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  * @ref 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_errors 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.  Use of this work is subject to license.
  122  */
  123 //--------------------------------------------------------------------------------------------------
  124 
  125 /** @file le_json.h
  126  *
  127  * Legato @ref c_json include file.
  128  *
  129  * Copyright (C) Sierra Wireless Inc. Use of this work is subject to license.
  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 /**
  227  * Stops parsing and cleans up memory allocated by the parser.
  228  *
  229  * @warning Be sure to stop parsing before closing the file descriptor.
  230  */
  231 //--------------------------------------------------------------------------------------------------
  232 void le_json_Cleanup
  233 (
  234     le_json_ParsingSessionRef_t session ///< The parsing session to clean up (see le_json_Parse()).
  235 );
  236 
  237 
  238 //--------------------------------------------------------------------------------------------------
  239 /**
  240  * Set the current context's event handler function.
  241  *
  242  * @warning This function can only be called inside event or error handlers.
  243  */
  244 //--------------------------------------------------------------------------------------------------
  245 void le_json_SetEventHandler
  246 (
  247     le_json_EventHandler_t  callbackFunc  ///< Function to call when parsing events happen.
  248 );
  249 
  250 
  251 //--------------------------------------------------------------------------------------------------
  252 /**
  253  * Enumeration of the different types of "contexts" that can exist during a parsing session.
  254  */
  255 //--------------------------------------------------------------------------------------------------
  256 typedef enum
  257 {
  258     LE_JSON_CONTEXT_DOC,    ///< Top level of document, outside the main object/array.
  259     LE_JSON_CONTEXT_OBJECT, ///< Parsing an object (set of named members).
  260     LE_JSON_CONTEXT_MEMBER, ///< Parsing a member of an object.
  261     LE_JSON_CONTEXT_ARRAY,  ///< Parsing an array (list of unnamed elements).
  262     LE_JSON_CONTEXT_STRING, ///< Parsing a string value.
  263     LE_JSON_CONTEXT_NUMBER, ///< Parsing number value.
  264     LE_JSON_CONTEXT_TRUE,   ///< Parsing a true value.
  265     LE_JSON_CONTEXT_FALSE,  ///< Parsing a false value.
  266     LE_JSON_CONTEXT_NULL,   ///< Parsing a null value.
  267 }
  268 le_json_ContextType_t;
  269 
  270 
  271 //--------------------------------------------------------------------------------------------------
  272 /**
  273  * Get the type of parsing context that the parser is currently in.
  274  *
  275  * @return The context type.
  276  *
  277  * @warning This function can only be called inside event or error handlers.
  278  */
  279 //--------------------------------------------------------------------------------------------------
  280 le_json_ContextType_t le_json_GetContextType
  281 (
  282     void
  283 );
  284 
  285 
  286 //--------------------------------------------------------------------------------------------------
  287 /**
  288  * Set the opaque pointer attached to the parser.
  289  *
  290  * @warning This function can only be called inside event or error handlers.
  291  */
  292 //--------------------------------------------------------------------------------------------------
  293 void le_json_SetOpaquePtr
  294 (
  295     void* ptr    ///< Opaque pointer to be fetched using le_json_GetOpaquePtr().
  296 );
  297 
  298 
  299 //--------------------------------------------------------------------------------------------------
  300 /**
  301  * Get the opaque pointer attached to the parser.
  302  *
  303  * @return The pointer previously set by le_json_Parse() or a subsequent call to
  304  *         le_json_SetOpaquePtr().
  305  *
  306  * @warning This function can only be called inside event or error handlers.
  307  */
  308 //--------------------------------------------------------------------------------------------------
  309 void* le_json_GetOpaquePtr
  310 (
  311     void
  312 );
  313 
  314 
  315 //--------------------------------------------------------------------------------------------------
  316 /**
  317  * Set the error handler function
  318  *
  319  * @warning This function can only be called inside event or error handlers.
  320  */
  321 //--------------------------------------------------------------------------------------------------
  322 void le_json_SetErrorHandler
  323 (
  324     le_json_ErrorHandler_t  callbackFunc    ///< Function to call when parsing errors happen.
  325 );
  326 
  327 
  328 //--------------------------------------------------------------------------------------------------
  329 /**
  330  * Fetches a pointer to a string value or object member name.
  331  *
  332  * This pointer is only valid until the event handler returns.
  333  *
  334  * @warning This function can only be called inside event handlers when LE_JSON_OBJECT_MEMBER
  335  *          or LE_JSON_STRING events are being handled.
  336  */
  337 //--------------------------------------------------------------------------------------------------
  338 const char* le_json_GetString
  339 (
  340     void
  341 );
  342 
  343 
  344 //--------------------------------------------------------------------------------------------------
  345 /**
  346  * Fetches the value of a parsed number.
  347  *
  348  * @warning This function can only be called inside event handlers when LE_JSON_NUMBER events are
  349  *          being handled.
  350  */
  351 //--------------------------------------------------------------------------------------------------
  352 double le_json_GetNumber
  353 (
  354     void
  355 );
  356 
  357 
  358 //--------------------------------------------------------------------------------------------------
  359 /**
  360  * @return Human readable string containing the name of a given JSON parsing event.
  361  */
  362 //--------------------------------------------------------------------------------------------------
  363 const char* le_json_GetEventName
  364 (
  365     le_json_Event_t event
  366 );
  367 
  368 
  369 //--------------------------------------------------------------------------------------------------
  370 /**
  371  * @return Human readable string containing the name of a given JSON parsing context.
  372  */
  373 //--------------------------------------------------------------------------------------------------
  374 const char* le_json_GetContextName
  375 (
  376     le_json_ContextType_t context
  377 );
  378 
  379 
  380 //--------------------------------------------------------------------------------------------------
  381 /**
  382  * @return The number of bytes that have been read from the input stream so far.
  383  */
  384 //--------------------------------------------------------------------------------------------------
  385 size_t le_json_GetBytesRead
  386 (
  387     le_json_ParsingSessionRef_t session ///< Parsing session.
  388 );
  389 
  390 
  391 //--------------------------------------------------------------------------------------------------
  392 /**
  393  * For use by an event handler or error handler to fetch the JSON parsing session reference for
  394  * the session that called its handler function.
  395  *
  396  * @return The session reference of the JSON parsing session.
  397  *
  398  * @warning This function can only be called inside event or error handlers.
  399  */
  400 //--------------------------------------------------------------------------------------------------
  401 le_json_ParsingSessionRef_t le_json_GetSession
  402 (
  403     void
  404 );
  405 
  406 
  407 #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:263
LE_JSON_CONTEXT_MEMBER
Parsing a member of an object. 
Definition: le_json.h:260
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:258
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:265
le_json_GetOpaquePtr
void * le_json_GetOpaquePtr(void)
LE_JSON_CONTEXT_TRUE
Parsing a true value. 
Definition: le_json.h:264
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:262
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:266
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:261
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_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:256
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:259
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)