How can I alter a Chocolatey package's $url for install - powershell

Question

TLDR version: I need to be able to append to the end of the URL that a chocolatey package specifies for its download source.
I'm trying to use Chocolatey to install the Android-SDK package and am having an issue with my filtering proxy (the functionality and provision of which, I have no control over). The proxy is detected properly but it will block URLs that contain certain patterns and issue a 403 return (in this case it's because the URL is to a .exe). So running choco install -y android-sdk causes the following error.
2015-03-12 15:14:47,639 [INFO ] - ============================================================
2015-03-12 15:14:47,664 [INFO ] - Chocolatey v0.9.9.2
2015-03-12 15:14:47,730 [INFO ] - Installing the following packages:
2015-03-12 15:14:47,753 [INFO ] - android-sdk
2015-03-12 15:14:47,754 [INFO ] - By installing you accept licenses for the packages.
2015-03-12 15:14:49,221 [INFO ] -
android-sdk v24.0.2
2015-03-12 15:14:50,525 [INFO ] - Using this proxyserver: xxx.xxx.xxx.xxx:xxxxx
2015-03-12 15:14:52,175 [INFO ] - Attempt to get headers for http://dl.google.com/android/installer_r24.0.2-windows.exe failed.
2015-03-12 15:14:52,175 [INFO ] - Exception calling "GetResponse" with "0" argument(s): "The remote server returned an error: (403) Forbidden."
2015-03-12 15:14:52,180 [INFO ] - Downloading android-sdk 32 bit
2015-03-12 15:14:52,180 [INFO ] - from 'http://dl.google.com/android/installer_r24.0.2-windows.exe'
2015-03-12 15:14:52,213 [INFO ] - Using this proxyserver: xxx.xxx.xxx.xxx:xxxxx
2015-03-12 15:14:52,329 [ERROR] - Exception calling "GetResponse" with "0" argument(s): "The remote server returned an error: (403) Forbidden."
2015-03-12 15:14:52,330 [ERROR] - At C:\ProgramData\chocolatey\helpers\functions\Get-WebFile.ps1:66 char:3
2015-03-12 15:14:52,330 [ERROR] - + $res = $req.GetResponse();
2015-03-12 15:14:52,330 [ERROR] - + ~~~~~~~~~~~~~~~~~~~~~~~~~
2015-03-12 15:14:52,331 [ERROR] - + CategoryInfo : NotSpecified: (:) [], MethodInvocationException
2015-03-12 15:14:52,331 [ERROR] - + FullyQualifiedErrorId : WebException
2015-03-12 15:14:52,354 [ERROR] - You cannot call a method on a null-valued expression.
2015-03-12 15:14:52,354 [ERROR] - At C:\ProgramData\chocolatey\helpers\functions\Get-WebFile.ps1:138 char:3
2015-03-12 15:14:52,355 [ERROR] - + $res.Close();
2015-03-12 15:14:52,356 [ERROR] - + ~~~~~~~~~~~~
2015-03-12 15:14:52,356 [ERROR] - + CategoryInfo : InvalidOperation: (:) [], RuntimeException
2015-03-12 15:14:52,357 [ERROR] - + FullyQualifiedErrorId : InvokeMethodOnNull
2015-03-12 15:14:54,374 [ERROR] - Chocolatey expected a file to be downloaded to
2015-03-12 15:14:54,375 [ERROR] - 'X:\Users\xxx\AppData\Local\Temp\chocolatey\android-sdk\android-sdkInstall.exe' but nothing exists at that
2015-03-12 15:14:54,375 [ERROR] - location.
2015-03-12 15:14:54,376 [ERROR] - At C:\ProgramData\chocolatey\helpers\functions\Get-ChocolateyWebFile.ps1:148 char:24
2015-03-12 15:14:54,376 [ERROR] - + if (!($fi.Exists)) {{ throw "Chocolatey expected a file to be downloaded to `'$ ...
2015-03-12 15:14:54,377 [ERROR] - + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2015-03-12 15:14:54,377 [ERROR] - + CategoryInfo : OperationStopped: (Chocolatey expe... that location.:String) [], RuntimeException
2015-03-12 15:14:54,378 [ERROR] - + FullyQualifiedErrorId : Chocolatey expected a file to be downloaded to 'X:\Users\xxx\AppData\Local\Temp\cho
2015-03-12 15:14:54,378 [ERROR] - colatey\android-sdk\android-sdkInstall.exe' but nothing exists at that location.
2015-03-12 15:14:54,618 [ERROR] - android-sdk install not successful.
2015-03-12 15:14:54,621 [ERROR] - Error while running 'C:\ProgramData\chocolatey\lib\android-sdk\tools\chocolateyInstall.ps1'.
See log for details.
2015-03-12 15:14:56,643 [WARN ] -
Chocolatey installed 0/1 package(s). 1 package(s) failed.
See the log for details.
2015-03-12 15:14:56,643 [ERROR] - Failures:
2015-03-12 15:14:56,645 [ERROR] - - android-sdk
I could create my own package with the chocolateyInstall.ps1 and chocolateyUninstall.ps1 listed on the package's web page and alter the URL, but that negates any benefit of using a package manager to simplify the process of managing programs and dependencies.
So I am wondering if there is some way that I can simply append a string that allows the URL through the proxy regardless of the file extension (to be clear, I know what this string is, I just don't know how to append it to the URL specified by the package).

Answer 1

This isn't a complete answer and I'm not sure how safe this answer is (in terms of surviving updates to Chocolatey itself), but it's resolved my immediate issue with the android-sdk package. Unfortunately, any package that implements its own download code bypasses this "fix".
I noticed the line in the error log that highlights one of the failure points as 2015-03-12 15:14:52,330 [ERROR] - At C:\ProgramData\chocolatey\helpers\functions\Get-WebFile.ps1:66 char:3 and wondered if I could alter the URL in that powershell script. After a bit of trial and error with the exact escaping that was needed for the appended string I managed to get it downloading the file, but the header check was still failing.
I then checked the other files in the helpers/functions/ directory and found Get-ChocolateyWebFile.ps1 which is what appears to call Get-WebFile.ps1 and also does the header check to see if it needs SSL.
So, I created a new powershell function file to perform the necessary URL rewrites in a function named Get-ProxyUrl and added this line to Get-ChocolateyWebFile.ps1 after the section that checks for 32bit/64bit URL but before the header check on the URL (line 101 in my version 0.9.9.2 file).
$url = Get-ProxyUrl($url)
I then also added it to the very beginning of the Get-WebFile function definition in Get-WebFile.ps1 to capture any direct calls to that function.
So, this will allow me to fix any packages that use Install-ChocolateyPackage, Get-ChocolateyWebFile or Get-WebFile, but still leaves some packages - such as JDK8 - that specify their own file download code and still fail.
So, a better solution would capture any URLs from a Chocolatey install... probably the only way to do this would be to install a local proxy server that chocolatey can use that would transform the URL before being passed on