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Understanding Publisher Policy Assemblies

The next configuration issue you’ll examine is the role of publisher policy assemblies. As you’ve just

seen, *.config files can be constructed to bind to a specific version of a shared assembly, thereby

bypassing the version recorded in the client manifest. While this is all well and good, imagine you’re

an administrator who now needs to reconfigure 

all client applications on a given machine to rebind

to version 2.0.0.0 of the CarLibrary.dll assembly. Given the strict naming convention of a configu-

ration file, you would need to duplicate the same XML content in numerous locations (assuming

you are, in fact, aware of the locations of the executables using CarLibrary!). Clearly this would be a

maintenance nightmare.

Publisher policy allows the publisher of a given assembly (you, your department, your com-

pany, or what have you) to ship a binary version of a *.config file that is installed into the GAC

along with the newest version of the associated assembly. The benefit of this approach is that client

application directories do 

not need to contain specific *.config files. Rather, the CLR will read the

current manifest and attempt to find the requested version in the GAC. However, if the CLR finds a

publisher policy assembly, it will read the embedded XML data and perform the requested redirec-

tion 

at the level of the GAC.

Publisher policy assemblies are created at the command line using a .NET utility named al.exe

(the assembly linker). While this tool provides a large number of options, building a publisher policy

assembly requires you only to pass in the following input parameters:

• The location of the *.config or *.xml file containing the redirecting instructions

• The name of the resulting publisher policy assembly

• The location of the *.snk file used to sign the publisher policy assembly

• The version numbers to assign the publisher policy assembly being constructed

If you wish to build a publisher policy assembly that controls CarLibrary.dll, the command

set is as follows (which must be entered on a single line within the command window):

al /link: CarLibraryPolicy.xml /out:policy.1.0.CarLibrary.dll

/keyf:C:\MyKey\myKey.snk /v:1.0.0.0

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