gpconfig: properly escape newlines when setting gucs

If we don't do this, the postgresql.conf file can easily be corrupted.
Co-authored-by: NJacob Champion <pchampion@pivotal.io>

gpMgmt/bin/gpconfig

@@ -375,8 +375,10 @@ def do_change(options):
 # the quote_literal() function in Postgres.
 def quote_string(guc, value):
     if value is not None and guc and guc.vartype == "string":
-        # Escape single quotes and backslashes
-        value = value.replace("'", "''").replace("\\", "\\\\")
+        # Escape single quotes, backslashes, and newlines
+        value = value.replace("'", "''") \
+                     .replace("\\", "\\\\") \
+                     .replace("\n", "\\n")
         # Single-quote the whole string
         value = "'" + value + "'"
     return value

gpMgmt/bin/gppylib/test/unit/test_unit_gpconfig.py

@@ -516,6 +516,12 @@ class GpConfig(GpTestCase):
         result = self.subject.quote_string(self.guc, value)
         self.assertEqual(result, expected)
 
+    def test_quote_string_with_newline(self):
+        value = "test\nstring"
+        expected = "'test\\nstring'"
+        result = self.subject.quote_string(self.guc, value)
+        self.assertEqual(result, expected)
+
     def setup_for_testing_quoting_string_values(self, vartype, value, additional_args=None):
         sys.argv = ["gpconfig", "--change", "my_property_name", "--value", value]
         if additional_args:

gpMgmt/test/behave/mgmt_utils/gpconfig.feature

@@ -118,6 +118,34 @@ Feature: gpconfig integration tests
         | application_name             |  string  | xxxxxx     | 'bod hi' | 'bod hi'   | bod hi     |
         | application_name             |  string  | xxxxxx     | ''       | ''         |            |
 
+    @concourse_cluster
+    @demo_cluster
+    Scenario: write a newline using gpconfig
+      Given the user runs "gpstop -u"
+        And gpstop should return a return code of 0
+        And the gpconfig context is setup
+        # we do this to make sure all segment files contain this <guc>, both in file and live
+        # todo: we should instead use a custom guc here once we fix the bug that prevents us from setting custom gucs
+        And the user runs "gpconfig -c default_text_search_config -v xxxxxx"
+        And gpconfig should return a return code of 0
+        And the user runs "gpstop -u"
+        And gpstop should return a return code of 0
+
+       When the user runs "gpconfig -c default_text_search_config -v $'a\nb'"
+       Then verify that the last line of the file "postgresql.conf" in the master data directory contains the string "default_text_search_config='a\nb'" escaped
+
+       # now make sure the last changes took full effect as seen by gpconfig
+       When the user runs "gpconfig -s default_text_search_config --file"
+       Then gpconfig should return a return code of 0
+        And gpconfig should print "Master  value: 'a\nb'" escaped to stdout
+
+       When the user runs "gpstop -u"
+       Then gpstop should return a return code of 0
+
+       When the user runs "gpconfig -s default_text_search_config"
+       Then gpconfig should return a return code of 0
+        And gpconfig should print "Master  value: a\nb" to stdout
+
     @concourse_cluster
     @demo_cluster
     Scenario Outline: gpconfig basic removal for type: <type>