postgrespro
diff --git a/‎doc/src/sgml/release-9.4.sgml
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diff --git a/‎src/backend/utils/adt/json.c
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diff --git a/‎src/test/regress/expected/json.out
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diff --git a/‎src/test/regress/expected/json_1.out
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diff --git a/‎src/test/regress/expected/jsonb.out
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diff --git a/‎src/test/regress/expected/jsonb_1.out
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diff --git a/‎src/test/regress/sql/json.sql
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@@ -180,6 +180,21 @@
      </para>
     </listitem>
 
+    <listitem>
+     <para>
+      Unicode escapes in <link linkend="datatype-json"><type>JSON</type></link>
+      text values are no longer rendered with the backslash escaped.
+      (Andrew Dunstan)
+     </para>
+
+     <para>
+      Previously all backslashes in text values being formed into JSON were
+      escaped. Now a backslash followed by "u" and four hexadecimal digits is
+      not escaped, as this is a legal sequence in a JSON string value, and
+      escaping the backslash led to some perverse results.
+     </para>
+    </listitem>
+
     <listitem>
      <para>
       Rename <link linkend="SQL-EXPLAIN"><command>EXPLAIN
 
@@ -2315,7 +2315,26 @@ escape_json(StringInfo buf, const char *str)
 				appendStringInfoString(buf, "\\\"");
 				break;
 			case '\\':
-				appendStringInfoString(buf, "\\\\");
+				/*
+				 * Unicode escapes are passed through as is. There is no
+				 * requirement that they denote a valid character in the
+				 * server encoding - indeed that is a big part of their
+				 * usefulness.
+				 *
+				 * All we require is that they consist of \uXXXX where
+				 * the Xs are hexadecimal digits. It is the responsibility
+				 * of the caller of, say, to_json() to make sure that the
+				 * unicode escape is valid.
+				 *
+				 * In the case of a jsonb string value being escaped, the
+				 * only unicode escape that should be present is \u0000,
+				 * all the other unicode escapes will have been resolved.
+				 */
+				if (p[1] == 'u' && isxdigit(p[2]) && isxdigit(p[3])
+					&& isxdigit(p[4]) && isxdigit(p[5]))
+					appendStringInfoCharMacro(buf, *p);
+				else
+					appendStringInfoString(buf, "\\\\");
 				break;
 			default:
 				if ((unsigned char) *p < ' ')
 
@@ -426,6 +426,20 @@ select to_json(timestamptz '2014-05-28 12:22:35.614298-04');
 (1 row)
 
 COMMIT;
+-- unicode escape - backslash is not escaped
+select to_json(text '\uabcd');
+ to_json  
+----------
+ "\uabcd"
+(1 row)
+
+-- any other backslash is escaped
+select to_json(text '\abcd');
+ to_json  
+----------
+ "\\abcd"
+(1 row)
+
 --json_agg
 SELECT json_agg(q)
   FROM ( SELECT $$a$$ || x AS b, y AS c,
 
@@ -426,6 +426,20 @@ select to_json(timestamptz '2014-05-28 12:22:35.614298-04');
 (1 row)
 
 COMMIT;
+-- unicode escape - backslash is not escaped
+select to_json(text '\uabcd');
+ to_json  
+----------
+ "\uabcd"
+(1 row)
+
+-- any other backslash is escaped
+select to_json(text '\abcd');
+ to_json  
+----------
+ "\\abcd"
+(1 row)
+
 --json_agg
 SELECT json_agg(q)
   FROM ( SELECT $$a$$ || x AS b, y AS c,
 
@@ -61,9 +61,9 @@ LINE 1: SELECT '"\u000g"'::jsonb;
 DETAIL:  "\u" must be followed by four hexadecimal digits.
 CONTEXT:  JSON data, line 1: "\u000g...
 SELECT '"\u0000"'::jsonb;		-- OK, legal escape
-   jsonb   
------------
- "\\u0000"
+  jsonb   
+----------
+ "\u0000"
 (1 row)
 
 -- use octet_length here so we don't get an odd unicode char in the
 
@@ -61,9 +61,9 @@ LINE 1: SELECT '"\u000g"'::jsonb;
 DETAIL:  "\u" must be followed by four hexadecimal digits.
 CONTEXT:  JSON data, line 1: "\u000g...
 SELECT '"\u0000"'::jsonb;		-- OK, legal escape
-   jsonb   
------------
- "\\u0000"
+  jsonb   
+----------
+ "\u0000"
 (1 row)
 
 -- use octet_length here so we don't get an odd unicode char in the
 
@@ -111,6 +111,14 @@ SET LOCAL TIME ZONE -8;
 select to_json(timestamptz '2014-05-28 12:22:35.614298-04');
 COMMIT;
 
+-- unicode escape - backslash is not escaped
+
+select to_json(text '\uabcd');
+
+-- any other backslash is escaped
+
+select to_json(text '\abcd');
+
 --json_agg
 
 SELECT json_agg(q)