Initialize a secretstream context for encryption

# sodium_crypto_secretstream_xchacha20poly1305_init_push

(PHP 7 >= 7.2.0, PHP 8)

sodium_crypto_secretstream_xchacha20poly1305_init_push — Initialize a secretstream context for encryption

### 说明

function sodium_crypto_secretstream_xchacha20poly1305_init_push(#[\SensitiveParameter]string `$key`): array

Initialize a secretstream context for encryption.

### 参数

`key`
  Cryptography key. See sodium_crypto_secretstream_xchacha20poly1305_keygen().

### 返回值

An array with two string values:

- The secretstream state, needed for further pushes
- The secretstream header, which needs to be provided to the recipient so they can pull data

### 示例

示例 #1 sodium_crypto_secretstream_xchacha20poly1305_init_push() example

    <?php
    function encrypt_file(string $inputFilePath, string $outputFilePath, string $key): void
    {
        [$state, $header] = sodium_crypto_secretstream_xchacha20poly1305_init_push($key);

        $inputFile = fopen($inputFilePath, 'rb');
        $outputFile = fopen($outputFilePath, 'wb');
        // Write the header:
        fwrite($outputFile, $header);
        $inputFileSize = fstat($inputFile)['size'];

        // Encrypt the file and write its contents to the output file:
        for ($i = 0; $i < $inputFileSize; $i += 8175) {
            $ptxt_chunk = fread($inputFile, 8175);
            $ctxt_chunk = sodium_crypto_secretstream_xchacha20poly1305_push($state, $ptxt_chunk);
            fwrite($outputFile, $ctxt_chunk);
        }

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

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

    file_put_contents('hello.txt', 'Hello world!');
    encrypt_file('hello.txt', 'hello.txt.encrypted', $key);
    var_dump(sodium_bin2hex(file_get_contents('hello.txt.encrypted')));
    ?>

以上示例的输出类似于：

    string(106) "971e33b255f0990ef3931caf761c59136efa77b434832f28ec719e3ff73f5aec38b3bba1574ab5b70a8844d8da36a668e802cfea2c"

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