[PATCH v2 2/9] svn-fe: avoid error on no-op imports in remote-svn-alpha

[Dmitry Ivankov <divanorama@gmail.com>]

Currently helpers' exit codes are not checked by transport_helper.
But a proper helper should check for all possible internal errors
anyway. svnrdump dump --incremental considers -rX:HEAD range as bad
if X is greater than the actual HEAD revision. And there is no option
to change this behavior.

One way to address this issue is to fire one more svn command to get
the HEAD value, but it is one more connection, one more tool (ok,
we can svnrdump HEAD but it looks slow) and possibly one more
password prompt, and maybe even a race condition (if we talk to a
svn servers farm frontend for example).

Another one is to patch svnrdump to report the revision, because
internally it asks svn for it anyway before doing a dump. Longer
term it looks nice, moreover it can be used to display percentage
progress.

Add a wrapper around svnrdump that captures stderr and exit code.
If stderr matches a hardcoded "LOWER cannot be greater than UPPER."
and the exit code is non-zero, don't produce any dump and emulate
exit 0, otherwise the wrapper is transparent. The only side effect
is dup2-ing stdout to fd=6, ugly but fine as only standard
descriptors are used currently.

Signed-off-by: Dmitry Ivankov <divanorama@gmail.com>
---
 contrib/svn-fe/git-remote-svn-alpha |   19 +++++++++++++++++--
 1 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/contrib/svn-fe/git-remote-svn-alpha b/contrib/svn-fe/git-remote-svn-alpha
index 61c9b07..2eac7d4 100755
--- a/contrib/svn-fe/git-remote-svn-alpha
+++ b/contrib/svn-fe/git-remote-svn-alpha
@@ -12,10 +12,25 @@ usage () {
 	exit 129
 }
 
+svnrdump_wrap () {
+	exec 6<&1 &&
+
+	EX=$(
+		(svnrdump dump --non-interactive --username=Guest --password= \
+			--quiet "$1" "$2" >&6) 2>&1; test $? -ne 0 || echo Success
+	) &&
+	if test "z$EX" != "zSuccess"; then
+		if test "z$EX" = "zLOWER cannot be greater than UPPER."; then
+			return 0
+		fi
+		echo "$EX" >&2
+		return 1
+	fi
+}
+
 do_import () {
 	revs=$1 url=$2
-	(svnrdump dump --non-interactive --username=Guest --password= \
-		-r"$revs" "$url" --quiet | svn-fe) 3<&0 || die "FAILURE"
+	(svnrdump_wrap "$url" -r"$revs" | svn-fe) 3<&0 || die "FAILURE"
 	exec 1>&-
 }
 
-- 
1.7.3.4