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Re: [Qemu-devel] [PULL 12/25] tests: Clean up string interpolation into

From: Eric Blake
Subject: Re: [Qemu-devel] [PULL 12/25] tests: Clean up string interpolation into QMP input (simple cases)
Date: Fri, 24 Aug 2018 17:41:40 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 08/16/2018 03:36 AM, Markus Armbruster wrote:
When you build QMP input manually like this

     cmd = g_strdup_printf("{ 'execute': 'migrate',"
                           "'arguments': { 'uri': '%s' } }",
     rsp = qmp(cmd);

you're responsible for escaping the interpolated values for JSON.  Not
done here, and therefore works only for sufficiently nice @uri.  For
instance, if @uri contained a single "'", qobject_from_vjsonf_nofail()
would abort.  A sufficiently nasty @uri could even inject unwanted
members into the arguments object.

Leaving interpolation into JSON to qmp() is more robust:

     rsp = qmp("{ 'execute': 'migrate', 'arguments': { 'uri': %s } }", uri);

It's also more concise.

Clean up the simple cases where we interpolate exactly a JSON value.

Bonus: gets rid of non-literal format strings.  A step towards
compile-time format string checking without triggering

+++ b/tests/test-qga.c

@@ -446,10 +443,10 @@ static void test_qga_file_ops(gconstpointer fix)
enc = g_base64_encode(helloworld, sizeof(helloworld));
      /* write */
-    cmd = g_strdup_printf("{'execute': 'guest-file-write',"
-                          " 'arguments': { 'handle': %" PRId64 ","
-                          " 'buf-b64': '%s' } }", id, enc);
-    ret = qmp_fd(fixture->fd, cmd);
+    ret = qmp_fd(fixture->fd,
+                 "{'execute': 'guest-file-write',"
+                 " 'arguments': { 'handle': %" PRId64 ", 'buf-b64': %s } }",
+                 id, enc);

This is a temporary regression of commit 1792d7d0, which affects test execution on Mac (with its weird %qd expansion for PRId64). Fortunately, you later fix it in commit 41, so I won't be upset if the pull request goes through without a v2 that avoids 'git bisect' breaking on Mac.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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