Autoset routes and requests pathname prefixes if DASH_APP_NAME is set

[rpkyle]

This PR proposes to modify the resolution logic for resolve_prefix, which is called by Dash when setting self$routes_pathname_prefix and self$requests_pathname_prefix:

• check if routes_pathname_prefix or requests_pathname_prefix has been passed to Dash for R directly, and use if available
• check if DASH_ROUTES_PATHNAME_PREFIX or DASH_REQUESTS_PATHNAME_PREFIX have been set in current environment, and use if available
• check if DASH_APP_NAME has been set in environment, and use if available
• check if DASH_URL_BASE_PATHNAME has been set in environment, and use if available
• return the value of base_pathname if resolution fails as directed above

In addition, the function name is camelCased instead of using snake case.

[HammadTheOne]

I made a slight change here to fix the conditional statement.

[rpkyle]

🤦‍♂ Yep, one too many else if statements here.

[HammadTheOne]

Hey Ryan,

After checking out the changes and testing out a couple of deployments to DE, it looks like the changes work well and the autoset prefixes add a bit of convenience as a first step to making the apps easier to deploy on DE.

There was a slight issue with a conditional but that's been sorted out with the last commit. I did notice however, that the changes aren't backwards compatible, I had to remove the references to some of the environment variables declared in previous versions of the deployment template, but I think (based on our discussion earlier) that that's by design and should be fine going forward with future apps/deployments.

💃

[rpkyle]

There was a slight issue with a conditional but that's been sorted out with the last commit. I did notice however, that the changes aren't backwards compatible, I had to remove the references to some of the environment variables declared in previous versions of the deployment template, but I think (based on our discussion earlier) that that's by design and should be fine going forward with future apps/deployments.

Thanks @HammadTheOne. There are definitely some changes introduced as a result of all this work, but the end effect is a smoother, simpler deployment process overall.

[chriddyp]

I did notice however, that the changes aren't backwards compatible

I find this surprising. Which line of code is backwards incompatible? I would've expected that if these variables are already set (as in our current examples), they would continue to be used.

[HammadTheOne]

I believe the line setting the pathPrefix was the one, here's the logs that popped up before I removed those lines:

        R version 3.6.2 (2019-12-12) -- "Dark and Stormy Night"
        Copyright (C) 2019 The R Foundation for Statistical Computing
        Platform: x86_64-pc-linux-gnu (64-bit)
        R is free software and comes with ABSOLUTELY NO WARRANTY.
        You are welcome to redistribute it under certain conditions.
        Type 'license()' or 'licence()' for distribution details.
        R is a collaborative project with many contributors.
        Type 'contributors()' for more information and
        'citation()' on how to cite R or R packages in publications.
        Type 'demo()' for some demos, 'help()' for on-line help, or
        'help.start()' for an HTML browser interface to help.
        Type 'q()' to quit R.
        > appName <- Sys.getenv("DASH_APP_NAME")
        > 
        > if (appName != "") {
        +   pathPrefix <- sprintf("/%s/", appName)
        +   
        +   Sys.setenv(DASH_ROUTES_PATHNAME_PREFIX = pathPrefix,
        +              DASH_REQUESTS_PATHNAME_PREFIX = pathPrefix,
        +              )
        + }
        Error in Sys.setenv(DASH_ROUTES_PATHNAME_PREFIX = pathPrefix, DASH_REQUESTS_PATHNAME_PREFIX = pathPrefix,  : 
          argument is missing, with no default
        Execution halted
 =====> end ctest web container output