lib: extend jsmn with simple JSONPath lookup helpers

Board code may not be interested in iterating fully over the JSON blob
and instead just wants to lookup a value at a specific JSONPath.

Add helpers to facilitate this.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20230110084930.3439001-3-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 57 insertions, 0 deletions

diff --git a/include/jsmn.h b/include/jsmn.h
index 394ffc4674..8f6db8d534 100644
--- a/include/jsmn.h
+++ b/include/jsmn.h
@@ -84,6 +84,63 @@ JSMN_API void jsmn_init(jsmn_parser *parser);
 JSMN_API int jsmn_parse(jsmn_parser *parser, const char *js, const size_t len,
 			jsmntok_t *tokens, const unsigned int num_tokens);
 
+/** Returns `true` if `token` is a string and equal to `str`. */
+JSMN_API bool jsmn_str_eq(const char *str, const char *json, const jsmntok_t *token);
+
+/** Returns `true` if `token` is to `str`. */
+JSMN_API bool jsmn_eq(const char *val, const char *json, const jsmntok_t *token);
+
+/** Returns the token after the value at `tokens[0]`. */
+JSMN_API const jsmntok_t *jsmn_skip_value(const jsmntok_t *tokens);
+
+/**
+ * Returns a pointer to the value associated with `key` inside `json` starting
+ * at `tokens[0]`, which is expected to be an object, or returns `NULL` if `key`
+ * cannot be found.
+ */
+JSMN_API const jsmntok_t *jsmn_find_value(const char *key, const char *json,
+					  const jsmntok_t *tokens);
+
+/**
+ * Locate the token at `path` inside `json` in a manner similar to JSONPath.
+ *
+ * Example:
+ * \code
+ * {
+ *   "date": "...",
+ *   "product": {
+ *	 "serial": "1234",
+ *   }
+ * }
+ * \endcode
+ *
+ * To locate the serial number in the JSON object above, you would use the
+ * JSONPath expression "$.product.serial". The same thing can be accomplished
+ * with this call:
+ *
+ * \code
+ * const char *path[] = {"product", "serial", NULL};
+ * const jsmntok_t *token = jsmn_locate(path, json, tokens);
+ * \endcode
+ *
+ * \remark This function cannot search inside arrays.
+ *
+ * @param path		Null-terminated list of path elements.
+ * @param json		JSON string to search in.
+ * @param tokens	Tokens for `json`.
+ *
+ * @return Pointer to the value token or `NULL` if the token could not be found.
+ */
+JSMN_API const jsmntok_t *jsmn_locate(const char *path[], const char *json,
+				      const jsmntok_t *tokens);
+
+/**
+ * Similar to `jsmn_locate` but returns a copy of the value or `NULL` if the
+ * value does not exist or is not a string. The caller takes ownership of the
+ * pointer returned.
+ */
+JSMN_API char *jsmn_strcpy(const char *path[], const char *json, const jsmntok_t *tokens);
+
 #ifdef __cplusplus
 }
 #endif