[PATCHv2] lib/oe/gpg_sign.py: Avoid race when creating .sig files in detach_sign

[Peter Kjellerstedt <pkj@axis.com>]

From: Tobias Hagelborn <tobias.hagelborn@axis.com>

Move the signature file into place only after it is successfully signed.
This to avoid race and corrupted .sig files in cases multiple onging
builds write to a shared sstate-cache dir.

Signed-off-by: Tobias Hagelborn <tobiasha@axis.com>
Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
---

PATCHv2: Use '.asc' as default suffix for the output file if the
         --armor option is used.

 meta/lib/oe/gpg_sign.py | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/meta/lib/oe/gpg_sign.py b/meta/lib/oe/gpg_sign.py
index 613dab8561..ede6186c84 100644
--- a/meta/lib/oe/gpg_sign.py
+++ b/meta/lib/oe/gpg_sign.py
@@ -5,11 +5,12 @@
 #
 
 """Helper module for GPG signing"""
-import os
 
 import bb
-import subprocess
+import os
 import shlex
+import subprocess
+import tempfile
 
 class LocalSigner(object):
     """Class for handling local (on the build host) signing"""
@@ -73,8 +74,6 @@ class LocalSigner(object):
             cmd += ['--homedir', self.gpg_path]
         if armor:
             cmd += ['--armor']
-        if output_suffix:
-            cmd += ['-o', input_file + "." + output_suffix]
         if use_sha256:
             cmd += ['--digest-algo', "SHA256"]
 
@@ -83,19 +82,27 @@ class LocalSigner(object):
         if self.gpg_version > (2,1,):
             cmd += ['--pinentry-mode', 'loopback']
 
-        cmd += [input_file]
-
         try:
             if passphrase_file:
                 with open(passphrase_file) as fobj:
                     passphrase = fobj.readline();
 
-            job = subprocess.Popen(cmd, stdin=subprocess.PIPE, stderr=subprocess.PIPE)
-            (_, stderr) = job.communicate(passphrase.encode("utf-8"))
+            if not output_suffix:
+                output_suffix = 'asc' if armor else 'sig'
+            output_file = input_file + "." + output_suffix
+            with tempfile.TemporaryDirectory(dir=os.path.dirname(output_file)) as tmp_dir:
+                tmp_file = os.path.join(tmp_dir, os.path.basename(output_file))
+                cmd += ['-o', tmp_file]
+
+                cmd += [input_file]
+
+                job = subprocess.Popen(cmd, stdin=subprocess.PIPE, stderr=subprocess.PIPE)
+                (_, stderr) = job.communicate(passphrase.encode("utf-8"))
 
-            if job.returncode:
-                bb.fatal("GPG exited with code %d: %s" % (job.returncode, stderr.decode("utf-8")))
+                if job.returncode:
+                    bb.fatal("GPG exited with code %d: %s" % (job.returncode, stderr.decode("utf-8")))
 
+                os.rename(tmp_file, output_file)
         except IOError as e:
             bb.error("IO error (%s): %s" % (e.errno, e.strerror))
             raise Exception("Failed to sign '%s'" % input_file)