(maint) Handle an invalid mirror gracefully

CHANGELOG.md

@@ -5,6 +5,8 @@ This project adheres to [Semantic Versioning](https://semver.org).
 This changelog adheres to [Keep a CHANGELOG](https://keepachangelog.com).
 
 ## [Unreleased]
+### Fixed
+- (maint) Handle an invalid mirror gracefully
 
 ## [0.39.1] - release 2023-08-25
 ### Fixed

lib/vanagon/component.rb

@@ -260,14 +260,21 @@ def fetch_mirrors(options)
           VanagonLogger.info %(Attempting to fetch from mirror URL "#{mirror}")
           @source = Vanagon::Component::Source.source(mirror, **options)
           return true if source.fetch
+        rescue Vanagon::InvalidSource
+          # This means that the URL was not a git repo or a valid downloadable file,
+          # which means either the URL is incorrect, or we don't have access to that
+          # resource. Return false, so that the pkg.url value can be used instead.
+          VanagonLogger.error %(Invalid source "#{mirror}")
         rescue SocketError
           # SocketError means that there was no DNS/name resolution
           # for whatever remote protocol the mirror tried to use.
           VanagonLogger.error %(Unable to resolve mirror URL "#{mirror}")
-        rescue RuntimeError
+        rescue StandardError
           # Source retrieval does not consistently return a meaningful
           # namespaced error message, which means we're brute-force rescuing
-          # RuntimeError. Not a good look, and we should fix this.
+          # StandardError. Also, we want to handle other unexpected things when
+          # we try reaching out to the URL, so that we can gracefully return
+          # false and fall back to fetching the pkg.url value instead.
           VanagonLogger.error %(Unable to retrieve mirror URL "#{mirror}")
         end
       end

lib/vanagon/component/source.rb

@@ -3,8 +3,11 @@
 require 'vanagon/component/source/http'
 require 'vanagon/component/source/git'
 require 'vanagon/component/source/local'
+require 'vanagon/errors'
 
 class Vanagon
+  class InvalidSource < Vanagon::Error
+  end
   class Component
     class Source
       SUPPORTED_PROTOCOLS = %w[file http https git].freeze
@@ -55,8 +58,8 @@ def source(uri_instance, **options) # rubocop:disable Metrics/AbcSize
           end
 
           # Unknown source type!
-          raise Vanagon::Error,
-            "Unknown file type: '#{uri}'; cannot continue"
+          raise Vanagon::InvalidSource,
+            "Source is invalid or of an unknown type: '#{uri}'; cannot continue"
         end
 
         def determine_source_type(uri)