eHUB Provider API Error Handling

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eHUB Provider API errors are communicated through HTTP status codes and a JSON messages that contain a more detailed explanation of the error. HTTP responses with a status code >399 should contain a message that explains the error. Aside from these the API might reply with a HTTP status code >= 500 for internal errors. Please note that errors should never send responses with HTTP status 200 (OK). Usually HTTP status 500 (Internal Server Error) is a good choice.

JSON messages have the following format:

    {
    "message": <error message>,
    "code": <error code>
    }

In the above:

<message> A detailed error message explaining the problem. This message is not shown to the eHUB users, but logged in the application log.
<code> Error code. There are 2 types of error codes:
  1. Standard error codes. Those error codes are translated into localized messages in eHUB and shown to the eHUB user, if the error occurs.
  2. Non-standard error codes. Those error codes are specific to the provider and can not be translated into a localized message and a general error message is shown to the eHUB user, if the error occurs.
It is recommended to use standard error codes whenever possible.
ex.: 
    {
    "message": "Not enough credit for this transaction",
    "code": "BORROWER_LIMIT_REACHED"
    }

The following standard error codes are defined in eHUB Provider API

BORROWER_LIMIT_REACHED You have reached your limit when it comes to the number of e-media loans
INACTIVE_LOAN The loan is no longer active
LIBRARY_LIMIT_REACHED The library has reached its limit when it comes to the number of e-media loans
MAX_NO_OF_DOWNLOADS_FOR_PRODUCT_REACHED The maximum number of downloads has been reached for this book
MISSING_CONTENT_IN_LOAN The loan does not contain any content
PRODUCT_INACTIVE The book is inactive and is therefore unavailable to loan
PRODUCT_UNAVAILABLE The book is unavailable to loan when it lacks a valid business model
INVALID_CONTENT_PROVIDER_RECORD_ID The provided Content Provider Record ID is invalid
INVALID_REGION_ID The configured Region ID is invalid
INVALID_FORMAT_ID The ID of the requested format is invalid
CREATE_LOAN_FAILED Could not create loan
INVALID_LOAN_ID The format of the provided loan ID is invalid
CHECKOUT_NOT_FOUND Your checkout for this title could not be found
ALREADY_ON_LOAN The record is already loaned to this patron
INVALID_PATRON Invalid patron
ANOTHER_FORMAT_LOCKED_IN Another format has already been locked in
UNFULFILLED_AGE_LIMIT Unfulfilled age limit