[PATCH for 7.4.0] conf: Avoid double indentation of <metadata/> element

[Michal Privoznik]

There was a recent change in libxml2 that caused a trouble for
us. To us, <metadata/> in domain or network XMLs are just opaque
value where management application can store whatever data it
finds fit. At XML parser/formatter level, we just make a copy of
the element during parsing and then format it back. For
formatting we use xmlNodeDump() which allows caller to specify
level of indentation. Previously, the indentation was not
applied onto the very first line, but as of v2.9.12-2-g85b1792e
libxml2 is applying indentation also on the first line.

This does not work well with out virBuffer because as soon as we
call virBufferAsprintf() to append <metadata/> element,
virBufferAsprintf() will apply another level of indentation.

Instead of version checking, let's skip any indentation added by
libxml2 before virBufferAsprintf() is called.

Note, the problem is only when telling xmlNodeDump() to use
indentation, i.e. level argument is not zero. Therefore,
virXMLNodeToString() which also calls xmlNodeDump() is safe as it
passes zero.

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---

I've raised this issue with libxml2 team:

https://gitlab.gnome.org/GNOME/libxml2/-/commit/85b1792e37b131e7a51af98a37f92472e8de5f3f

but I'm not sure it'll be fixed. Unfortunately, the patch that's causing
us trouble is being backported all over the place, because it's
supposedly fixing a regression.

 src/conf/domain_conf.c  | 9 ++++++++-
 src/conf/network_conf.c | 9 ++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 4f78b7b43d..84a8c269be 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -27808,6 +27808,7 @@ virDomainDefFormatInternalSetRootName(virDomainDef *def,
 
     if (def->metadata) {
         g_autoptr(xmlBuffer) xmlbuf = NULL;
+        const char *xmlbufContent = NULL;
         int oldIndentTreeOutput = xmlIndentTreeOutput;
 
         /* Indentation on output requires that we previously set
@@ -27824,7 +27825,13 @@ virDomainDefFormatInternalSetRootName(virDomainDef *def,
             xmlIndentTreeOutput = oldIndentTreeOutput;
             return -1;
         }
-        virBufferAsprintf(buf, "%s\n", (char *) xmlBufferContent(xmlbuf));
+
+        /* After libxml2-v2.9.12-2-g85b1792e even the first line is indented.
+         * But virBufferAsprintf() also adds indentation. Skip one of them. */
+        xmlbufContent = (const char *) xmlBufferContent(xmlbuf);
+        virSkipSpaces(&xmlbufContent);
+
+        virBufferAsprintf(buf, "%s\n", xmlbufContent);
         xmlIndentTreeOutput = oldIndentTreeOutput;
     }
 
diff --git a/src/conf/network_conf.c b/src/conf/network_conf.c
index a9eadff29c..20c6dc091a 100644
--- a/src/conf/network_conf.c
+++ b/src/conf/network_conf.c
@@ -2488,6 +2488,7 @@ virNetworkDefFormatBuf(virBuffer *buf,
 
     if (def->metadata) {
         g_autoptr(xmlBuffer) xmlbuf = NULL;
+        const char *xmlbufContent = NULL;
         int oldIndentTreeOutput = xmlIndentTreeOutput;
 
         /* Indentation on output requires that we previously set
@@ -2504,7 +2505,13 @@ virNetworkDefFormatBuf(virBuffer *buf,
             xmlIndentTreeOutput = oldIndentTreeOutput;
             return -1;
         }
-        virBufferAsprintf(buf, "%s\n", (char *) xmlBufferContent(xmlbuf));
+
+        /* After libxml2-v2.9.12-2-g85b1792e even the first line is indented.
+         * But virBufferAsprintf() also adds indentation. Skip one of them. */
+        xmlbufContent = (const char *) xmlBufferContent(xmlbuf);
+        virSkipSpaces(&xmlbufContent);
+
+        virBufferAsprintf(buf, "%s\n", xmlbufContent);
         xmlIndentTreeOutput = oldIndentTreeOutput;
     }
 
-- 
2.26.3