.htaccess چیست و چگونه مورد استفاده قرار میگیرد؟

[Vahid]

What is .htaccess and how is it being used?
An .htaccess file is a simple ASCII file similar to that created through text editor such as Notepad or Simple Text. Most people are confused with the naming convention for the file. The term .htaccess is not a file .htaccess or somepage.htaccess because it is the file extension simply named as such. Its widely known use is related to implementing custom error page or password protected directories.
Creating the File
The creation of the file is done by opening up a text editor and saving an empty page as .htaccess. If it is not allowed to save an empty page, simply type in one character. An editor probably appends its default file extension to the name. Notepad for one would call the file .htaccess.txt but the .txt or other file extension need to be removed to enable the user to start “htaccessing”. This can be done by clicking the file and renaming it by removing anything that doesn’t say .htaccess. It can also be renamed via telnet or the ftp program.
These files must not be uploaded as binary but rather as ASCII mode. Users can CHMOP the .htaccess file to 644 to make the file usable by the server while preventing it from being read by a browser since this can seriously compromise security. When there are passwords protected directories and a browser can read the .htaccess file, the location of the authentication file can be acquired to reverse engineer the list and thereby completely access any portion that had previously been protected. This can be prevented by either placing all authentication files above root directory thereby rendering the www inaccessible or through an .htaccess series of commands that prevents itself from being accessed by a browser.
Most commands in .htaccess are meant to be placed on one line only thus if a text editor uses word wrap, it should be disabled as it is possible that it might throw in a few characters that might contradict Apache. .htaccess is not for NT servers and is considered an Apache thing. Apache is generally very tolerant of malformed content in an .htaccess file.
The directory in which .htaccess file is placed is “affected” as well as all sub-directories. It a user wishes not to have certain .htaccess commands affect a specific directory, this is done by placing a new .htaccess file within the directory that should not be affected with certain changes and removing the specific command/s. from the new .htaccess file which should not affect the directory. The nearest .htaccess file to the current directory is the one considered as the .htaccess file. A global .htaccess located in the root, if considered the nearest, affects every single directory in the entire site.
Placement of .htaccess should not be done indiscriminately as this may result to redundancy and may cause an infinite loop of redirects or errors. There are sites that do not allow the use of .htaccess files because a server overloaded with domains can be slowed down when all are using .htaccess files. It is possible that .htaccess can compromise a server configuration specifically set-up by the administrator. It is therefore necessary to make sure that the use of .htaccess is allowed before its actual use.
Error documents are only a part of the general use of .htaccess. Specifying one’s own customized error documents will require a command within the .htaccess file. The pages can be named anything and can be placed anywhere within the site as long as they are web-accessible through a URL. The best names are those that would prevent the user from forgetting what the page is being used for.
Password protection is effectively dealt with by .htaccess. By creating a file called .htpasswd, username and the encrypted password of the people to be allowed access are placed in the .htpasswd file. The .htpasswd file should likewise be not uploaded to a directory that is web accessible for maximum security.
Whole directories of a site can be redirected using the .htaccess file without the need to specify each file. Thus any request made for an old site will be redirected to the new site, with the extra information in the URL added on. This is a very powerful feature when used correctly.
Aside from custom error pages, password protecting folders and automatic redirection of users, .htaccess is also capable of changing file extension, banning users with extra certain IP address allowing only users with certain IP addresses, stopping directory listing and using a different file as the index file. Accessing a site that has been protected by .htaccess will require a browser to pop-up a standard username/password display box. However, there are certain scripts available which will allow the user to embed a username/password box in a website to do the authentication. The wide variety of uses of .htaccess facilitates time saving options and increased security in a website.
Many hosts support .htaccess but do not publicize it while many others have the capability for it but do not allow their users to have an .htaccess file. Generally, a server that runs UNIX or any version of the Apache web server will support .htaccess although the host may not allow its use.
When to Use .htaccess Files
The .htaccess files should not be used when there is no access to the main server configuration file. Contrary to common belief, user authentication is not always done in .htaccess files. The preferred way is to put user authentication configuration in the main server configuration.
It should be used in situations where the content provider needs to make configuration changes to the server on a per-directory basis but does not have root access on the server system. Individual users can be permitted to make these changes in .htaccess files for themselves if the server administrator is unwilling to make frequent configuration. As a general rule, the use of .htaccess should be avoided when possible since configuration can be effectively made in a Directory Section in the main server configuration file.
Two main factors warrant avoiding the use of .htaccess files – performance and security. Permitting .htaccess files causes a performance hit whether or not it is actually used, since Apache will look in every directory for such file. The .htaccess file is also looked into every time a document is requested. The Apache search will include .htaccess files in all higher-level directories to have a full complement of directories of application. As such, each file accessed out of the directory results to 4 additional file system accesses even if none was originally present.
The use of .htaccess permits users to modify server configuration which may produce uncontrolled changes. This privilege should be carefully considered before it is given to users. The use of the .htaccess files can be completely disabled by setting the Allow Overide directive to none.