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Download one OB.DAAC file, refusing the login page

Usage

obdaac_download(file, destination, credentials)

Arguments

file

the filename to fetch

destination

where to write it

credentials

from obdaac_credentials()

Value

NULL on success, or a one-line description of the failure

Why the status code is not enough

An unauthenticated request is answered with HTTP 200 and the Earthdata Login page, not with a 401. A download that trusts the status code therefore writes nine kilobytes of HTML into a file named .nc, and the mistake surfaces much later as a corrupt netCDF, naming neither the credential nor the file.

The first bytes are checked instead. Every file here is netCDF, which begins either CDF or the HDF5 signature, and an HTML document begins with neither.