Apache Rewrite Tricks
It is possible to use Apache’s Rewrite Module features to perform a number of useful tricks that can make people’s lives much easier.
Short URLs
Making short URLs for common destinations can simplify making printed media as well as shortening or simplifying what people need to type. These are also easy to add and require minimal maintenance, and generally can be implemented with a single line addition to your eg_vhost.conf file.
# My Account - http://host.ext/myaccount -> My Account Page RewriteRule ^/myaccount https://%{HTTP_HOST}/eg/opac/myopac/main [R] # ISBN Search - http://host.ext/search/isbn/<ISBN NUMBER> -> Search Page RewriteRule ^/search/isbn/(.*) /eg/opac/results?_special=1&qtype=identifier|isbn&query=$1 [R]
conf
Domain Based Content with RewriteMaps
One creative use of Rewrite features is domain-based configuration in a single eg_vhost.conf file. Regardless of how many VirtualHost blocks use the configuration you don’t need to duplicate things for minor changes, and can in fact use wildcard VirtualHost blocks to serve multiple subdomains.
For the wildcard blocks you will want to use a ServerAlias directive, and for SSL VirtualHost blocks ensure you have a wildcard SSL certificate.
ServerAlias *.example.com
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For actually changing things based on the domain, or subdomain, you can use RewriteMaps. Each RewriteMap is generally a lookup table of some kind. In the following examples we will generally use text files, though database lookups and external programs are also possible.
Note that in the examples below we generally store things in Environment Variables. From within Template Toolkit templates you can access environment variables with the ENV object.
[% IF ENV.eglibname && ENV.egliburl %]<a href="[% ENV.egliburl %]">[% ENV.eglibname %]</a>[% END %]
html
The first lookup to do is a domain to identifier, allowing us to re-use identifiers for multiple domains. In addition we can also supply a default identifier, for when the domain isn’t present in the lookup table.
# This internal map allows us to lowercase our hostname, removing case issues in our lookup table # If you prefer uppercase you can use "uppercase int:toupper" instead. RewriteMap lowercase int:tolower # This provides a hostname lookup RewriteMap eglibid txt:/openils/conf/libid.txt # This stores the identifier in a variable (eglibid) for later use # In this case CONS is the default value for when the lookup table has no entry RewriteRule . - [E=eglibid:${eglibid:${lowercase:%{HTTP_HOST}}|CONS}]
conf
# Comments can be included # Multiple hostnames for Branch 1 branch1.example.com BRANCH1 branch1.example.net BRANCH1 # Branches 2 and 3 don't have alternate hostnames branch2.example.com BRANCH2 branch3.example.com BRANCH3
txt
Once we have identifiers we can look up other information, when appropriate. For example, say we want to look up library names and URLs:
# Library Name Lookup - Note we provide no default in this case. RewriteMap eglibname txt:/openils/conf/libname.txt RewriteRule . - [E=eglibname:${eglibname:%{ENV:eglibid}}] # Library URL Lookup - Also with no default. RewriteMap egliburl txt:/openils/conf/liburl.txt RewriteRule . - [E=egliburl:${egliburl:%{ENV:eglibid}}]
conf
# Note that we cannot have spaces in the "value", so instead   is used. is also an option. BRANCH1 Branch One BRANCH2 Branch Two BRANCH3 Branch Three CONS Example Consortium Name
txt
BRANCH1 http://branch1.example.org BRANCH2 http://branch2.example.org BRANCH3 http://branch3.example.org CONS http://example.org
txt
Or, perhaps set the "physical location" variable for default search/display library:
# Lookup "physical location" IDs RewriteMap eglibphysloc txt:/openils/conf/libphysloc.txt # Note: physical_loc is a variable used in the TTOPAC and should not be re-named RewriteRule . - [E=physical_loc:${eglibphysloc:%{ENV:eglibid}}]
conf
BRANCH1 4 BRANCH2 5 BRANCH3 6 CONS 1
txt
Going further, you could also replace files to be downloaded, such as images or stylesheets, on the fly:
# Check if a file exists based on eglibid and the requested file name # Say, BRANCH1/opac/images/main_logo.png RewriteCond %{DOCUMENT_ROOT}/%{ENV:eglibid}%{REQUEST_URI} -f # Serve up the eglibid version of the file instead RewriteRule (.*) /%{ENG:eglibid}$1
conf
Note that template files themselves cannot be replaced in that manner.