Sketch to show that populating download cache on conan upload is possible

conan/cli/commands/upload.py

@@ -1,3 +1,5 @@
+import os
+
 from conan.api.conan_api import ConanAPI
 from conan.api.model import ListPattern, MultiPackagesList
 from conan.api.output import ConanOutput

conan/internal/conan_app.py

@@ -38,6 +38,7 @@ def __init__(self, requester, cmd_wrapper, global_conf, cache):
 
 class ConanApp(object):
     def __init__(self, cache_folder, global_conf):
+        self.global_conf = global_conf
 
         self.cache_folder = cache_folder
         self.cache = ClientCache(self.cache_folder, global_conf)

conans/client/cmd/uploader.py

@@ -4,6 +4,7 @@
 
 from conan.internal.conan_app import ConanApp
 from conan.api.output import ConanOutput
+from conans.client.downloaders.download_cache import DownloadCache
 from conans.client.source import retrieve_exports_sources
 from conans.errors import ConanException, NotFoundException
 from conans.paths import (CONAN_MANIFEST, CONANFILE, EXPORT_SOURCES_TGZ_NAME,
@@ -244,6 +245,18 @@ def upload_package(self, pref, prev_bundle, remote):
         self._app.remote_manager.upload_package(pref, cache_files, remote)
         duration = time.time() - t1
         self._output.debug(f"Upload {pref} in {duration} time")
+        for cache_file in cache_files:
+            self._local_cache_file(pref, cache_file, remote)
+
+    def _local_cache_file(self, pref, cache_file, remote):
+        approved_files = ["conaninfo.txt", "conan_package.tgz", "conanmanifest.txt"]
+        if cache_file not in approved_files:
+            return
+        _download_cache = self._app.global_conf.get("core.download:download_cache")
+        if _download_cache and os.path.isabs(_download_cache):
+            url = self._app.remote_manager._auth_manager._get_rest_client(remote)._get_api().router.package_file(pref, cache_file)
+            cached_path = DownloadCache(_download_cache).cached_path(url)
+            self._output.info(f"Caching {cache_file} to local cache '{cached_path}' - was uploaded to {url}")
 
 
 def compress_files(files, name, dest_dir, compresslevel=None, ref=None):

conans/test/integration/command/upload/upload_test.py

@@ -15,6 +15,7 @@
 from conans.test.utils.tools import NO_SETTINGS_PACKAGE_ID, TestClient, TestServer, \
     TurboTestClient, GenConanfile, TestRequester, TestingResponse
 from conans.util.files import gzopen_without_timestamps, is_dirty, save, set_dirty
+from utils.test_files import temp_folder
 
 conanfile = """from conan import ConanFile
 from conan.tools.files import copy
@@ -231,10 +232,14 @@ def test_upload_unmodified_package(self):
 
         client.save({"conanfile.py": conanfile,
                      "hello.cpp": ""})
+        download_cache = temp_folder()
+        client.save_home({"global.conf": f"core.download:download_cache={download_cache}"})
         ref = RecipeReference.loads("hello0/1.2.1@frodo/stable")
         client.run("create . --user=frodo --channel=stable")
         client.run("upload hello0/1.2.1@frodo/stable -r default")
 
+        assert "Caching conan_package.tgz to local cache" in client.out
+
         client2 = TestClient(servers=client.servers, inputs=["admin", "password"])
         client2.save({"conanfile.py": conanfile,
                       "hello.cpp": ""})