Initial implementation of json_path function.

Currently, it re-encodes JSON nodes rather than preserving original text. This is subject to change.
author: Joey Adams 2010-06-15 02:49:13 +0000
committer: Joey Adams 2010-06-15 02:49:13 +0000
commit: 599940cb2fcde6e26b095b8accf7c3a70b2ba05b (patch)
tree: a16053467276d9c009904718bddb910519159e88 /jsonpath.c
parent: 58b696fc6c16123fb8206c386d6d398e47a6c21f (diff)
1 files changed, 172 insertions, 1 deletions
diff --git a/jsonpath.c b/jsonpath.c
index 8de8327..d816beb 100644
--- a/jsonpath.c
+++ b/jsonpath.c
@@ -1,6 +1,7 @@
 #include "jsonpath.h"
 
 #include <ctype.h>
+#include "mb/pg_wchar.h"
 
 /* NB: These macros evaluate their argument multiple times. */
 
@@ -15,6 +16,29 @@
 #define integer_start(c) (isdigit(c) || (c) == '+' || (c) == '-')
 
 /*
+ * In a valid JSONPath list, the first element is always of type JP_ROOT.
+ * This element is used so an otherwise empty JSONPath list won't be NULL.
+ * This allows us to use NULL to indicate an invalid JSONPath.
+ *
+ * This function returns the second cell,
+ * making sure the first is of type JP_ROOT.
+ */
+static ListCell *jp_head(JSONPath *jp)
+{
+	ListCell	*cell;
+	jp_element	*elem;
+
+	Assert(jp != NULL);
+
+	cell = list_head(jp);
+	elem = lfirst(cell);
+	Assert(elem->type == JP_ROOT);
+
+	cell = lnext(cell);
+	return cell;
+}
+
+/*
  * Note that skip_spaces differs from skip_whitespace in json.c
  * in that this function treats '\f' and '\v' as whitespace.
  * This is because JSON does not accept these characters as
@@ -240,7 +264,154 @@ failed:
 	return NULL;
 }
 
-List *jp_match(JSONPath *jp, json_node *json)
+static size_t utf8_substring(
+	const char *src, size_t srcbytes,
+	size_t start, size_t length,
+	const char **out_start, size_t *out_bytes)
+{
+	const char	*e = src + srcbytes;
+	const char	*sub_start;
+	const char	*sub_end;
+	size_t		sub_length;
+
+	sub_start = src;
+	while (start > 0 && sub_start < e) {
+		sub_start += pg_utf_mblen((const unsigned char*)sub_start);
+		start--;
+	}
+
+	sub_end = sub_start;
+	sub_length = 0;
+	while (sub_length < length && sub_end < e) {
+		sub_end += pg_utf_mblen((const unsigned char*)sub_end);
+		sub_length++;
+	}
+
+	/* Make sure the input didn't have a clipped UTF-8 character */
+	if(sub_start > e) {
+		Assert(false);
+		sub_start = sub_end = e;
+	} else if (sub_end > e) {
+		Assert(false);
+		sub_end = e;
+	}
+
+	*out_start = sub_start;
+	*out_bytes = sub_end - sub_start;
+	return sub_length;
+}
+
+static json_node *json_head(json_node *parent)
 {
+	switch (parent->type) {
+		case JSON_ARRAY:
+		case JSON_OBJECT:
+			return parent->v.children.head;
+		default:
+			return NULL;
+	}
+}
+
+#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)
+{
+	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;
+
+			sub_json = json_mkstring(sub_start, sub_bytes);
+			sub_json->parent = json;
+			return sub_json;
+		}
+		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 child;
+		}
+		default:
+			return NULL;
+	}
+}
+
+static void match_recurse(List **results, ListCell *path, json_node *json)
+{
+	jp_element	*elem;
+	json_node	*child;
+
+	if (path == NULL) {
+		/* The end of the JSONPath list is the "accept" state. */
+		*results = lappend(*results, json);
+		return;
+	}
+
+	elem = lfirst(path);
+
+	switch (elem->type) {
+		case JP_WILDCARD:
+			json_foreach(child, json)
+				match_recurse(results, lnext(path), child);
+			break;
+
+		case JP_INDEX_SUBSCRIPT:
+			child = json_index_subscript(json, elem->data.index);
+			if (child != NULL)
+				match_recurse(results, lnext(path), child);
+			break;
+
+		case JP_KEY_SUBSCRIPT:
+			json_foreach(child, json) {
+				if (child->key != NULL &&
+				    child->key_length == elem->data.key.length &&
+					!memcmp(child->key, elem->data.key.ptr, child->key_length))
+				{
+					match_recurse(results, lnext(path), child);
+				}
+			}
+			break;
+
+		default:;
+	}
+
+	if (elem->recursive_descent) {
+		json_foreach(child, json)
+			match_recurse(results, path, child);
+	}
+}
+
+List *jp_match(JSONPath *jp, json_node *json)
+{
+	ListCell	*lc			= jp_head(jp);
+	List		*results	= NIL;
+
+	match_recurse(&results, lc, json);
+
+	return results;
 }
author	Joey Adams	2010-06-15 02:49:13 +0000
committer	Joey Adams	2010-06-15 02:49:13 +0000
commit	599940cb2fcde6e26b095b8accf7c3a70b2ba05b (patch)
tree	a16053467276d9c009904718bddb910519159e88 /jsonpath.c
parent	58b696fc6c16123fb8206c386d6d398e47a6c21f (diff)