Initialize a secretstream context for decryption

# sodium_crypto_secretstream_xchacha20poly1305_init_pull

(PHP 7 >= 7.2.0, PHP 8)

sodium_crypto_secretstream_xchacha20poly1305_init_pull — Initialize a secretstream context for decryption

### 说明

function sodium_crypto_secretstream_xchacha20poly1305_init_pull(string `$header`, #[\SensitiveParameter]string `$key`): string

Initialize a secretstream context for decryption.

### 参数

`header`
  The header of the secretstream. This should be one of the values produced by sodium_crypto_secretstream_xchacha20poly1305_init_push().
`key`
  Encryption key (256-bit).

### 返回值

Secretstream state.

### 示例

示例 #1 sodium_crypto_secretstream_xchacha20poly1305_init_pull() example

    <?php
    function decrypt_file(string $inputFilePath, string $outputFilePath, string $key): void
    {
        $inputFile = fopen($inputFilePath, 'rb');
        $outputFile = fopen($outputFilePath, 'wb');
        $header = fread($inputFile, 24);

        $state = sodium_crypto_secretstream_xchacha20poly1305_init_pull($header, $key);
        $inputFileSize = fstat($inputFile)['size'];

        // Decrypt the file and write its contents to the output file:
        for ($i = 24; $i < $inputFileSize; $i += 8192) {
            $ctxt_chunk = fread($inputFile, 8192);

            // We're not using $tag, but in real protocols you can use this on encrypt to e.g.
            // trigger a re-key or indicate the end of file. Then, on decrypt, you can assert
            // this behavior.
            [$ptxt_chunk, $tag] = sodium_crypto_secretstream_xchacha20poly1305_pull($state, $ctxt_chunk);
            fwrite($outputFile, $ptxt_chunk);
        }

        sodium_memzero($state);
        fclose($inputFile);
        fclose($outputFile);
    }

    // sodium_crypto_secretstream_xchacha20poly1305_keygen()
    $key = sodium_base642bin('MS0lzb7HC+thY6jY01pkTE/cwsQxnRq0/2L1eL4Hxn8=', SODIUM_BASE64_VARIANT_ORIGINAL);

    $example = sodium_hex2bin('971e33b255f0990ef3931caf761c59136efa77b434832f28ec719e3ff73f5aec38b3bba1574ab5b70a8844d8da36a668e802cfea2c');
    file_put_contents('hello.enc', $example);
    decrypt_file('hello.enc', 'hello.txt.decrypted', $key);
    var_dump(file_get_contents('hello.txt.decrypted'));
    ?>

以上示例的输出类似于：

    string(12) "Hello world!"

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