psqlscanslash.l

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%top{
/*-------------------------------------------------------------------------
 *
 * psqlscanslash.l
 *    lexical scanner for psql backslash commands
 *
 * XXX Avoid creating backtracking cases --- see the backend lexer for info.
 *
 * See fe_utils/psqlscan_int.h for additional commentary.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/bin/psql/psqlscanslash.l
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"
 
#include <ctype.h>
 
#include "common.h"
#include "psqlscanslash.h"
 
#include "common/logging.h"
#include "fe_utils/conditional.h"
 
#include "libpq-fe.h"
}
 
%{
#include "fe_utils/psqlscan_int.h"
 
/*
 * We must have a typedef YYSTYPE for yylex's first argument, but this lexer
 * doesn't presently make use of that argument, so just declare it as int.
 */
typedef int YYSTYPE;
 
/*
 * These variables do not need to be saved across calls.  Yeah, it's a bit
 * of a hack, but putting them into PsqlScanStateData would be klugy too.
 */
static enum slash_option_type option_type;
static char *option_quote;
static int  unquoted_option_chars;
static int  backtick_start_offset;
 
 
/* Return values from yylex() */
#define LEXRES_EOL          0   /* end of input */
#define LEXRES_OK           1   /* OK completion of backslash argument */
 
 
static void evaluate_backtick(PsqlScanState state);
 
#define ECHO psqlscan_emit(cur_state, yytext, yyleng)
 
/* LCOV_EXCL_START */
 
%}
 
/* Except for the prefix, these options should match psqlscan.l */
%option reentrant
%option bison-bridge
%option 8bit
%option never-interactive
%option nodefault
%option noinput
%option nounput
%option noyywrap
%option warn
%option prefix="slash_yy"
 
/*
 * Set the type of yyextra; we use it as a pointer back to the containing
 * PsqlScanState.
 */
%option extra-type="PsqlScanState"
 
/*
 * OK, here is a short description of lex/flex rules behavior.
 * The longest pattern which matches an input string is always chosen.
 * For equal-length patterns, the first occurring in the rules list is chosen.
 * INITIAL is the starting state, to which all non-conditional rules apply.
 * Exclusive states change parsing rules while the state is active.  When in
 * an exclusive state, only those rules defined for that state apply.
 */
 
/* Exclusive states for lexing backslash commands */
%x xslashcmd
%x xslashargstart
%x xslasharg
%x xslashquote
%x xslashbackquote
%x xslashdquote
%x xslashwholeline
%x xslashend
 
/*
 * Assorted character class definitions that should match psqlscan.l.
 */
space           [ \t\n\r\f\v]
quote           '
xeoctesc        [\\][0-7]{1,3}
xehexesc        [\\]x[0-9A-Fa-f]{1,2}
xqdouble        {quote}{quote}
dquote          \"
variable_char   [A-Za-z\200-\377_0-9]
 
other           .
 
%%
 
%{
        /* Declare some local variables inside yylex(), for convenience */
        PsqlScanState cur_state = yyextra;
        PQExpBuffer output_buf = cur_state->output_buf;
 
        /*
         * Force flex into the state indicated by start_state.  This has a
         * couple of purposes: it lets some of the functions below set a new
         * starting state without ugly direct access to flex variables, and it
         * allows us to transition from one flex lexer to another so that we
         * can lex different parts of the source string using separate lexers.
         */
        BEGIN(cur_state->start_state);
%}
 
    /*
     * We don't really expect to be invoked in the INITIAL state in this
     * lexer; but if we are, just spit data to the output_buf until EOF.
     */
 
{other}|\n      { ECHO; }
 
    /*
     * Exclusive lexer states to handle backslash command lexing
     */
 
<xslashcmd>{
    /* command name ends at whitespace or backslash; eat all else */
 
{space}|"\\"    {
                    yyless(0);
                    cur_state->start_state = YY_START;
                    return LEXRES_OK;
                }
 
{other}         { ECHO; }
 
}
 
<xslashargstart>{
    /*
     * Discard any whitespace before argument, then go to xslasharg state.
     * An exception is that "|" is only special at start of argument, so we
     * check for it here.
     */
 
{space}+        { }
 
"|"             {
                    if (option_type == OT_FILEPIPE)
                    {
                        /* treat like whole-string case */
                        ECHO;
                        BEGIN(xslashwholeline);
                    }
                    else
                    {
                        /* vertical bar is not special otherwise */
                        yyless(0);
                        BEGIN(xslasharg);
                    }
                }
 
{other}         {
                    yyless(0);
                    BEGIN(xslasharg);
                }
 
}
 
<xslasharg>{
    /*
     * Default processing of text in a slash command's argument.
     *
     * Note: unquoted_option_chars counts the number of characters at the
     * end of the argument that were not subject to any form of quoting.
     * psql_scan_slash_option needs this to strip trailing semicolons safely.
     */
 
{space}|"\\"    {
                    /*
                     * Unquoted space is end of arg; do not eat.  Likewise
                     * backslash is end of command or next command, do not eat
                     *
                     * XXX this means we can't conveniently accept options
                     * that include unquoted backslashes; therefore, option
                     * processing that encourages use of backslashes is rather
                     * broken.
                     */
                    yyless(0);
                    cur_state->start_state = YY_START;
                    return LEXRES_OK;
                }
 
{quote}         {
                    *option_quote = '\'';
                    unquoted_option_chars = 0;
                    BEGIN(xslashquote);
                }
 
"`"             {
                    backtick_start_offset = output_buf->len;
                    *option_quote = '`';
                    unquoted_option_chars = 0;
                    BEGIN(xslashbackquote);
                }
 
{dquote}        {
                    ECHO;
                    *option_quote = '"';
                    unquoted_option_chars = 0;
                    BEGIN(xslashdquote);
                }
 
:{variable_char}+   {
                    /* Possible psql variable substitution */
                    if (cur_state->callbacks->get_variable == NULL)
                        ECHO;
                    else
                    {
                        char       *varname;
                        char       *value;
 
                        varname = psqlscan_extract_substring(cur_state,
                                                             yytext + 1,
                                                             yyleng - 1);
                        value = cur_state->callbacks->get_variable(varname,
                                                                   PQUOTE_PLAIN,
                                                                   cur_state->cb_passthrough);
                        free(varname);
 
                        /*
                         * The variable value is just emitted without any
                         * further examination.  This is consistent with the
                         * pre-8.0 code behavior, if not with the way that
                         * variables are handled outside backslash commands.
                         * Note that we needn't guard against recursion here.
                         */
                        if (value)
                        {
                            appendPQExpBufferStr(output_buf, value);
                            free(value);
                        }
                        else
                            ECHO;
 
                        *option_quote = ':';
                    }
                    unquoted_option_chars = 0;
                }
 
:'{variable_char}+' {
                    psqlscan_escape_variable(cur_state, yytext, yyleng,
                                             PQUOTE_SQL_LITERAL);
                    *option_quote = ':';
                    unquoted_option_chars = 0;
                }
 
 
:\"{variable_char}+\"   {
                    psqlscan_escape_variable(cur_state, yytext, yyleng,
                                             PQUOTE_SQL_IDENT);
                    *option_quote = ':';
                    unquoted_option_chars = 0;
                }
 
:\{\?{variable_char}+\} {
                    psqlscan_test_variable(cur_state, yytext, yyleng);
                }
 
:'{variable_char}*  {
                    /* Throw back everything but the colon */
                    yyless(1);
                    unquoted_option_chars++;
                    ECHO;
                }
 
:\"{variable_char}* {
                    /* Throw back everything but the colon */
                    yyless(1);
                    unquoted_option_chars++;
                    ECHO;
                }
 
:\{\?{variable_char}*   {
                    /* Throw back everything but the colon */
                    yyless(1);
                    unquoted_option_chars++;
                    ECHO;
                }
 
:\{     {
                    /* Throw back everything but the colon */
                    yyless(1);
                    unquoted_option_chars++;
                    ECHO;
                }
 
{other}         {
                    unquoted_option_chars++;
                    ECHO;
                }
 
}
 
<xslashquote>{
    /*
     * single-quoted text: copy literally except for '' and backslash
     * sequences
     */
 
{quote}         { BEGIN(xslasharg); }
 
{xqdouble}      { appendPQExpBufferChar(output_buf, '\''); }
 
"\\n"           { appendPQExpBufferChar(output_buf, '\n'); }
"\\t"           { appendPQExpBufferChar(output_buf, '\t'); }
"\\b"           { appendPQExpBufferChar(output_buf, '\b'); }
"\\r"           { appendPQExpBufferChar(output_buf, '\r'); }
"\\f"           { appendPQExpBufferChar(output_buf, '\f'); }
 
{xeoctesc}      {
                    /* octal case */
                    appendPQExpBufferChar(output_buf,
                                          (char) strtol(yytext + 1, NULL, 8));
                }
 
{xehexesc}      {
                    /* hex case */
                    appendPQExpBufferChar(output_buf,
                                          (char) strtol(yytext + 2, NULL, 16));
                }
 
"\\".           { psqlscan_emit(cur_state, yytext + 1, 1); }
 
{other}|\n      { ECHO; }
 
}
 
<xslashbackquote>{
    /*
     * backticked text: copy everything until next backquote (expanding
     * variable references, but doing nought else), then evaluate.
     */
 
"`"             {
                    /* In an inactive \if branch, don't evaluate the command */
                    if (cur_state->cb_passthrough == NULL ||
                        conditional_active((ConditionalStack) cur_state->cb_passthrough))
                        evaluate_backtick(cur_state);
                    BEGIN(xslasharg);
                }
 
:{variable_char}+   {
                    /* Possible psql variable substitution */
                    if (cur_state->callbacks->get_variable == NULL)
                        ECHO;
                    else
                    {
                        char       *varname;
                        char       *value;
 
                        varname = psqlscan_extract_substring(cur_state,
                                                             yytext + 1,
                                                             yyleng - 1);
                        value = cur_state->callbacks->get_variable(varname,
                                                                   PQUOTE_PLAIN,
                                                                   cur_state->cb_passthrough);
                        free(varname);
 
                        if (value)
                        {
                            appendPQExpBufferStr(output_buf, value);
                            free(value);
                        }
                        else
                            ECHO;
                    }
                }
 
:'{variable_char}+' {
                    psqlscan_escape_variable(cur_state, yytext, yyleng,
                                             PQUOTE_SHELL_ARG);
                }
 
:'{variable_char}*  {
                    /* Throw back everything but the colon */
                    yyless(1);
                    ECHO;
                }
 
{other}|\n      { ECHO; }
 
}
 
<xslashdquote>{
    /* double-quoted text: copy verbatim, including the double quotes */
 
{dquote}        {
                    ECHO;
                    BEGIN(xslasharg);
                }
 
{other}|\n      { ECHO; }
 
}
 
<xslashwholeline>{
    /* copy everything until end of input line */
    /* but suppress leading whitespace */
 
{space}+        {
                    if (output_buf->len > 0)
                        ECHO;
                }
 
{other}         { ECHO; }
 
}
 
<xslashend>{
    /* at end of command, eat a double backslash, but not anything else */
 
"\\\\"          {
                    cur_state->start_state = YY_START;
                    return LEXRES_OK;
                }
 
{other}|\n      {
                    yyless(0);
                    cur_state->start_state = YY_START;
                    return LEXRES_OK;
                }
 
}
 
<<EOF>>         {
                    if (cur_state->buffer_stack == NULL)
                    {
                        cur_state->start_state = YY_START;
                        return LEXRES_EOL;      /* end of input reached */
                    }
 
                    /*
                     * We were expanding a variable, so pop the inclusion
                     * stack and keep lexing
                     */
                    psqlscan_pop_buffer_stack(cur_state);
                    psqlscan_select_top_buffer(cur_state);
                }
 
%%
 
/* LCOV_EXCL_STOP */
 
/*
 * Scan the command name of a psql backslash command.  This should be called
 * after psql_scan() returns PSCAN_BACKSLASH.  It is assumed that the input
 * has been consumed through the leading backslash.
 *
 * The return value is a malloc'd copy of the command name, as parsed off
 * from the input.
 */
char *
psql_scan_slash_command(PsqlScanState state)
{
    PQExpBufferData mybuf;
 
    /* Must be scanning already */
    Assert(state->scanbufhandle != NULL);
 
    /* Build a local buffer that we'll return the data of */
    initPQExpBuffer(&mybuf);
 
    /* Set current output target */
    state->output_buf = &mybuf;
 
    /* Set input source */
    if (state->buffer_stack != NULL)
        yy_switch_to_buffer(state->buffer_stack->buf, state->scanner);
    else
        yy_switch_to_buffer(state->scanbufhandle, state->scanner);
 
    /*
     * Set lexer start state.  Note that this is sufficient to switch
     * state->scanner over to using the tables in this lexer file.
     */
    state->start_state = xslashcmd;
 
    /* And lex. */
    yylex(NULL, state->scanner);
 
    /* There are no possible errors in this lex state... */
 
    /*
     * In case the caller returns to using the regular SQL lexer, reselect the
     * appropriate initial state.
     */
    psql_scan_reselect_sql_lexer(state);
 
    return mybuf.data;
}
 
/*
 * Parse off the next argument for a backslash command, and return it as a
 * malloc'd string.  If there are no more arguments, returns NULL.
 *
 * type tells what processing, if any, to perform on the option string;
 * for example, if it's a SQL identifier, we want to downcase any unquoted
 * letters.
 *
 * if quote is not NULL, *quote is set to 0 if no quoting was found, else
 * the last quote symbol used in the argument.
 *
 * if semicolon is true, unquoted trailing semicolon(s) that would otherwise
 * be taken as part of the option string will be stripped.
 *
 * NOTE: the only possible syntax errors for backslash options are unmatched
 * quotes, which are detected when we run out of input.  Therefore, on a
 * syntax error we just throw away the string and return NULL; there is no
 * need to worry about flushing remaining input.
 */
char *
psql_scan_slash_option(PsqlScanState state,
                       enum slash_option_type type,
                       char *quote,
                       bool semicolon)
{
    PQExpBufferData mybuf;
    int         lexresult PG_USED_FOR_ASSERTS_ONLY;
    int         final_state;
    char        local_quote;
 
    /* Must be scanning already */
    Assert(state->scanbufhandle != NULL);
 
    if (quote == NULL)
        quote = &local_quote;
    *quote = 0;
 
    /* Build a local buffer that we'll return the data of */
    initPQExpBuffer(&mybuf);
 
    /* Set up static variables that will be used by yylex */
    option_type = type;
    option_quote = quote;
    unquoted_option_chars = 0;
 
    /* Set current output target */
    state->output_buf = &mybuf;
 
    /* Set input source */
    if (state->buffer_stack != NULL)
        yy_switch_to_buffer(state->buffer_stack->buf, state->scanner);
    else
        yy_switch_to_buffer(state->scanbufhandle, state->scanner);
 
    /* Set lexer start state */
    if (type == OT_WHOLE_LINE)
        state->start_state = xslashwholeline;
    else
        state->start_state = xslashargstart;
 
    /* And lex. */
    lexresult = yylex(NULL, state->scanner);
 
    /* Save final state for a moment... */
    final_state = state->start_state;
 
    /*
     * In case the caller returns to using the regular SQL lexer, reselect the
     * appropriate initial state.
     */
    psql_scan_reselect_sql_lexer(state);
 
    /*
     * Check the lex result: we should have gotten back either LEXRES_OK or
     * LEXRES_EOL (the latter indicating end of string).  If we were inside a
     * quoted string, as indicated by final_state, EOL is an error.
     */
    Assert(lexresult == LEXRES_EOL || lexresult == LEXRES_OK);
 
    switch (final_state)
    {
        case xslashargstart:
            /* empty arg */
            break;
        case xslasharg:
            /* Strip any unquoted trailing semicolons if requested */
            if (semicolon)
            {
                while (unquoted_option_chars-- > 0 &&
                       mybuf.len > 0 &&
                       mybuf.data[mybuf.len - 1] == ';')
                {
                    mybuf.data[--mybuf.len] = '\0';
                }
            }
 
            /*
             * If SQL identifier processing was requested, then we strip out
             * excess double quotes and optionally downcase unquoted letters.
             */
            if (type == OT_SQLID || type == OT_SQLIDHACK)
            {
                dequote_downcase_identifier(mybuf.data,
                                            (type != OT_SQLIDHACK),
                                            state->encoding);
                /* update mybuf.len for possible shortening */
                mybuf.len = strlen(mybuf.data);
            }
            break;
        case xslashquote:
        case xslashbackquote:
        case xslashdquote:
            /* must have hit EOL inside quotes */
            pg_log_error("unterminated quoted string");
            termPQExpBuffer(&mybuf);
            return NULL;
        case xslashwholeline:
 
            /*
             * In whole-line mode, we interpret semicolon = true as stripping
             * trailing whitespace as well as semicolons; this gives the
             * nearest equivalent to what semicolon = true does in normal
             * mode.  Note there's no concept of quoting in this mode.
             */
            if (semicolon)
            {
                while (mybuf.len > 0 &&
                       (mybuf.data[mybuf.len - 1] == ';' ||
                        (isascii((unsigned char) mybuf.data[mybuf.len - 1]) &&
                         isspace((unsigned char) mybuf.data[mybuf.len - 1]))))
                {
                    mybuf.data[--mybuf.len] = '\0';
                }
            }
            break;
        default:
            /* can't get here */
            fprintf(stderr, "invalid YY_START\n");
            exit(1);
    }
 
    /*
     * An unquoted empty argument isn't possible unless we are at end of
     * command.  Return NULL instead.
     */
    if (mybuf.len == 0 && *quote == 0)
    {
        termPQExpBuffer(&mybuf);
        return NULL;
    }
 
    /* Else return the completed string. */
    return mybuf.data;
}
 
/*
 * Eat up any unused \\ to complete a backslash command.
 */
void
psql_scan_slash_command_end(PsqlScanState state)
{
    /* Must be scanning already */
    Assert(state->scanbufhandle != NULL);
 
    /* Set current output target */
    state->output_buf = NULL;   /* we won't output anything */
 
    /* Set input source */
    if (state->buffer_stack != NULL)
        yy_switch_to_buffer(state->buffer_stack->buf, state->scanner);
    else
        yy_switch_to_buffer(state->scanbufhandle, state->scanner);
 
    /* Set lexer start state */
    state->start_state = xslashend;
 
    /* And lex. */
    yylex(NULL, state->scanner);
 
    /* There are no possible errors in this lex state... */
 
    /*
     * We expect the caller to return to using the regular SQL lexer, so
     * reselect the appropriate initial state.
     */
    psql_scan_reselect_sql_lexer(state);
}
 
/*
 * Fetch current paren nesting depth
 */
int
psql_scan_get_paren_depth(PsqlScanState state)
{
    return state->paren_depth;
}
 
/*
 * Set paren nesting depth
 */
void
psql_scan_set_paren_depth(PsqlScanState state, int depth)
{
    Assert(depth >= 0);
    state->paren_depth = depth;
}
 
/*
 * De-quote and optionally downcase a SQL identifier.
 *
 * The string at *str is modified in-place; it can become shorter,
 * but not longer.
 *
 * If downcase is true then non-quoted letters are folded to lower case.
 * Ideally this behavior will match the backend's downcase_identifier();
 * but note that it could differ if LC_CTYPE is different in the frontend.
 *
 * Note that a string like FOO"BAR"BAZ will be converted to fooBARbaz;
 * this is somewhat inconsistent with the SQL spec, which would have us
 * parse it as several identifiers.  But for psql's purposes, we want a
 * string like "foo"."bar" to be treated as one option, so there's little
 * choice; this routine doesn't get to change the token boundaries.
 */
void
dequote_downcase_identifier(char *str, bool downcase, int encoding)
{
    bool        inquotes = false;
    char       *cp = str;
 
    while (*cp)
    {
        if (*cp == '"')
        {
            if (inquotes && cp[1] == '"')
            {
                /* Keep the first quote, remove the second */
                cp++;
            }
            else
                inquotes = !inquotes;
            /* Collapse out quote at *cp */
            memmove(cp, cp + 1, strlen(cp));
            /* do not advance cp */
        }
        else
        {
            if (downcase && !inquotes)
                *cp = pg_tolower((unsigned char) *cp);
            cp += PQmblenBounded(cp, encoding);
        }
    }
}
 
/*
 * Evaluate a backticked substring of a slash command's argument.
 *
 * The portion of output_buf starting at backtick_start_offset is evaluated
 * as a shell command and then replaced by the command's output.
 */
static void
evaluate_backtick(PsqlScanState state)
{
    PQExpBuffer output_buf = state->output_buf;
    char       *cmd = output_buf->data + backtick_start_offset;
    PQExpBufferData cmd_output;
    FILE       *fd;
    bool        error = false;
    int         exit_code = 0;
    char        buf[512];
    size_t      result;
 
    initPQExpBuffer(&cmd_output);
 
    fflush(NULL);
    fd = popen(cmd, "r");
    if (!fd)
    {
        pg_log_error("%s: %m", cmd);
        error = true;
        exit_code = -1;
    }
 
    if (!error)
    {
        do
        {
            result = fread(buf, 1, sizeof(buf), fd);
            if (ferror(fd))
            {
                pg_log_error("%s: %m", cmd);
                error = true;
                break;
            }
            appendBinaryPQExpBuffer(&cmd_output, buf, result);
        } while (!feof(fd));
    }
 
    if (fd)
    {
        /*
         * Although pclose's result always sets the shell result variables, we
         * historically have abandoned the backtick substitution only if it
         * returns -1.
         */
        exit_code = pclose(fd);
        if (exit_code == -1)
        {
            pg_log_error("%s: %m", cmd);
            error = true;
        }
    }
 
    if (PQExpBufferDataBroken(cmd_output))
    {
        pg_log_error("%s: out of memory", cmd);
        error = true;
    }
 
    /* Now done with cmd, delete it from output_buf */
    output_buf->len = backtick_start_offset;
    output_buf->data[output_buf->len] = '\0';
 
    /* If no error, transfer result to output_buf */
    if (!error)
    {
        /* strip any trailing newline (but only one) */
        if (cmd_output.len > 0 &&
            cmd_output.data[cmd_output.len - 1] == '\n')
            cmd_output.len--;
        appendBinaryPQExpBuffer(output_buf, cmd_output.data, cmd_output.len);
    }
 
    /* And finally, set the shell result variables */
    SetShellResultVariables(exit_code);
 
    termPQExpBuffer(&cmd_output);
}