Description:
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The "return value" section of the page describing bzread() shoutd explain more in detail what really this function may return:

- FALSE: error reading from the stream. An error of level E_WARNING is also raised in this case; you may retrieve the text of the error message from the $php_errormsg magic variable, if enabled.

- Empty string: end of the file or BZIP2 deconding error. Use feof($bz) to detect the first case, and use bzerrno($bz) != 0 to detect the latter.

- Non empty string: decoded data. Check bzerror($bz) != 0 for possible BZIP2 decoding errors. Data may still be garbage because the BZIP2 checksum is checked only after a whole block of BZIP2 data has been read or at the end of the stream, so in general data read cannot be trusted until the whole content of the file has been read.