read.c

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/*-------------------------------------------------------------------------
 *
 * read.c
 *    routines to convert a string (legal ascii representation of node) back
 *    to nodes
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/nodes/read.c
 *
 * HISTORY
 *    AUTHOR            DATE            MAJOR EVENT
 *    Andrew Yu         Nov 2, 1994     file creation
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <ctype.h>

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


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

/* State flag that determines how readfuncs.c should treat location fields */
#ifdef WRITE_READ_PARSE_PLAN_TREES
bool        restore_location_fields = false;
#endif


/*
 * stringToNode -
 *    builds a Node tree from its string representation (assumed valid)
 *
 * restore_loc_fields instructs readfuncs.c whether to restore location
 * fields rather than set them to -1.  This is currently only supported
 * in builds with the WRITE_READ_PARSE_PLAN_TREES debugging flag set.
 */
static void *
stringToNodeInternal(const char *str, bool restore_loc_fields)
{
    void       *retval;
    const char *save_strtok;
#ifdef WRITE_READ_PARSE_PLAN_TREES
    bool        save_restore_location_fields;
#endif

    /*
     * 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 */

    /*
     * If enabled, likewise save/restore the location field handling flag.
     */
#ifdef WRITE_READ_PARSE_PLAN_TREES
    save_restore_location_fields = restore_location_fields;
    restore_location_fields = restore_loc_fields;
#endif

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

    pg_strtok_ptr = save_strtok;

#ifdef WRITE_READ_PARSE_PLAN_TREES
    restore_location_fields = save_restore_location_fields;
#endif

    return retval;
}

/*
 * Externally visible entry points
 */
void *
stringToNode(const char *str)
{
    return stringToNodeInternal(str, false);
}

#ifdef WRITE_READ_PARSE_PLAN_TREES

void *
stringToNodeWithLocations(const char *str)
{
    return stringToNodeInternal(str, true);
}

#endif


/*****************************************************************************
 *
 * 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.
 */
const char *
pg_strtok(int *length)
{
    const char *local_str;      /* working pointer to string */
    const 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(const 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(const char *token, int length)
{
    NodeTag     retval;
    const 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. strtoint() can do both for
         * us. We know the token will end at a character that strtoint will
         * stop at, so we do not need to modify the string.
         */
        char       *endptr;

        errno = 0;
        (void) strtoint(token, &endptr, 10);
        if (endptr != token + length || errno == ERANGE)
            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(const 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 ((int) 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 atoi will stop at
             */
            result = (Node *) makeInteger(atoi(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;
}