le_json.h

    1 //--------------------------------------------------------------------------------------------------
    2 /**
    3  * @page c_json JSON Parsing API
    4  *
    5  * @warning This API is experimental, and is therefore likely to change.
    6  *
    7  * @subpage le_json.h "API Reference" <br>
    8  *
    9  * <hr>
   10  *
   11  * The JSON Parsing API is intended to provide fast parsing of a JSON data stream with very
   12  * little memory required.  It is an event-driven API that uses callbacks (handlers) to report
   13  * when things are found in the JSON document.  The parser does not build a document structure
   14  * for you.  You build your structure as needed in response to callbacks from the parser.
   15  * In this way, the JSON parser avoids potential memory fragmentation issues that can arise
   16  * when document object models are constructed on the heap (e.g., using malloc()).
   17  *
   18  *  @section c_json_start Starting and Stopping Parsing
   19  *
   20  * The function le_json_Parse() is used to start parsing a JSON document obtained from a
   21  * file descriptor.  This function returns immediately, and further parsing proceeds in an
   22  * event-driven manner: As JSON data is received, asynchronous call-back functions are called
   23  * to deliver parsed information or an error message.
   24  *
   25  * Parsing stops automatically when the end of the document is reached or an error is encountered.
   26  *
   27  * le_json_Cleanup() must be called to release memory resources allocated by the parser.
   28  *
   29  * If the document starts with a '{', then it will finish with the matching '}'.
   30  *
   31  * If it starts with a '[', then it will finish with the matching ']'.
   32  *
   33  * All documents must start with either '{' or '['.
   34  *
   35  * To stop parsing early, call le_json_Cleanup() early.
   36  *
   37  * @warning Be sure to stop parsing before closing the file descriptor.
   38  *
   39  *  @section c_json_events Event Handling
   40  *
   41  * As parsing progresses and the parser finds things inside the JSON document, the parser calls
   42  * the event handler function to report the findings.
   43  *
   44  * For example, when the parser finds an object member, it calls the event handler function
   45  * with the event code LE_JSON_OBJECT_MEMBER; and when if finds a string value, an LE_JSON_STRING
   46  * event is reported.
   47  *
   48  * The event handler function can call functions to fetch values, depending on the event:
   49  * - LE_JSON_OBJECT_MEMBER: le_json_GetString() fetches the object member name.
   50  * - LE_JSON_STRING: le_json_GetString() fetches the string value.
   51  * - LE_JSON_NUMBER: le_json_GetNumber() fetches the number value.
   52  *
   53  * le_json_GetString() and le_json_GetNumber() can only be called from inside of a JSON parsing
   54  * event handler function or any function being called (directly or indirectly) from a JSON
   55  * parsing event handler.  Calling these functions elsewhere will be fatal to the calling process.
   56  *
   57  *  @section c_json_context Context
   58  *
   59  * Each JSON object, object member and array in the JSON document is a "context".
   60  * Each context has an event handler function and an opaque pointer associated with it.
   61  * The top level context's event handler and opaque pointer are passed into le_json_Parse().
   62  * Sub-contexts (object members or array elements) will inherit their context from their parent.
   63  *
   64  * The current context's event handler can be changed from within an event handler function by
   65  * calling le_json_SetEventHandler().  This will remain in effect until the parser finishes parsing
   66  * that part of the document and returns back to its parent, at which time the current context
   67  * will be automatically restored to the parent's context.
   68  *
   69  *  @section c_json_errors Error Handling
   70  *
   71  * There is a global error handler that is also set when the parsing is started, and can be changed
   72  * by calling le_json_SetErrorHandler().  Unlike other event handlers, this is not part of the
   73  * context, and will therefore not get restored to a previous handler when the parsing of a member
   74  * finishes.  The error handler function is passed parameters that indicate what type of error
   75  * occurred.
   76  *
   77  *  @section c_json_otherFunctions Other Functions
   78  *
   79  * For diagnostic purposes, le_json_GetEventName() can be called to get a human-readable
   80  * string containing the name of a given event.
   81  *
   82  * To get the number of bytes that have been read by the parser since le_json_Parse() was called,
   83  * call le_json_GetBytesRead().
   84  *
   85  *  @section c_json_example Example
   86  *
   87  * If the JSON document is
   88  *
   89  * @code
   90  * { "x":1, "y":2, "name":"joe" }
   91  * @endcode
   92  *
   93  * The following sequence of events will be reported by the parser:
   94  * 1. LE_JSON_OBJECT_START
   95  * 2. LE_JSON_OBJECT_MEMBER - If the event handler calls le_json_GetString(), it will return "x".
   96  * 3. LE_JSON_NUMBER - If the event handler calls le_json_GetNumber(), it will return 1.
   97  * 4. LE_JSON_OBJECT_MEMBER - If the event handler calls le_json_GetString(), it will return "y".
   98  * 5. LE_JSON_NUMBER - If the event handler calls le_json_GetNumber(), it will return 2.
   99  * 6. LE_JSON_OBJECT_MEMBER - If the event handler calls le_json_GetString(), it will return "name".
  100  * 7. LE_JSON_STRING - If the event handler calls le_json_GetString(), it will return "joe".
  101  * 8. LE_JSON_OBJECT_END
  102  * 8. LE_JSON_DOC_END - At this point, parsing stops.
  103  *
  104  * If the handler function passed to le_json_Parse() is called "<c>TopLevelHandler()</c>",
  105  * TopLevelHandler() will be called for the all events.  But, when <c>TopLevelHandler()</c> gets
  106  * the event LE_JSON_OBJECT_MEMBER for the member "x" and responds by calling
  107  * <c>le_json_SetEventHandler(XHandler(), NULL)</c>, then the LE_JSON_NUMBER event for "x" will
  108  * be passed to <c>XHandler()</c>.  But, the following LE_JSON_OBJECT_MEMBER event for "y" will
  109  * still go to <c>TopLevelHandler()</c>, because the context returns to the top level object
  110  * after the parser finishes parsing member "x".
  111  *
  112  *  @section c_json_threads Multi-Threading
  113  *
  114  * This API is not thread safe.  DO NOT attempt to SHARE parsers between threads.
  115  *
  116  * If a thread dies, any parsers in use by that thread that have not been cleaned-up by calls to
  117  * le_json_Cleanup() will be cleaned up automatically.
  118  *
  119  * <hr>
  120  *
  121  * Copyright (C) Sierra Wireless Inc.
  122  */
  123 //--------------------------------------------------------------------------------------------------
  124 
  125 /** @file le_json.h
  126  *
  127  * Legato @ref c_json include file.
  128  *
  129  * Copyright (C) Sierra Wireless Inc.
  130  */
  131 
  132 #ifndef LEGATO_JSON_H_INCLUDE_GUARD
  133 #define LEGATO_JSON_H_INCLUDE_GUARD
  134 
  135 
  136 //--------------------------------------------------------------------------------------------------
  137 /**
  138  * Enumeration of all the different events that can be reported during JSON document parsing.
  139  */
  140 //--------------------------------------------------------------------------------------------------
  141 typedef enum
  142 {
  143     LE_JSON_OBJECT_START,   ///< object started, subsequent object members are part of this object
  144     LE_JSON_OBJECT_MEMBER,  ///< object member name received: Call le_json_GetString() to get name
  145     LE_JSON_OBJECT_END,     ///< object finished, subsequent members/values are outside this object
  146     LE_JSON_ARRAY_START,    ///< array started, upcoming values are elements of this array
  147     LE_JSON_ARRAY_END,      ///< array finished, subsequent values are outside this array
  148     LE_JSON_STRING,         ///< string value received: call le_json_GetString() to get value
  149     LE_JSON_NUMBER,         ///< number value received: call le_json_GetNumber() to get value
  150     LE_JSON_TRUE,           ///< true value received
  151     LE_JSON_FALSE,          ///< false value received
  152     LE_JSON_NULL,           ///< null value received
  153     LE_JSON_DOC_END,        ///< End of the document reached.  Parsing has stopped.
  154 }
  155 le_json_Event_t;
  156 
  157 
  158 //--------------------------------------------------------------------------------------------------
  159 /**
  160  * Callbacks for (non-error) parsing events look like this.
  161  *
  162  * @param event     [in] Indicates what type of event occured.
  163  */
  164 //--------------------------------------------------------------------------------------------------
  165 typedef void (* le_json_EventHandler_t)
  166 (
  167     le_json_Event_t event
  168 );
  169 
  170 
  171 //--------------------------------------------------------------------------------------------------
  172 /**
  173  * Enumeration of the different types of errors that can be reported during JSON document parsing.
  174  */
  175 //--------------------------------------------------------------------------------------------------
  176 typedef enum
  177 {
  178     LE_JSON_SYNTAX_ERROR,   ///< Syntax error, such as a missing comma or extra comma.
  179     LE_JSON_READ_ERROR,     ///< Error when reading from the input byte stream.
  180 }
  181 le_json_Error_t;
  182 
  183 
  184 //--------------------------------------------------------------------------------------------------
  185 /**
  186  * Callbacks for errors look like this.
  187  *
  188  * @param error     [in] Indicates what type of error occured.
  189  *
  190  * @param msg       [in] Human-readable message describing the error. (Valid until handler returns.)
  191  */
  192 //--------------------------------------------------------------------------------------------------
  193 typedef void (* le_json_ErrorHandler_t)
  194 (
  195     le_json_Error_t error,
  196     const char* msg
  197 );
  198 
  199 
  200 //--------------------------------------------------------------------------------------------------
  201 /**
  202  * Parsing session reference.  Refers to a parsing session started by le_json_Parse().  Pass this
  203  * to le_json_Cleanup() to stop the parsing and clean up memory allocated by the parser.
  204  */
  205 //--------------------------------------------------------------------------------------------------
  206 typedef struct le_json_ParsingSession* le_json_ParsingSessionRef_t;
  207 
  208 
  209 //--------------------------------------------------------------------------------------------------
  210 /**
  211  * Parse a JSON document received via a file descriptor.
  212  *
  213  * @return Reference to the JSON parsing session started by this function call.
  214  */
  215 //--------------------------------------------------------------------------------------------------
  216 le_json_ParsingSessionRef_t le_json_Parse
  217 (
  218     int fd, ///< File descriptor to read the JSON document from.
  219     le_json_EventHandler_t  eventHandler,   ///< Function to call when normal parsing events happen.
  220     le_json_ErrorHandler_t  errorHandler,   ///< Function to call when errors happen.
  221     void* opaquePtr   ///< Opaque pointer to be fetched by handlers using le_json_GetOpaquePtr().
  222 );
  223 
  224 //--------------------------------------------------------------------------------------------------
  225 /**
  226  * Parse a JSON document received via C string.
  227  *
  228  * @return Reference to the JSON parsing session started by this function call.
  229  */
  230 //--------------------------------------------------------------------------------------------------
  231 le_json_ParsingSessionRef_t le_json_ParseString
  232 (
  233     const char *jsonString, ///< JSON string to parse.
  234     le_json_EventHandler_t  eventHandler,   ///< Function to call when normal parsing events happen.
  235     le_json_ErrorHandler_t  errorHandler,   ///< Function to call when errors happen.
  236     void* opaquePtr   ///< Opaque pointer to be fetched by handlers using le_json_GetOpaquePtr().
  237 );
  238 
  239 //--------------------------------------------------------------------------------------------------
  240 /**
  241  * Stops parsing and cleans up memory allocated by the parser.
  242  *
  243  * @warning Be sure to stop parsing before closing the file descriptor.
  244  */
  245 //--------------------------------------------------------------------------------------------------
  246 void le_json_Cleanup
  247 (
  248     le_json_ParsingSessionRef_t session ///< The parsing session to clean up (see le_json_Parse()).
  249 );
  250 
  251 
  252 //--------------------------------------------------------------------------------------------------
  253 /**
  254  * Set the current context's event handler function.
  255  *
  256  * @warning This function can only be called inside event or error handlers.
  257  */
  258 //--------------------------------------------------------------------------------------------------
  259 void le_json_SetEventHandler
  260 (
  261     le_json_EventHandler_t  callbackFunc  ///< Function to call when parsing events happen.
  262 );
  263 
  264 
  265 //--------------------------------------------------------------------------------------------------
  266 /**
  267  * Enumeration of the different types of "contexts" that can exist during a parsing session.
  268  */
  269 //--------------------------------------------------------------------------------------------------
  270 typedef enum
  271 {
  272     LE_JSON_CONTEXT_DOC,    ///< Top level of document, outside the main object/array.
  273     LE_JSON_CONTEXT_OBJECT, ///< Parsing an object (set of named members).
  274     LE_JSON_CONTEXT_MEMBER, ///< Parsing a member of an object.
  275     LE_JSON_CONTEXT_ARRAY,  ///< Parsing an array (list of unnamed elements).
  276     LE_JSON_CONTEXT_STRING, ///< Parsing a string value.
  277     LE_JSON_CONTEXT_NUMBER, ///< Parsing number value.
  278     LE_JSON_CONTEXT_TRUE,   ///< Parsing a true value.
  279     LE_JSON_CONTEXT_FALSE,  ///< Parsing a false value.
  280     LE_JSON_CONTEXT_NULL,   ///< Parsing a null value.
  281 }
  282 le_json_ContextType_t;
  283 
  284 
  285 //--------------------------------------------------------------------------------------------------
  286 /**
  287  * Get the type of parsing context that the parser is currently in.
  288  *
  289  * @return The context type.
  290  *
  291  * @warning This function can only be called inside event or error handlers.
  292  */
  293 //--------------------------------------------------------------------------------------------------
  294 le_json_ContextType_t le_json_GetContextType
  295 (
  296     void
  297 );
  298 
  299 
  300 //--------------------------------------------------------------------------------------------------
  301 /**
  302  * Set the opaque pointer attached to the parser.
  303  *
  304  * @warning This function can only be called inside event or error handlers.
  305  */
  306 //--------------------------------------------------------------------------------------------------
  307 void le_json_SetOpaquePtr
  308 (
  309     void* ptr    ///< Opaque pointer to be fetched using le_json_GetOpaquePtr().
  310 );
  311 
  312 
  313 //--------------------------------------------------------------------------------------------------
  314 /**
  315  * Get the opaque pointer attached to the parser.
  316  *
  317  * @return The pointer previously set by le_json_Parse() or a subsequent call to
  318  *         le_json_SetOpaquePtr().
  319  *
  320  * @warning This function can only be called inside event or error handlers.
  321  */
  322 //--------------------------------------------------------------------------------------------------
  323 void* le_json_GetOpaquePtr
  324 (
  325     void
  326 );
  327 
  328 
  329 //--------------------------------------------------------------------------------------------------
  330 /**
  331  * Set the error handler function
  332  *
  333  * @warning This function can only be called inside event or error handlers.
  334  */
  335 //--------------------------------------------------------------------------------------------------
  336 void le_json_SetErrorHandler
  337 (
  338     le_json_ErrorHandler_t  callbackFunc    ///< Function to call when parsing errors happen.
  339 );
  340 
  341 
  342 //--------------------------------------------------------------------------------------------------
  343 /**
  344  * Fetches a pointer to a string value or object member name.
  345  *
  346  * This pointer is only valid until the event handler returns.
  347  *
  348  * @warning This function can only be called inside event handlers when LE_JSON_OBJECT_MEMBER
  349  *          or LE_JSON_STRING events are being handled.
  350  */
  351 //--------------------------------------------------------------------------------------------------
  352 const char* le_json_GetString
  353 (
  354     void
  355 );
  356 
  357 
  358 //--------------------------------------------------------------------------------------------------
  359 /**
  360  * Fetches the value of a parsed number.
  361  *
  362  * @warning This function can only be called inside event handlers when LE_JSON_NUMBER events are
  363  *          being handled.
  364  */
  365 //--------------------------------------------------------------------------------------------------
  366 double le_json_GetNumber
  367 (
  368     void
  369 );
  370 
  371 
  372 //--------------------------------------------------------------------------------------------------
  373 /**
  374  * @return Human readable string containing the name of a given JSON parsing event.
  375  */
  376 //--------------------------------------------------------------------------------------------------
  377 const char* le_json_GetEventName
  378 (
  379     le_json_Event_t event
  380 );
  381 
  382 
  383 //--------------------------------------------------------------------------------------------------
  384 /**
  385  * @return Human readable string containing the name of a given JSON parsing context.
  386  */
  387 //--------------------------------------------------------------------------------------------------
  388 const char* le_json_GetContextName
  389 (
  390     le_json_ContextType_t context
  391 );
  392 
  393 
  394 //--------------------------------------------------------------------------------------------------
  395 /**
  396  * @return The number of bytes that have been read from the input stream so far.
  397  */
  398 //--------------------------------------------------------------------------------------------------
  399 size_t le_json_GetBytesRead
  400 (
  401     le_json_ParsingSessionRef_t session ///< Parsing session.
  402 );
  403 
  404 
  405 //--------------------------------------------------------------------------------------------------
  406 /**
  407  * For use by an event handler or error handler to fetch the JSON parsing session reference for
  408  * the session that called its handler function.
  409  *
  410  * @return The session reference of the JSON parsing session.
  411  *
  412  * @warning This function can only be called inside event or error handlers.
  413  */
  414 //--------------------------------------------------------------------------------------------------
  415 le_json_ParsingSessionRef_t le_json_GetSession
  416 (
  417     void
  418 );
  419 
  420 
  421 #endif // LEGATO_JSON_H_INCLUDE_GUARD
LE_JSON_ARRAY_END
array finished, subsequent values are outside this array 
Definition: le_json.h:147
LE_JSON_SYNTAX_ERROR
Syntax error, such as a missing comma or extra comma. 
Definition: le_json.h:178
LE_JSON_CONTEXT_NUMBER
Parsing number value. 
Definition: le_json.h:277
LE_JSON_CONTEXT_MEMBER
Parsing a member of an object. 
Definition: le_json.h:274
le_json_SetEventHandler
void le_json_SetEventHandler(le_json_EventHandler_t callbackFunc)
le_json_ErrorHandler_t
void(* le_json_ErrorHandler_t)(le_json_Error_t error, const char *msg)
Definition: le_json.h:194
le_json_GetSession
le_json_ParsingSessionRef_t le_json_GetSession(void)
LE_JSON_OBJECT_START
object started, subsequent object members are part of this object 
Definition: le_json.h:143
le_json_GetString
const char * le_json_GetString(void)
LE_JSON_TRUE
true value received 
Definition: le_json.h:150
LE_JSON_STRING
string value received: call le_json_GetString() to get value 
Definition: le_json.h:148
LE_JSON_CONTEXT_DOC
Top level of document, outside the main object/array. 
Definition: le_json.h:272
le_json_GetEventName
const char * le_json_GetEventName(le_json_Event_t event)
LE_JSON_DOC_END
End of the document reached. Parsing has stopped. 
Definition: le_json.h:153
LE_JSON_OBJECT_MEMBER
object member name received: Call le_json_GetString() to get name 
Definition: le_json.h:144
LE_JSON_OBJECT_END
object finished, subsequent members/values are outside this object 
Definition: le_json.h:145
LE_JSON_CONTEXT_FALSE
Parsing a false value. 
Definition: le_json.h:279
le_json_GetOpaquePtr
void * le_json_GetOpaquePtr(void)
LE_JSON_CONTEXT_TRUE
Parsing a true value. 
Definition: le_json.h:278
LE_JSON_READ_ERROR
Error when reading from the input byte stream. 
Definition: le_json.h:179
LE_JSON_CONTEXT_STRING
Parsing a string value. 
Definition: le_json.h:276
LE_JSON_NUMBER
number value received: call le_json_GetNumber() to get value 
Definition: le_json.h:149
LE_JSON_CONTEXT_NULL
Parsing a null value. 
Definition: le_json.h:280
le_json_Parse
le_json_ParsingSessionRef_t le_json_Parse(int fd, le_json_EventHandler_t eventHandler, le_json_ErrorHandler_t errorHandler, void *opaquePtr)
LE_JSON_CONTEXT_ARRAY
Parsing an array (list of unnamed elements). 
Definition: le_json.h:275
le_json_SetErrorHandler
void le_json_SetErrorHandler(le_json_ErrorHandler_t callbackFunc)
le_json_GetContextType
le_json_ContextType_t le_json_GetContextType(void)
le_json_ParseString
le_json_ParsingSessionRef_t le_json_ParseString(const char *jsonString, le_json_EventHandler_t eventHandler, le_json_ErrorHandler_t errorHandler, void *opaquePtr)
LE_JSON_NULL
null value received 
Definition: le_json.h:152
le_json_GetBytesRead
size_t le_json_GetBytesRead(le_json_ParsingSessionRef_t session)
le_json_ParsingSessionRef_t
struct le_json_ParsingSession * le_json_ParsingSessionRef_t
Definition: le_json.h:206
le_json_Event_t
le_json_Event_t
Definition: le_json.h:141
le_json_Error_t
le_json_Error_t
Definition: le_json.h:176
le_json_SetOpaquePtr
void le_json_SetOpaquePtr(void *ptr)
LE_JSON_FALSE
false value received 
Definition: le_json.h:151
LE_JSON_ARRAY_START
array started, upcoming values are elements of this array 
Definition: le_json.h:146
le_json_ContextType_t
le_json_ContextType_t
Definition: le_json.h:270
le_json_EventHandler_t
void(* le_json_EventHandler_t)(le_json_Event_t event)
Definition: le_json.h:166
LE_JSON_CONTEXT_OBJECT
Parsing an object (set of named members). 
Definition: le_json.h:273
le_json_GetNumber
double le_json_GetNumber(void)
le_json_Cleanup
void le_json_Cleanup(le_json_ParsingSessionRef_t session)
le_json_GetContextName
const char * le_json_GetContextName(le_json_ContextType_t context)