NAME Apache2::Translation - Configuring Apache dynamically SYNOPSIS LoadModule perl_module /path/to/mod_perl.so PerlLoadModule Apache2::Translation PerlTransHandler Apache2::Translation TranslationEvalCache 1000 TranslationKey MyKey TranslationProvider DB \ database=dbi:mysql:dbname:host \ user=username password=password \ singleton=1 \ table=tablename \ key=keycolumn \ uri=uricolumn \ block=blockcolumn \ order=ordercolumn \ action=actioncolumn \ cachetbl=cachetablename \ cachecol=cachecolumn \ cachesize=1000 INSTALLATION perl Makefile.PL make make test make install DEPENDENCIES mod_perl2: 2.0.2 recommended patch: http://www.gossamer-threads.com/lists/modperl/modperl/87487#87487 DESCRIPTION As the name implies "Apache2::Translation" lives mostly in the URI Translation Phase. It is somehow similar to "mod_rewrite" but configuration statements are read at runtime, thus, making it possible to reconfigure a server without restarting it. The actual configuration statements are read by means of a *Translation Provider*, a Perl class offering a particular interface, see below. Currently there is one provider implemented, Apache2::Translation::DB. It reads the configuration from a database via DBI. An Example Let's begin with an example. Given some database table: id key uri blk ord action 1 front :PRE: 0 0 Cond: $HOSTNAME !~ /^(?:www\.)xyz\.(?:com|de)$/ 2 front :PRE: 0 1 Redirect: 'http://xyz.com'.$URI, 301 3 front :PRE: 1 0 Do: $ctx->{lang}='en' 4 front :PRE: 1 1 Cond: $HOSTNAME =~ /de$/ 5 front :PRE: 1 2 Do: $ctx->{lang}='de' 6 front /static 0 0 File: $DOCROOT.'/'.$ctx->{lang}.$MATCHED_PATH_INFO 7 front /appl1 0 0 Proxy: 'http://backend/'.$ctx->{lang}.$URI 8 front /appl2 0 0 Proxy: 'http://backend/'.$URI.'?l='.$ctx->{lang} 9 front / 0 0 Config: ['AuthName "secret"'], ['AuthType Basic'] 10 back :PRE: 0 0 Cond: $r->connection->remote_ip ne '127.0.0.1' 11 back :PRE: 0 1 Error: 403, 'Forbidden by Apache2::Translation(11)' 12 back /appl1 0 0 PerlHandler: 'My::Application1' 13 back /appl2 0 0 PerlHandler: 'My::Application2' The "id" column in this table is not really necessary. It is given to refer to single records. Well, here we have a frontend/backend configuration. The frontend records are labeled with the key "front", the backend records with "back". When a request comes in first the records with a ":PRE:" uri are examined. Suppose, a request for "http://abc.com/static/img.png" comes in. Record 1 (id=1) checks the "Host" header. The expression afer "Cond:" is evaluated as Perl code. It obviously returns true. "Cond" stands for *condition*. But how does it affect the further workflow? Here "blk" and "ord" come in. All records with the same "key", "uri" and "blk" form a block. "ord" gives an order within this block. Within a block all actions are executed up to the first condition that is false. Now, because our condition in record 1 is true the action in record 2 (within the same block) is executed. It redirects the browser with a HTTP code of 301 (MOVED PERMANENTLY) to "http://xyz.com/static/img.png". When the redirected request comes back the condition in record 1 is false. Hence, the next block (key=front, uri=:PRE:, blk=1) is evaluated. First a "lang" member of a context hash is set to "en". A "Do" action is similar to a condition, only its value is ignored. Record 4 then checks if the "Host" header matches "/de$/". If so, then record 5 sets the *language* to "de". Now, the records labeled with ":PRE:" are finished. The handler starts looking for blocks labeled with the request uri. That is, it looks for a block with key=front, uri=/static/img.png. None is found. Then it cuts off the last part of the uri (/img.png), repeats the lookup and finds record 6. The "File" action sets "$r-"filename> to "$DOCROOT/en/img.png". "Apache2::Translation" provides some convenience variables. They are tied to members of the request record or to elements of $ctx. $MATCHED_PATH_INFO contains the uri part cut off ("/img.png"). More on them below. Now another round is started and the next uri part is cut off. Record 9 matches. We see a "Config" action that sets "AuthName" and "AuthType". At the end the translation handler checks if "$r-"filename> was set and returns "Apache2::Const::OK" or "Apache2::Const::DECLINED" respectively. I think that example gives a general idea, what "Apache2::Translation" does. Processing States Internally "Apache2::Translation" is implemented as a state machine. It starts in the *START* state, where some variables are initialized. From there it shifts immediately to the *PREPOC* state. Here all ":PRE:" rules are evaluated. From *PREPROC* it shifts to *PROC*. Now the rules with real uris are examined. The "/" uri is handled in a special state called *LAST ROUND*. When the *DONE* state is reached processing is finished. You can control the current state by means of the "State", "Done" and "Restart" actions. Blocks and Lists of Blocks Above, we have defined a block as all records with the same "key", "uri" and "block". The actions within a block are ordered by the "order" field. A list of blocks is then an ordered list of all blocks with the same "key" and "uri". The order is given by the "block" number. Actions An action starts with a key word optionally followed by a colon and some arguments. The key words are case insensitive. "Apache2::Translation" provides some environment for code snippets in actions. They are compiled into perl functions. The compiled result is cached. 2 variables, $r and $ctx, are provided plus a few convenience variables. $r is the current "Apache2::RequestRec". $ctx points to a hash that can be used to store arbitrary data. All keys beginning with a space character in that hash are reserved for "Apache2::Translation". Do: perl_code This is the simplest action. The Perl code is evaluated in scalar context. The return value is ignored. Cond: perl_code This is almost the same as "Do". The return value is taken as boolean. If it is false, the current block is finished. Processing continues with the next block. Key: string "string" is evaluated in scalar context. The result is assigned to the current key. The new key takes effect if the list of blocks matching the current uri is finished. For example: id key uri blk ord action 1 dflt :PRE: 0 0 Cond: $r->connection->remote_ip eq '192.168.0.1' 2 dflt :PRE: 0 1 Key: 'spec' 3 dflt :PRE: 0 2 Do: $DEBUG=3 4 dflt :PRE: 1 0 Config: 'Options None' 5 dflt / 0 0 File: $DOCROOT.$URI 6 spec / 0 0 File: '/very/special'.$URI Here an entirely different directory tree is shown to a client with the IP address 192.168.0.1. In record 2 the current key is set to "spec" if the condition in record 1 matches. Also, $DEBUG is set in this case (record 3). The next block in record 4 is executed for all clients, because the key change is not in effect, yet. Records 5 and 6 are new lists of blocks. Hence, record 6 is executed only for 192.168.0.1 and record 5 for the rest. The action "Key: 'string'" is equivalent to "Do: $KEY='string'". State: string This action affects the current state directly. Thus, you can loop back to the *PREPROC* state from *PROC*. It is mostly used the prematurely finish the translation handler from the *PREPROC* state. As the "Key" action it takes effect, when the current list of blocks is finished. "string" is evaluated as perl code. It is expected to result in one of the following strings. If not, a warning is printed in the "error_log". State names are case insensitive: start preproc proc last round done The "State" action is similar to setting the convenience variable $STATE. Only in the latter case you must use the state constants, e.g. "$STATE=DONE". Last This action finishes the current list of blocks (just like a false condition finishes the current block). It is used together with "State" to finish the translation handler from a conditional block in the *PREPROC* state: :PRE: 0 0 Cond: $finish :PRE: 0 1 State: 'done' :PRE: 0 2 Last Another application of "Last" is as a return from a "Call" action, see below. Done This action is a combination of "State: next_state" and "Last". That means it shifts to the next normal state and finishes the current block list. Restart: ?uri? "Restart" restarts the processing. The optional uri argument is evaluated by perl and assigned to "$r-"uri>. Call: string Well, the name suggests it is calling a subroutine. Assume you have several WEB applications running on the same server, say one application for each department. Each department needs of course some kind of authorization: #uri blk ord action AUTH 0 0 Config: "AuthName \"$ctx->{name}\"" AUTH 0 1 Config: 'AuthType Basic' AUTH 0 2 Config: 'AuthUserFile /etc/htaccess/user/'.$ctx->{file} /dep1 0 0 Do: @{$ctx}{qw/name file/}=('Department 1', 'dep1') /dep1 0 1 Call: 'AUTH' /dep2 0 0 Do: @{$ctx}{qw/name file/}=('Department 2', 'dep2') /dep2 0 1 Call: 'AUTH' The "AUTH" in the "Call" actions refer to the "AUTH" block list in the "uri" column. "Call" fetches the block list for a given uri and processes it. If a "Last" action is executed the processing of that block list is finished. Redirect: url, ?http_code? The "Redirect" action sends a HTTP redirect response to the client and abort the current request. The optional "http_code" specifies the HTTP response code. Default is 302 (MOVED TEMPORARILY). Error: ?http_code?, ?message? "Error" aborts the entire request. A HTTP response is sent to the client. The optional "http_code" specifies the HTTP response code. The optional "message" is logged as reason to the "error_log". "http_code" defaults to 500 (INTERNAL SERVER ERROR), "message" to "unspecified error". Config: list_of_strings_or_arrays Surprisingly, this is the most complex action of all. This action changes the Apache configuration regarding the current request. Think of it as a kind of ".htaccess". Arguments to "Config" can be strings or arrays of one or two elements: Config: 'AuthName "secret"', ['AuthType Basic'], ['ProxyPassReverse http://...', '/path'], ['', ''], ['AllowOverride Options', ''], ['', ''] To understand the different meaning, you have to know about how Apache applies its configuration to a request. Hence, let's digress a little. Each Apache directive can be used in certain contexts. Some for example can occur only in server config context, that means outside any "Directory", "Location" or even "VirtualHost" container. "Listen" or "PidFile" are examples. Other directives insist on being placed in a container, some even want to be only in a "Directory" container. For example "AllowOverride" demands a "Directory" container. Also, the point in time when a directive takes effect differs for different directives. "PidFile" is clearly be applied during server startup before any request is processed. Hence, our "Config" action cannot apply "PidFile". It's simply too late. "AllowOverride" can be applied to single requests. But since it affects the processing of ".htaccess" files it must be applied before that processing takes place. To make things even more confusing some directives take effect at several points in time. Consider Options FollowSymLinks ExecCGI "FollowSymLinks" is applied when Apache looks up a file in the file system, while "ExecCGI" influences the way the response is generated ages later. Apache solves this complexity by computing a configuration for each single request. As a starting point it uses the server default configuration. That is the configuration outside any "Location" or "Directory" for a virtual host. This basic configuration is assigned to the request just between the *Uri Translation Phase* and *Map to Storage*. At the very end of *Map to Storage* Apache's core *Map to Storage* handler incorporates matching "Directory" containers and ".htaccess" files into the request's current configuration. "Location" containers are merged after *Map to Storage* is finished. Our "Config" action is applied early in *Map to Storage*. That means it affects the way Apache maps the request file name computed in the translation phase to the file system, because that comes later. But it also means, your static configuration (config file based) overrides our "Config" actions. This limitation can be partly overcome using "FixupConfig" instead of "Config". Now, what does the various syntaxes mean? The simplest one: #uri blk ord action /uri 0 0 Config: 'ProxyPassReverse http://my.backend.org' is very close to ProxyPassReverse http://my.backend.org Only, it is applied before any "Directory" container takes effect. Note, the location uri is the value of $MATCHED_URI, see below. This is also valid if the "Config" action is used from a "Call"ed block. The location uri is sometimes important. "ProxyPassReverse", for example, uses the path given to the location container for its own purpose. All other forms of "Config" are not influenced by $MATCHED_URI. The next one: Config: ['ProxyPassReverse http://my.backend.org'] is equivalent to ProxyPassReverse http://my.backend.org Note, the location uri differs. This is also the only form of this action, that is available with mod_perl before 2.0.3. The next one: Config: ['ProxyPassReverse http://my.backend.org', '/path'] is equivalent to ProxyPassReverse http://my.backend.org and Config: ['ProxyPassReverse /path http://my.backend.org', ''] is equivalent to ProxyPassReverse /path http://my.backend.org This last form evaluates configuration directives as if they appear outside any container. It is also a little dangerous, because it causes segfaults for some directives that are not prepared to be used this way. But it is the only way to apply an "AllowOverride", for example. FixupConfig: list_of_strings_or_arrays Syntax and sematic of this action is equivalent to "Config". The only difference, it is applied in the fixup phase, just before the response is generated. It can be seen as a hook to override static configuration in your "httpd.conf". Suppose your "httpd.conf" contains these lines: Options None But now you want to run files contained in /web/cgi as CGI scripts. "Config: 'Options ExecCGI'" would not help because it is overridden by the directory container that is merged later. Here: FixupConfig: 'Options ExecCGI' can be used. Uri: string This action sets "$r->uri" to string. It is equivalent to Do: $URI=do{ string } File: string This action sets "$r->filename" to string. It is equivalent to Do: $FILENAME=do{ string } Proxy: ?url? This tells Apache to forward the request to "url" as a proxy. "url" is optional. If ommitted "$r->unparsed_uri" is used. That means Apache must be used as a proxy by the browser. CgiScript (without parameter) is equivalent to Do: $r->handler( 'cgi-script' ); FixupConfig: ['Options ExecCGI'] PerlScript (without parameter) is equivalent to Do: $r->handler( 'perl-script' ); FixupConfig: ['Options ExecCGI'], ['PerlOptions +ParseHeaders'] PerlHandler: string This action checks that either "modperl" or "perl-script" is set as handler for the request. If not, "modperl" is set. "string" is evaluated as Perl code. The result is expected to be a package name or a fully qualified function name. If a package name is given "::handler" is appended to build a fully qualified function name. The action checks if the function is defined. If not, it tries to load the appropriate module. The function is the used as "PerlResponseHandler". Further, a "PerlMapToStorageHandler" is installed that skips the handling of "Directory" containers and ".htaccess" files. If not set, this handler also sets "path_info". Assumed, #uri blk ord action /some/path 0 0 PerlHandler: ... and a request comes in for "/some/path/foo/bar". Then "path_info" is set to "/foo/bar". Convenience Variables and Data Structures These variables are tied to elements of the current request ($r) or the current context hash ($ctx). Reading them returns the current value, setting changes it. $URI = "$r->uri" $REAL_URI = "$r->unparsed_uri" $METHOD = "$r->method" $QUERY_STRING = "$r->args" $FILENAME = "$r->filename" $DOCROOT = "$r->document_root" $HOSTNAME = "$r->hostname" $PATH_INFO = "$r->path_info" for more information see Apache2::RequestRec. $MATCHED_URI = "$ctx->{' uri'}" $MATCHED_PATH_INFO = "$ctx->{' pathinfo'}" While in "PROC" state the incoming uri is split in 2 parts. The first part is matching the "uri" field of a database record. The second part is the rest. They can be accessed as $MATCHED_URI and $MATCHED_PATH_INFO. $KEY = "$ctx->{' key'}" the current key. $STATE = "$ctx->{' state'}" the current processing state. $RC = "$ctx->{' rc'}" Normally, "Apache2::Translation" checks at the end if "$r->filename" is set. If so, it returns "Apache2::Const::OK" to its caller. If not, "Apache2::Const::DECLINED" is returned. The first alternative signals that the *Uri Translation Phase* is done and no further handlers are called in this phase. The second alternative signals that subsequent handlers are to be called. Thus, "mod_alias" or even the core translation handler see the request. Setting $RC your action decide what is returned. $RC is also set by the "PerlHandler" action. Modperl generated responses are normally not associated with a single file on disk. $DEBUG = "$ctx->{' debug'}" If set to 1 or 2 debugging output is sent to the "error_log". APACHE CONFIGURATION DIRECTIVES After installed and loaded by PerlLoadModule Apache2::Translation in your "httpd.conf" "Apache2::Translation" is configured with the following directives: TranslationProvider class param1 param2 ... Currently there is only one provider class implemented, "Apache2::Translation::DB". Hence, "class" is always "DB" or "Apache2::Translation::DB". Each parameter is expected to be a string formatted as NAME=VALUE There must be no spaces around the equal sign. The list is passed to the constructor of the provider class as named parameters: $class->new( NAME1=>VALUE1, NAME2=>VALUE2, ... ); The following parameters are expected by the "DB" provider: database=DSN a string describing a DBI database user=NAME password=PW the user and password to use table=NAME names the translation table. key=NAME uri=NAME block=NAME order=NAME action=NAME name the columns of the translation table to use. cachetbl=NAME cachecol=NAME name the cache table and its column cachesize=NUMBER|infinite sets the maximum number of cached block lists, default is 1000. If set to "infinite" the cache has no limits. A Tie::Cache::LRU cache is used. "Apache2::Translation::DB" caches database entries as lists of blocks. Each list of blocks consumes one cache entry. For each request first the following lookup is done: SELECT MAX($cachecol) FROM $cachetbl The resulting value is then compared with the previous read value. If it has changed, it means the cache is invalid. If not, the cache is valid and if all information is found in the cache, no further database lookups are needed. singleton=BOOLEAN Normally, "Apache2::Translation" tries to connect to the database at server startup. Then it inspects the database handle to see if "Apache::DBI" or "Apache::DBI::Cache" are loaded. If so, it will connect and disconnect for each translation phase / request, thus, put back the connection to the connection pool. If neither of them is loaded the DB connection is used as a singleton. It is connected once at server startup and then held open (and reconnected if dropped by the database server). With the optional "singleton" parameter you can decide to use a singleton connection even if a connection pool is in effect. If no connection pool is loaded, then of course setting "singleton" to false has no effect. TranslationKey initial-key This sets the initial value for the key. Default is the empty string. TranslationEvalCache number "Apache2::Translation" compiles all code snippets into functions and caches these functions. Normally, an ordinary hash is used for this. Strictly speaking this is a memory hole if your translation table changes. I think that can be ignored, if the number of requests per worker is limited, see "MaxRequestsPerChild". If you think this is too lax, put a number here. If set the cache is tied to Tie::Cache::LRU. The number of cached code snippets will then be limited by "number". PROVIDER INTERFACE A provider must support the following methods: new( NAME=>VALUE, ... ) the constructor. It is called once from the master Apache during its configuration. child_init This method is optional. If defined it is called from a "PerlChildInitHandler" and can be used to do some initializations. The "DB" provider connects here to the database and decides to use a singleton or not. start This method is called at start of each uri translation. The DB provider checks the cache here. stop is called after each uri translation. fetch( $key, $uri ) is called to fetch a list of blocks. The result is a list of arrays: ([block, order, action], [block, order, action], ...) SEE ALSO mod_perl: http://perl.apache.org AUTHOR Torsten Foertsch, SPONSORING Sincere thanks to Arvato Direct Services (http://www.arvato.com/) for sponsoring this module. COPYRIGHT AND LICENSE Copyright (C) 2005, 2006 by Torsten Foertsch This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.