Revert "Accept responses with no etag header"

This reverts commit 8414706.

Since we made that change we added one spec that relied on responses
without an Etag being accepted. That spec needs to be updated with a
correct checksum since we no longer do that.

Also, we add a regression spec for the issue being fixed here. Namely,
if the gem server does not provide ETags, its responses don't have
incremental content, but it still replies to partial range requests.
In this situation, we want to fallback to making a full update so that
things work.

bundler/lib/bundler/compact_index_client/updater.rb

@@ -58,16 +58,16 @@ def update(local_path, remote_path, retrying = nil)
             end
           end
 
-          etag = (response["ETag"] || "").gsub(%r{\AW/}, "")
-          if etag.length.zero? || etag_for(local_temp_path) == etag
+          response_etag = (response["ETag"] || "").gsub(%r{\AW/}, "")
+          if etag_for(local_temp_path) == response_etag
             SharedHelpers.filesystem_access(local_path) do
               FileUtils.mv(local_temp_path, local_path)
             end
             return nil
           end
 
           if retrying
-            raise MisMatchedChecksumError.new(remote_path, etag, etag_for(local_temp_path))
+            raise MisMatchedChecksumError.new(remote_path, response_etag, etag_for(local_temp_path))
           end
 
           update(local_path, remote_path, :retrying)

bundler/spec/bundler/compact_index_client/updater_spec.rb

@@ -16,11 +16,14 @@
     # Regression test for https://github.com/rubygems/bundler/issues/5463
     let(:response) { double(:response, :body => "abc123") }
 
-    it "treats the response as an update" do
-      expect(response).to receive(:[]).with("ETag") { nil }
-      expect(fetcher).to receive(:call) { response }
+    it "MisMatchedChecksumError is raised" do
+      # Twice: #update retries on failure
+      expect(response).to receive(:[]).with("ETag").twice { nil }
+      expect(fetcher).to receive(:call).twice { response }
 
-      updater.update(local_path, remote_path)
+      expect do
+        updater.update(local_path, remote_path)
+      end.to raise_error(Bundler::CompactIndexClient::Updater::MisMatchedChecksumError)
     end
   end
 
@@ -56,7 +59,7 @@
       begin
         $VERBOSE = false
         Encoding.default_internal = "ASCII"
-        expect(response).to receive(:[]).with("ETag") { nil }
+        expect(response).to receive(:[]).with("ETag").and_return('"348dd9e974848a61e8abe2dffcfcce93"')
         expect(fetcher).to receive(:call) { response }
 
         updater.update(local_path, remote_path)

bundler/spec/install/gems/compact_index_spec.rb

@@ -826,6 +826,28 @@ def start
     expect(the_bundle).to include_gems "rack 1.0.0"
   end
 
+  it "performs full update if server endpoints serve partial content responses but don't have incremental content and provide no Etag" do
+    build_repo4 do
+      build_gem "rack", "0.9.1"
+    end
+
+    install_gemfile <<-G, :artifice => "compact_index", :env => { "BUNDLER_SPEC_GEM_REPO" => gem_repo4.to_s }
+      source "#{source_uri}"
+      gem 'rack', '0.9.1'
+    G
+
+    update_repo4 do
+      build_gem "rack", "1.0.0"
+    end
+
+    install_gemfile <<-G, :artifice => "compact_index_partial_update_no_etag_not_incremental", :env => { "BUNDLER_SPEC_GEM_REPO" => gem_repo4.to_s }
+      source "#{source_uri}"
+      gem 'rack', '1.0.0'
+    G
+
+    expect(the_bundle).to include_gems "rack 1.0.0"
+  end
+
   it "performs full update of compact index info cache if range is not satisfiable" do
     gemfile <<-G
       source "#{source_uri}"

bundler/spec/support/artifice/compact_index_partial_update_no_etag_not_incremental.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+require_relative "compact_index"
+
+Artifice.deactivate
+
+class CompactIndexPartialUpdateNoEtagNotIncremental < CompactIndexAPI
+  def partial_update_no_etag
+    response_body = yield
+    headers "Surrogate-Control" => "max-age=2592000, stale-while-revalidate=60"
+    content_type "text/plain"
+    requested_range_for(response_body)
+  end
+
+  get "/versions" do
+    partial_update_no_etag do
+      file = tmp("versions.list")
+      FileUtils.rm_f(file)
+      file = CompactIndex::VersionsFile.new(file.to_s)
+      file.create(gems)
+      lines = file.contents.split("\n")
+
+      # shuffle versions so new versions are not appended to the end
+      [*lines[0..-2], lines.last.split(",").reverse.join(",")].join("\n")
+    end
+  end
+
+  get "/info/:name" do
+    partial_update_no_etag do
+      gem = gems.find {|g| g.name == params[:name] }
+      lines = CompactIndex.info(gem ? gem.versions : []).split("\n")
+
+      # shuffle versions so new versions are not appended to the end
+      [lines.first, lines.last, *lines[1..-2]].join("\n")
+    end
+  end
+end
+
+Artifice.activate_with(CompactIndexPartialUpdateNoEtagNotIncremental)