14. Networking and Other Topics

What We Will Cover Announcements Please silence all cell phones and pagers When class is over, please shut down your computer if it is on Continuations 14.1: Improving Verification With Patterns 14.1.1: About Regular Expressions 14.1.2: Using the preg_match() Function 14.1.3: Using Regular Expressions with preg_match() 14.1.4: Grouping Characters 14.1.5: Building Regular Expressions That Work 14.1.6: Summary Activity 14.1 14.2: Scripting the Internet 14.2.1: Sending Email 14.2.2: Verifying Network Information 14.2.3: Reading Pages from a URL 14.2.4: Parsing a Web Page 14.2.5: Uploading Files 14.2.6: Summary Activity 14.2 14.3: Finishing the Course 14.3.1: About the Final Project Presentation 14.3.2: Lecture Finale Wrap Up Due Next: Final Project Report and Presentation (6/1/07) Continuations Questions from last class? Making Select Lists The algorithm for making a select list from a SQL query is straightforward: Write a SQL query that returns the rows with the data you need. $sql = "SELECT ProductName FROM Products"; Use a loop to extract the data from the result set and create an array. $prodList = array(); while ($row = mysql_fetch_assoc($result)) { $prodList[$row["ProductName"]] = $row["ProductName"]; } Use the array to code the HTML data. echo $f->makeSelect('products', $prodList); Here is an example querying the products table of the Artzy database: Cannot find file: examples/selectlistdb.php Try it and view the source before and after you press the Select button ^ top 14.1: Improving Verification With Patterns Learner Outcomes At the end of the lesson the student will be able to: Use PHP pattern-matching functions Code regular expressions to match string patterns ^ top 14.1.1: About Regular Expressions Many programming problems require matching a pattern in string variables Verifying the data received from HTML forms is one such problem For example, if you are expecting an email address, your script needs to verify the string meets requirements for email addresses john.doe@hotmail.com Regular Expression Standards There are two main standards for regular expressions: POSIX and Perl PHP supports both standards We will use Perl-compatible functions and focus on using preg_match() Commonly Used Pattern-Matching Functions (Perl Compatible) Function Description preg_match() Searches a string for matches to a regular expression. preg_replace() Searches a string for matches to a regular expression and replaces them with the specified text. preg_split() Searches a string for boundaries matched by a regular expression and splits the string into an array of strings along the boundaries. ^ top 14.1.2: Using the preg_match() Function You use preg_match() to search a string for matches to a regular expression If the regular expression pattern matches a part of the string, then it returns the number 1 (meaning true) Basic Syntax int preg_match(string pattern, string subject) pattern: regular expression pattern subject: the string to search for pattern matches returns the number 1 For Example Cannot find file: examples/regex1.php Try it! Put the regular expression pattern between forward slashes: / / If the pattern "se" is found, then $found is set to the number 1 Otherwise, $found is set to the number 0 Further Information preg_match() ^ top 14.1.3: Using Regular Expressions with preg_match() PHP has a special set of pattern-matching characters (meta characters) These characters form a small language with each character having a special meaning These characters are part of an industry standard Commonly Used Pattern-Matching Characters Symbol Description ^ Matches when the characters that follow start the string. $ Matches when the preceding characters end the string * Matches zero or more occurences of the preceeding character + Matches one or more occurences of the preceeding character ? Matches zero or one occurences of the preceeding character . A wildcard symbol that matches any one character | Alternation symbol (OR) that matches either the pattern on the left or the right For Example We can test our regular expressions with a simple form script Try it! (See the code) To match when starting with "She": ^She To match when ending with "shells": shells$ To match an "se" followed by one or more l's: sel+ To match an "se" followed by zero or more a's: sea* To match any character followed by an "e": .e To match "He" or "She": He|She Note that you can ignore case by putting an "i" after the closing slash /^she/i "Escaped" Character Literals You can match one of the special characters However, you must prefix it with the backslash character /\.\*/ To match one backslash, your regular expression should include "\\" The backslash is also used to specify non-printing characters like: Sequence Meaning \a Alert \f Formfeed \n Newline \r Carriage return \t Horizontal tab Further Information: Backslash ^ top 14.1.4: Grouping Characters Regular expressions use parenthesis, curly brackets and square brackets to group characters Each type of grouping character has different meanings You can combine these grouping characters with other special characters to get flexible and specific matching patterns Using Parenthsis to Group Characters Use parenthesis to group characters in a regular expression For example, to match "Dave" or David" in a string" /Dav(e|id)/ To match "Dave" or David" whether the name starts with a "D" or "d": /(D|d)av(e|id)/ Further Information: Subpatterns Using Curly Brackets to Specify Repetitions You use curly brackets to specify a range of repetitions for the preceeding character You can specify a range of values such as between 3 and 5 z's /^z{3,5}$/ You can specify a minimum value such as 3 or more z's /^z{3,}$/ You can specify a maximum value such as 3 or fewer z's /^z{0,3}$/ You can specify an exact value such as exactly 3 z's /^z{3}$/ Further Information: Repetition Using Square Brackets to Specify Character Classes You use square brackets to specify a character class Classes match only one of the characters found between the square brackets For example, to match either sea or sel: /se[al]/ A more common use is to specify a range of values to match To specify a range, use a dash (-) For example, to specify the numbers from 0 to 9: /[0-9]/ To specify a capital letter from "A" to "Z": /[A-Z]/ You can specify multiple ranges within one square bracket /[0-9a-zA-Z_]/ When the caret symbol (^) appears first, it reverses the meaning Thus to matches any character not between 0 and 9: /[^0-9]/ Further Information: Square brackets ^ top 14.1.5: Building Regular Expressions That Work Regular expressions are very powerful -- but can be almost unreadable To build complex regular expressions, start with a simple expression After a simple start, refine your regular expression incrementally Build it one piece at a time and test each addition as you go Incremental Refinement Example This example incrementally builds a regular expression for form verification We want to verify that a form field meets requirements for email addresses The steps that follow detail a process for building this verification incrementally Determine the precise rules for your field john.doe@hotmail.com You determine what is valid and invalid input by examining email addresses and reading specifications. Some of the rules you come up with are: User names can have almost any printable ASCII character An @ symbol seperates the user name from the domain name Domain names can have letters, digits, and hyphens Each part of a domain name is separated by a dot Set up your test environment Next you build a form with an element to verify and the receiving function. You decide to use the FormVerifier class and add a verification function like that shown. Make sure these work before you add regular expressions. function isEmailAddress($field, $msg) { $value = $this->getValue($field); $pattern = "/.+/"; if(preg_match($pattern, $value)) { return true; } else { $this->addError($field, $value, $msg); return false; } } Code the most specific term possible You look at the rules and code the most specific line you can easily come up with. Then you test the regular expression to verify it works. $pattern = "/[_a-z0-9+.-]+@([a-z0-9-]+\.)+com/i"; Set anchors if you can Add the ^ and $ quantifiers where possible. This prevents characters before and after the acceptable pattern to be invalidated. $pattern = "/^[_a-z0-9+.-]+@([a-z0-9-]+\.)+com$/i"; Get more specific if you can, testing each addition carefully You may decide to restrict the top level domain (TLD) to only those authorized. This turns out to be quite complicated. Almost every two-letter combination is used by some country. In addition to the well-known generic TLD's of com, edu, net, org, mil and gov, there are many new TLD's: biz, info, name, coop, aero and museum. More are being suggested and adopted every year. We leave the coding of a TLD regular expression as an exercise for the student. ^ top 14.1.6: Summary Regular expressions enable a script to look for character patterns in a string PHP supports many functions useful for use with regular expressions The most useful function for verifying user input is preg_match() Regular characters are matched in an expression like: /She sells/i Special "meta" characters are used to form a small language for matching patterns You use parenthesis to goup characters /(D|d)av(e|id)/ You use curly brackets to specify a range of repetitions for the preceeding character /^z{3,5}$/ You use square brackets to specify a character class: /[0-9a-z_]/i Regular expressions are very powerful -- but can be almost unreadable You must build them carefully by starting with simple expressions that work Refine and test your regular expression incrementally Build it one piece at a time and test each addition as you go ^ top Activity 14.1 Develop a regular expression for verifying top-level-domain (TLD) names. Make sure your regular expression works with the email pattern we have devloped so far. $pattern = "/^[_a-z0-9+.-]+@([a-z0-9-]+\.)+com$/i"; You may use this test script to test your changes. Cannot find file: examples/regexer.php ^ top 14.2: Scripting the Internet Learner Outcomes At the end of the lesson the student will be able to: Send email from PHP scripts Work with URLs Read and parse web pages ^ top 14.2.1: Sending Email Sometimes you want to send email: New password Order confirmation Survey results PHP provides a function called mail() that sends e-mail via SMTP Basic Syntax bool mail(toAddress, subject, message); toAddress: destination address of the e-mail subject: subject line of the email message: text of the email message For Example Cannot find file: examples/email.php Security Considerations Do not use a web form for the toAddress Also, do not read a form variable for the toAddress This would let anyone use your mail server to send anything More Information mail: PHP function documentation ^ top 14.2.2: Verifying Network Information Sometimes you need to verify network information For example, you want to verify that an email address or URL is valid With PHP, you can look up hostnames, IP address and MX records An MX record is short for mail exchange record MX records are stored at the DNS and are looked up like a hostname If no MX record exists, there is nowhere for the email to go There can be more than one MX record, so the function getmxrr() returns an array Note that getmxrr() is not implemented on Windows Commonly Used Functions to Verify Network Information Function Description gethostbyaddr(ipAddress) Returns the host name of the Internet host specified by the string ipAddress. gethostbyname(hostname) Returns the IP address of the Internet host specified by the string hostname. getmxrr(hostName, mxArray) Returns an array of MX host names in mxArray from an email hostName. (Not implemented on Windows) parse_url(url) Returns from the URL string an associative array with the following indexes (if present): scheme, host, port, user, pass, path, query, and fragment. Example Checking a URL Cannot find file: examples/urlcheck.php Try it! Example Checking an Email for MX Records Cannot find file: examples/emailmxcheck.php Try it! More Information Email Address Verification with PHP Network Functions ^ top 14.2.3: Reading Pages from a URL You can easily read a page from a URL $page = file_get_contents($url); Many of PHP's Filesystem functions work with Internet sources Some Functions that Read from URL's Function Description file(url) Returns an array containing the contents read from the string url, with each element of the array corresponding to a line in the file. file_get_contents(url) Returns a string containing the contents read from the string url. Note: Needs PHP version 4.3 or later and so does not work on classroom computers. Example Script to Read From a URL Cannot find file: examples/urlread.php Try it! ^ top 14.2.4: Parsing a Web Page You can use information from other parts of the web in your own pages In general, the steps you follow are: Find an original source URL Read the information from the URL Parse (extract) the data you want to use Finding the information might involve some detective work We looked how to read the information in the previous section To parse the information, you often use regular expressions Function preg_match() allows you to include an extra parameter for matches to the pattern Syntax int preg_match(string pattern, string subject, array matches) pattern: regular expression pattern subject: the string to search for pattern matches matches: optional argument that is filled with the results of search Example Script to Parse a URL Cannot find file: examples/urlparse.php Try it! ^ top 14.2.5: Uploading Files Most browsers let you upload files using the POST method PHP is capable of receiving and processing uploaded files An Upload Form The following HTML creates a file upload form Cannot find file: examples/upload.html The attribute enctype="multipart/form-data" is needed to load files into PHPs $_FILES superglobal array The optional hidden field MAX_FILE_SIZE tells the browser the maximum file size to upload The MAX_FILE_SIZE field must be placed before the file field This field can be ignored by the browser and is easy to circumvent Thus you will need to verify the value in your script as well The file field creates the upload form element <input type="file" name="uploadFile"> Processing the Uploaded File The following is a minimal script to process an uploaded file Cannot find file: examples/upload1.php PHP first places the uploaded file in a temporary directory using a temporary name Your code should move the file to its permanent location before the script finishes processing move_uploaded_file($tmp_name, $name); PHP stores all the uploaded file information in the $_FILES array Each file has an its own array of information in the $_FILES array Thus, you need to specify both the file name and data element to retrieve the value $tmp_name = $_FILES["uploadFile"]["tmp_name"]; Explanations of all the available data values are listed in the documentation for Handling file uploads Error Checking and Validation We need to both validate the file upload and check for errors First of all, you should require a user to authenticate before uploading files That way you can keep records of anyone atacking your uploading system Note that the move_uploaded_file() checks to ensure that the file is a valid upload file If any error occurs, then the file is not moved Thus you can check for errors easily with with the following code Cannot find file: examples/upload2.php Part of the information returned about the file is an error code $errorCode = $_FILES['uploadFile']['error']; Error codes are explained in: Error Messages Explained These codes can help you to check for user error and other problems You can use the other file information to check file types and sizes as well The following code shows how to check file type and size before uploading Cannot find file: examples/upload.php More Information Handling file uploads Uploading Files To MySQL Database File Uploading in PHP 4 Working with Forms in PHP, Part 2 Large File Uploads PHP has a limit on file upload sizes -- usually about 2 MB You can change this limit in the php.ini file Also, the web server may limit the amount of information processed during one POST operation Sometimes this limit is as low as 512 KB To upload large file sizes, you may need another solution like Java or Perl More info: PHP Upload Configuration Includes links to other solutions like Applets and Perl scripts ^ top 14.2.6: Summary PHP has numerous functions for using the Internet PHP provides a funtion called mail() that sends e-mail via SMTP Function parse_url() parses a URL and returns its various parts You can use PHP functions to verify user-supplied information gethostbyname(): returns the IP address of a host, if found getmxrr(): returns the MX records for an email host, if found Also, you can read entire pages off the web: $page = file_get_contents($url); Once you read the page, you can use regular expressions to extract information preg_match($pattern, $page, $matches); The information extracted is returned in the $matches array echo $matches[0]; Browsers allow you to upload files using HTML forms PHP can recieve and process the uploaded files You should require a user to authenticate before uploading files That way you can keep records of anyone atacking your uploading system Also, you need to both validate the file upload and check for errors ^ top Activity 14.2 Modify the following script to extract information from a web page of your choosing. Cannot find file: examples/urlparse2.php ^ top 14.3: Finishing the Course Learner Outcomes At the end of the lesson the student will be able to: Discuss the final preparation for the project presentation Advise the instructor on how to improve future courses ^ top 14.3.1: About the Final Project Presentation Important Final Exam Information Date and Time: 7:00 9:50 P.M. Friday, June 1 Location: Room 2501 (regular classroom) Before the Presentation Submit your project to WebCT before the presentation: Bring a written report on paper to give to the instructor before the presentation During the Presentation The presentation should have the following: Your name and your project's name A brief introduction describing the purpose of your project A demonstration and discussion of the user interface including: Entry page Page layout Navigation features A demonstration of a multi-form sequence where you pass information from one page to another A demonstration of user-input error handling Checking of form input for errors Highlighting of errors so users easily see them Explanation to user of how to correct errors Retention of prior entries on error (except passwords) A discussion or demonstration of user authentication How the database is used for authentication How passwords are encrypted in database A discussion or demonstration of security features How data types are checked before insertion into a database How data sizes are checked before insertion into a database How taint checking of special characters is implemented (e.g. '"$#) How special symbols and spaces do not cause database errors A discussion or demonstration of cool features Point them out so we can all appreciate them Feel free to display your written report during the presentation Keep the presentation to 10 minutes or less After the Presentation Feel free to leave (or stay) after your presentation You can present to the instructor alone after the other presentations are through ^ top 14.3.2: Lecture Finale During the semester we have covered many topics and learned at least two languages: SQL and PHP With this knowledge you can develop professional-looking database-driven Web sites Your project will allow you to demonstrate what you have learned There is no substitute for a working application! I hope that everyone has enjoyed taking the course as much as I have enjoyed presenting it I am always open to suggestions for improving the course ^ top Wrap Up Due Next: Final Project Report and Presentation (6/1/07) When class is over, please shut down your computer if it is on ^ top Home | WebCT | Announcements | Course info | Expectations | Schedule Project | Help | FAQ's | HowTo's | Links Last Updated: May 21 2007 @19:17:07