Add xml_escape_text_append and use it

[This patch should go on top of "linux_qxfer_libraries_svr4: Use
 std::string", I should have sent them together as a series.]

I noticed that linux_qxfer_libraries_svr4 used xml_escape_text, which
returns an std::string.  That string is then copied into a larger
buffer.  It would be more efficient if we had a version of
xml_escape_text which appended to an existing string instead of
returning a new one.  This is what this patch does.

I manually verified that the output of linux_qxfer_libraries_svr4 didn't
change before/after the patch.

gdb/ChangeLog:

	* common/xml-utils.c (xml_escape_text): Move code to...
	(xml_escape_text_append): ... this new function.
	* common/xml-utils.h (xml_escape_text_append): New declaration.
	* unittests/xml-utils-selftests.c (test_xml_escape_text_append):
	New function.
	(_initialize_xml_utils): register test_xml_escape_text_append as
	a selftest.

gdb/gdbserver/ChangeLog:

	* linux-low.c (linux_qxfer_libraries_svr4): Use
	xml_escape_text_append.

1 files changed, 14 insertions, 0 deletions

diff --git a/gdb/unittests/xml-utils-selftests.c b/gdb/unittests/xml-utils-selftests.c
index 2457494..1412773 100644
--- a/gdb/unittests/xml-utils-selftests.c
+++ b/gdb/unittests/xml-utils-selftests.c
@@ -33,6 +33,18 @@ static void test_xml_escape_text ()
   SELF_CHECK (actual_output == expected_output);
 }
 
+static void test_xml_escape_text_append ()
+{
+  /* Make sure that we do indeed append.  */
+  std::string actual_output = "foo<xml>";
+  const char *input = "<this isn't=\"xml\"> &";
+  const char *expected_output
+    = "foo<xml>&lt;this isn&apos;t=&quot;xml&quot;&gt; &amp;";
+  xml_escape_text_append (&actual_output, input);
+
+  SELF_CHECK (actual_output == expected_output);
+}
+
 }
 }
 
@@ -41,4 +53,6 @@ _initialize_xml_utils ()
 {
   selftests::register_test ("xml_escape_text",
 			    selftests::xml_utils::test_xml_escape_text);
+  selftests::register_test ("xml_escape_text_append",
+			    selftests::xml_utils::test_xml_escape_text_append);
 }