variables.c

Go to the documentation of this file.

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

#include "common.h"
#include "common/logging.h"
#include "variables.h"

/*
 * Check whether a variable's name is allowed.
 *
 * We allow any non-ASCII character, as well as ASCII letters, digits, and
 * underscore.  Keep this in sync with the definition of variable_char in
 * psqlscan.l and psqlscanslash.l.
 */
static bool
valid_variable_name(const char *name)
{
    const unsigned char *ptr = (const unsigned char *) name;

    /* Mustn't be zero-length */
    if (*ptr == '\0')
        return false;

    while (*ptr)
    {
        if (IS_HIGHBIT_SET(*ptr) ||
            strchr("ABCDEFGHIJKLMNOPQRSTUVWXYZ" "abcdefghijklmnopqrstuvwxyz"
                   "_0123456789", *ptr) != NULL)
            ptr++;
        else
            return false;
    }

    return true;
}

/*
 * A "variable space" is represented by an otherwise-unused struct _variable
 * that serves as list header.
 *
 * The list entries are kept in name order (according to strcmp).  This
 * is mainly to make the results of PrintVariables() more pleasing.
 */
VariableSpace
CreateVariableSpace(void)
{
    struct _variable *ptr;

    ptr = pg_malloc(sizeof *ptr);
    ptr->name = NULL;
    ptr->value = NULL;
    ptr->substitute_hook = NULL;
    ptr->assign_hook = NULL;
    ptr->next = NULL;

    return ptr;
}

/*
 * Get string value of variable, or NULL if it's not defined.
 *
 * Note: result is valid until variable is next assigned to.
 */
const char *
GetVariable(VariableSpace space, const char *name)
{
    struct _variable *current;

    if (!space)
        return NULL;

    for (current = space->next; current; current = current->next)
    {
        int         cmp = strcmp(current->name, name);

        if (cmp == 0)
        {
            /* this is correct answer when value is NULL, too */
            return current->value;
        }
        if (cmp > 0)
            break;              /* it's not there */
    }

    return NULL;
}

/*
 * Try to interpret "value" as a boolean value, and if successful,
 * store it in *result.  Otherwise don't clobber *result.
 *
 * Valid values are: true, false, yes, no, on, off, 1, 0; as well as unique
 * prefixes thereof.
 *
 * "name" is the name of the variable we're assigning to, to use in error
 * report if any.  Pass name == NULL to suppress the error report.
 *
 * Return true when "value" is syntactically valid, false otherwise.
 */
bool
ParseVariableBool(const char *value, const char *name, bool *result)
{
    size_t      len;
    bool        valid = true;

    /* Treat "unset" as an empty string, which will lead to error below */
    if (value == NULL)
        value = "";

    len = strlen(value);

    if (len > 0 && pg_strncasecmp(value, "true", len) == 0)
        *result = true;
    else if (len > 0 && pg_strncasecmp(value, "false", len) == 0)
        *result = false;
    else if (len > 0 && pg_strncasecmp(value, "yes", len) == 0)
        *result = true;
    else if (len > 0 && pg_strncasecmp(value, "no", len) == 0)
        *result = false;
    /* 'o' is not unique enough */
    else if (pg_strncasecmp(value, "on", (len > 2 ? len : 2)) == 0)
        *result = true;
    else if (pg_strncasecmp(value, "off", (len > 2 ? len : 2)) == 0)
        *result = false;
    else if (pg_strcasecmp(value, "1") == 0)
        *result = true;
    else if (pg_strcasecmp(value, "0") == 0)
        *result = false;
    else
    {
        /* string is not recognized; don't clobber *result */
        if (name)
            pg_log_error("unrecognized value \"%s\" for \"%s\": Boolean expected",
                         value, name);
        valid = false;
    }
    return valid;
}

/*
 * Try to interpret "value" as an integer value, and if successful,
 * store it in *result.  Otherwise don't clobber *result.
 *
 * "name" is the name of the variable we're assigning to, to use in error
 * report if any.  Pass name == NULL to suppress the error report.
 *
 * Return true when "value" is syntactically valid, false otherwise.
 */
bool
ParseVariableNum(const char *value, const char *name, int *result)
{
    char       *end;
    long        numval;

    /* Treat "unset" as an empty string, which will lead to error below */
    if (value == NULL)
        value = "";

    errno = 0;
    numval = strtol(value, &end, 0);
    if (errno == 0 && *end == '\0' && end != value && numval == (int) numval)
    {
        *result = (int) numval;
        return true;
    }
    else
    {
        /* string is not recognized; don't clobber *result */
        if (name)
            pg_log_error("invalid value \"%s\" for \"%s\": integer expected",
                         value, name);
        return false;
    }
}

/*
 * Print values of all variables.
 */
void
PrintVariables(VariableSpace space)
{
    struct _variable *ptr;

    if (!space)
        return;

    for (ptr = space->next; ptr; ptr = ptr->next)
    {
        if (ptr->value)
            printf("%s = '%s'\n", ptr->name, ptr->value);
        if (cancel_pressed)
            break;
    }
}

/*
 * Set the variable named "name" to value "value",
 * or delete it if "value" is NULL.
 *
 * Returns true if successful, false if not; in the latter case a suitable
 * error message has been printed, except for the unexpected case of
 * space or name being NULL.
 */
bool
SetVariable(VariableSpace space, const char *name, const char *value)
{
    struct _variable *current,
               *previous;

    if (!space || !name)
        return false;

    if (!valid_variable_name(name))
    {
        /* Deletion of non-existent variable is not an error */
        if (!value)
            return true;
        pg_log_error("invalid variable name: \"%s\"", name);
        return false;
    }

    for (previous = space, current = space->next;
         current;
         previous = current, current = current->next)
    {
        int         cmp = strcmp(current->name, name);

        if (cmp == 0)
        {
            /*
             * Found entry, so update, unless assign hook returns false.
             *
             * We must duplicate the passed value to start with.  This
             * simplifies the API for substitute hooks.  Moreover, some assign
             * hooks assume that the passed value has the same lifespan as the
             * variable.  Having to free the string again on failure is a
             * small price to pay for keeping these APIs simple.
             */
            char       *new_value = value ? pg_strdup(value) : NULL;
            bool        confirmed;

            if (current->substitute_hook)
                new_value = current->substitute_hook(new_value);

            if (current->assign_hook)
                confirmed = current->assign_hook(new_value);
            else
                confirmed = true;

            if (confirmed)
            {
                if (current->value)
                    pg_free(current->value);
                current->value = new_value;

                /*
                 * If we deleted the value, and there are no hooks to
                 * remember, we can discard the variable altogether.
                 */
                if (new_value == NULL &&
                    current->substitute_hook == NULL &&
                    current->assign_hook == NULL)
                {
                    previous->next = current->next;
                    free(current->name);
                    free(current);
                }
            }
            else if (new_value)
                pg_free(new_value); /* current->value is left unchanged */

            return confirmed;
        }
        if (cmp > 0)
            break;              /* it's not there */
    }

    /* not present, make new entry ... unless we were asked to delete */
    if (value)
    {
        current = pg_malloc(sizeof *current);
        current->name = pg_strdup(name);
        current->value = pg_strdup(value);
        current->substitute_hook = NULL;
        current->assign_hook = NULL;
        current->next = previous->next;
        previous->next = current;
    }
    return true;
}

/*
 * Attach substitute and/or assign hook functions to the named variable.
 * If you need only one hook, pass NULL for the other.
 *
 * If the variable doesn't already exist, create it with value NULL, just so
 * we have a place to store the hook function(s).  (The substitute hook might
 * immediately change the NULL to something else; if not, this state is
 * externally the same as the variable not being defined.)
 *
 * The substitute hook, if given, is immediately called on the variable's
 * value.  Then the assign hook, if given, is called on the variable's value.
 * This is meant to let it update any derived psql state.  If the assign hook
 * doesn't like the current value, it will print a message to that effect,
 * but we'll ignore it.  Generally we do not expect any such failure here,
 * because this should get called before any user-supplied value is assigned.
 */
void
SetVariableHooks(VariableSpace space, const char *name,
                 VariableSubstituteHook shook,
                 VariableAssignHook ahook)
{
    struct _variable *current,
               *previous;

    if (!space || !name)
        return;

    if (!valid_variable_name(name))
        return;

    for (previous = space, current = space->next;
         current;
         previous = current, current = current->next)
    {
        int         cmp = strcmp(current->name, name);

        if (cmp == 0)
        {
            /* found entry, so update */
            current->substitute_hook = shook;
            current->assign_hook = ahook;
            if (shook)
                current->value = (*shook) (current->value);
            if (ahook)
                (void) (*ahook) (current->value);
            return;
        }
        if (cmp > 0)
            break;              /* it's not there */
    }

    /* not present, make new entry */
    current = pg_malloc(sizeof *current);
    current->name = pg_strdup(name);
    current->value = NULL;
    current->substitute_hook = shook;
    current->assign_hook = ahook;
    current->next = previous->next;
    previous->next = current;
    if (shook)
        current->value = (*shook) (current->value);
    if (ahook)
        (void) (*ahook) (current->value);
}

/*
 * Convenience function to set a variable's value to "on".
 */
bool
SetVariableBool(VariableSpace space, const char *name)
{
    return SetVariable(space, name, "on");
}

/*
 * Attempt to delete variable.
 *
 * If unsuccessful, print a message and return "false".
 * Deleting a nonexistent variable is not an error.
 */
bool
DeleteVariable(VariableSpace space, const char *name)
{
    return SetVariable(space, name, NULL);
}

/*
 * Emit error with suggestions for variables or commands
 * accepting enum-style arguments.
 * This function just exists to standardize the wording.
 * suggestions should follow the format "fee, fi, fo, fum".
 */
void
PsqlVarEnumError(const char *name, const char *value, const char *suggestions)
{
    pg_log_error("unrecognized value \"%s\" for \"%s\"\n"
                 "Available values are: %s.",
                 value, name, suggestions);
}