PHP字符编码地狱用fgets读取csv文件

我有一个网站,每月一次通过FTP接收CSV文件.多年来它是一个ASCII文件.现在我接受一个月的UTF-8,然后是接下来的UTF-16BE和之后一个月的UTF-16LE.也许下个月我会得到UTF-32. fgets返回UTF文件开头的字节顺序标记.如何让 PHP自动识别字符编码？我曾尝试过mb_detect_encoding,无论文件类型如何,它都会返回ASCII.我更改了代码以读取BOM并明确将字符编码放入mb_convert_encoding.这工作到最新文件,即UTF-16LE.在此文件中,它正确读取第一行,所有后续行显示为问号(“？”).我究竟做错了什么？

$fhandle = fopen( $file_in,"r" );
if ( fhandle === false )
    {
    echo "<p class=redbold>Error opening file $file_in.</p>";
    die();
    }

$i = 0;
while( ( $line = fgets( $fhandle ) ) !== false )
{
$i++;

// Detect encoding on first line. Actual text always begins with string "Document"
if ( $i == 1 )
    {
    $line_start = substr( $line,4 );
    $line_start_hex = bin2hex( $line_start );
    $utf16_start = 'fffe4400';
    $utf8_start = 'efbbbf44';
    if ( strcmp( $line_start,'Docu' ) == 0 )
        { $char_encoding = 'ASCII'; }
    elseif ( strcmp( $line_start_hex,'efbbbf44' ) == 0 )
        {
        $char_encoding = 'UTF-8';
        $line = substr( $line,3 );
        }
    elseif ( strcmp( $line_start_hex,'fffe4400' ) == 0 )
        {
        $char_encoding = 'UTF-16LE';
        $line = substr( $line,2 );
        }
    elseif ( strcmp( $line_start_hex,'feff4400' ) == 0 )
        {
        $char_encoding = 'UTF-16BE';
        $line = substr( $line,2 );
        }
    else
        {
        echo "<p class=redbold>Error,unkNown character encoding. Line =<br>",$line_start_hex,'</p>';
        require( '../footer.PHP' );
        die();
        }
    echo "<p>char_encoding = $char_encoding</p>";
    }

// Convert UTF
if ( $char_encoding != 'ASCII' )
    {
    $line = mb_convert_encoding( $line,'ASCII',$char_encoding);
    }

echo '<p>'; var_dump( $line ); echo '</p>';
}

输出：

char_encoding = UTF-16LE

string(101) "DocumentNumber,RecordedTS,Title,PageCount,City,TransTaxAccountCode,TotalTransferTax,Description,Name
"

string(83) "???????????????????????????????????????????????????????????????????????????????????"

string(88) "????????????????????????????????????????????????????????????????????????????????????????"

string(84) "????????????????????????????????????????????????????????????????????????????????????"

string(80) "????????????????????????????????????????????????????????????????????????????????"

<?PHP
header( "Content-Type: text/html; charset=utf-8");
$input = file_get_contents( $file_in );

$encoding = mb_detect_encoding( $input,array(
    "UTF-8","UTF-32","UTF-32BE","UTF-32LE","UTF-16","UTF-16BE","UTF-16LE"
),TRUE );

if( $encoding !== "UTF-8" ) {
    $input = mb_convert_encoding( $input,"UTF-8",$encoding );
}
echo "<p>$encoding</p>";

foreach( explode( PHP_EOL,$input ) as $line ) {
    var_dump( $line );
}