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read.c
/*-------------------------------------------------------------------------
 *
 * read.c
 *      routines to convert a string (legal ascii representation of node) back
 *      to nodes
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      $PostgreSQL: pgsql/src/backend/nodes/read.c,v 1.52 2009/01/01 17:23:43 momjian Exp $
 *
 * HISTORY
 *      AUTHOR                DATE              MAJOR EVENT
 *      Andrew Yu             Nov 2, 1994       file creation
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <ctype.h>

#include "nodes/pg_list.h"
#include "nodes/readfuncs.h"
#include "nodes/value.h"


/* Static state for pg_strtok */
static char *pg_strtok_ptr = NULL;


/*
 * stringToNode -
 *      returns a Node with a given legal ASCII representation
 */
void *
stringToNode(char *str)
{
      char     *save_strtok;
      void     *retval;

      /*
       * We save and restore the pre-existing state of pg_strtok. This makes the
       * world safe for re-entrant invocation of stringToNode, without incurring
       * a lot of notational overhead by having to pass the next-character
       * pointer around through all the readfuncs.c code.
       */
      save_strtok = pg_strtok_ptr;

      pg_strtok_ptr = str;          /* point pg_strtok at the string to read */

      retval = nodeRead(NULL, 0); /* do the reading */

      pg_strtok_ptr = save_strtok;

      return retval;
}

/*****************************************************************************
 *
 * the lisp token parser
 *
 *****************************************************************************/

/*
 * pg_strtok --- retrieve next "token" from a string.
 *
 * Works kinda like strtok, except it never modifies the source string.
 * (Instead of storing nulls into the string, the length of the token
 * is returned to the caller.)
 * Also, the rules about what is a token are hard-wired rather than being
 * configured by passing a set of terminating characters.
 *
 * The string is assumed to have been initialized already by stringToNode.
 *
 * The rules for tokens are:
 *    * Whitespace (space, tab, newline) always separates tokens.
 *    * The characters '(', ')', '{', '}' form individual tokens even
 *      without any whitespace around them.
 *    * Otherwise, a token is all the characters up to the next whitespace
 *      or occurrence of one of the four special characters.
 *    * A backslash '\' can be used to quote whitespace or one of the four
 *      special characters, so that it is treated as a plain token character.
 *      Backslashes themselves must also be backslashed for consistency.
 *      Any other character can be, but need not be, backslashed as well.
 *    * If the resulting token is '<>' (with no backslash), it is returned
 *      as a non-NULL pointer to the token but with length == 0.  Note that
 *      there is no other way to get a zero-length token.
 *
 * Returns a pointer to the start of the next token, and the length of the
 * token (including any embedded backslashes!) in *length.  If there are
 * no more tokens, NULL and 0 are returned.
 *
 * NOTE: this routine doesn't remove backslashes; the caller must do so
 * if necessary (see "debackslash").
 *
 * NOTE: prior to release 7.0, this routine also had a special case to treat
 * a token starting with '"' as extending to the next '"'.  This code was
 * broken, however, since it would fail to cope with a string containing an
 * embedded '"'.  I have therefore removed this special case, and instead
 * introduced rules for using backslashes to quote characters.    Higher-level
 * code should add backslashes to a string constant to ensure it is treated
 * as a single token.
 */
char *
pg_strtok(int *length)
{
      char     *local_str;          /* working pointer to string */
      char     *ret_str;            /* start of token to return */

      local_str = pg_strtok_ptr;

      while (*local_str == ' ' || *local_str == '\n' || *local_str == '\t')
            local_str++;

      if (*local_str == '\0')
      {
            *length = 0;
            pg_strtok_ptr = local_str;
            return NULL;                  /* no more tokens */
      }

      /*
       * Now pointing at start of next token.
       */
      ret_str = local_str;

      if (*local_str == '(' || *local_str == ')' ||
            *local_str == '{' || *local_str == '}')
      {
            /* special 1-character token */
            local_str++;
      }
      else
      {
            /* Normal token, possibly containing backslashes */
            while (*local_str != '\0' &&
                     *local_str != ' ' && *local_str != '\n' &&
                     *local_str != '\t' &&
                     *local_str != '(' && *local_str != ')' &&
                     *local_str != '{' && *local_str != '}')
            {
                  if (*local_str == '\\' && local_str[1] != '\0')
                        local_str += 2;
                  else
                        local_str++;
            }
      }

      *length = local_str - ret_str;

      /* Recognize special case for "empty" token */
      if (*length == 2 && ret_str[0] == '<' && ret_str[1] == '>')
            *length = 0;

      pg_strtok_ptr = local_str;

      return ret_str;
}

/*
 * debackslash -
 *      create a palloc'd string holding the given token.
 *      any protective backslashes in the token are removed.
 */
char *
debackslash(char *token, int length)
{
      char     *result = palloc(length + 1);
      char     *ptr = result;

      while (length > 0)
      {
            if (*token == '\\' && length > 1)
                  token++, length--;
            *ptr++ = *token++;
            length--;
      }
      *ptr = '\0';
      return result;
}

#define RIGHT_PAREN (1000000 + 1)
#define LEFT_PAREN      (1000000 + 2)
#define LEFT_BRACE      (1000000 + 3)
#define OTHER_TOKEN (1000000 + 4)

/*
 * nodeTokenType -
 *      returns the type of the node token contained in token.
 *      It returns one of the following valid NodeTags:
 *          T_Integer, T_Float, T_String, T_BitString
 *      and some of its own:
 *          RIGHT_PAREN, LEFT_PAREN, LEFT_BRACE, OTHER_TOKEN
 *
 *      Assumption: the ascii representation is legal
 */
static NodeTag
nodeTokenType(char *token, int length)
{
      NodeTag           retval;
      char     *numptr;
      int               numlen;

      /*
       * Check if the token is a number
       */
      numptr = token;
      numlen = length;
      if (*numptr == '+' || *numptr == '-')
            numptr++, numlen--;
      if ((numlen > 0 && isdigit((unsigned char) *numptr)) ||
            (numlen > 1 && *numptr == '.' && isdigit((unsigned char) numptr[1])))
      {
            /*
             * Yes.  Figure out whether it is integral or float; this requires
             * both a syntax check and a range check. strtol() can do both for us.
             * We know the token will end at a character that strtol will stop at,
             * so we do not need to modify the string.
             */
            long        val;
            char     *endptr;

            errno = 0;
            val = strtol(token, &endptr, 10);
            if (endptr != token + length || errno == ERANGE
#ifdef HAVE_LONG_INT_64
            /* if long > 32 bits, check for overflow of int4 */
                  || val != (long) ((int32) val)
#endif
                  )
                  return T_Float;
            return T_Integer;
      }

      /*
       * these three cases do not need length checks, since pg_strtok() will
       * always treat them as single-byte tokens
       */
      else if (*token == '(')
            retval = LEFT_PAREN;
      else if (*token == ')')
            retval = RIGHT_PAREN;
      else if (*token == '{')
            retval = LEFT_BRACE;
      else if (*token == '\"' && length > 1 && token[length - 1] == '\"')
            retval = T_String;
      else if (*token == 'b')
            retval = T_BitString;
      else
            retval = OTHER_TOKEN;
      return retval;
}

/*
 * nodeRead -
 *      Slightly higher-level reader.
 *
 * This routine applies some semantic knowledge on top of the purely
 * lexical tokenizer pg_strtok().   It can read
 *    * Value token nodes (integers, floats, or strings);
 *    * General nodes (via parseNodeString() from readfuncs.c);
 *    * Lists of the above;
 *    * Lists of integers or OIDs.
 * The return value is declared void *, not Node *, to avoid having to
 * cast it explicitly in callers that assign to fields of different types.
 *
 * External callers should always pass NULL/0 for the arguments.  Internally
 * a non-NULL token may be passed when the upper recursion level has already
 * scanned the first token of a node's representation.
 *
 * We assume pg_strtok is already initialized with a string to read (hence
 * this should only be invoked from within a stringToNode operation).
 */
void *
nodeRead(char *token, int tok_len)
{
      Node     *result;
      NodeTag           type;

      if (token == NULL)                  /* need to read a token? */
      {
            token = pg_strtok(&tok_len);

            if (token == NULL)            /* end of input */
                  return NULL;
      }

      type = nodeTokenType(token, tok_len);

      switch (type)
      {
            case LEFT_BRACE:
                  result = parseNodeString();
                  token = pg_strtok(&tok_len);
                  if (token == NULL || token[0] != '}')
                        elog(ERROR, "did not find '}' at end of input node");
                  break;
            case LEFT_PAREN:
                  {
                        List     *l = NIL;

                        /*----------
                         * Could be an integer list:  (i int int ...)
                         * or an OID list:                        (o int int ...)
                         * or a list of nodes/values: (node node ...)
                         *----------
                         */
                        token = pg_strtok(&tok_len);
                        if (token == NULL)
                              elog(ERROR, "unterminated List structure");
                        if (tok_len == 1 && token[0] == 'i')
                        {
                              /* List of integers */
                              for (;;)
                              {
                                    int               val;
                                    char     *endptr;

                                    token = pg_strtok(&tok_len);
                                    if (token == NULL)
                                          elog(ERROR, "unterminated List structure");
                                    if (token[0] == ')')
                                          break;
                                    val = (int) strtol(token, &endptr, 10);
                                    if (endptr != token + tok_len)
                                          elog(ERROR, "unrecognized integer: \"%.*s\"",
                                                 tok_len, token);
                                    l = lappend_int(l, val);
                              }
                        }
                        else if (tok_len == 1 && token[0] == 'o')
                        {
                              /* List of OIDs */
                              for (;;)
                              {
                                    Oid               val;
                                    char     *endptr;

                                    token = pg_strtok(&tok_len);
                                    if (token == NULL)
                                          elog(ERROR, "unterminated List structure");
                                    if (token[0] == ')')
                                          break;
                                    val = (Oid) strtoul(token, &endptr, 10);
                                    if (endptr != token + tok_len)
                                          elog(ERROR, "unrecognized OID: \"%.*s\"",
                                                 tok_len, token);
                                    l = lappend_oid(l, val);
                              }
                        }
                        else
                        {
                              /* List of other node types */
                              for (;;)
                              {
                                    /* We have already scanned next token... */
                                    if (token[0] == ')')
                                          break;
                                    l = lappend(l, nodeRead(token, tok_len));
                                    token = pg_strtok(&tok_len);
                                    if (token == NULL)
                                          elog(ERROR, "unterminated List structure");
                              }
                        }
                        result = (Node *) l;
                        break;
                  }
            case RIGHT_PAREN:
                  elog(ERROR, "unexpected right parenthesis");
                  result = NULL;          /* keep compiler happy */
                  break;
            case OTHER_TOKEN:
                  if (tok_len == 0)
                  {
                        /* must be "<>" --- represents a null pointer */
                        result = NULL;
                  }
                  else
                  {
                        elog(ERROR, "unrecognized token: \"%.*s\"", tok_len, token);
                        result = NULL;    /* keep compiler happy */
                  }
                  break;
            case T_Integer:

                  /*
                   * we know that the token terminates on a char atol will stop at
                   */
                  result = (Node *) makeInteger(atol(token));
                  break;
            case T_Float:
                  {
                        char     *fval = (char *) palloc(tok_len + 1);

                        memcpy(fval, token, tok_len);
                        fval[tok_len] = '\0';
                        result = (Node *) makeFloat(fval);
                  }
                  break;
            case T_String:
                  /* need to remove leading and trailing quotes, and backslashes */
                  result = (Node *) makeString(debackslash(token + 1, tok_len - 2));
                  break;
            case T_BitString:
                  {
                        char     *val = palloc(tok_len);

                        /* skip leading 'b' */
                        memcpy(val, token + 1, tok_len - 1);
                        val[tok_len - 1] = '\0';
                        result = (Node *) makeBitString(val);
                        break;
                  }
            default:
                  elog(ERROR, "unrecognized node type: %d", (int) type);
                  result = NULL;          /* keep compiler happy */
                  break;
      }

      return (void *) result;
}

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