the base64 couldn't be decoded then olm_session_last_error() will be &quot;INVALID_BASE64&quot;. If the message is for an unsupported version of the protocol then olm_session_la