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I've been working on a project involving use of the various Blockchain.info APIs (specifically the Blockchain Data API), and am wondering if anyone has tips regarding error handling: the API documentation says nothing about how errors are handled, and my experiments seem to indicate that errors are returned with HTTP status 200 and a strictly HTML response.

Has anyone implemented a client for this API and can shed some light on whether this is the "usual" state of affairs or a bug? Any additional tips would be greatly appreciated.

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Error handling is not particularly well done. If you are specifying format=json errors should respond with status 500 and a text/plain message. But there may be errors HTML based errors as well.

If the response is not JSON parsable then it should be considered the server has encountered a generic error.

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I ended up implementing a response handler that implements the following heuristic:

  • If status code is 200 and Content-Type header is "application/json" (with or without charset), the response is valid.
  • If the status code is 200 or 500 (I've observed both) and the Content-Type header is "text/html" (with or without charset), the response is erroneous and the error message may be extracted with the following regular expression: (?s).*<div.*?class="alert alert-error">.*?<h4>(.*?)</h4>.*.
  • Otherwise the response is erroneous but the specific error message cannot be extracted.

This seems to work well in practice.

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