[EnvironmentCookbookVersionsEndpoint] Use cookbook_obj_cache in depsolve before calling get_data

lib/chef_zero/endpoints/environment_cookbook_versions_endpoint.rb

@@ -84,7 +84,8 @@ def depsolve(request, unsolved, desired_versions, environment_constraints, cookb
           new_unsolved = unsolved[1..-1]
 
           # Pick this cookbook, and add dependencies
-          cookbook_obj = FFI_Yajl::Parser.parse(get_data(request, request.rest_path[0..1] + ["cookbooks", solve_for, desired_version]))
+          cookbook_obj = cookbook_obj_cache.dig(solve_for, desired_version) ||
+            FFI_Yajl::Parser.parse(get_data(request, request.rest_path[0..1] + ["cookbooks", solve_for, desired_version]))
           cookbook_obj_cache[solve_for] ||= {}
           cookbook_obj_cache[solve_for][desired_version] = cookbook_obj
           cookbook_metadata = cookbook_obj["metadata"] || {}
@@ -110,7 +111,8 @@ def depsolve(request, unsolved, desired_versions, environment_constraints, cookb
           next if dep_not_found
 
           # Depsolve children with this desired version!  First solution wins.
-          result, cookbook_obj_cache = depsolve(request, new_unsolved, new_desired_versions, environment_constraints, cookbook_obj_cache)
+          result, returned_cache = depsolve(request, new_unsolved, new_desired_versions, environment_constraints, cookbook_obj_cache)
+          cookbook_obj_cache = returned_cache || cookbook_obj_cache
           return [result, cookbook_obj_cache] if result
         end
         [nil, nil]

spec/endpoints/environment_cookbook_versions_endpoint_spec.rb

@@ -362,6 +362,42 @@ def cookbook_json(name, version, dependencies = {})
         expect(result).to be_nil
       end
 
+      it "uses cached cookbook data instead of re-fetching during backtracking" do
+        desired = {
+          "web" => ["1.0.0", "2.0.0"],
+          "db" => ["1.0.0"],
+        }
+        # web 2.0.0 depends on lib, which depends on missing (doesn't exist) → branch fails
+        # web 1.0.0 has no deps → backtracks here, db must be re-solved
+        # db 1.0.0 should be fetched only once (cached from the first branch)
+        allow(data_store).to receive(:get)
+          .with(org_prefix + ["cookbooks", "web", "2.0.0"], request)
+          .and_return(cookbook_json("web", "2.0.0", { "lib" => ">= 1.0.0" }))
+        allow(data_store).to receive(:get)
+          .with(org_prefix + ["cookbooks", "web", "1.0.0"], request)
+          .and_return(cookbook_json("web", "1.0.0"))
+        expect(data_store).to receive(:get)
+          .with(org_prefix + ["cookbooks", "db", "1.0.0"], request)
+          .once
+          .and_return(cookbook_json("db", "1.0.0"))
+        allow(data_store).to receive(:exists_dir?)
+          .with(org_prefix + %w{cookbooks lib})
+          .and_return(true)
+        allow(data_store).to receive(:list)
+          .with(org_prefix + %w{cookbooks lib})
+          .and_return(["1.0.0"])
+        allow(data_store).to receive(:get)
+          .with(org_prefix + ["cookbooks", "lib", "1.0.0"], request)
+          .and_return(cookbook_json("lib", "1.0.0", { "missing" => ">= 1.0.0" }))
+        allow(data_store).to receive(:exists_dir?)
+          .with(org_prefix + %w{cookbooks missing})
+          .and_return(false)
+
+        result, _cache = endpoint.depsolve(request, %w{web db}, desired, {})
+        expect(result["web"]).to eq(["1.0.0"])
+        expect(result["db"]).to eq(["1.0.0"])
+      end
+
       it "resolves a deep dependency chain" do
         desired = { "app" => ["1.0.0"] }
         allow(data_store).to receive(:get)