Lecture 10: Working with Files. CS 383 Web Development II Monday, March 12, 2018

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1 Lecture 10: Working with Files CS 383 Web Development II Monday, March 12, 2018

2 Working with Files Last week, we began to do some work with files through uploads, and we talked a little bit about headers Now, we ll talk more about what we can do with files 1

3 File Handlers Most of the other file functions use file handlers / file pointers To create a file pointer, use the function fopen($path_to_file, $mode) The mode should be sent as a string The mode will tell what operation(s) you re allowed to run The result will be a PHP resource, which should be saved in a variable to pass to the other file function 2

4 Mode r Description File Modes Read only; file pointer placed at beginning of file r+ Same as r but opens for write also w Write only; truncates file to 0 length; creates file if it does not exist; file pointer placed at the beginning w+ Same as w but opens for read also a Write only; place file pointer at end of file (appends data) a+ Same as a but opens for read also x Same as w except it will fail if the file already exists x+ Same as x except opens for read also c Write only; creates file if it does not exist; if it exists, it is neither truncated (as w does) nor fails (as x does) c+ Same as c except opens for read also 3

5 File Functions feof($fh) fgetc($fh) fgets($fh[, $length]) fread($fh, $length) Fscanf($fh, $format) ftell($fh) fwrite($fh, $string[, $length]) 4

6 File Handlers When you are finished reading/writing a file, use fclose($fh) 5

7 file_get_contents & file_put_contents You can also read/write data through the functions file_get_contents() and file_put_contents() These are easier to use, but will not work with very large files In short, to read all of the data from a file, we use file_get_contents($path_to_file) This function returns a string, which we can assign to a variable, print out, pass to a function, etc. You can also, rather than a path to a file, provide a website URL 6

8 file_get_contents & file_put_contents To write data to a file, we use file_put_contents($path_to_file, $data) Data can be any type If the file does not exist, it is created If the file does exist, it is overwritten, unless a third argument, the FILE_APPEND flag, is added Returns false if there was a failure, or number of bytes written to the file if successful 7

9 Permissions Remember that any files you create are created by whoever executed the PHP script Remember that any files you access through PHP must be able to be read by whoever executed the PHP script 8

10 Security Suppose you want to create a form that allows somebody to enter a file name and text, and when submitted, writes that text to the file with that name What s wrong with the following code snippets? 9

11 Security Filename form.html submit.php Code Snippet <form action="submit.php" method="post"> <input type="text" name="filename"> <textarea name="data"></textarea> <input type="submit" value="create File"> </form> <?php $dir = "/var/www/html/cs383/textfiles/"; $path = $dir.$_post['filename']; $data = $_POST['data']; file_put_contents($path, $data);?> 10

12 More Functions The file($path_to_file) function returns an array, where each element is a line from the file Equivalent results (although the first is much more efficient, particularly for large files): o $lines = file("myfile.txt"); o $lines = explode("\n", file_get_contents("myfile.txt"); 11

13 Functions: Filesystem Operations chgrp($filename, $group) chmod($filename, $mode) chown($filename, $user) copy($source, destination) flock($fh, $operation) ($operation is FILE_SH, FILE_EX, LOCK_UN) mkdir($pathname[, $mode = 0777]) rename($source, destination) rmdir($pathname) unlink($filename) 12

14 Functions: Checks file_exists($filename) is_dir($pathname) is_file($pathname) is_readable($filename) is_writable($filename) is_executable($filename) 13

15 Functions: Attributes fileatime($filename) filectime/filemtime($filename) filegroup($filename) fileowner($filename) fileperms($filename) filesize($filename) fstat($filename) 14

16 Functions: Directories chdir($path) getcwd($path) scandir($path) 15

17 fgetcsv & fputcsv fgetcsv and fputcsv are specifically for working with CSV files, as they automatically handle rules for delimiters, containing strings which contain the delimiter, etc. fgetcsv($fh [, $length = 0[, $delim = ","[, $enclosure = '" [, $escape_char = "\"]]]]) returns an array, with fields numerically indexed fputcsv($fh, $array[, $delim = ","[, $enclosure = '" [, $escape_char = "\"]]]) takes the second argument as an array of the fields and returns the length of the data written in bytes (or false on failure) 16

18 Headers Last week, we talked about using headers to redirect a file We can also use them to change the content type Example: o Suppose we have our images stored in /var/www/html/cs383/pictures/ so they aren t publicly accessible through a directory that is web accessible o We want to create a script that checks if the user is logged in, and loads the image, through the script in /var/www/html/cs383/webdocs/viewimage.php (taking a query string parameter, p, to get the filename of the image) 17

19 Headers <?php session_start(); if($_session["username"] == 'jason.wagner1') { header("content-type: image/jpg"); header("content-transfer-encoding: Binary"); header("content-disposition: attachment; filename=".$_get['p']); readfile("/var/www/html/cs383/pictures/".$_get ["p"]); }?> 18

20 Headers The first header tells the browser that this is an image o If the browser does not know to treat it as an image, it will think it is HTML and print out the binary character encoding, thinking it is meant to be text The second tells the browser that it is a binary file, not ASCII The third tells the browser that it is an attachment, and thus, should be downloaded when the user visits this page rather than shown directly inside the browser o The filename is what the default filename would be saved as in the users Downloads folder 19