The basic syntax of fpassthru is as follows:

<br>
int fpassthru ( resource $handle )<br>

It reads the file pointed to by $handle until the end of the file and directly outputs the data to the browser, returning the number of bytes output.

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1. Set the correct HTTP headers: Ensure that the browser knows this is a file download request.
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2. Open the file: Use fopen to open the compressed file you want to send.
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3. Use fpassthru to output the file contents: Directly transfer the file contents to the browser.
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4. Close the file pointer: Free the resources.
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\$fp = fopen(\$file, 'rb');
if (\$fp) {
    fpassthru(\$fp);
    fclose(\$fp);
    exit;
}

}
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3. Practical Methods

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• Use readfile or fpassthru to avoid loading large files into memory at once.
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• Use ob_clean() and flush() to clean the output buffer, ensuring the file is transferred correctly.
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• Inform the browser of the file size in advance using Content-Length, improving the download experience.
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• For large files, read and output them in chunks, using set_time_limit(0) to prevent timeouts.
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• Ensure there is no output before sending the file, including spaces and HTML, as it will corrupt the HTTP headers.
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• Correctly set the MIME type, e.g., use application/zip for ZIP and application/gzip for GZ.
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• The server permissions must allow PHP to read the target file.
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• When downloading large files, consider bandwidth limitations and timeout settings.
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Using fpassthru allows efficiently sending compressed files from the server to the browser, avoiding high memory usage. During the process, attention must be given to HTTP header settings, output buffer handling, and file permissions. Mastering these techniques can make the file download functionality more stable and efficient.