JSON: Basic documentation

diff --git a/ucw-json/doc/index.txt b/ucw-json/doc/index.txt
index 0f1fc691cfbf14143937eb7b63dd4694b11536d3..de7080852c7ba2c7b222c55903866da9c1bf6d05 100644 (file)
--- a/ucw-json/doc/index.txt
+++ b/ucw-json/doc/index.txt
@@ -3,9 +3,11 @@ The UCW-JSON library
 
 This library provides a light-weight JSON parser and generator built atop <<../ucw/index:,LibUCW>>.
 
 
 This library provides a light-weight JSON parser and generator built atop <<../ucw/index:,LibUCW>>.
 

+It follows the specification of JSON in RFC 7159.
+

 Modules
 -------
 Modules
 -------

-- <<json:,JSON Parser>>
+- <<json:,JSON Parser and Generator>>

 
 Authors
 -------
 
 Authors
 -------

diff --git a/ucw-json/doc/json.txt b/ucw-json/doc/json.txt
index 3d88e035aad7e81a310d71a2b8a454eada75800d..a4e77ee290614af4f488c85838959a6cb16adf9e 100644 (file)
--- a/ucw-json/doc/json.txt
+++ b/ucw-json/doc/json.txt
@@ -1,14 +1,12 @@
-JSON Parser
-===========
+JSON Parser and Generator
+=========================

 
 ucw-json/json.h
 
 ucw-json/json.h

--------------
+---------------

 
 

-FIXME
+To use the JSON library, you need to create a context (<<struct json_context,struct json_context>>)
+by calling <<json_new()>> first.

 
 

-To parse a document, create a parser context (<<struct_xml_context,struct xml_context>>),
-initialize it with <<xml_init()>>, fill in requested parsing mode, pointers to hooks, and
-other parameters. Then call <<xml_parse()>> or <<xml_next()>> as you need. At the end, dispose
-of the context by <<xml_cleanup()>> or recycle it by <<xml_reset()>>.
+FIXME

 
 !!ucw-json/json.h
 
 !!ucw-json/json.h

diff --git a/ucw-json/json.h b/ucw-json/json.h
index aa1d9f8ade4673fa1235dfb38401dfd622385550..aff1fccc9e8ab0e07449aaf2b4da45d1f39c773c 100644 (file)
--- a/ucw-json/json.h
+++ b/ucw-json/json.h
@@ -36,30 +36,65 @@
 #endif
 
 /***
 #endif
 
 /***

- * === FIXME
+ * === JSON library context
+ *
+ * FIXME: Document memory management

  ***/
 
  ***/
 

+/**
+ * The context is represented a pointer to this structure.
+ * The fields marked with [*] are publicly accessible, the rest is private.
+ **/

 struct json_context {
 struct json_context {

+  // Memory management

   struct mempool *pool;
   struct mempool_state init_state;
 
   struct mempool *pool;
   struct mempool_state init_state;
 

+  // Parser context

   struct fastbuf *in_fb;
   struct fastbuf *in_fb;

-  uint in_line;
-  uint in_column;
-  bool in_eof;
+  uint in_line;                                // [*] Current line number
+  uint in_column;                      // [*] Current column number
+  bool in_eof;                         //     End of file was encountered

   struct json_node *next_token;
   struct json_node *trivial_token;
   int next_char;
 
   struct json_node *next_token;
   struct json_node *trivial_token;
   int next_char;
 

+  // Formatter context

   struct fastbuf *out_fb;
   uint out_indent;
   struct fastbuf *out_fb;
   uint out_indent;

-  uint format_options;         // Public
+  uint format_options;                 // [*] Formatting options (a combination of JSON_FORMAT_xxx)

 };
 
 };
 

+/** Creates a new JSON context. **/

 struct json_context *json_new(void);
 struct json_context *json_new(void);

+
+/** Deletes a JSON context, deallocating all memory associated with it. **/

 void json_delete(struct json_context *js);
 void json_delete(struct json_context *js);

+
+/**
+ * Recycles a JSON context. All state is reset, allocated objects are freed.
+ * This is equivalent to mp_delete() followed by mp_new(), but it is faster
+ * and the address of the context is preserved.
+ **/

 void json_reset(struct json_context *js);
 
 void json_reset(struct json_context *js);
 

+/***
+ * === JSON values
+ *
+ * Each JSON value is represented by <<struct json_node,struct json_node>>,
+ * which is either an elementary value (null, boolean, number, string),
+ * or a container (array, object) pointing to other values.
+ *
+ * A value can belong to multiple containers simultaneously, so in general,
+ * the relationships between values need not form a tree, but a directed
+ * acyclic graph.
+ *
+ * You are allowed to read contents of nodes directly, but construction
+ * and modification of nodes must be always performed using the appropriate
+ * library functions.
+ ***/
+
+/** Node types **/

 enum json_node_type {
   JSON_INVALID,
   JSON_NULL,
 enum json_node_type {
   JSON_INVALID,
   JSON_NULL,


@@ -68,7 +103,9 @@ enum json_node_type {
   JSON_STRING,
   JSON_ARRAY,
   JSON_OBJECT,
   JSON_STRING,
   JSON_ARRAY,
   JSON_OBJECT,

-  // These are not real nodes, but raw tokens
+  // These are not real nodes, but raw tokens.
+  // They are not present in the tree of values, but you may see them
+  // if you call json_next_token() and friends.

   JSON_BEGIN_ARRAY,
   JSON_END_ARRAY,
   JSON_BEGIN_OBJECT,
   JSON_BEGIN_ARRAY,
   JSON_END_ARRAY,
   JSON_BEGIN_OBJECT,


@@ -78,30 +115,35 @@ enum json_node_type {
   JSON_EOF,
 };
 
   JSON_EOF,
 };
 

+/** Each value is represented by a single node. **/

 struct json_node {
   enum json_node_type type;
 struct json_node {
   enum json_node_type type;

-  union {
+  union {                              // Data specific to individual value types

     bool boolean;
     double number;
     const char *string;
     bool boolean;
     double number;
     const char *string;

-    struct json_node **elements;       // Growing array
-    struct json_pair *pairs;           // Growing array
+    struct json_node **elements;       // Arrays: Growing array of values
+    struct json_pair *pairs;           // Objects: Growing array of pairs

   };
 };
 
   };
 };
 

+/** Attributes of objects are stored as (key, value) pairs of this format. **/

 struct json_pair {
   const char *key;
   struct json_node *value;
   // FIXME: Hash table
 };
 
 struct json_pair {
   const char *key;
   struct json_node *value;
   // FIXME: Hash table
 };
 

+// Used internally

 struct json_node *json_new_node(struct json_context *js, enum json_node_type type);
 
 struct json_node *json_new_node(struct json_context *js, enum json_node_type type);
 

+/** Creates a new null value. **/

 static inline struct json_node *json_new_null(struct json_context *js)
 {
   return json_new_node(js, JSON_NULL);
 }
 
 static inline struct json_node *json_new_null(struct json_context *js)
 {
   return json_new_node(js, JSON_NULL);
 }
 

+/** Creates a new boolean value. **/

 static inline struct json_node *json_new_bool(struct json_context *js, bool value)
 {
   struct json_node *n = json_new_node(js, JSON_BOOLEAN);
 static inline struct json_node *json_new_bool(struct json_context *js, bool value)
 {
   struct json_node *n = json_new_node(js, JSON_BOOLEAN);


@@ -109,6 +151,7 @@ static inline struct json_node *json_new_bool(struct json_context *js, bool valu
   return n;
 }
 
   return n;
 }
 

+/** Creates a new numeric value. **/

 static inline struct json_node *json_new_number(struct json_context *js, double value)
 {
   struct json_node *n = json_new_node(js, JSON_NUMBER);
 static inline struct json_node *json_new_number(struct json_context *js, double value)
 {
   struct json_node *n = json_new_node(js, JSON_NUMBER);


@@ -116,6 +159,7 @@ static inline struct json_node *json_new_number(struct json_context *js, double
   return n;
 }
 
   return n;
 }
 

+/** Creates a new string value. The @value is kept only as a reference. **/

 static inline struct json_node *json_new_string_ref(struct json_context *js, const char *value)
 {
   struct json_node *n = json_new_node(js, JSON_STRING);
 static inline struct json_node *json_new_string_ref(struct json_context *js, const char *value)
 {
   struct json_node *n = json_new_node(js, JSON_STRING);


@@ -123,34 +167,89 @@ static inline struct json_node *json_new_string_ref(struct json_context *js, con
   return n;
 }
 
   return n;
 }
 

+/** Creates a new string value, making a private copy of @value. **/

 static inline struct json_node *json_new_string(struct json_context *js, const char *value)
 {
   return json_new_string_ref(js, mp_strdup(js->pool, value));
 }
 
 static inline struct json_node *json_new_string(struct json_context *js, const char *value)
 {
   return json_new_string_ref(js, mp_strdup(js->pool, value));
 }
 

+/** Creates a new array value with no elements. **/

 struct json_node *json_new_array(struct json_context *js);
 struct json_node *json_new_array(struct json_context *js);

+
+/** Appends a new element to the given array. **/

 void json_array_append(struct json_node *array, struct json_node *elt);
 
 void json_array_append(struct json_node *array, struct json_node *elt);
 

+/** Creates a new object value with no attributes. **/

 struct json_node *json_new_object(struct json_context *js);
 struct json_node *json_new_object(struct json_context *js);

-// FIXME: key must not be freed
+
+/**
+ * Adds a new (@key, @value) pair to the given object. If @key is already
+ * present, the pair is replaced. If @value is NULL, no new pair is created
+ * and a pre-existing pair is deleted.
+ *
+ * The @key is referenced by the object, you must not free it during
+ * the lifetime of the JSON context.
+ *
+ * FIXME: Add json_copy_key().
+ **/

 void json_object_set(struct json_node *n, const char *key, struct json_node *value);
 void json_object_set(struct json_node *n, const char *key, struct json_node *value);

+
+/** Returns the value associated with @key, or NULL if no such value exists. **/

 struct json_node *json_object_get(struct json_node *n, const char *key);
 
 struct json_node *json_object_get(struct json_node *n, const char *key);
 

+/***
+ * === Parser
+ *
+ * The simplest way to parse a complete JSON file is to call json_parse(),
+ * which returns a value tree representing the contents of the file.
+ *
+ * Alternatively, you can read the input token by token: call json_set_input()
+ * and then repeat json_next_token(). Note that even in this mode, the tokens
+ * are kept in memory. (If you need to parse huge JSON files, please ask the
+ * maintainer of this library to improve memory allocation.)
+ ***/
+
+/** Parses a JSON file from the given fastbuf stream. **/
+struct json_node *json_parse(struct json_context *js, struct fastbuf *fb);
+
+/** Selects the given fastbuf stream as parser input. **/

 void json_set_input(struct json_context *js, struct fastbuf *in);
 void json_set_input(struct json_context *js, struct fastbuf *in);

-struct json_node *json_peek_token(struct json_context *js);
+
+/** Reads the next token from the input. **/

 struct json_node *json_next_token(struct json_context *js);
 
 struct json_node *json_next_token(struct json_context *js);
 

+/** Reads the next token, but keeps it in the input. **/
+struct json_node *json_peek_token(struct json_context *js);
+
+/** Reads the next JSON value, including nested values. **/

 struct json_node *json_next_value(struct json_context *js);
 
 struct json_node *json_next_value(struct json_context *js);
 

-struct json_node *json_parse(struct json_context *js, struct fastbuf *fb);
+/***
+ * === Writer
+ *
+ * JSON files can be produced by simply calling json_write().
+ *
+ * If you want to generate the output on the fly (for example if it is huge),
+ * call json_set_output() and then iterate json_write_value().
+ *
+ * By default, we produce a single-line compact representation,
+ * but you can choose differently by setting the appropriate
+ * `format_options` in the `json_context`.
+ ***/

 
 

+/** Writes a JSON file to the given fastbuf stream, containing the JSON value @n. **/
+void json_write(struct json_context *js, struct fastbuf *fb, struct json_node *n);
+
+/** Selects the given fastbuf stream as output. **/

 void json_set_output(struct json_context *js, struct fastbuf *fb);
 void json_set_output(struct json_context *js, struct fastbuf *fb);

+
+/** Writes a single JSON value to the output stream. **/

 void json_write_value(struct json_context *js, struct json_node *n);
 void json_write_value(struct json_context *js, struct json_node *n);

-void json_write(struct json_context *js, struct fastbuf *fb, struct json_node *n);

 
 

+/** Formatting options. The `format_options` field in the context is a bitwise OR of these flags. **/

 enum json_format_option {
 enum json_format_option {

-  JSON_FORMAT_ESCAPE_NONASCII = 1,
-  JSON_FORMAT_INDENT = 2,
+  JSON_FORMAT_ESCAPE_NONASCII = 1,     // Produce pure ASCII output by escaping all Unicode characters in strings
+  JSON_FORMAT_INDENT = 2,              // Produce pretty indented output

 };
 
 #endif
 };
 
 #endif