4 files changed, 345 insertions, 160 deletions
diff --git a/expected/json_path.out b/expected/json_path.out
index a77497c..22c0f10 100644
--- a/expected/json_path.out
+++ b/expected/json_path.out
@@ -301,83 +301,197 @@ $$);
  $..["\"hello\"\\\"world\""][5]..[3][*][*]
 (1 row)
 
-SELECT json_path($$"⁰¹\u0000³"$$, '[0]');
+select parse_json_path('$char');
+ parse_json_path 
+-----------------
+ 
+(1 row)
+
+select parse_json_path('$.char');
+ parse_json_path 
+-----------------
+ $["char"]
+(1 row)
+
+select parse_json_path('$.char()');
+ parse_json_path 
+-----------------
+ 
+(1 row)
+
+select parse_json_path('$.char(5)');
+ parse_json_path 
+-----------------
+ $.char(5)
+(1 row)
+
+select parse_json_path('$.char(  -1  )');
+ parse_json_path 
+-----------------
+ $.char(-1)
+(1 row)
+
+select parse_json_path('$.char(  -1  )  . char(0)');
+  parse_json_path   
+--------------------
+ $.char(-1).char(0)
+(1 row)
+
+select parse_json_path('$.char(  -1  )  . char  ( 0 )  ');
+  parse_json_path   
+--------------------
+ $.char(-1).char(0)
+(1 row)
+
+select parse_json_path('$.char(  +1  )  . char  ( 0 )  ');
+  parse_json_path  
+-------------------
+ $.char(1).char(0)
+(1 row)
+
+select parse_json_path('$ . char(  +1  )  . char  ( 0 )  ');
+  parse_json_path  
+-------------------
+ $.char(1).char(0)
+(1 row)
+
+select parse_json_path('$ .. char(  +1  )  . char  ( 0 )  ');
+  parse_json_path   
+--------------------
+ $..char(1).char(0)
+(1 row)
+
+select parse_json_path('$ .. char(  +1  )  .. char  ( 0 )  ');
+   parse_json_path   
+---------------------
+ $..char(1)..char(0)
+(1 row)
+
+select parse_json_path('$ . char(  +1  )  .. char  ( 0 )  ');
+  parse_json_path   
+--------------------
+ $.char(1)..char(0)
+(1 row)
+
+select parse_json_path('$ . char(  +1  )  char  ( 0 )  ');
+ parse_json_path 
+-----------------
+ 
+(1 row)
+
+select parse_json_path('$ char(  +1  )  char  ( 0 )  ');
+ parse_json_path 
+-----------------
+ 
+(1 row)
+
+select parse_json_path('char(  +1  )  . char  ( 0 )  ');
+  parse_json_path  
+-------------------
+ $.char(1).char(0)
+(1 row)
+
+select parse_json_path('.char(  +1  )  . char  ( 0 )  ');
+  parse_json_path  
+-------------------
+ $.char(1).char(0)
+(1 row)
+
+select parse_json_path('..char(  +1  )  . char  ( 0 )  ');
+  parse_json_path   
+--------------------
+ $..char(1).char(0)
+(1 row)
+
+select parse_json_path('...char(  +1  )  . char  ( 0 )  ');
+ parse_json_path 
+-----------------
+ 
+(1 row)
+
+select parse_json_path('[char(5)]');
+ parse_json_path 
+-----------------
+ 
+(1 row)
+
+SELECT json_path($$"⁰¹\u0000³"$$, 'char(0)');
  json_path 
 -----------
  "⁰"
 (1 row)
 
-SELECT json_path($$"⁰¹\u0000³"$$, '[1]');
+SELECT json_path($$"⁰¹\u0000³"$$, 'char(1)');
  json_path 
 -----------
  "¹"
 (1 row)
 
-SELECT json_path($$"⁰¹\u0000³"$$, '[2]');
+SELECT json_path($$"⁰¹\u0000³"$$, 'char(2)');
  json_path 
 -----------
  "\u0000"
 (1 row)
 
-SELECT json_path($$"⁰¹\u0000³"$$, '[3]');
+SELECT json_path($$"⁰¹\u0000³"$$, 'char(3)');
  json_path 
 -----------
  "³"
 (1 row)
 
-SELECT json_path('"0123"', '[-1]');
+SELECT json_path('"0123"', 'char(-1)');
  json_path 
 -----------
 (0 rows)
 
-SELECT json_path('"0123"', '[0]');
+SELECT json_path('"0123"', 'char(0)');
  json_path 
 -----------
  "0"
 (1 row)
 
-SELECT json_path('"0123"', '[1]');
+SELECT json_path('"0123"', 'char(1)');
  json_path 
 -----------
  "1"
 (1 row)
 
-SELECT json_path('"0123"', '[2]');
+SELECT json_path('"0123"', 'char(2)');
  json_path 
 -----------
  "2"
 (1 row)
 
-SELECT json_path('"0123"', '[3]');
+SELECT json_path('"0123"', 'char(3)');
  json_path 
 -----------
  "3"
 (1 row)
 
-SELECT json_path('"0123"', '[4]');
+SELECT json_path('"0123"', 'char(4)');
  json_path 
 -----------
 (0 rows)
 
-SELECT json_path('"⁰¹²³"', '[0]');
+SELECT json_path('"⁰¹²³"', 'char(0)');
  json_path 
 -----------
  "⁰"
 (1 row)
 
-SELECT json_path('"⁰¹²³"', '[1]');
+SELECT json_path('"⁰¹²³"', 'char(1)');
  json_path 
 -----------
  "¹"
 (1 row)
 
-SELECT json_path('"⁰¹²³"', '[2]');
+SELECT json_path('"⁰¹²³"', 'char(2)');
  json_path 
 -----------
  "²"
 (1 row)
 
-SELECT json_path('"⁰¹²³"', '[3]');
+SELECT json_path('"⁰¹²³"', 'char(3)');
  json_path 
 -----------
  "³"
@@ -600,26 +714,17 @@ SELECT json_path(json, 'store.toys[*]') FROM sample;
 SELECT json_path(json, 'store.toys[*][0]') FROM sample;
  json_path 
 -----------
- "Y"
- "B"
- "B"
-(3 rows)
+(0 rows)
 
 SELECT json_path(json, 'store.toys[*][1]') FROM sample;
  json_path 
 -----------
- "o"
- "o"
- "a"
-(3 rows)
+(0 rows)
 
 SELECT json_path(json, 'store.toys[*][0][0]') FROM sample;
  json_path 
 -----------
- "Y"
- "B"
- "B"
-(3 rows)
+(0 rows)
 
 SELECT json_path(json, 'store.toys[*][0][1]') FROM sample;
  json_path 
@@ -725,20 +830,11 @@ SELECT json_path(json, '..[0]') FROM sample;
                                  "author": "author 0",+
                                  "prices": [1,2,3]    +
                          }
- "b"
- "a"
  1
- "b"
- "a"
  4
- "b"
- "a"
  7
  "Yo-yo"
- "Y"
- "B"
- "B"
-(14 rows)
+(5 rows)
 
 SELECT json_path(json, '..[1]') FROM sample;
                        json_path                       
@@ -748,20 +844,11 @@ SELECT json_path(json, '..[1]') FROM sample;
                                  "author": "author 1",+
                                  "prices": [4,5,6]    +
                          }
- "o"
- "u"
  2
- "o"
- "u"
  5
- "o"
- "u"
  8
  "Boomerang"
- "o"
- "o"
- "a"
-(14 rows)
+(5 rows)
 
 SELECT json_path(json, '..[2]') FROM sample;
                        json_path                       
@@ -771,34 +858,16 @@ SELECT json_path(json, '..[2]') FROM sample;
                                  "author": "author 2",+
                                  "prices": [7,8,9]    +
                          }
- "o"
- "t"
  3
- "o"
- "t"
  6
- "o"
- "t"
  9
  "Basketball"
- "-"
- "o"
- "s"
-(14 rows)
+(5 rows)
 
 SELECT json_path(json, '..[3]') FROM sample;
  json_path 
 -----------
- "k"
- "h"
- "k"
- "h"
- "k"
- "h"
- "y"
- "m"
- "k"
-(9 rows)
+(0 rows)
 
 SELECT json_path(json, '$') FROM sample;
                        json_path                       
@@ -912,3 +981,69 @@ SELECT json_path(json, '..*') FROM sample;
  "Basketball"
 (27 rows)
 
+SELECT json_path(json, '..char(-1)') FROM sample;
+ json_path 
+-----------
+(0 rows)
+
+SELECT json_path(json, '..char(0)') FROM sample;
+ json_path 
+-----------
+ "b"
+ "a"
+ "b"
+ "a"
+ "b"
+ "a"
+ "Y"
+ "B"
+ "B"
+(9 rows)
+
+SELECT json_path(json, '..char(1)') FROM sample;
+ json_path 
+-----------
+ "o"
+ "u"
+ "o"
+ "u"
+ "o"
+ "u"
+ "o"
+ "o"
+ "a"
+(9 rows)
+
+SELECT json_path(json, '..char(2)') FROM sample;
+ json_path 
+-----------
+ "o"
+ "t"
+ "o"
+ "t"
+ "o"
+ "t"
+ "-"
+ "o"
+ "s"
+(9 rows)
+
+SELECT json_path(json, '..char(3)') FROM sample;
+ json_path 
+-----------
+ "k"
+ "h"
+ "k"
+ "h"
+ "k"
+ "h"
+ "y"
+ "m"
+ "k"
+(9 rows)
+
+SELECT json_path(json, '..char(100)') FROM sample;
+ json_path 
+-----------
+(0 rows)
+
diff --git a/jsonpath.c b/jsonpath.c
index 9d53259..b3a0b76 100644
--- a/jsonpath.c
+++ b/jsonpath.c
@@ -81,7 +81,7 @@ static jp_element *mkWildcard(bool rd)
 	return elem;
 }
 
-static jp_element *mkIndexSubscript(int index, bool rd)
+static jp_element *mkIndexSubscript(long index, bool rd)
 {
 	jp_element *elem = mkElement(JP_INDEX_SUBSCRIPT, rd);
 	elem->data.index = index;
@@ -96,6 +96,13 @@ static jp_element *mkKeySubscript(char *key, size_t length, bool rd)
 	return elem;
 }
 
+static jp_element *mkCallChar(long index, bool rd)
+{
+	jp_element *elem = mkElement(JP_CALL_CHAR, rd);
+	elem->data.index = index;
+	return elem;
+}
+
 static JPRef *mkRef(JPRefType type)
 {
 	JPRef *ref = palloc0(sizeof(*ref));
@@ -148,6 +155,9 @@ char *jp_show(JSONPath *jp)
 				appendStringInfo(string, "%s[%s]", rd ? ".." : "", tmp);
 				pfree(tmp);
 				break;
+			case JP_CALL_CHAR:
+				appendStringInfo(string, "%s(%ld)", rd ? "..char" : ".char", elem->data.index);
+				break;
 			default:
 				Assert(false);
 		}
@@ -156,11 +166,25 @@ char *jp_show(JSONPath *jp)
 	return string->data;
 }
 
+static bool parse_long(const char **s, long *out)
+{
+	const char *p = *s;
+
+	errno = 0;
+	*out = strtol(*s, (char**)&p, 10);
+	if (p <= *s || errno != 0)
+		return false;
+
+	*s = p;
+	return true;
+}
+
 JSONPath *jp_parse(const char *pattern)
 {
 	JSONPath	*jp					= NIL;
 	const char	*s					= pattern;
-	const char	*p;
+	const char	*start;
+	const char	*end;
 	bool		recursive_descent 	= false;
 	bool		bracket				= false;
 	const char	*err_msg			= NULL;
@@ -185,6 +209,7 @@ JSONPath *jp_parse(const char *pattern)
 	
 begin_element:
 	skip_spaces(&s);
+begin_element_noskip:
 
 	recursive_descent = false;
 	bracket = false;
@@ -258,26 +283,36 @@ wildcard:
 	goto next_element;
 
 integer:
-	p = s;
-	errno = 0;
-	index = strtol(s, (char**)&p, 10);
-	if (p <= s || errno != 0)
+	if (!parse_long(&s, &index))
 		goto failed;
-	s = p;
 	
 	jp = lappend(jp, mkIndexSubscript(index, recursive_descent));
 	goto next_element;
 
 identifier:
-	p = s;
-	while (identifier_char(*p))
-		p++;
-	key = pnstrdup(s, p - s);
-	key_length = p - s;
-	s = p;
+	start = s;
+	while (identifier_char(*s))
+		s++;
+	end = s;
+
+	skip_spaces(&s);
+
+	if (*s == '(') {
+		if (end - start == 4 && !memcmp(start, "char", 4))
+		{
+			s++;
+			skip_spaces(&s);
+			goto call_char;
+		}
+
+		goto failed;
+	}
+
+	key = pnstrdup(start, end - start);
+	key_length = end - start;
 
 	jp = lappend(jp, mkKeySubscript(key, key_length, recursive_descent));
-	goto next_element;
+	goto begin_element_noskip;
 
 string:
 	key = json_decode_string(&s, &key_length, false);
@@ -287,6 +322,18 @@ string:
 	jp = lappend(jp, mkKeySubscript(key, key_length, recursive_descent));
 	goto next_element;
 
+call_char:
+	if (!parse_long(&s, &index))
+		goto failed;
+
+	skip_spaces(&s);
+
+	if (*s++ != ')')
+		goto failed;
+
+	jp = lappend(jp, mkCallChar(index, recursive_descent));
+	goto begin_element;
+
 end:
 	return jp;
 
@@ -331,66 +378,6 @@ static size_t utf8_substring(
 	return sub_length;
 }
 
-static JPRef *json_index_subscript(JPRef *ref, long index)
-{
-	json_node *json;
-
-	if (index < 0)
-		return NULL;
-	
-	switch (ref->type) {
-		case JP_REF_NODE:
-			json = ref->u.node;
-
-			switch (json->type) {
-				case JSON_STRING: {
-					const char	*sub_start;
-					size_t		sub_bytes;
-					size_t		sub_length;
-
-					sub_length = utf8_substring(
-						json->v.string.str, json->v.string.length,
-						index, 1,
-						&sub_start, &sub_bytes);
-
-					if (sub_length != 1)
-						return NULL;
-
-					return mkRefChar(sub_start, sub_bytes);
-				}
-				case JSON_ARRAY: {
-					json_node	*child;
-
-					if ((size_t)index >= json->v.children.count)
-						return NULL;
-
-					for (child = json->v.children.head;
-						 index && child;
-						 child = child->next, index--) {}
-
-					if (index != 0 || child == NULL) {
-						Assert(false);
-						return NULL;
-					}
-
-					return mkRefNode(child);
-				}
-				default:
-					return NULL;
-			}
-			break;
-
-		case JP_REF_CHAR:
-			if (index != 0)
-				return NULL;
-			return ref;
-
-		default:
-			Assert(false);
-			return NULL;
-	}
-}
-
 /*
 Currently, a lot of JPRef nodes are allocated just to pass json_node pointers
 to match_recurse.  If this becomes a memory/performance issue in the future,
@@ -402,7 +389,6 @@ static void match_recurse(void on_match(void *ctx, JPRef *ref), void *ctx,
 	ListCell *path, JPRef *ref)
 {
 	jp_element	*elem;
-	JPRef		*child_ref;
 	json_node	*json, *child;
 
 	if (path == NULL) {
@@ -427,13 +413,30 @@ static void match_recurse(void on_match(void *ctx, JPRef *ref), void *ctx,
 			break;
 
 		case JP_INDEX_SUBSCRIPT:
-			child_ref = json_index_subscript(ref, elem->data.index);
-			if (child_ref != NULL)
-				match_recurse(on_match, ctx, lnext(path), child_ref);
+			if (json && json->type == JSON_ARRAY) {
+				size_t	i;
+				size_t	index = elem->data.index;
+				/* Note: elem->data.index is signed (long),
+				   while index is unsigned (size_t). */
+
+				if (elem->data.index >= 0 && index < json->v.children.count) {
+					for (child = json->v.children.head, i = 0;
+					     child != NULL && i < index;
+						 child = child->next, i++)
+					{
+					}
+
+					/* If this fails, it means json->v.children.count
+					   was greater than the actual number of children. */
+					Assert(i == index && child != NULL);
+
+					match_recurse(on_match, ctx, lnext(path), mkRefNode(child));
+				}
+			}
 			break;
 
 		case JP_KEY_SUBSCRIPT:
-			if (json->type == JSON_OBJECT) {
+			if (json && json->type == JSON_OBJECT) {
 				json_foreach(child, json) {
 					if (child->key != NULL &&
 						child->key_length == elem->data.key.length &&
@@ -445,6 +448,25 @@ static void match_recurse(void on_match(void *ctx, JPRef *ref), void *ctx,
 			}
 			break;
 
+		case JP_CALL_CHAR:
+			if (json && json->type == JSON_STRING && elem->data.index >= 0) {
+				const char  *sub_start;
+				size_t      sub_bytes;
+				size_t      sub_length;
+
+				sub_length = utf8_substring(
+					json->v.string.str, json->v.string.length,
+					elem->data.index, 1,
+					&sub_start, &sub_bytes);
+
+				if (sub_length == 1)
+					match_recurse(on_match, ctx, lnext(path), mkRefChar(sub_start, sub_bytes));
+			} else if (ref->type == JP_REF_CHAR && elem->data.index == 0) {
+				/* char(0) on a character yields itself. */
+				match_recurse(on_match, ctx, lnext(path), ref);
+			}
+			break;
+
 		default:;
 	}
 
diff --git a/jsonpath.h b/jsonpath.h
index 82915ac..109b785 100644
--- a/jsonpath.h
+++ b/jsonpath.h
@@ -9,7 +9,8 @@ typedef enum {
 	JP_ROOT,
 	JP_WILDCARD,
 	JP_INDEX_SUBSCRIPT,
-	JP_KEY_SUBSCRIPT
+	JP_KEY_SUBSCRIPT,
+	JP_CALL_CHAR
 } jp_element_type;
 
 typedef struct {
diff --git a/sql/json_path.sql b/sql/json_path.sql
index 72a4c7e..01d972b 100644
--- a/sql/json_path.sql
+++ b/sql/json_path.sql
@@ -52,20 +52,40 @@ SELECT parse_json_path($$
 	[ 5 ] .. [3] . * [ * ]
 $$);
 
-SELECT json_path($$"⁰¹\u0000³"$$, '[0]');
-SELECT json_path($$"⁰¹\u0000³"$$, '[1]');
-SELECT json_path($$"⁰¹\u0000³"$$, '[2]');
-SELECT json_path($$"⁰¹\u0000³"$$, '[3]');
-SELECT json_path('"0123"', '[-1]');
-SELECT json_path('"0123"', '[0]');
-SELECT json_path('"0123"', '[1]');
-SELECT json_path('"0123"', '[2]');
-SELECT json_path('"0123"', '[3]');
-SELECT json_path('"0123"', '[4]');
-SELECT json_path('"⁰¹²³"', '[0]');
-SELECT json_path('"⁰¹²³"', '[1]');
-SELECT json_path('"⁰¹²³"', '[2]');
-SELECT json_path('"⁰¹²³"', '[3]');
+select parse_json_path('$char');
+select parse_json_path('$.char');
+select parse_json_path('$.char()');
+select parse_json_path('$.char(5)');
+select parse_json_path('$.char(  -1  )');
+select parse_json_path('$.char(  -1  )  . char(0)');
+select parse_json_path('$.char(  -1  )  . char  ( 0 )  ');
+select parse_json_path('$.char(  +1  )  . char  ( 0 )  ');
+select parse_json_path('$ . char(  +1  )  . char  ( 0 )  ');
+select parse_json_path('$ .. char(  +1  )  . char  ( 0 )  ');
+select parse_json_path('$ .. char(  +1  )  .. char  ( 0 )  ');
+select parse_json_path('$ . char(  +1  )  .. char  ( 0 )  ');
+select parse_json_path('$ . char(  +1  )  char  ( 0 )  ');
+select parse_json_path('$ char(  +1  )  char  ( 0 )  ');
+select parse_json_path('char(  +1  )  . char  ( 0 )  ');
+select parse_json_path('.char(  +1  )  . char  ( 0 )  ');
+select parse_json_path('..char(  +1  )  . char  ( 0 )  ');
+select parse_json_path('...char(  +1  )  . char  ( 0 )  ');
+select parse_json_path('[char(5)]');
+
+SELECT json_path($$"⁰¹\u0000³"$$, 'char(0)');
+SELECT json_path($$"⁰¹\u0000³"$$, 'char(1)');
+SELECT json_path($$"⁰¹\u0000³"$$, 'char(2)');
+SELECT json_path($$"⁰¹\u0000³"$$, 'char(3)');
+SELECT json_path('"0123"', 'char(-1)');
+SELECT json_path('"0123"', 'char(0)');
+SELECT json_path('"0123"', 'char(1)');
+SELECT json_path('"0123"', 'char(2)');
+SELECT json_path('"0123"', 'char(3)');
+SELECT json_path('"0123"', 'char(4)');
+SELECT json_path('"⁰¹²³"', 'char(0)');
+SELECT json_path('"⁰¹²³"', 'char(1)');
+SELECT json_path('"⁰¹²³"', 'char(2)');
+SELECT json_path('"⁰¹²³"', 'char(3)');
 SELECT json_path('[1,2,3]', '$');
 SELECT json_path('[1,2,3]', '$.+1');
 SELECT json_path('[1,2,3]', '$.-1');
@@ -144,3 +164,10 @@ SELECT json_path(json, '..[3]') FROM sample;
 
 SELECT json_path(json, '$') FROM sample;
 SELECT json_path(json, '..*') FROM sample;
+
+SELECT json_path(json, '..char(-1)') FROM sample;
+SELECT json_path(json, '..char(0)') FROM sample;
+SELECT json_path(json, '..char(1)') FROM sample;
+SELECT json_path(json, '..char(2)') FROM sample;
+SELECT json_path(json, '..char(3)') FROM sample;
+SELECT json_path(json, '..char(100)') FROM sample;