php应用开发之文件下载详解

1，php下载函数
借助header()函数与readfile()函数实现文件下载功能。

<?php 
function DownloadFile($filename) 
{ 
    // Check filename 
    if (empty($filename) || !file_exists($filename)) 
    { 
        return FALSE; 
    } 
    // Create download file name to be displayed to user 
    $saveasname = basename($filename); 
    // Send binary filetype HTTP header 
    header('Content-Type: application/octet-stream'); 
    // Send content-length HTTP header 
    header('Content-Length: '.filesize($filename)); 
    // Send content-disposition with save file name HTTP header 
    header('Content-Disposition: attachment; filename="'.$saveasname.'"'); 
    // Output file 
    readfile($filename); 
    // Done 
    return TRUE; 
} 
?>

2，php文件下载脚本
更完善的php下载的自定义函数。

<?php 
////////////////////////////////////////////////////////////////////// 
// DOWNLOAD.PHP -- Download Utility 

// Get download file id (assume it's passed as a form or URL parameter) 
$id = getGlobalVar('id', 1); 

// Check download file id parameter, get download file name, download file 
// (assuming (global) variable $id specifies download file id) 
if (empty($id) || !DownloadFile(getDownloadFileName($id))) 
{ 
    die("No Download!"); 
} 

// Only functions beyond this point 

function getDownloadFilename($fileid) 
// Get download file pathname 
// Returns: download file pathname 
// Parameters: 
//    $fileid : File identifier 
{ 
    // Download file list 
    $DLFILES = array( 
        'TOOL1' => 'download/tool1_v30.exe', 
        'PROG2' => 'download/prog2setup.exe', 
        ); 
    // Get/check download file name 
    if (empty($fileid) || empty($DLFILES[$fileid])) 
    { 
        return ''; 
    } 
    // Set base directory to document root directory 
    // (could also be set to a directory outside document root!) 
    $basedir = getGlobalVar('DOCUMENT_ROOT'); 
    // Build and return download file name 
    return $basedir.'/'.$DLFILES[$fileid]; 
} 

function DownloadFile($filename) 
// Download file 
// Returns: TRUE if download successfully started, FALSE if download failed 
// Parameters: 
//    $filename : Download file pathname 
{ 
    // Verify filename 
    if (empty($filename) || !file_exists($filename)) 
    { 
        return FALSE; 
    } 
    // Create download file name to be displayed to user 
    $saveasname = basename($filename); 
    // Send binary filetype HTTP header 
    header('Content-Type: application/octet-stream'); 
    // Send content-length HTTP header 
    header('Content-Length: '.filesize($filename)); 
    // Send content-disposition with save file name HTTP header 
    header('Content-Disposition: attachment; filename="'.$saveasname.'"'); 
    // Output file 
    readfile($filename); 
    // Download successfully started 
    return TRUE; 
} 

function getGlobalVar($g, $formflag = 0) 
// Get global PHP variable value 
// Returns: global variable value or empty string if not available 
// Parameters: 
//  $g        : Global PHP variable name 
//  $formflag : Flag - global var from GET/POST input 
{ 
    if (empty($g)) 
    { 
        return 0; 
    } 
    // Try superglobal access (PHP 4.1.0+) 
    if ($formflag) 
    { 
        if (isset($_POST[$g])) 
        { 
            return $_POST[$g]; 
        } 
        if (isset($_GET[$g])) 
        { 
            return $_GET[$g]; 
        } 
        if (isset($_REQUEST[$g])) 
        { 
            return $_REQUEST[$g]; 
        } 
    } 
    else 
    { 
        if (isset($_SERVER[$g])) 
        { 
            return $_SERVER[$g]; 
        } 
        if (isset($_ENV[$g])) 
        { 
            return $_ENV[$g]; 
        } 
    } 
    // Try superglobal access (PHP 3.0.0+) 
    if (isset($GLOBALS[$g])) 
    { 
        return $GLOBALS[$g]; 
    } 
    // Try global variable access (PHP 3+) 
    global $$g; 
    if (!empty($$g)) 
    { 
        return $$g; 
    } 
    // Assume global variable empty/not set 
    return ''; 
} 
?>

将以上脚本保存为dl.php，在应用时传入id参数即可。

例如：
<a href="http://www.YourDomain.com/dl.php?id=PROG2">Download Program 2</a>
也可以通过php的重定向语句Location来实现，例如：

<?php
header("Location: http://www.YourDomain.com/dl.php?id=PROG2");
exit;
?>

以上的代码，可以防止用户直接访问下载文件，起到了一定的文件保护，甚至是防盗链的功能。

以下的代码，可以依据http头信息，作些介绍，从而提供更安全的文件下载。

代码：

<?php 
function DownloadFile($filename) 
{ 
    // Check filename 
    if (empty($filename) || !file_exists($filename)) 
    { 
        return FALSE; 
    } 
    // Create download file name to be displayed to user 
    $saveasname = basename($filename); 
    // Send binary filetype HTTP header 
    header('Content-Type: application/octet-stream'); 
    // Send content-length HTTP header 
    header('Content-Length: '.filesize($filename)); 
    // Send content-disposition with save file name HTTP header 
    // (using workaround for MSIE 5.5 SP1 / MSIE 6.01 bugs/problems) 
    $browser = getGlobalVar('HTTP_USER_AGENT'); 
    if (strstr('MSIE 5.5', $browser) 
     || strstr('MSIE 6.01', $browser)) 
    { 
        header('Content-Disposition: filename="'.$saveasname.'"'); 
    } 
    else 
    { 
        header('Content-Disposition: attachment; filename="'.$saveasname.'"'); 
    } 
    // Send Content-Transfer-Encoding HTTP header 
    // (use binary to prevent files from being encoded/messed up during transfer) 
    header('Content-Transfer-Encoding: binary'); 
    // Output file 
    readfile($filename); 
    // Done 
    return TRUE; 
} 

function getGlobalVar($g, $formflag = 0) 
// Get global PHP variable value 
// Returns: global variable value or empty string if not available 
// Parameters: 
//  $g        : Global PHP variable name 
//  $formflag : Flag - global var from GET/POST input 
{ 
    if (empty($g)) 
    { 
        return 0; 
    } 
    // Try superglobal access (PHP 4.1.0+) 
    if ($formflag) 
    { 
        if (isset($_GET[$g])) 
        { 
            return $_GET[$g]; 
        } 
        if (isset($_POST[$g])) 
        { 
            return $_POST[$g]; 
        } 
        if (isset($_REQUEST[$g])) 
        { 
            return $_REQUEST[$g]; 
        } 
    } 
    else 
    { 
        if (isset($_SERVER[$g])) 
        { 
            return $_SERVER[$g]; 
        } 
        if (isset($_ENV[$g])) 
        { 
            return $_ENV[$g]; 
        } 
    } 
    // Try superglobal access (PHP 3.0.0+) 
    if (isset($GLOBALS[$g])) 
    { 
        return $GLOBALS[$g]; 
    } 
    // Try global variable access (PHP 3+) 
    global $$g; 
    if (!empty($$g)) 
    { 
        return $$g; 
    } 
    // Assume global variable empty/not set 
    return ''; 
} 
?> 
<?php 
function DownloadFile($filename) 
{ 
    // Check filename 
    if (empty($filename) || !file_exists($filename)) 
    { 
        return FALSE; 
    } 
    // Create download file name to be displayed to user 
    $saveasname = basename($filename); 
    // Send binary filetype HTTP header 
    header('Content-Type: application/octet-stream'); 
    // Send content-length HTTP header 
    header('Content-Length: '.filesize($filename)); 
    // Send content-disposition with save file name HTTP header 
    // (using workaround for MSIE 5.5 SP1 / MSIE 6.01 bugs/problems) 
    $browser = getGlobalVar('HTTP_USER_AGENT'); 
    if (strstr('MSIE 5.5', $browser) 
     || strstr('MSIE 6.01', $browser)) 
    { 
        header('Content-Disposition: filename="'.$saveasname.'"'); 
    } 
    else 
    { 
        header('Content-Disposition: attachment; filename="'.$saveasname.'"'); 
    } 
    // Send Content-Transfer-Encoding HTTP header 
    // (use binary to prevent files from being encoded/messed up during transfer) 
    header('Content-Transfer-Encoding: binary'); 
    // Output file 
    readfile($filename); 
    // Done 
    return TRUE; 
} 

function getGlobalVar($g, $formflag = 0) 
// Get global PHP variable value 
// Returns: global variable value or empty string if not available 
// Parameters: 
//  $g        : Global PHP variable name 
//  $formflag : Flag - global var from GET/POST input 
{ 
    if (empty($g)) 
    { 
        return 0; 
    } 
    // Try superglobal access (PHP 4.1.0+) 
    if ($formflag) 
    { 
        if (isset($_GET[$g])) 
        { 
            return $_GET[$g]; 
        } 
        if (isset($_POST[$g])) 
        { 
            return $_POST[$g]; 
        } 
        if (isset($_REQUEST[$g])) 
        { 
            return $_REQUEST[$g]; 
        } 
    } 
    else 
    { 
        if (isset($_SERVER[$g])) 
        { 
            return $_SERVER[$g]; 
        } 
        if (isset($_ENV[$g])) 
        { 
            return $_ENV[$g]; 
        } 
    } 
    // Try superglobal access (PHP 3.0.0+) 
    if (isset($GLOBALS[$g])) 
    { 
        return $GLOBALS[$g]; 
    } 
    // Try global variable access (PHP 3+) 
    global $$g; 
    if (!empty($$g)) 
    { 
        return $$g; 
    } 
    // Assume global variable empty/not set 
    return ''; 
} 
?>