From 5bfaa4a6f355a6820fe16c1aea77a01ba7b97eaa Mon Sep 17 00:00:00 2001
From: Jonathan Rosser <jonathan.rosser@rd.bbc.co.uk>
Date: Tue, 4 Jan 2022 17:42:03 +0000
Subject: [PATCH] Force use of scp rather than sftp when possible

OpenSSH has deprecated its use of scp/rcp protocol in favor of SFTP,
which the embedded Apache mina-sshd in widely-deployed Gerrit
versions does not yet support. The default officially changed in
OpenSSH 9.0 (some distributions, such as Fedora and CentOS, switched
their default behavior to this as early as OpenSSH 8.7 or 8.8),
leading to a ``subsystem request failed on channel 0`` error during
commit-msg hook retrieval. Now git-review will attempt to detect
whether scp's -O option is available to force use of the legacy
scp/rcp protocol, and apply it if so.

Change-Id: Ib64c03c3e12a3a8390e38f6ca9393db3b3c2a9e3
---
 git_review/cmd.py                                 |  8 ++++++++
 .../notes/scp-subsystem-c8d78aa8f7f69f66.yaml     | 15 +++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 releasenotes/notes/scp-subsystem-c8d78aa8f7f69f66.yaml

diff --git a/git_review/cmd.py b/git_review/cmd.py
index 9215b5d1..566bf224 100644
--- a/git_review/cmd.py
+++ b/git_review/cmd.py
@@ -373,9 +373,17 @@ def set_hooks_commit_msg(remote, target_file):
                 userhost = hostname
             # OS independent target file
             scp_target_file = target_file.replace(os.sep, "/")
+
+            # Get scp options
+            scp_out = run_command("scp")
+            scp_opts = scp_out[scp_out.index("[") + 2:scp_out.index("]")]
+
             cmd = ["scp", userhost + ":hooks/commit-msg", scp_target_file]
             if port is not None:
                 cmd.insert(1, "-P%s" % port)
+            # Force scp protocol if the -O option is available
+            if "O" in scp_opts:
+                cmd.insert(1, "-O")
 
             if VERBOSE:
                 hook_url = 'scp://%s%s/hooks/commit-msg' \
diff --git a/releasenotes/notes/scp-subsystem-c8d78aa8f7f69f66.yaml b/releasenotes/notes/scp-subsystem-c8d78aa8f7f69f66.yaml
new file mode 100644
index 00000000..15214450
--- /dev/null
+++ b/releasenotes/notes/scp-subsystem-c8d78aa8f7f69f66.yaml
@@ -0,0 +1,15 @@
+---
+fixes:
+  - |
+    OpenSSH has deprecated its use of scp/rcp protocol in favor of
+    SFTP, which the embedded Apache mina-sshd in widely-deployed
+    Gerrit versions does not yet support. The default officially
+    changed in OpenSSH 9.0 (some distributions, such as Fedora and
+    CentOS, switched their default behavior to this as early as
+    OpenSSH 8.7 or 8.8), leading to a ``subsystem request failed on
+    channel 0`` error during commit-msg hook retrieval. Now
+    git-review will attempt to detect whether scp's -O option is
+    available to force use of the legacy scp/rcp protocol, and apply
+    it if so. Future git-review versions may change the fallback
+    behavior once an SFTP subsystem is implemented and available for
+    a new Gerrit release.