Refactored jsonpath a bit by introducing JPRef.

JPRef is a structure representing an item matched by jp_match. Before, plain old json_node was used, which couldn't distinguish between mutable references (actual JSON nodes from the original input) and immutable references (e.g. characters in a string). Yes, characters in a string are regarded as immutable because: * That's how it is in JavaScript. * It's easier to implement.
author: Joey Adams 2010-07-14 04:05:24 +0000
committer: Joey Adams 2010-07-14 04:05:24 +0000
commit: 46d4111846c2fdd0a2790c25ba51c8998d8ab218 (patch)
tree: 551e0be5d2569a248cf2ca95864d9bbd33fe5c74 /jsonpath.c
parent: 442fe529e29fc5538dc4172246758f68a4156106 (diff)
1 files changed, 109 insertions, 43 deletions
diff --git a/jsonpath.c b/jsonpath.c
index a6ca56f..b8e4527 100644
--- a/jsonpath.c
+++ b/jsonpath.c
@@ -96,6 +96,28 @@ static jp_element *mkKeySubscript(char *key, size_t length, bool rd)
 	return elem;
 }
 
+static JPRef *mkRef(JPRefType type)
+{
+	JPRef *ref = palloc0(sizeof(*ref));
+	ref->type = type;
+	return ref;
+}
+
+static JPRef *mkRefNode(json_node *node)
+{
+	JPRef *ref = mkRef(JP_REF_NODE);
+	ref->u.node = node;
+	return ref;
+}
+
+static JPRef *mkRefChar(const char *bytes, size_t length)
+{
+	JPRef *ref = mkRef(JP_REF_CHAR);
+	ref->u.chr.bytes = bytes;
+	ref->u.chr.length = length;
+	return ref;
+}
+
 char *jp_show(JSONPath *jp)
 {
 	StringInfoData	string[1];
@@ -323,75 +345,104 @@ static json_node *json_head(json_node *parent)
 #define json_foreach(child, parent) \
 	for ((child) = json_head(parent); (child) != NULL; (child) = (child)->next)
 
-static json_node *json_index_subscript(json_node *json, long index)
+static JPRef *json_index_subscript(JPRef *ref, long index)
 {
+	json_node *json;
+
 	if (index < 0)
 		return NULL;
 	
-	switch (json->type) {
-		case JSON_STRING: {
-			const char	*sub_start;
-			size_t		sub_bytes;
-			size_t		sub_length;
-			json_node	*sub_json;
-
-			sub_length = utf8_substring(
-				json->v.string.str, json->v.string.length,
-				index, 1,
-				&sub_start, &sub_bytes);
-
-			if (sub_length != 1)
-				return NULL;
+	switch (ref->type) {
+		case JP_REF_NODE:
+			json = ref->u.node;
 
-			sub_json = json_mkstring(sub_start, sub_bytes);
-			sub_json->parent = json;
-			return sub_json;
-		}
-		case JSON_ARRAY: {
-			json_node	*child;
+			switch (json->type) {
+				case JSON_STRING: {
+					const char	*sub_start;
+					size_t		sub_bytes;
+					size_t		sub_length;
 
-			if ((size_t)index >= json->v.children.count)
-				return NULL;
+					sub_length = utf8_substring(
+						json->v.string.str, json->v.string.length,
+						index, 1,
+						&sub_start, &sub_bytes);
 
-			for (child = json->v.children.head;
-			     index && child;
-				 child = child->next, index--) {}
+					if (sub_length != 1)
+						return NULL;
 
-			if (index != 0 || child == NULL) {
-				Assert(false);
-				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;
 
-			return child;
-		}
 		default:
+			Assert(false);
 			return NULL;
 	}
 }
 
-static void match_recurse(List **results, ListCell *path, json_node *json)
+/*
+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,
+JPRef could merged with json_node by adding JPRef's specialty types to the
+json_type enum and json_node union.  JPRef is currently not merged with
+json_node in an attempt to keep the codebase tidy and easier to extend.
+*/
+static void match_recurse(List **results, ListCell *path, JPRef *ref)
 {
 	jp_element	*elem;
-	json_node	*child;
+	JPRef		*child_ref;
+	json_node	*json, *child;
 
 	if (path == NULL) {
 		/* The end of the JSONPath list is the "accept" state. */
-		*results = lappend(*results, json);
+		*results = lappend(*results, ref);
 		return;
 	}
 
 	elem = lfirst(path);
 
+	if (ref->type == JP_REF_NODE)
+		json = ref->u.node;
+	else
+		json = NULL;
+
 	switch (elem->type) {
 		case JP_WILDCARD:
-			json_foreach(child, json)
-				match_recurse(results, lnext(path), child);
+			if (json) {
+				json_foreach(child, json)
+					match_recurse(results, lnext(path), mkRefNode(child));
+			}
 			break;
 
 		case JP_INDEX_SUBSCRIPT:
-			child = json_index_subscript(json, elem->data.index);
-			if (child != NULL)
-				match_recurse(results, lnext(path), child);
+			child_ref = json_index_subscript(ref, elem->data.index);
+			if (child_ref != NULL)
+				match_recurse(results, lnext(path), child_ref);
 			break;
 
 		case JP_KEY_SUBSCRIPT:
@@ -400,7 +451,7 @@ static void match_recurse(List **results, ListCell *path, json_node *json)
 				    child->key_length == elem->data.key.length &&
 					!memcmp(child->key, elem->data.key.ptr, child->key_length))
 				{
-					match_recurse(results, lnext(path), child);
+					match_recurse(results, lnext(path), mkRefNode(child));
 				}
 			}
 			break;
@@ -408,9 +459,9 @@ static void match_recurse(List **results, ListCell *path, json_node *json)
 		default:;
 	}
 
-	if (elem->recursive_descent) {
+	if (elem->recursive_descent && json) {
 		json_foreach(child, json)
-			match_recurse(results, path, child);
+			match_recurse(results, path, mkRefNode(child));
 	}
 }
 
@@ -419,7 +470,22 @@ List *jp_match(JSONPath *jp, json_node *json)
 	ListCell	*lc			= jp_head(jp);
 	List		*results	= NIL;
 
-	match_recurse(&results, lc, json);
+	match_recurse(&results, lc, mkRefNode(json));
 
 	return results;
 }
+
+char *jpref_encode(JPRef *ref)
+{
+	switch (ref->type) {
+		case JP_REF_NODE:
+			return json_encode(ref->u.node, JSONOPT_USE_ORIG);
+
+		case JP_REF_CHAR:
+			return json_encode_string(ref->u.chr.bytes, ref->u.chr.length, '"', false);
+
+		default:
+			Assert(false);
+			return NULL;
+	}
+}
author	Joey Adams	2010-07-14 04:05:24 +0000
committer	Joey Adams	2010-07-14 04:05:24 +0000
commit	46d4111846c2fdd0a2790c25ba51c8998d8ab218 (patch)
tree	551e0be5d2569a248cf2ca95864d9bbd33fe5c74 /jsonpath.c
parent	442fe529e29fc5538dc4172246758f68a4156106 (diff)