sexp.h

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 * continuations.  Manipulating continuations by hand is required if the
 * continuation-based parser is called directly.  This is <b>not
 * recommended</b> unless you are willing to deal with potential errors and
 * are willing to learn exactly how the continuation relates to the
 * internals of the parser.  A simpler approach is to use either the
 * <i>parse_sexp</i> function that simply returns an s-expression without
 * exposing the continuations, or the <i>iparse_sexp</i> function that
 * allows iteratively popping one s-expression at a time from a string
 * containing one or more s-expressions.  Refer to the documentation for
 * each parsing function for further details on behavior and usage.
 */
typedef struct pcont {
  /**
   * The parser stack used for iterative parsing.
   */
  faststack_t *stack;

  /**
   * The last full s-expression encountered by the parser.  If this is
   * NULL, the parser has not encountered a full s-expression and more
   * data is required for the current s-expression being parsed.  If this
   * is non-NULL, then the parser has encountered one s-expression and may
   * be partially through parsing the next s-expression.
   */
  sexp_t     *last_sexp;

  /**
   * Pointer to a temporary buffer used to store atom values during parsing.
   */
  char        *val;

  /**
   * Current number of bytes allocated for val.
   */
  int          val_allocated;

  /**
   * Current number of used bytes in val.
   */
  int          val_used;

  /**
   * Pointer to the character following the last character in the current
   * atom value being parsed.
   */
  char        *vcur;

  /**
   * Pointer to the last character to examine in the string being parsed.
   * When the parser is called with the continuation, this is the first
   * character that will be processed.  If this is NULL, the parser will
   * start parsing at the beginning of the string passed into the parser.
   */
  char        *lastPos;

  /**
   * This is a pointer to the beginning of the current string being
   * processed.  lastPos is a pointer to some value inside the string
   * that this points to.
   */
  char        *sbuffer;

  /**
   * This is the depth of parenthesis (the number of left parens encountered)
   * that the parser is currently working with.
   */
  unsigned int depth;

  /**
   * This is the depth of parenthesis encountered after a single quote (tick)
   * if the character immediately following the tick was a left paren.
   */
  unsigned int qdepth;

  /**
   * This is the state ID of the current state of the parser in the
   * DFA representing the parser.  The current parser is a DFA based parser
   * to simplify restoring the proper state from a continuation.
   */
  unsigned int state;

  /**
   * This is a flag indicating whether the next character to be processed
   * should be assumed to have been prefaced with a '\' character to escape
   * it.
   */
  unsigned int esc;

  /**
   * Flag whether or not we are processing an atom that was preceeded by
   * a single quote.
   */
  unsigned int squoted;

  /**
   * Error code.  Used to indicate that the continuation being returned does
   * not represent a successful parsing and thus the contents aren't of much
   * value.  If this value is 0, no error occurred.  Otherwise, it will be 1.
   */
  unsigned int error;

  /**
   * Mode.  The parsers' specialized behaviours can be activated by
   * tweaking the mode setting.  There are currently two available:
   * normal and inline_binary.  Inline_binary treats atoms that start
   * with #b# specially, assuming that they have the structure:
   *
   *    #b#s#data
   *
   * Where s is a positive (greater than 0) integer representing the length
   * of the data, and data is s bytes of binary data following the #
   * sign.  After the s bytes, it is assumed normal s-expression data
   * continues.
   */
  parsermode_t mode;

  /* -----------------------------------------------------------------
   * These fields below are related to dealing with INLINE_BINARY mode
   * ----------------------------------------------------------------- */

  /**
   * Length to expect of the current binary data being read in.
   * this also corresponds to the size of the memory allocated for
   * reading this binary data into.
   */
  unsigned int binexpected;

  /**
   * Number of bytes of the binary blob that have already been read in.
   */
  unsigned int binread;
  
  /**
   * Pointer to the memory containing the binary data being read in.
   */
  char *bindata;
} pcont_t;

/**
 * This structure is a wrapper around a standard I/O file descriptor and
 * the parsing infrastructure (continuation and a buffer) required to
 * parse off of it.  This is used so that routines can hide the loops and
 * details required to accumulate up data read off of the file descriptor
 * and parse expressions individually out of it.
 */
typedef struct sexp_iowrap {
  /**
   * Continuation used to parse off of the file descriptor.
   */
  pcont_t *cc;

  /**
   * The file descriptor.  Currently CANNOT be a socket since implementation
   * uses read(), not recv().
   */
  int fd;

  /**
   * Buffer to read data into before parsing.
   */
  char buf[BUFSIZ];
  
  /**
   * Byte count for last read.  If it is -1, there was an error.  Otherwise,
   * it will be a value from 0 to BUFSIZ.
   */
  int cnt;
} sexp_iowrap_t;

/*===========*/
/* FUNCTIONS */
/*===========*/

/* this is for C++ users */
#ifdef __cplusplus
extern "C" {
#endif
  /**
   * Set the parameters on atom value buffer allocation and growth sizes.
   * This is an important point for performance tuning, as many factors in
   * the expected expression structure must be taken into account such as:
   *
   *   - Average size of atom values
   *   - Variance in sizes of atom values
   *   - Amount of memory that is tolerably ''wasted'' (allocated but not
   *     used)
   *
   * The \a ss parameter specifies the initial size of all atom buffers.
   * Ideally, this should be sufficiently large to capture MOST atom values,
   * or at least close enough such that one growth is required.  The
   * \a gs parameter specifies the number of bytes to increase the buffer size
   * by when space is exhausted.  A safe choice for parameter sizes would
   * be on the order of the average size for \a ss, and one standard
   * deviation for \a gs.  This ensures that 50% of all expressions are
   * guaranteed to fit in the initial buffer, and rougly 80-90% will fit in
   * one growth.  If memory is not an issue, choosing ss to be the mean plus
   * one standard deviation will capture 80-90% of expressions in the initial
   * buffer, and a gs of one standard deviation will capture nearly all
   * expressions.
   *
   * Note: These parameters can be tuned at runtime as needs change, and they
   * will be applied to all expressions and expression elements parsed after
   * they are modified.  They will not be applied retroactively to expressions
   * that have already been parsed.
   */
  void set_parser_buffer_params(int ss, int gs);

  /**
   * return an allocated sexp_t.  This structure may be an already allocated
   * one from the stack or a new one if none are available.  Use this instead
   * of manually mallocing if you want to avoid excessive mallocs.  <I>Note:
   * Mallocing your own expressions is fine - you can even use 
   * sexp_t_deallocate to deallocate them and put them in the pool.</I>
   * Also, if the stack has not been initialized yet, this does so.
   */
  sexp_t *sexp_t_allocate();

  /**
   * given a malloc'd sexp_t element, put it back into the already-allocated
   * element stack.  This method will allocate a stack if one has not been
   * allocated already.
   */
  void sexp_t_deallocate(sexp_t *s);
  
  /**
   * In the event that someone wants us to release ALL of the memory used
   * between calls by the library, they can free it.  If you don't call
   * this, the caches will be persistent for the lifetime of the library
   * user.
   */
  void sexp_cleanup();

  /**
   * print a sexp_t struct as a string in the LISP style.  If the buffer
   * is large enough and the conversion is successful, the return value
   * represents the length of the string contained in the buffer.  If the
   * buffer was too small, or some other error occurred, the return
   * value is -1 and the contents of the buffer should not be assumed to
   * contain any useful information.
   */
  int print_sexp(char *loc, int size, sexp_t *e);

  /**
   * print a sexp_t structure to a buffer, growing it as necessary instead
   * of relying on fixed size buffers like print_sexp.  Important arguments
   * to tune for performance reasons are <tt>ss</tt> and <tt>gs</tt> - the
   * buffer start size and growth size.
   */
  int print_sexp_cstr(CSTRING **s, sexp_t *e, int ss, int gs);

  /**
   * Allocate a new sexp_t element representing a list.
   */
  sexp_t *new_sexp_list(sexp_t *l);
  
  /**
   * allocate a new sexp_t element representing a value 
   */
  sexp_t *new_sexp_atom(char *buf, int bs);
    
  /** 
   * create an initial continuation for parsing the given string 
   */
  pcont_t *init_continuation(char *str);

  /**
   * destroy a continuation.  This involves cleaning up what it contains,
   * and cleaning up the continuation itself.
   */
  void destroy_continuation (pcont_t * pc);

  /**
   * create an IO wrapper structure around a file descriptor.
   */
  sexp_iowrap_t *init_iowrap(int fd);

  /**
   * destroy an IO wrapper structure
   */
  void destroy_iowrap(sexp_iowrap_t *iow);

  /**
   * given and IO wrapper handle, read one s-expression off of it.  this
   * expression may be contained in a continuation, so there is no
   * guarantee that under the covers an IO read actually is occuring.
   * returning null implies no s-expression was able to be read.
   */
  sexp_t *read_one_sexp(sexp_iowrap_t *iow);
  
  /** 
   * wrapper around parser for compatibility. 
   */
  sexp_t *parse_sexp(char *s, int len);

  /** 
   * wrapper around parser for friendlier continuation use 
   * pre-condition : continuation (cc) is NON-NULL! 
   */
  sexp_t *iparse_sexp(char *s, int len, pcont_t *cc);
  
  /**
   * given a LISP style s-expression string, parse it into a set of
   * connected sexp_t structures. 
   */
  pcont_t *cparse_sexp(char *s, int len, pcont_t *pc);
  
  /**
   * given a sexp_t structure, free the memory it uses (and recursively free
   * the memory used by all sexp_t structures that it references).  Note
   * that this will call the deallocation routine for sexp_t elements.
   * This means that memory isn't freed, but stored away in a cache of
   * pre-allocated elements.  This is an optimization to speed up the
   * parser to eliminate wasteful free and re-malloc calls.
   */
  void destroy_sexp(sexp_t *s);

/* this is for C++ users */
#ifdef __cplusplus
}
#endif

#include "sexp_ops.h"

#endif /* __SEXP_H__ */