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@@ -0,0 +1,198 @@ + + + + JSON(2) JSON(2) + + + + + + NAME + Jinit, Jtokenise, Jfind, Jnext, Jtokstr - JSON parser + + SYNOPSIS + #include <u.h> + #include <libc.h> + #include <json.h> + + typedef enum{ + JBool, + JNum, + JNil, + JObj, + JArr, + JStr, + } Jtype; + + typedef struct{ + Jtype type; + char *start; + char *end; + uint nsub; + } Jtok; + + typedef struct{ + uint ntok, mtok; + Jtok *tokens; + uint stktop; + uint tokstk[JStksz]; + } Jparser; + + void Jinit(Jparser *p) + + void Jterm(Jparser *p); + + int Jtokenise(Jparser *p, char *s) + + char *Jtokstr(Jtok *t) + + int Jfind(Jparser *p, uint i, char *s) + + uint Jnext(Jparser *p, uint i) + + DESCRIPTION + These routines implement a fast, in-memory JSON parser. The + parser operates on a string which is expected to contain the + full JSON text. The string is not altered in any way. + + A parser object p is initialised using Jinit. The parser + object contains the number of tokens found ntok and an array + + + + + + + + + + + JSON(2) JSON(2) + + + + of tokens tokens. The other fields are for internal use. As + memory is dynamically allocated, an initialised parser p + must be terminated with Jterm after use. + + An initialised parser object is populated with tokens using + Jtokenise. Jtokenise accepts parser p and a string s and + returns a filled Jparser structure containing tokens found + in s. S is unaltered. + + Each token Jtoken has a type Jtype, pointers to the start + and end of the token's location in the JSON string, and a + count nsub of the number of subtokens. The types of a token + are + + JBool + Boolean value. Token must be either 't' or 'f'. + + JNum A real number. + + JNil Nill token matching 'n'. + + JObj An object (dictionary) containing key:value pairs. + + JArr An array. + + JStr A string. + + The pointers start and end point to the beginning character + of the token and to one character after the end of the token + respectively. The exception are JStr tokens, where start + points to the first character after the double quote and end + points to the terminating double quote. As arrays JArr and + objects JObj are the only types allowing subelements, nsub + is necessarily 0 for JBool, JNum, JNil, and JStr. + + The functions Jtokstr, Jfind and Jnext are functions for + working with Jtokstr takes a token and extracts out the + string pointed to by the token. The string is null termi- + nated and escaped characters are handled appropriately. As + Jtokstr uses a static buffer, the string returned is + destroyed on the next call. + + Jfind is used to find specifically named attributes within a + JObj. Given an index into the tokens array of p– which must + be a JObj – and the name of an attribute s, Jfind returns + the index of the token corresponding to the value matching + the attribute name. If no attribute is found then Jfind + returns -1. + + Finally, Jnext takes and index and calculates the index of + the next element at that depth. It is used for skipping + over JObjs and JArrs which can contain a number of + + + + + + + + + + + JSON(2) JSON(2) + + + + subelements. + + BUGS + The parser does not implement a full grammar so some JSON + errors are not detected when parsing. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + |