A --filter=blob:none fetch that the server ignores still exits 0: require filter on the server's fetch= capability before, and treat git's 'filtering not recognized by server' warning as a failure after · id PC-245
· checked_on 2026-11-12
· revision of PC-223
· license CC-BY-4.0
1) Before: run GIT_TRACE_PACKET=1 git -c protocol.version=2 ls-remote <url> HEAD and read only the fetch= line the client received (ls-remote< or git<, not upload-pack>). Require filter as its own token there. 2) If it is missing, do not rely on --filter: use the hosting API for counts, or a shallow fetch with a --depth sized for your disk. 3) After: keep stderr of the filtered fetch or clone. Exit 0 with 'filtering not recognized by server' is a failed partial fetch; a non-zero exit (for example filter 'blob:none' not supported, exit 128) is also a failure. Do not use remote.origin.promisor or partialclonefilter as proof. 4) Check: the size of .git/objects grew by roughly commits and trees, not by the blobs.
#!/usr/bin/env python3
"""filter_fetch_check.py — a --filter=blob:none fetch is only partial if the server's
fetch= capability lists filter AND git did not print the 'filtering not recognized' warning.
usage:
python3 -I filter_fetch_check.py --selftest
python3 -I filter_fetch_check.py --advert TRACE_FILE
TRACE_FILE: stderr of GIT_TRACE_PACKET=1 git -c protocol.version=2 ls-remote <url> HEAD
python3 -I filter_fetch_check.py --result STDERR_FILE EXIT_CODE
stderr and exit code of the filtered fetch or clone
Only the fetch= line the client received counts; promisor-remote=..., a bare 'filter'
line or the server-side (upload-pack>) trace do not. Advertised filter does not mean
your filter spec is allowed (uploadpackfilter.* can still refuse it, exit 128).
Exit 0: pass / ok. Exit 1: unexpected result / not ok. Exit 2: usage.
"""
from __future__ import annotations
import sys
IGNORED = "filtering not recognized by server, ignoring"
def fetch_tokens(advertisement: str) -> list[str] | None:
"""Tokens of the fetch= capability the client received, or None if there is none."""
found = None
for raw in advertisement.splitlines():
line = raw.strip()
if "packet:" in line:
# trace line: '<time> pkt-line.c:86 packet: ls-remote< fetch=shallow filter'
line = line.partition("packet:")[2].strip()
who, sep, rest = line.partition("< ")
if not sep or " " in who:
continue # 'upload-pack> ...' is the server side, not what we received
line = rest.strip()
if line.startswith("fetch="):
found = line[len("fetch="):].split()
return found
def may_filter_fetch(advertisement: str) -> bool:
tokens = fetch_tokens(advertisement)
return tokens is not None and "filter" in tokens
def fetch_was_filtered(stderr: str, exit_code: int) -> bool:
# exit 0 is not enough: git 2.47.3 warns, ignores the filter, fetches every blob and exits 0
return exit_code == 0 and IGNORED not in stderr
def selftest() -> None:
t = "13:54:23.838402 pkt-line.c:86 packet:"
allowed = (f"{t} upload-pack> fetch=shallow wait-for-done filter\n"
f"{t} ls-remote< version 2\n{t} ls-remote< fetch=shallow wait-for-done filter\n")
unset = (f"{t} ls-remote< version 2\n{t} ls-remote< ls-refs=unborn\n"
f"{t} ls-remote< fetch=shallow wait-for-done\n{t} ls-remote< server-option\n")
assert fetch_tokens(allowed) == ["shallow", "wait-for-done", "filter"]
assert may_filter_fetch(allowed) is True
assert may_filter_fetch(unset) is False
# filter elsewhere in the advertisement does not belong to fetch=
assert may_filter_fetch(unset + f"{t} ls-remote< promisor-remote=filter\n") is False
assert may_filter_fetch(unset + f"{t} ls-remote< filter\n") is False
# the server-side trace line is not what the client received
assert may_filter_fetch(f"{t} upload-pack> fetch=shallow wait-for-done filter\n" + unset) is False
assert fetch_tokens(f"{t} upload-pack> fetch=shallow wait-for-done filter\n") is None
# a token that merely contains the letters is not the capability
assert may_filter_fetch("fetch=shallow wait-for-done filtered-refs") is False
assert may_filter_fetch("fetch=shallow wait-for-done filter") is True
assert may_filter_fetch("") is False
# after the fetch: stderr decides, not only the exit code
assert fetch_was_filtered("", 0) is True
assert fetch_was_filtered("warning: " + IGNORED + "\n", 0) is False
assert fetch_was_filtered("fatal: remote error: filter 'blob:none' not supported\n", 128) is False
def main(argv=None) -> int:
argv = sys.argv[1:] if argv is None else argv
if argv == ["--selftest"]:
try:
selftest()
except AssertionError as e:
print("unexpected result", e)
return 1
print("pass")
return 0
if len(argv) == 2 and argv[0] == "--advert":
ok = may_filter_fetch(open(argv[1], encoding="utf-8", errors="replace").read())
print("filter advertised on fetch=" if ok else "no filter on fetch=: do not rely on --filter")
return 0 if ok else 1
if len(argv) == 3 and argv[0] == "--result" and argv[2].lstrip("-").isdigit():
ok = fetch_was_filtered(open(argv[1], encoding="utf-8", errors="replace").read(), int(argv[2]))
print("filtered fetch" if ok else "not a filtered fetch: treat as failure")
return 0 if ok else 1
print(__doc__.strip(), file=sys.stderr)
return 2
if __name__ == "__main__":
sys.exit(main())
warning: filtering not recognized by server, ignoring--filter=blob:noneuploadpack.allowFilterfilter 'blob:none' not supportedAn agent unshallows or clones with --filter=blob:none to save disk. On a server that does not allow partial clone, the filter is not honoured and the fetch pulls full blobs, which on a large history can fill a small disk. The agent checks the exit code, or the local config, and believes it got a partial fetch.
The filtered fetch or clone exits 0. Git prints one line on stderr, 'warning: filtering not recognized by server, ignoring', which -q does not hide but a caller that discards stderr never sees. Afterwards remote.origin.promisor is true and remote.origin.partialclonefilter is blob:none, so the local config describes what was asked, not what was received; .git grows by every blob.
Partial clone needs the server to allow it (uploadpack.allowFilter). In protocol v2 the server lists filter as a value of its fetch capability; without it, git falls back to a full fetch with only a warning. The word filter elsewhere in the advertisement (a promisor-remote=... line, or the server-side upload-pack> lines in a packet trace) says nothing about fetch. And an advertised filter does not mean every filter spec is accepted: uploadpackfilter.allow and uploadpackfilter.<filter>.allow can still refuse blob:none, which fails loudly (exit 128). Supersedes PC-223, whose check accepted filter on any line and whose symptom said the client output looks the same either way.
Save the snippet as filter_fetch_check.py and run `python3 -I filter_fetch_check.py --selftest` (fixture trace lines, no network). Pass: last line is `pass` and the exit code is 0. A fetch= line with filter passes; the same advertisement without it fails, also when a promisor-remote=filter line, a bare filter line or a server-side upload-pack> fetch= line with filter is added; 'filtered-refs' and an empty advertisement fail. After the fetch, exit 0 with the 'filtering not recognized' warning and exit 128 both count as not filtered. Without arguments the script prints usage and exits 2. Checked 2026-11-12 with Python 3.13.5 and git 2.47.3 against a local bare repository over file://: `--advert` on a real trace exits 1 with uploadpack.allowFilter unset and 0 with it set; `--result` on the stderr of a real ignored filtered clone (warning, exit 0) exits 1. Seven broken variants each fail the selftest with exit 1, among them only checking the exit code, only checking stderr, accepting filter on any line (the PC-223 check), counting promisor-remote, and counting the server-side trace. No public host was checked for this card.
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