command: handle empty buffer argument correctly

virBufferContentAndReset (intentionally) returns NULL for a buffer
with no content, but it is feasible to invoke a command with an
explicit empty string.

* src/util/command.c (virCommandAddEnvBuffer): Reject empty string.
(virCommandAddArgBuffer): Allow explicit empty argument.
* tests/commandtest.c (test9): Test it.
* tests/commanddata/test9.log: Adjust.

1 files changed, 12 insertions, 1 deletions

diff --git a/tests/commandtest.c b/tests/commandtest.c
index dd6c24887..efc48fe20 100644
--- a/tests/commandtest.c
+++ b/tests/commandtest.c
@@ -352,11 +352,22 @@ static int test9(const void *unused ATTRIBUTE_UNUSED)
 {
     virCommandPtr cmd = virCommandNew(abs_builddir "/commandhelper");
     const char* const args[] = { "arg1", "arg2", NULL };
+    virBuffer buf = VIR_BUFFER_INITIALIZER;
 
     virCommandAddArg(cmd, "-version");
     virCommandAddArgPair(cmd, "-log", "bar.log");
     virCommandAddArgSet(cmd, args);
-    virCommandAddArgList(cmd, "arg3", "arg4", NULL);
+    virCommandAddArgBuffer(cmd, &buf);
+    virBufferAddLit(&buf, "arg4");
+    virCommandAddArgBuffer(cmd, &buf);
+    virCommandAddArgList(cmd, "arg5", "arg6", NULL);
+
+    if (virBufferUse(&buf)) {
+        printf("Buffer not transferred\n");
+        virBufferFreeAndReset(&buf);
+        virCommandFree(cmd);
+        return -1;
+    }
 
     if (virCommandRun(cmd, NULL) < 0) {
         virErrorPtr err = virGetLastError();