feat: allow resuming a partial promote without manual cleanup

lua/copy_build.lua

@@ -14,19 +14,35 @@ if res.status ~= 200 then
   return
 end
 
--- Check that build_tgt is empty
+-- Check that build_tgt is empty, or allow resuming a partial promote.
+-- A partial target (files present but no .final_status) is resumed by skipping
+-- already-copied objects.  A fully promoted target (.final_status present) is
+-- rejected immediately.
 --
 ngx.say("Checking if the target reference '" .. build_tgt .. "' is empty")
 ngx.flush(true)
+local target_files = {}
 url = "/force_real_request/download/" .. build_tgt .. "/?format=txt"
 res = ngx.location.capture(url)
 if res.body == "" and res.truncated == false then
   ngx.say('DONE')
   ngx.flush(true)
 else
-  ngx.say('FAILED')
+  local fs_res = ngx.location.capture(
+    "/force_real_request/download/" .. build_tgt .. "/.final_status"
+  )
+  if fs_res.status == 200 then
+    ngx.say('FAILED: target already fully promoted')
+    ngx.flush(true)
+    return
+  end
+  local already_copied = 0
+  for file in res.body:gmatch("([^\r\n]+)[\r\n]+") do
+    target_files[file] = true
+    already_copied = already_copied + 1
+  end
+  ngx.say('Target not empty (' .. already_copied .. ' file(s)), resuming partial promote')
   ngx.flush(true)
-  return
 end
 
 -- Add a reference to the original build, if needed.
@@ -179,6 +195,19 @@ local function multipart_copy(object, file_size_hint)
   return true
 end
 
+-- When resuming a partial promote, skip objects already present in the target.
+if next(target_files) ~= nil then
+  local remaining = {}
+  for _, obj in ipairs(objects) do
+    if not target_files[obj] then
+      table.insert(remaining, obj)
+    end
+  end
+  ngx.say(#objects - #remaining .. ' file(s) already in target, copying ' .. #remaining .. ' remaining')
+  ngx.flush(true)
+  objects = remaining
+end
+
 local total_number_of_objects = #objects
 local batch_size = 16
 local current_object = 0

tests/end2end/test_copy.py

@@ -53,13 +53,13 @@ def test_copy_source_and_target_listings_are_identical(
 def test_copy_fails_when_target_already_exists(
     session, artifacts_url, upload_file, finish_build
 ):
-    """A second copy to the same target is rejected with FAILED."""
+    """A second copy to a fully-promoted target is rejected."""
     upload_file(STAGING_BUILD, 'file.txt', b'data')
     finish_build(STAGING_BUILD)
 
     session.get(f'{artifacts_url}/copy/{STAGING_BUILD}/{COPY_BUILD}/')
 
-    # Second attempt — target is not empty
+    # Second attempt — target is fully promoted (has .final_status)
     resp = session.get(f'{artifacts_url}/copy/{STAGING_BUILD}/{COPY_BUILD}/')
     assert resp.status_code == 200
     lines = resp.content.splitlines()
@@ -68,7 +68,7 @@ def test_copy_fails_when_target_already_exists(
         % COPY_BUILD.encode()
     )
     assert lines[-2] == expected_check_line
-    assert lines[-1] == b'FAILED'
+    assert lines[-1] == b'FAILED: target already fully promoted'
 
 
 def test_copy_promotes_staging_to_promoted_bucket(
@@ -121,6 +121,57 @@ def test_copy_via_multipart_copy(
     assert dl.content == content
 
 
+def test_resume_partial_promote(
+    session, artifacts_url, upload_file, finish_build
+):
+    """Promote succeeds when the target already has some but not all files.
+
+    Simulates a previous promote that was interrupted: a subset of files has
+    been uploaded to the target directly (no .final_status).  Re-running the
+    promote should copy only the missing files and complete successfully.
+    """
+    n = 5
+    for i in range(n):
+        upload_file(STAGING_BUILD, f'obj-{i}', f'content-{i}'.encode())
+    finish_build(STAGING_BUILD)
+
+    # Pre-populate the target with the first two objects (partial state).
+    upload_file(COPY_BUILD, 'obj-0', b'content-0')
+    upload_file(COPY_BUILD, 'obj-1', b'content-1')
+
+    resp = session.get(f'{artifacts_url}/copy/{STAGING_BUILD}/{COPY_BUILD}/')
+    assert resp.status_code == 200
+    assert resp.content.splitlines()[-1] == b'BUILD COPIED'
+
+    # All source objects must be present in the target.
+    for i in range(n):
+        dl = session.get(f'{artifacts_url}/download/{COPY_BUILD}/obj-{i}')
+        assert dl.status_code == 200, f'obj-{i} missing from resumed target'
+        assert dl.content == f'content-{i}'.encode()
+
+    assert session.get(f'{artifacts_url}/download/{COPY_BUILD}/.final_status').status_code == 200
+
+
+def test_resume_already_complete_promote(
+    session, artifacts_url, upload_file, finish_build
+):
+    """Resuming a fully-promoted target is rejected with a clear error.
+
+    A target that already has a .final_status is considered complete; a second
+    promote attempt must fail rather than silently overwriting it.
+    """
+    upload_file(STAGING_BUILD, 'file.txt', b'data')
+    finish_build(STAGING_BUILD)
+
+    # First promote — completes successfully.
+    session.get(f'{artifacts_url}/copy/{STAGING_BUILD}/{COPY_BUILD}/')
+
+    # Second attempt — target is fully promoted.
+    resp = session.get(f'{artifacts_url}/copy/{STAGING_BUILD}/{COPY_BUILD}/')
+    assert resp.status_code == 200
+    assert resp.content.splitlines()[-1] == b'FAILED: target already fully promoted'
+
+
 def test_copy_behind_ingress(session, artifacts_url, upload_file, finish_build):
     """Copy works correctly when a Script-Name ingress header is present."""
     upload_file(STAGING_BUILD, '.final_status', b'SUCCESSFUL',)