input.c

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/*
 * psql - the PostgreSQL interactive terminal
 *
 * Copyright (c) 2000-2020, PostgreSQL Global Development Group
 *
 * src/bin/psql/input.c
 */
#include "postgres_fe.h"

#ifndef WIN32
#include <unistd.h>
#endif
#include <fcntl.h>
#include <limits.h>

#include "common.h"
#include "common/logging.h"
#include "input.h"
#include "settings.h"
#include "tab-complete.h"

#ifndef WIN32
#define PSQLHISTORY ".psql_history"
#else
#define PSQLHISTORY "psql_history"
#endif

/* Runtime options for turning off readline and history */
/* (of course there is no runtime command for doing that :) */
#ifdef USE_READLINE
static bool useReadline;
static bool useHistory;

static char *psql_history;

static int  history_lines_added;


/*
 *  Preserve newlines in saved queries by mapping '\n' to NL_IN_HISTORY
 *
 *  It is assumed NL_IN_HISTORY will never be entered by the user
 *  nor appear inside a multi-byte string.  0x00 is not properly
 *  handled by the readline routines so it can not be used
 *  for this purpose.
 */
#define NL_IN_HISTORY   0x01
#endif

static void finishInput(void);


/*
 * gets_interactive()
 *
 * Gets a line of interactive input, using readline if desired.
 *
 * prompt: the prompt string to be used
 * query_buf: buffer containing lines already read in the current command
 * (query_buf is not modified here, but may be consulted for tab completion)
 *
 * The result is a malloc'd string.
 *
 * Caller *must* have set up sigint_interrupt_jmp before calling.
 */
char *
gets_interactive(const char *prompt, PQExpBuffer query_buf)
{
#ifdef USE_READLINE
    if (useReadline)
    {
        char       *result;

        /*
         * Some versions of readline don't notice SIGWINCH signals that arrive
         * when not actively reading input.  The simplest fix is to always
         * re-read the terminal size.  This leaves a window for SIGWINCH to be
         * missed between here and where readline() enables libreadline's
         * signal handler, but that's probably short enough to be ignored.
         */
#ifdef HAVE_RL_RESET_SCREEN_SIZE
        rl_reset_screen_size();
#endif

        /* Make current query_buf available to tab completion callback */
        tab_completion_query_buf = query_buf;

        /* Enable SIGINT to longjmp to sigint_interrupt_jmp */
        sigint_interrupt_enabled = true;

        /* On some platforms, readline is declared as readline(char *) */
        result = readline((char *) prompt);

        /* Disable SIGINT again */
        sigint_interrupt_enabled = false;

        /* Pure neatnik-ism */
        tab_completion_query_buf = NULL;

        return result;
    }
#endif

    fputs(prompt, stdout);
    fflush(stdout);
    return gets_fromFile(stdin);
}


/*
 * Append the line to the history buffer, making sure there is a trailing '\n'
 */
void
pg_append_history(const char *s, PQExpBuffer history_buf)
{
#ifdef USE_READLINE
    if (useHistory && s)
    {
        appendPQExpBufferStr(history_buf, s);
        if (!s[0] || s[strlen(s) - 1] != '\n')
            appendPQExpBufferChar(history_buf, '\n');
    }
#endif
}


/*
 * Emit accumulated history entry to readline's history mechanism,
 * then reset the buffer to empty.
 *
 * Note: we write nothing if history_buf is empty, so extra calls to this
 * function don't hurt.  There must have been at least one line added by
 * pg_append_history before we'll do anything.
 */
void
pg_send_history(PQExpBuffer history_buf)
{
#ifdef USE_READLINE
    static char *prev_hist = NULL;

    char       *s = history_buf->data;
    int         i;

    /* Trim any trailing \n's (OK to scribble on history_buf) */
    for (i = strlen(s) - 1; i >= 0 && s[i] == '\n'; i--)
        ;
    s[i + 1] = '\0';

    if (useHistory && s[0])
    {
        if (((pset.histcontrol & hctl_ignorespace) &&
             s[0] == ' ') ||
            ((pset.histcontrol & hctl_ignoredups) &&
             prev_hist && strcmp(s, prev_hist) == 0))
        {
            /* Ignore this line as far as history is concerned */
        }
        else
        {
            /* Save each previous line for ignoredups processing */
            if (prev_hist)
                free(prev_hist);
            prev_hist = pg_strdup(s);
            /* And send it to readline */
            add_history(s);
            /* Count lines added to history for use later */
            history_lines_added++;
        }
    }

    resetPQExpBuffer(history_buf);
#endif
}


/*
 * gets_fromFile
 *
 * Gets a line of noninteractive input from a file (which could be stdin).
 * The result is a malloc'd string, or NULL on EOF or input error.
 *
 * Caller *must* have set up sigint_interrupt_jmp before calling.
 *
 * Note: we re-use a static PQExpBuffer for each call.  This is to avoid
 * leaking memory if interrupted by SIGINT.
 */
char *
gets_fromFile(FILE *source)
{
    static PQExpBuffer buffer = NULL;

    char        line[1024];

    if (buffer == NULL)         /* first time through? */
        buffer = createPQExpBuffer();
    else
        resetPQExpBuffer(buffer);

    for (;;)
    {
        char       *result;

        /* Enable SIGINT to longjmp to sigint_interrupt_jmp */
        sigint_interrupt_enabled = true;

        /* Get some data */
        result = fgets(line, sizeof(line), source);

        /* Disable SIGINT again */
        sigint_interrupt_enabled = false;

        /* EOF or error? */
        if (result == NULL)
        {
            if (ferror(source))
            {
                pg_log_error("could not read from input file: %m");
                return NULL;
            }
            break;
        }

        appendPQExpBufferStr(buffer, line);

        if (PQExpBufferBroken(buffer))
        {
            pg_log_error("out of memory");
            return NULL;
        }

        /* EOL? */
        if (buffer->len > 0 && buffer->data[buffer->len - 1] == '\n')
        {
            buffer->data[buffer->len - 1] = '\0';
            return pg_strdup(buffer->data);
        }
    }

    if (buffer->len > 0)        /* EOF after reading some bufferload(s) */
        return pg_strdup(buffer->data);

    /* EOF, so return null */
    return NULL;
}


#ifdef USE_READLINE

/*
 * Macros to iterate over each element of the history list in order
 *
 * You would think this would be simple enough, but in its inimitable fashion
 * libedit has managed to break it: in libreadline we must use next_history()
 * to go from oldest to newest, but in libedit we must use previous_history().
 * To detect what to do, we make a trial call of previous_history(): if it
 * fails, then either next_history() is what to use, or there's zero or one
 * history entry so that it doesn't matter which direction we go.
 *
 * In case that wasn't disgusting enough: the code below is not as obvious as
 * it might appear.  In some libedit releases history_set_pos(0) fails until
 * at least one add_history() call has been done.  This is not an issue for
 * printHistory() or encode_history(), which cannot be invoked before that has
 * happened.  In decode_history(), that's not so, and what actually happens is
 * that we are sitting on the newest entry to start with, previous_history()
 * fails, and we iterate over all the entries using next_history().  So the
 * decode_history() loop iterates over the entries in the wrong order when
 * using such a libedit release, and if there were another attempt to use
 * BEGIN_ITERATE_HISTORY() before some add_history() call had happened, it
 * wouldn't work.  Fortunately we don't care about either of those things.
 *
 * Usage pattern is:
 *
 *      BEGIN_ITERATE_HISTORY(varname);
 *      {
 *          loop body referencing varname->line;
 *      }
 *      END_ITERATE_HISTORY();
 */
#define BEGIN_ITERATE_HISTORY(VARNAME) \
    do { \
        HIST_ENTRY *VARNAME; \
        bool        use_prev_; \
        \
        history_set_pos(0); \
        use_prev_ = (previous_history() != NULL); \
        history_set_pos(0); \
        for (VARNAME = current_history(); VARNAME != NULL; \
             VARNAME = use_prev_ ? previous_history() : next_history()) \
        { \
            (void) 0

#define END_ITERATE_HISTORY() \
        } \
    } while(0)


/*
 * Convert newlines to NL_IN_HISTORY for safe saving in readline history file
 */
static void
encode_history(void)
{
    BEGIN_ITERATE_HISTORY(cur_hist);
    {
        char       *cur_ptr;

        /* some platforms declare HIST_ENTRY.line as const char * */
        for (cur_ptr = (char *) cur_hist->line; *cur_ptr; cur_ptr++)
        {
            if (*cur_ptr == '\n')
                *cur_ptr = NL_IN_HISTORY;
        }
    }
    END_ITERATE_HISTORY();
}

/*
 * Reverse the above encoding
 */
static void
decode_history(void)
{
    BEGIN_ITERATE_HISTORY(cur_hist);
    {
        char       *cur_ptr;

        /* some platforms declare HIST_ENTRY.line as const char * */
        for (cur_ptr = (char *) cur_hist->line; *cur_ptr; cur_ptr++)
        {
            if (*cur_ptr == NL_IN_HISTORY)
                *cur_ptr = '\n';
        }
    }
    END_ITERATE_HISTORY();
}
#endif                          /* USE_READLINE */


/*
 * Put any startup stuff related to input in here. It's good to maintain
 * abstraction this way.
 *
 * The only "flag" right now is 1 for use readline & history.
 */
void
initializeInput(int flags)
{
#ifdef USE_READLINE
    if (flags & 1)
    {
        const char *histfile;
        char        home[MAXPGPATH];

        useReadline = true;

        /* these two things must be done in this order: */
        initialize_readline();
        rl_initialize();

        useHistory = true;
        using_history();
        history_lines_added = 0;

        histfile = GetVariable(pset.vars, "HISTFILE");

        if (histfile == NULL)
        {
            char       *envhist;

            envhist = getenv("PSQL_HISTORY");
            if (envhist != NULL && strlen(envhist) > 0)
                histfile = envhist;
        }

        if (histfile == NULL)
        {
            if (get_home_path(home))
                psql_history = psprintf("%s/%s", home, PSQLHISTORY);
        }
        else
        {
            psql_history = pg_strdup(histfile);
            expand_tilde(&psql_history);
        }

        if (psql_history)
        {
            read_history(psql_history);
            decode_history();
        }
    }
#endif

    atexit(finishInput);
}


/*
 * This function saves the readline history when psql exits.
 *
 * fname: pathname of history file.  (Should really be "const char *",
 * but some ancient versions of readline omit the const-decoration.)
 *
 * max_lines: if >= 0, limit history file to that many entries.
 */
#ifdef USE_READLINE
static bool
saveHistory(char *fname, int max_lines)
{
    int         errnum;

    /*
     * Suppressing the write attempt when HISTFILE is set to /dev/null may
     * look like a negligible optimization, but it's necessary on e.g. macOS,
     * where write_history will fail because it tries to chmod the target
     * file.
     */
    if (strcmp(fname, DEVNULL) != 0)
    {
        /*
         * Encode \n, since otherwise readline will reload multiline history
         * entries as separate lines.  (libedit doesn't really need this, but
         * we do it anyway since it's too hard to tell which implementation we
         * are using.)
         */
        encode_history();

        /*
         * On newer versions of libreadline, truncate the history file as
         * needed and then append what we've added.  This avoids overwriting
         * history from other concurrent sessions (although there are still
         * race conditions when two sessions exit at about the same time). If
         * we don't have those functions, fall back to write_history().
         */
#if defined(HAVE_HISTORY_TRUNCATE_FILE) && defined(HAVE_APPEND_HISTORY)
        {
            int         nlines;
            int         fd;

            /* truncate previous entries if needed */
            if (max_lines >= 0)
            {
                nlines = Max(max_lines - history_lines_added, 0);
                (void) history_truncate_file(fname, nlines);
            }
            /* append_history fails if file doesn't already exist :-( */
            fd = open(fname, O_CREAT | O_WRONLY | PG_BINARY, 0600);
            if (fd >= 0)
                close(fd);
            /* append the appropriate number of lines */
            if (max_lines >= 0)
                nlines = Min(max_lines, history_lines_added);
            else
                nlines = history_lines_added;
            errnum = append_history(nlines, fname);
            if (errnum == 0)
                return true;
        }
#else                           /* don't have append support */
        {
            /* truncate what we have ... */
            if (max_lines >= 0)
                stifle_history(max_lines);
            /* ... and overwrite file.  Tough luck for concurrent sessions. */
            errnum = write_history(fname);
            if (errnum == 0)
                return true;
        }
#endif

        pg_log_error("could not save history to file \"%s\": %m", fname);
    }
    return false;
}
#endif



/*
 * Print history to the specified file, or to the console if fname is NULL
 * (psql \s command)
 *
 * We used to use saveHistory() for this purpose, but that doesn't permit
 * use of a pager; moreover libedit's implementation behaves incompatibly
 * (preferring to encode its output) and may fail outright when the target
 * file is specified as /dev/tty.
 */
bool
printHistory(const char *fname, unsigned short int pager)
{
#ifdef USE_READLINE
    FILE       *output;
    bool        is_pager;

    if (!useHistory)
        return false;

    if (fname == NULL)
    {
        /* use pager, if enabled, when printing to console */
        output = PageOutput(INT_MAX, pager ? &(pset.popt.topt) : NULL);
        is_pager = true;
    }
    else
    {
        output = fopen(fname, "w");
        if (output == NULL)
        {
            pg_log_error("could not save history to file \"%s\": %m", fname);
            return false;
        }
        is_pager = false;
    }

    BEGIN_ITERATE_HISTORY(cur_hist);
    {
        fprintf(output, "%s\n", cur_hist->line);
    }
    END_ITERATE_HISTORY();

    if (is_pager)
        ClosePager(output);
    else
        fclose(output);

    return true;
#else
    pg_log_error("history is not supported by this installation");
    return false;
#endif
}


static void
finishInput(void)
{
#ifdef USE_READLINE
    if (useHistory && psql_history)
    {
        (void) saveHistory(psql_history, pset.histsize);
        free(psql_history);
        psql_history = NULL;
    }
#endif
}