Changing the Filename of a File Downloaded over a PHP Script

You may be downloading files on your server with PHP by a combination of the header() and readfile() functions, like so...

header("Content-disposition: attachment;filename=MyFileName.txt");
readfile("../data/MyFileName.txt");

The filename on the server, and the one the user sees, will both have the same name. But you can change the filename the user sees, with something like this...

header("Content-disposition: attachment;filename=MyUSERONLYFileName.txt");
readfile("../data/MyFileName.txt");

Your server knows to look for the file in ../data/MyFileName.txt, and now, your user will receive a file with teh name of MyUSERONLYFilename.txt, instead of MyFileName.txt.

How do I Download a File to the User with my PHP script?

If you have a text file on your PHP server, you may have tried to download it through your PHP script with just this...

readfile("../data/MyTextFileName.txt");

But, as you would have noticed, it doesn't download the file. It displays the file contents in the browser.

To download the file, you must also include headers, used by HTTP to determine how to treat the web server's response, like this...

header("Content-disposition: attachment;filename=MyFileName.txt");
readfile("../data/MyTextFileName.txt");

After running the above, the user will be prompted with a question about whether they want to open or save a downloaded file, or however their particular browser is configured to handle downloads.

Creating a GZip Archive on Your PHP Server to Serve to Web Users

Gzip is a popular zip-archive format for storing files in the long-term. Users benefit from this by reducing the download time, or by being able to group files together in a single download link.

You may have files on your PHP server, of any type (image, documents, code, etc.), and you may want to zip these files in a GZip archive automatically with your PHP script.

You can create a gzip file with something like this...

$filep = gzopen("../data/MyZipFileName.gz", 'w9');

Then you write whatever text you want to it with something like this...

gzwrite($filep, $text);

When you are finished, you let the PHP server know you're done by adding this to the end of your script...

gzclose($filep);

If you want to download this as a file, you need to send file headers, so that you download the gzip file at the PHP URL, instead of just looking at the gzip file contents through the browser (which would be a garbled mess, as it is a compressed archive).

You can do that with this...

header("Content-disposition: attachment;filename=MyArchiveFile.gz");
readfile("../data/MyZipFileName.gz");

Downloading and Unzipping GZip on Your PHP Server From Another Web Server

Some site may offer a gzip file that you want to run with your PHP script, but that gzip file is always being updated and you want your script to download the newest version and use its contents.

This can be done very easily.

First, download the file you want to unzip, using something like this...

$file = file_put_contents("../data/SomeZipFileLocation.gz", fopen("SomeURL", 'r'), LOCK_EX);

Then you can read the contents like this...

$file = gzopen("../data/SomeZipFileLocation.gz", 'rb');
while (!gzeof($file)) {
print(gzread($file, 4000));
}

This will loop through each of the 4,000 bytes in the file from the gzip and display them.

Using this technique, you won't ever have to manually download and unzip these gzipped files to use the newest version with your code.

Using HTAccess to Redirect All Users (and POST data) to the Same URL

With the Apache .htaccess file, you can control a good number of things on your server.

If you turn on the RewriteEngine, you can have one URL example.com/123, always return the results of another URL, like example.com/index.php?id=123.

To do this, you need to have a .htaccess file in the base directory of your apache htdocs folder. It should start with this...

RewriteEngine On
RewriteBase /

And, it can redirect everyone to index.php with this...

RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php [QSA,NC,L]

You can change index.php to anything you like, of course. Then you can get the information about the original URL by using the $_POST parameters, which you can see with...

print_r($_POST);

How do I Salt and Encrypt Passwords in PHP?

Salting a password occurs when you add text to a password to make it longer and more complex.

For instance, "myPassWord" would be "myPassWordSomeSalt". Since this is longer, when it is encrypted, it will become a more complex result.

Then when you compare the "salted password" to a user's password, you just append "SomeSalt" to the user's input. Your condition looks like...

if(COMPARE($_POST['password'] . 'SomeSalt', $db['password'])) {...}

While this was useful at one time, this concept of salting is now built-in to passwords in PHP. You can simply do...

$hash = password_hash($password, PASSWORD_DEFAULT);
if(password_verify($password, $hash) {
// password is valid!
}

This saves you time in coding, and also means that a more reliable, mathematically-based password salt is generated and used.

Source: http://php.net/manual/en/function.password-hash.php

What values are valid for an ID attribute in an HTML element?

When naming id attributes of HTML tags, you do have some limits.

As stated by the HTML4 specification...

>> ID and NAME tokens must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"), and periods (".").

Source: https://www.w3.org/TR/html4/types.html#type-id

HTML5 has more-relaxed specifications...

There are no other restrictions on what form an ID can take; in particular, IDs can consist of just digits, start with a digit, start with an underscore, consist of just punctuation, etc.

Source: https://www.w3.org/TR/html5/dom.html#element-attrdef-global-id

How to Detect the Character Set Encoding of a MySQL Database

You may want to know if your MySQL DB is encoded in latin1 or UTF-8, or maybe some other charset.

You can see the default character set encoding and collation with these commands...

SELECT @@character_set_database;
SELECT @@collation_database;

But this is just for the current database. There are various other default encodings and collations at different levels, which you will only be able to see with commands like these...

show variables like 'char%';
show variables like 'collation%';

If you want to see the encoding for a particular table, you can find its encoding with...

SHOW CREATE TABLE MyTable;

To see ONLY the encoding of a particular Table's field, you can search the INFORMATION_SCHEMA tables...

SELECT COLLATION_NAME
FROM information_schema.columns
WHERE TABLE_SCHEMA = 'MySchema'
AND TABLE_NAME = 'MyTable'
AND COLUMN_NAME = 'MyField';

Full UTF-8 Web Application Development - How to Do It Right

With UTF-8 support, you can be guaranteed that any language will work with your code. But there are two fundamental things that you need to make sure happens:

First, convert your database to UTF-8. This is the data part of it.

To convert your database requires changing the default settings and converting the tables themselves. You can change the default settings with...

MyDB@sys mysql> ALTER DATABASE MyDatabase DEFAULT CHARACTER SET utf8 DEFAULT COLLATE utf8_general_ci;

And you can convert your tables with...

MyDB@sys mysql> ALTER TABLE MyTable DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;
MyDB@sys mysql> ALTER TABLE MyTable MODIFY MyColumn VARCHAR(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT '';

Second, send all web pages with a UTF-8 header. This is the networking part of it.

For example, in PHP, to send the UTF-8 header, you will run this command being sending any output to the browser...

header('Content-type: text/html; charset=utf-8');

Every program, protocol, etc., has its exceptions and variations, so these are just the two basics you need to handle.

"bind_param() expects parameter 1 to be resource, boolean given" -- Possible Fixes?

Your MySQL and PHP code may be fully and logically thought-out. You may have even tested and verified it worked. But now you have this error:

"bind_param() expects parameter 1 to be resource, boolean given"

Your code probably looks something like this...

$db_link = new mysqli($hostname, $username, $password, $database);
$sql = "SELECT * FROM SomeTable WHERE id = ?";
$statement = $db_link->prepare($sql);
$statement->bind_param($_POST['id']);

How do you fix it? The problem is not with the bind_param() function, it's with the prepare() or the mysqli() functions!

If statement is a boolean, that means it is true or false, and in this case, false means that either mysqli() could not connect to the DB, or that prepare() had a problem.

If mysqli() has a problem, it could be a bad username/password combination, a networking issue, a bad db name, or something else. If prepare() has a problem, it could be a bad query, an unescaped term in the query, or something like that.

You can verify that mysqli() worked, by displaying its result and seeing that it's not false, and similarly with prepare().

Should Or Shouldn't I Use the MySQL_* functions in PHP?

There are a number of ways to access your MySQL server from PHP.

The first way, and the one originally taught, was to use the specialized MySQL functions in PHP, such as mysql_query(), mysql_connect(), and mysql_real_escape_string().

However, there are two problems with this function set.

First, it uses escaped strings, which are ultimately unsafer, slower, and less reliable than using Prepared Statements in MySQL.

Second, the developers behind the MySQL_* functions are no longer developing it, they no longer accept feedback on it, and they ask users to move onto something more reliable, with Prepared Statements, for MySQL uses.

This second reason is so strong, that all MySQL_* functions have been removed from PHP version 7.0 and up. Learn to do prepared statements, or these two reasons will perpetually haunt your code.

How do I prevent MySQL Injection with PHP?

We all know that you can make a simple form with some HTML, put together a quick PHP script, build a few MySQL tables, and you have yourself a full, working application in a matter of minutes.

Your PHP may end up initally looking like this...

$sql = "SELECT * FROM SomeTable WHERE id = " . $_POST['id'];

The HTML script would contain the necessary form and input elements, and SomeTable would be in the database. But this creates the possibility of a MySQL injection.

To prevent mysql injection, we send the SQL query and user input in SEPARATE statements, called Prepared Statements. Put a question mark where you want the variable to be...

$db_link = new mysqli($hostname, $username, $password, $database);
$sql = "SELECT * FROM SomeTable WHERE id = ?";
$statement = $db_link->prepare($sql);
$statement->bind_param($_POST['id']);

This will prevent users from submitting malicious data. Imagine, for example, if someone tried to submit an 'id' of value "0 AND DROP TABLES;", which would have a negative consequence on your app.

How to Wrap Text in Pre-Tags in HTML

You can use PRE tags to make text look like code in most computer terminals, which is a monospaced, Courier font.

But the problem with PRE tags is that the text does not wrap automatically. If the user wants to see a long paragraph, they need to scroll RIGHT on their computer screen, instead of DOWN, which is more intuitive.

To make PRE tagged text autowrap, the code is very simple...

pre {
white-space: pre-wrap;
}

All PRE-tags are now wrapped. This solution will work on all modern browsers.

If you want a solution that works on older machines, the code is a bit more complex...

pre {
white-space: pre-wrap; /* css-3 */
white-space: -moz-pre-wrap; /* Mozilla, since 1999 */
white-space: -pre-wrap; /* Opera 4-6 */
white-space: -o-pre-wrap; /* Opera 7 */
word-wrap: break-word; /* Internet Explorer 5.5+ */
}

(Multi-Browser Solution Source: https://longren.io/wrapping-text-inside-pre-tags/ )

MySQL Limit Pagination is Slow on Large Offset Quantities - How do I resolve?

With MySQL field indexing on fields you regularly use in WHERE clauses, you can speed up your performance.

You can also use LIMIT to either limit your results, or to get paginated results. If you show 20 results per page and you want page 7's results, you would select with...

MyDB@sys mysql> SELECT * FROM ... LIMIT 7, 20;
...
20 rows in set (0.01 sec)

But this query becomes intensely slow with higher offsets, such as this query...

MyDB@sys mysql> SELECT * FROM ... LIMIT 50000, 20;
...
20 rows in set (0.35 sec)

The same exact query, using different offset limits, has very different performance!

But it is very easy to get around! Just use a subquery to select the id's first, which has your LIMIT.

MyDB@sys mysql> SELECT * FROM ... WHERE id IN(SELECT id FROM ... LIMIT 50000, 20);

Bypassing this problem shouldn't really work, and yet it does! That is because this has been a bug with MySQL for about the past decade: https://bugs.mysql.com/bug.php?id=41871

How do I remove a MySQL Index on a Table and Column?

MySQL indices can make your DB faster, but at times, you may need to remove them, for instance, when they are no longer needed or when a compound index is more appropriate.

For a MySQL DB named MyDB, you can remove a table index with...

MyDB@sys mysql> DROP INDEX `SomeIndexedColumn` ON `MyTable`;

Then, you can verify that this change took place, by showing the indices on the table afterwards...

MyDB@sys mysql> SHOW KEYS FROM MyTable;

Then you can proceed to add the indices or compound indices that your table needs.

MySQL is Not Using Index Key on Field - How do I resolve?

If you need to speed up your MySQL DB, you're adding indices on your columns. You will see a massive, immediate improvement in performance.

But sometimes you won't, and there are a number of ways to diagnose and resolve those problems.

1) Run the Analyze command on the table. For instance...

MyDB@sys mysql> ANALYZE `MyTable`

This tells your MySQL storage engine to look at the possible ways to join or select this table.

2) MySQL is using a different keys than the one you specified indices for. If your where clause is on multiple statements, you may want a compound index to make it more clear to the storage engine...

MyDB@sys mysql> ALTER TABLE `MyTable`
ADD INDEX `ComboIndex` (`Column1`,`Column2`)

And this will work with...

MyDB@sys mysql> SELECT .... WHERE
Column1 = "ABC" OR COLUMN2 = "DEF";

3) Your query may be simply too complicated for MySQL to grasp. In this case, simplifying the query into multiple UNION'd statements will produce the desired output at amazing speed...

MyDB@sys mysql> (SELECT .... WHERE
Column1 = "ABC") UNION (SELECT .... WHERE COLUMN2 = "DEF");

How do I add a MySQL Index Key to Improve Select Performance?

If you have a MySQL database, you can improve performance by adding index keys.

Indexing makes it so that SELECT statements will execute faster, when you have a WHERE clause that uses an indexed key. The speed different can be insignificant (on small DB's), or tremendous (on bigger DB's).

Add a MYSQL index to a column like this....

MyDB@sys mysql> ALTER TABLE `MyTable` ADD INDEX `MyColumn` (`MyColumn`);

Then you will get better performance with statements like...

MyDB@sys mysql> SELECT * FROM MyTable WHERE MyColumn = 'SomethingIWant';

You can also verify the keys a table has with....

MyDB@sys mysql> SHOW KEYS FROM MyTable;

Or, even with this....

MyDB@sys mysql> SHOW CREATE TABLE MyTable;

How do I list all tables in a MySQL Database?

If you have a MySQL database named MyDB, you can see all of the tables with...

MyDB@sys mysql> show tables;

If you have a bit more time, you can see all the tablenames for just the current DB with...

MyDB@sys mysql> select TABLE_NAME from INFORMATION_SCHEMA.tables WHERE TABLE_SCHEMA = 'MyDB';

Or, if you want to see all tablenames for all databases in MySQL, you can run this....

MyDB@sys mysql> select TABLE_SCHEMA, TABLE_NAME from INFORMATION_SCHEMA.tables;

You're now on your way to seeing all the database information.

How to Fix Getting Errcode 28 on MySQL?

Query3 failed: Error writing file '/tmp/MY9uc2x7' (Errcode: 28)

If you are seeing this error, it is not a MySQL Error Code, but a Linux OS Error Code.

See the full message with the C++ debugging tool, perror:

perror 28

And this will output:

OS error code 28: No space left on device

So the problem is easily solved! Delete some stuff on the server hosting your DB.

How to Grep files in Linux, but only certain file extensions?

Want to search your file system on Linux?  It's easy!

    grep -r --include=\*.txt 'searchterm' ./

...or case-insensitive version...

    grep -r -i --include=\*.txt 'searchterm' ./

• grep : command
  
• -r : recursively
  
• -i : ignore-case
  
• --include : all *.txt: text files (escape with \ just in case you have a directory with asterisks in the filenames)
  
• 'searchterm' : What to search
  
• ./ : Start at current directory.