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How to Access a Global Application Variable

Overview​

In this project, we access application variables (environment variables or other variables we set for the application) by adding them to the handler config. Through the context we pass the variables to the functions that require them.

Why we do it this way​

Environment variables should only be accessed in the main serve.go file and turned into real variables for passing around at that point. Accessing environment vars in other parts of the code increases the scope of our problems if there is something wrong with the environment vars. Also it increases problems with security if people are using the os package directly to get them instead of using the spf13/viper package which reads both environment vars and command line flags.

We use spf13/viper and spf13/pflags to access environment variables today. It replaces using the os package and the flag package because it does both. The pattern is the 12-factor-app pattern.

Getting Environment Variables​

We use command line flags to get the environment variables. The flags are set in the cli package. Viper can take the flag and gets the value associated with that flag. For example:

dbEnv := v.GetString(cli.DbEnvFlag) returns the database environment name

loginGovSecretKey := v.GetString(cli.LoginGovSecretKeyFlag)) grabs the LOGIN_GOV_SECRET_KEY from the .envrc

Setting up global variables in the Handler Config​

To add an application variable to the handler config, we create essentially a getter and setter in the handler config. (Ex. SetUseSecureCookie and UseSecureCookie) Follow the pattern in pkg/handlers/config.go

Then, in the cmd/milmove/serve.go file, in the function serveFunction set the value using the setter.

For example:

dbEnv := v.GetString(cli.DbEnvFlag)
isDevOrTest := dbEnv == "development" || dbEnv == "test"
useSecureCookie := !isDevOrTest
handlerConfig.SetUseSecureCookie(useSecureCookie)

In your handler, you should now be able to access the value through the handler config by calling the getter (ex. h.HandlerConfig.UseSecureCookie())