Fix cached download file extension for certain URL

PHP URLs have the downloadable file in the middle of the pathname. If no
extension is detected, continue up the pathname.

Library/Homebrew/download_strategy.rb

@@ -303,7 +303,11 @@ class AbstractFileDownloadStrategy < AbstractDownloadStrategy
     # We can't use basename_without_params, because given a URL like
     #   https://example.com/download.php?file=foo-1.0.tar.gz
     # the extension we want is ".tar.gz", not ".php".
-    Pathname.new(@url).extname[/[^?]+/]
+    url_pathname = Pathname.new(@url)
+    while !ext = url_pathname.extname[/[^?]+/]
+      url_pathname = url_pathname.dirname
+    end
+    ext
   end
 end
 

Library/Homebrew/test/download_strategies_spec.rb

@@ -209,6 +209,19 @@ describe CurlDownloadStrategy do
   it "parses the opts and sets the corresponding args" do
     expect(subject.send(:_curl_opts)).to eq(["--user", "download:123456"])
   end
+
+  describe "#tarball_path" do
+    subject { described_class.new(name, resource).tarball_path }
+
+    context "when URL ends with file" do
+      it { is_expected.to eq(HOMEBREW_CACHE/"foo-.tar.gz") }
+    end
+
+    context "when URL file is in middle" do
+      let(:url) { "http://example.com/foo.tar.gz/from/this/mirror" }
+      it { is_expected.to eq(HOMEBREW_CACHE/"foo-.tar.gz") }
+    end
+  end
 end
 
 describe DownloadStrategyDetector do