Apache HTTP Server Version 1.3

Overview of new features

New Features with Apache 1.3

New features with this release, as extensions of the Apache functionality. Because the core code has changed so significantly, there are certain liberties that earlier versions of Apache (and the NCSA daemon) took that recent Apache versions are pickier about - please check the compatibility notes if you have any problems.

In addition to a number of bug fixes and internal performance enhancements, Apache 1.3 has the following specific new user features:

• Optional «Spelling Correction» module added to distribution
  This optional module corrects frequently occurring spelling errors in document names requested from the server. This includes the correction of miscapitalized requests (as was available in a separately available mod_speling module as of Apache 1.1 already) but extends spelling correction to single inserted, omitted, transposed or mistyped characters. This catches the majority of mistyped requests. To make use of this module, it must be enabled in the server's Configuration file, and the CheckSpelling directive must be set to on.
• Enhanced Conditional Setting of Environment Variables
  The BrowserMatch* directives of Apache 1.2 have been joined by some more powerful brethren: SetEnvIf and SetEnvIfNoCase. These allow you to set environment variables for server and CGI use based upon all sorts of attributes of the request.
• Better Logging for Proxy Connect Errors
  In Apache 1.2 and earlier, when the proxy had difficulty connecting to a system it would log the error but no details. It now includes the IP address and port to which it couldn't connect.
• Enhanced SSI String Comparisons
  The string-based server-side include (SSI) flow-control directives provided by mod_include now include comparison for less-than (<), less-than-or-equal (<=), greater-than (>), and greater-than-or-equal (>=). Previously comparisons could only be made for equality or inequality.
• Re-organised Sources
  The source files for Apache have been re-organised. The main difference for Apache users is that the "Module" lines in Configuration have been replaced with "AddModule" with a slightly different syntax. For module authors there are some changes designed to make it easier for users to add their module.
• Default Apache directory path changed to /usr/local/apache/
  The default directory for the apache ServerRoot changed from the NCSA-compatible /usr/local/etc/httpd/ to /usr/local/apache/. This change covers only the default setting (and the documentation); it is of course possible to override it using the -d ServerRoot and -f httpd.conf switches when starting apache.
• Sortable Directory Listings
  If a directory listing is displayed using FancyIndexing, clicking on a column title will now sort the listing in order by the values in that column. Selecting the column repeatedly will toggle between ascending and descending order. This feature can be disabled with the SuppressColumnSorting IndexOptions keyword.
• SuppressHTMLPreamble Option for FancyIndexed Directories
  If a directory is marked for display with FancyIndexing, the listing page usually follows a predefined format using server-generated HTML. If the IndexOptions directive for the directory includes the SuppressHTMLPreamble option, and a file specified by the HeaderName directive is found in the directory, and the header file is recognized as containing HTML (determined by the file extension), then the module will assume that the header file contains the necessary introductory HTML tags and will not generate them itself.
• Less Buffering of CGI Script Output
  In previous versions of Apache, the output from CGI scripts would be internally buffered by the server, and wouldn't be forwarded to the client until either the buffers were full or the CGI script completed. As of Apache 1.3, the buffer to the client is flushed any time it contains something and the server is waiting for more information from the script. This allows CGI script to provide partial status reports during long processing operations.
• Support for Windows NT/95
  Apache now supports the Windows NT and Windows 95 operating systems, as well as the Unix systems supported in previos releases. Although the Windows version of Apache may not be perform as well as on the Unix systems for which Apache was originally written, the ability to run on Windows gives Apache the ability to run on a large number of web servers it was not previously able to.
• Regular Expression support for Alias and Redirect
  New AliasMatch, ScriptAliasMatch, and RedirectMatch directives allow for the use of regular expression matching. Additionally, new <DirectoryMatch>, <LocationMatch>, and <FilesMatch> sections provide a new syntax for regular expression sectioning.
• New "Magic" MIME-typing module
  A new module, the optional mod_mime_magic, has been added. It uses "magic numbers" and other hints from a file's contents to figure out what the contents are. It then uses this information to set the file's media type, if it cannot be determined by the file's extension.
• Directory indexing modules split
  The mod_dir module has been split in two, with mod_dir handling directory index files, and mod_autoindex creating directory listings. Thus allowing folks to remove the indexing function from critical servers.
• Support for Directory Icon Sizing
  The mod_autoindex module provides listings of directory contents when appropriate. If the FancyIndexing option is enabled, each file in the list is preceded by an icon representing the content type. In earlier versions of Apache, the HTML IMG tags for these icons weren't sized, so the browser had to wait until the images were loaded before it could lay out the page. With 1.3, the IndexOptions directive has two new keywords which allow you to control whether pre-sized IMG tags are used. This can substantially speed up the display of large directory listings.
• AccessFileName Enhancement
  The AccessFileName directive can now take more than one filename. This lets sites serving pages from network file systems and more than one Apache web server, configure access based on the server through which shared pages are being served.
• HostNameLookups now defaults to "Off"
  The HostNameLookups directive now defaults to "Off". This means that, unless explictly turned on, the server will not resolve IP addresses into names. This was done to spare the Internet from unnecessary DNS traffic.
• Double-Reverse DNS enforced
  The HostnameLookups directive now supports double-reverse DNS. (Known as PARANOID in the terminology of tcp_wrappers.) An IP address passes a double-reverse DNS test if the forward map of the reverse map includes the original IP. Regardless of the HostnameLookups setting, mod_access access lists using DNS names require all names to pass a double-reverse DNS test. (Prior versions of Apache required a compile-time switch to enable double-reverse DNS.)
• CIDR and Netmask access control
  mod_access directives now support CIDR (Classless Inter-Domain Routing) style prefixes, and netmasks for greater control over IP access lists.
• NoProxy and ProxyDomain directives added to proxy, useful for intranets.
• AddModuleInfo directive added to mod_info
  Allows additional information to be listed along with a specified module.
• Performance Improvements
  • IP-based virtual hosts are looked up via hash table, giving a performance boost on servers with large numbers of vhosts.
  • <Directory> parsing of requests has been vastly improved, giving speedups on configs with a lot of sections.
  • The critical path for static requests has fewer system calls. This generally helps all requests. (45 syscalls for a static request in 1.2 versus 22 in 1.3 in a well tuned configuration).
  • ReceiveBufferSize directive gives mod_proxy's outgoing connections larger network buffers, for increased throughput.
  • The low level I/O routines use writev (where available) to issue multiple writes with a single system call. They also avoid copying memory into buffers as much as possible. The result is less CPU time spent on transferring large files.
  • Static requests are served using mmap, which means bytes are only copied from the disk buffer to the network buffer directly by the kernel. The program never copies bytes around, which reduces CPU time. (Only where available/tested.)
  • When presented with a load spike, the server quickly adapts by spawning children at faster rates.
  • The code which dispatches modules was optimized to avoid repeatedly skipping over modules that don't implement certain phases of the API. (This skipping showed up as 5% of the cpu time on profiles of a server with the default module mix.)
  • Revamp of the Unix scoreboard management code so that less time is spent counting children in various states. Previously a scan was performed for each hit, now it is performed only once per second. This should be noticeable on servers running with hundreds of children and high loads.
  • New serialization choices improve performance on Linux, Solaris, and IRIX.
  • mod_log_config can be compile-time configured to buffer writes.

  See the new performance documentation for more information.

• Unique Identifiers
  mod_unique_id can be included to generate a unique identifier that distinguishes a hit from every other hit. ("Unique" has some restrictions on it.) The identifier is available in the environment variable UNIQUE_ID.
• Reliable Piped Logs
  On almost all Unix architectures Apache now implements "reliable" piped logs in mod_log_config. Where reliable means that if the logging child dies for whatever reason, Apache will recover and respawn it without having to restart the entire server. Furthermore if the logging child becomes "stuck" and isn't reading its pipe frequently enough Apache will also restart it. This opens up more opportunities for log rotation, hit filtering, real-time splitting of multiple vhosts into separate logs, and asynchronous DNS resolving on the fly.
• ServerRoot relative auth filenames
  Auth filenames for the various authentication modules are now treated as relative to the ServerRoot if they are not full paths.
• Include directive
  The Include directive includes other config files immediately at that point in parsing.
• Absence of any TransferLog disables logging
  If no TransferLog directive is given then no log is written. This supports co-existence with other logging modules.
• Ability to name logging formats
  The LogFormat directive has been enhanced to allow you to give nicknames to specific logging formats. You can then use these nicknames in other LogFormat and CustomLog directives, rather than having to spell out the complete log format string each time.
• mod_cern_meta configurable per-directory
  mod_cern_meta is now configurable on a per-directory basis.
• Detaching from stdin/out/err
  On boot Apache will now detach from stdin, stdout, and stderr. It does not detach from stderr until it has successfully read the config files. So you will see errors in the config file. This should make it easier to start Apache via rsh or crontab.
• Improved HTTP/1.1-style Virtual Hosts
  The new NameVirtualHost directive is used to list IP address:port pairs on which HTTP/1.1-style virtual hosting occurs. This is vhosting based on the Host: header from the client. Previously this address was implicitly the same as the "main address" of the machine, and this caused no end of problems for users, and was not powerful enough. Please see the Apache Virtual Host documentation for further details on configuration.
• API Additions
  For all those module writers and code hackers:
  • child_init function for module API
    A new phase for Apache's API is called once per "heavy-weight process," before any requests are handled. This allows the module to set up anything that need to be done once per processes. For example, connections to databases.
  • child_exit function for module API
    A new phase called once per "heavy-weight process," when it is terminating. Note that it can't be called in some fatal cases (such as segfaults and kill -9). The child_init and child_exit functions are passed a pool whose lifetime is the same as the lifetime of the child (modulo completely fatal events in which apache has no hope of recovering). In contrast, the module init function is passed a pool whose lifetime ends when the parent exits or restarts.
  • child_terminate
    Used in the child to indicate the child should exit after finishing the current request.
  • register_other_child
    See http_main.h. This is used in the parent to register a child for monitoring. The parent will report status to a supplied callback function. This allows modules to create their own children which are monitored along with the httpd children.
  • piped_log
    See http_log.h. This API provides the common code for implementing piped logs. In particular it implements a reliable piped log on architectures supporting it (i.e., Unix at the moment).
  • MD5 functions renamed ap_*
    MD5 functions renamed to avoid conflicts with other libraries.
  • scoreboard format changed
    The scoreboard format is quite different. It is considered a "private" interface in general, so it's only mentioned here as an FYI.
  • set_last_modified split into three
    The old function set_last_modified performed multiple jobs including the setting of the Last-Modified header, the ETag header, and processing conditional requests (such as IMS). These functions have been split into three functions: set_last_modified, set_etag, and meets_conditions. The field mtime has been added to request_rec to facilitate meets_conditions.
  • New error logging function: aplog_error
    All old logging functions are deprecated, we are in the process of replacing them with a single function called aplog_error. This is still a work in progress.
  • set_file_slot for config parsing
    The set_file_slot routine provides a standard routine that prepends ServerRoot to non-absolute paths.
  • post_read_request module API
    This request phase occurs immediately after reading the request (headers), and immediately after creating an internal redirect. It is most useful for setting environment variables to affect future phases.
  • psocket, and popendir
    The psocket and pclosesocket functions allow for race-condition free socket creation with resource tracking. Similarly popendir and pclosedir protect directory reading.
  • is_initial_req
    Test if the request is the initial request (i.e., the one coming from the client).
  • kill_only_once
    An option to spawn_child functions which prevents Apache from aggressively trying to kill off the child.
  • alloc debugging code
    Defining ALLOC_DEBUG provides a rudimentary memory debugger which can be used on live servers with low impact -- it sets all allocated and freed memory bytes to 0xa5. Defining ALLOC_USE_MALLOC will cause the alloc code to use malloc() and free() for each object. This is far more expensive and should only be used for testing with tools such as Electric Fence and Purify. See main/alloc.c for more details.
• Year-2000 Improvements
  The default timefmt string used by mod_include has been modified to display the year using four digits rather than the two-digit format used previously. The mod_autoindex module has also been modified to display years using four digits in FancyIndexed directory listings.
• ap_*() Routines Moving to a Separate Library
  There are a number of functions and routines that have been developed for the Apache project that supplement or supersede library routines that differ from one operating system to another. While most of these are used only by the Apache server itself, some are referenced by supporting applications (such as htdigest), and these other applications would fail to build because the routines were built only into the server. These routines are now being migrated to a separate subdirectory and library so they can be used by other applications than just the server.

Apache HTTP Server Version 1.3