ext/dbm/dbm.c

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/************************************************

  dbm.c -

  $Author: naruse $
  created at: Mon Jan 24 15:59:52 JST 1994

  Copyright (C) 1995-2001 Yukihiro Matsumoto

************************************************/

#include "ruby.h"

#ifdef HAVE_CDEFS_H
# include <cdefs.h>
#endif
#ifdef HAVE_SYS_CDEFS_H
# include <sys/cdefs.h>
#endif
#include DBM_HDR
#include <fcntl.h>
#include <errno.h>

static VALUE rb_cDBM, rb_eDBMError;

#define RUBY_DBM_RW_BIT 0x20000000

struct dbmdata {
    long di_size;
    DBM *di_dbm;
};

static void
closed_dbm(void)
{
    rb_raise(rb_eDBMError, "closed DBM file");
}

#define GetDBM(obj, dbmp) {\
    Data_Get_Struct((obj), struct dbmdata, (dbmp));\
    if ((dbmp) == 0) closed_dbm();\
    if ((dbmp)->di_dbm == 0) closed_dbm();\
}

#define GetDBM2(obj, data, dbm) {\
    GetDBM((obj), (data));\
    (dbm) = dbmp->di_dbm;\
}

static void
free_dbm(struct dbmdata *dbmp)
{
    if (dbmp) {
        if (dbmp->di_dbm) dbm_close(dbmp->di_dbm);
        xfree(dbmp);
    }
}

/*
 * call-seq:
 *   dbm.close
 *
 * Closes the database.
 */
static VALUE
fdbm_close(VALUE obj)
{
    struct dbmdata *dbmp;

    GetDBM(obj, dbmp);
    dbm_close(dbmp->di_dbm);
    dbmp->di_dbm = 0;

    return Qnil;
}

/*
 * call-seq:
 *   dbm.closed? -> true or false
 *
 * Returns true if the database is closed, false otherwise.
 */
static VALUE
fdbm_closed(VALUE obj)
{
    struct dbmdata *dbmp;

    Data_Get_Struct(obj, struct dbmdata, dbmp);
    if (dbmp == 0)
        return Qtrue;
    if (dbmp->di_dbm == 0)
        return Qtrue;

    return Qfalse;
}

static VALUE
fdbm_alloc(VALUE klass)
{
    return Data_Wrap_Struct(klass, 0, free_dbm, 0);
}

/*
 * call-seq:
 *   DBM.new(filename[, mode[, flags]]) -> dbm
 *
 * Open a dbm database with the specified name, which can include a directory
 * path. Any file extensions needed will be supplied automatically by the dbm
 * library. For example, Berkeley DB appends '.db', and GNU gdbm uses two
 * physical files with extensions '.dir' and '.pag'.
 *
 * The mode should be an integer, as for Unix chmod.
 *
 * Flags should be one of READER, WRITER, WRCREAT or NEWDB.
 */
static VALUE
fdbm_initialize(int argc, VALUE *argv, VALUE obj)
{
    volatile VALUE file;
    VALUE vmode, vflags;
    DBM *dbm;
    struct dbmdata *dbmp;
    int mode, flags = 0;

    if (rb_scan_args(argc, argv, "12", &file, &vmode, &vflags) == 1) {
        mode = 0666;            /* default value */
    }
    else if (NIL_P(vmode)) {
        mode = -1;              /* return nil if DB not exist */
    }
    else {
        mode = NUM2INT(vmode);
    }

    if (!NIL_P(vflags))
        flags = NUM2INT(vflags);

    FilePathValue(file);

    if (flags & RUBY_DBM_RW_BIT) {
        flags &= ~RUBY_DBM_RW_BIT;
        dbm = dbm_open(RSTRING_PTR(file), flags, mode);
    }
    else {
        dbm = 0;
        if (mode >= 0) {
            dbm = dbm_open(RSTRING_PTR(file), O_RDWR|O_CREAT, mode);
        }
        if (!dbm) {
            dbm = dbm_open(RSTRING_PTR(file), O_RDWR, 0);
        }
        if (!dbm) {
            dbm = dbm_open(RSTRING_PTR(file), O_RDONLY, 0);
        }
    }

    if (!dbm) {
        if (mode == -1) return Qnil;
        rb_sys_fail(RSTRING_PTR(file));
    }

    dbmp = ALLOC(struct dbmdata);
    DATA_PTR(obj) = dbmp;
    dbmp->di_dbm = dbm;
    dbmp->di_size = -1;

    return obj;
}

/*
 * call-seq:
 *   DBM.open(filename[, mode[, flags]]) -> dbm
 *   DBM.open(filename[, mode[, flags]]) {|dbm| block}
 *
 * Open a dbm database and yields it if a block is given. See also
 * <code>DBM.new</code>.
 */
static VALUE
fdbm_s_open(int argc, VALUE *argv, VALUE klass)
{
    VALUE obj = Data_Wrap_Struct(klass, 0, free_dbm, 0);

    if (NIL_P(fdbm_initialize(argc, argv, obj))) {
        return Qnil;
    }

    if (rb_block_given_p()) {
        return rb_ensure(rb_yield, obj, fdbm_close, obj);
    }

    return obj;
}

static VALUE
fdbm_fetch(VALUE obj, VALUE keystr, VALUE ifnone)
{
    datum key, value;
    struct dbmdata *dbmp;
    DBM *dbm;

    ExportStringValue(keystr);
    key.dptr = RSTRING_PTR(keystr);
    key.dsize = (int)RSTRING_LEN(keystr);

    GetDBM2(obj, dbmp, dbm);
    value = dbm_fetch(dbm, key);
    if (value.dptr == 0) {
        if (ifnone == Qnil && rb_block_given_p())
            return rb_yield(rb_tainted_str_new(key.dptr, key.dsize));
        return ifnone;
    }
    return rb_tainted_str_new(value.dptr, value.dsize);
}

/*
 * call-seq:
 *   dbm[key] -> string value or nil
 *
 * Return a value from the database by locating the key string
 * provided.  If the key is not found, returns nil.
 */
static VALUE
fdbm_aref(VALUE obj, VALUE keystr)
{
    return fdbm_fetch(obj, keystr, Qnil);
}

/*
 * call-seq:
 *   dbm.fetch(key[, ifnone]) -> value
 *
 * Return a value from the database by locating the key string
 * provided.  If the key is not found, returns +ifnone+. If +ifnone+
 * is not given, raises IndexError.
 */
static VALUE
fdbm_fetch_m(int argc, VALUE *argv, VALUE obj)
{
    VALUE keystr, valstr, ifnone;

    rb_scan_args(argc, argv, "11", &keystr, &ifnone);
    valstr = fdbm_fetch(obj, keystr, ifnone);
    if (argc == 1 && !rb_block_given_p() && NIL_P(valstr))
        rb_raise(rb_eIndexError, "key not found");

    return valstr;
}

/*
 * call-seq:
 *   dbm.key(value) -> string
 *
 * Returns the key for the specified value.
 */
static VALUE
fdbm_key(VALUE obj, VALUE valstr)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;

    ExportStringValue(valstr);
    val.dptr = RSTRING_PTR(valstr);
    val.dsize = (int)RSTRING_LEN(valstr);

    GetDBM2(obj, dbmp, dbm);
    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        val = dbm_fetch(dbm, key);
        if ((long)val.dsize == (int)RSTRING_LEN(valstr) &&
            memcmp(val.dptr, RSTRING_PTR(valstr), val.dsize) == 0) {
            return rb_tainted_str_new(key.dptr, key.dsize);
        }
    }
    return Qnil;
}

/* :nodoc: */
static VALUE
fdbm_index(VALUE hash, VALUE value)
{
    rb_warn("DBM#index is deprecated; use DBM#key");
    return fdbm_key(hash, value);
}

/*
 * call-seq:
 *   dbm.select {|key, value| block} -> array
 *
 * Returns a new array consisting of the [key, value] pairs for which the code
 * block returns true.
 */
static VALUE
fdbm_select(VALUE obj)
{
    VALUE new = rb_ary_new();
    datum key, val;
    DBM *dbm;
    struct dbmdata *dbmp;

    GetDBM2(obj, dbmp, dbm);
    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        VALUE assoc, v;
        val = dbm_fetch(dbm, key);
        assoc = rb_assoc_new(rb_tainted_str_new(key.dptr, key.dsize),
                             rb_tainted_str_new(val.dptr, val.dsize));
        v = rb_yield(assoc);
        if (RTEST(v)) {
            rb_ary_push(new, assoc);
        }
        GetDBM2(obj, dbmp, dbm);
    }

    return new;
}

/*
 * call-seq:
 *   dbm.values_at(key, ...) -> Array
 *
 * Returns an array containing the values associated with the given keys.
 */
static VALUE
fdbm_values_at(int argc, VALUE *argv, VALUE obj)
{
    VALUE new = rb_ary_new2(argc);
    int i;

    for (i=0; i<argc; i++) {
        rb_ary_push(new, fdbm_fetch(obj, argv[i], Qnil));
    }

    return new;
}

static void
fdbm_modify(VALUE obj)
{
    rb_secure(4);
    if (OBJ_FROZEN(obj)) rb_error_frozen("DBM");
}

/*
 * call-seq:
 *   dbm.delete(key)
 *
 * Deletes an entry from the database.
 */
static VALUE
fdbm_delete(VALUE obj, VALUE keystr)
{
    datum key, value;
    struct dbmdata *dbmp;
    DBM *dbm;
    VALUE valstr;

    fdbm_modify(obj);
    ExportStringValue(keystr);
    key.dptr = RSTRING_PTR(keystr);
    key.dsize = (int)RSTRING_LEN(keystr);

    GetDBM2(obj, dbmp, dbm);

    value = dbm_fetch(dbm, key);
    if (value.dptr == 0) {
        if (rb_block_given_p()) return rb_yield(keystr);
        return Qnil;
    }

    /* need to save value before dbm_delete() */
    valstr = rb_tainted_str_new(value.dptr, value.dsize);

    if (dbm_delete(dbm, key)) {
        dbmp->di_size = -1;
        rb_raise(rb_eDBMError, "dbm_delete failed");
    }
    else if (dbmp->di_size >= 0) {
        dbmp->di_size--;
    }
    return valstr;
}

/*
 * call-seq:
 *   dbm.shift() -> [key, value]
 *
 * Removes a [key, value] pair from the database, and returns it.
 * If the database is empty, returns nil.
 * The order in which values are removed/returned is not guaranteed.
 */
static VALUE
fdbm_shift(VALUE obj)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;
    VALUE keystr, valstr;

    fdbm_modify(obj);
    GetDBM2(obj, dbmp, dbm);
    dbmp->di_size = -1;

    key = dbm_firstkey(dbm);
    if (!key.dptr) return Qnil;
    val = dbm_fetch(dbm, key);
    keystr = rb_tainted_str_new(key.dptr, key.dsize);
    valstr = rb_tainted_str_new(val.dptr, val.dsize);
    dbm_delete(dbm, key);

    return rb_assoc_new(keystr, valstr);
}

/*
 * call-seq:
 *   dbm.reject! {|key, value| block} -> self
 *   dbm.delete_if {|key, value| block} -> self
 *
 * Deletes all entries for which the code block returns true.
 * Returns self.
 */
static VALUE
fdbm_delete_if(VALUE obj)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;
    VALUE keystr, valstr;
    VALUE ret, ary = rb_ary_new();
    int i, status = 0;
    long n;

    fdbm_modify(obj);
    GetDBM2(obj, dbmp, dbm);
    n = dbmp->di_size;
    dbmp->di_size = -1;

    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        val = dbm_fetch(dbm, key);
        keystr = rb_tainted_str_new(key.dptr, key.dsize);
        valstr = rb_tainted_str_new(val.dptr, val.dsize);
        ret = rb_protect(rb_yield, rb_assoc_new(rb_str_dup(keystr), valstr), &status);
        if (status != 0) break;
        if (RTEST(ret)) rb_ary_push(ary, keystr);
        GetDBM2(obj, dbmp, dbm);
    }

    for (i = 0; i < RARRAY_LEN(ary); i++) {
        keystr = RARRAY_PTR(ary)[i];
        ExportStringValue(keystr);
        key.dptr = RSTRING_PTR(keystr);
        key.dsize = (int)RSTRING_LEN(keystr);
        if (dbm_delete(dbm, key)) {
            rb_raise(rb_eDBMError, "dbm_delete failed");
        }
    }
    if (status) rb_jump_tag(status);
    if (n > 0) dbmp->di_size = n - RARRAY_LEN(ary);

    return obj;
}

/*
 * call-seq:
 *   dbm.clear
 *
 * Deletes all data from the database.
 */
static VALUE
fdbm_clear(VALUE obj)
{
    datum key;
    struct dbmdata *dbmp;
    DBM *dbm;

    fdbm_modify(obj);
    GetDBM2(obj, dbmp, dbm);
    dbmp->di_size = -1;
    while (key = dbm_firstkey(dbm), key.dptr) {
        if (dbm_delete(dbm, key)) {
            rb_raise(rb_eDBMError, "dbm_delete failed");
        }
    }
    dbmp->di_size = 0;

    return obj;
}

/*
 * call-seq:
 *   dbm.invert -> hash
 *
 * Returns a Hash (not a DBM database) created by using each value in the
 * database as a key, with the corresponding key as its value.
 */
static VALUE
fdbm_invert(VALUE obj)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;
    VALUE keystr, valstr;
    VALUE hash = rb_hash_new();

    GetDBM2(obj, dbmp, dbm);
    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        val = dbm_fetch(dbm, key);
        keystr = rb_tainted_str_new(key.dptr, key.dsize);
        valstr = rb_tainted_str_new(val.dptr, val.dsize);
        rb_hash_aset(hash, valstr, keystr);
    }
    return hash;
}

static VALUE fdbm_store(VALUE,VALUE,VALUE);

static VALUE
update_i(VALUE pair, VALUE dbm)
{
    Check_Type(pair, T_ARRAY);
    if (RARRAY_LEN(pair) < 2) {
        rb_raise(rb_eArgError, "pair must be [key, value]");
    }
    fdbm_store(dbm, RARRAY_PTR(pair)[0], RARRAY_PTR(pair)[1]);
    return Qnil;
}

/*
 * call-seq:
 *   dbm.update(obj)
 *
 * Updates the database with multiple values from the specified object.
 * Takes any object which implements the each_pair method, including
 * Hash and DBM objects.
 */
static VALUE
fdbm_update(VALUE obj, VALUE other)
{
    rb_block_call(other, rb_intern("each_pair"), 0, 0, update_i, obj);
    return obj;
}

/*
 * call-seq:
 *   dbm.replace(obj)
 *
 * Replaces the contents of the database with the contents of the specified
 * object. Takes any object which implements the each_pair method, including
 * Hash and DBM objects.
 */
static VALUE
fdbm_replace(VALUE obj, VALUE other)
{
    fdbm_clear(obj);
    rb_block_call(other, rb_intern("each_pair"), 0, 0, update_i, obj);
    return obj;
}

/*
 * call-seq:
 *   dbm.store(key, value) -> value
 *   dbm[key] = value
 *
 * Stores the specified string value in the database, indexed via the
 * string key provided.
 */
static VALUE
fdbm_store(VALUE obj, VALUE keystr, VALUE valstr)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;

    fdbm_modify(obj);
    keystr = rb_obj_as_string(keystr);
    valstr = rb_obj_as_string(valstr);

    key.dptr = RSTRING_PTR(keystr);
    key.dsize = (int)RSTRING_LEN(keystr);

    val.dptr = RSTRING_PTR(valstr);
    val.dsize = (int)RSTRING_LEN(valstr);

    GetDBM2(obj, dbmp, dbm);
    dbmp->di_size = -1;
    if (dbm_store(dbm, key, val, DBM_REPLACE)) {
#ifdef HAVE_DBM_CLEARERR
        dbm_clearerr(dbm);
#endif
        if (errno == EPERM) rb_sys_fail(0);
        rb_raise(rb_eDBMError, "dbm_store failed");
    }

    return valstr;
}

/*
 * call-seq:
 *   dbm.length -> integer
 *
 * Returns the number of entries in the database.
 */
static VALUE
fdbm_length(VALUE obj)
{
    datum key;
    struct dbmdata *dbmp;
    DBM *dbm;
    int i = 0;

    GetDBM2(obj, dbmp, dbm);
    if (dbmp->di_size > 0) return INT2FIX(dbmp->di_size);

    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        i++;
    }
    dbmp->di_size = i;

    return INT2FIX(i);
}

/*
 * call-seq:
 *   dbm.empty?
 *
 * Returns true if the database is empty, false otherwise.
 */
static VALUE
fdbm_empty_p(VALUE obj)
{
    datum key;
    struct dbmdata *dbmp;
    DBM *dbm;
    int i = 0;

    GetDBM2(obj, dbmp, dbm);
    if (dbmp->di_size < 0) {
        dbm = dbmp->di_dbm;

        for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
            i++;
        }
    }
    else {
        i = (int)dbmp->di_size;
    }
    if (i == 0) return Qtrue;
    return Qfalse;
}

/*
 * call-seq:
 *   dbm.each_value {|value| block} -> self
 *
 * Calls the block once for each value string in the database. Returns self.
 */
static VALUE
fdbm_each_value(VALUE obj)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;

    RETURN_ENUMERATOR(obj, 0, 0);

    GetDBM2(obj, dbmp, dbm);
    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        val = dbm_fetch(dbm, key);
        rb_yield(rb_tainted_str_new(val.dptr, val.dsize));
        GetDBM2(obj, dbmp, dbm);
    }
    return obj;
}

/*
 * call-seq:
 *   dbm.each_key {|key| block} -> self
 *
 * Calls the block once for each key string in the database. Returns self.
 */
static VALUE
fdbm_each_key(VALUE obj)
{
    datum key;
    struct dbmdata *dbmp;
    DBM *dbm;

    RETURN_ENUMERATOR(obj, 0, 0);

    GetDBM2(obj, dbmp, dbm);
    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        rb_yield(rb_tainted_str_new(key.dptr, key.dsize));
        GetDBM2(obj, dbmp, dbm);
    }
    return obj;
}

/*
 * call-seq:
 *   dbm.each_pair {|key,value| block} -> self
 *
 * Calls the block once for each [key, value] pair in the database.
 * Returns self.
 */
static VALUE
fdbm_each_pair(VALUE obj)
{
    datum key, val;
    DBM *dbm;
    struct dbmdata *dbmp;
    VALUE keystr, valstr;

    RETURN_ENUMERATOR(obj, 0, 0);

    GetDBM2(obj, dbmp, dbm);

    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        val = dbm_fetch(dbm, key);
        keystr = rb_tainted_str_new(key.dptr, key.dsize);
        valstr = rb_tainted_str_new(val.dptr, val.dsize);
        rb_yield(rb_assoc_new(keystr, valstr));
        GetDBM2(obj, dbmp, dbm);
    }

    return obj;
}

/*
 * call-seq:
 *   dbm.keys -> array
 *
 * Returns an array of all the string keys in the database.
 */
static VALUE
fdbm_keys(VALUE obj)
{
    datum key;
    struct dbmdata *dbmp;
    DBM *dbm;
    VALUE ary;

    GetDBM2(obj, dbmp, dbm);

    ary = rb_ary_new();
    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        rb_ary_push(ary, rb_tainted_str_new(key.dptr, key.dsize));
    }

    return ary;
}

/*
 * call-seq:
 *   dbm.values -> array
 *
 * Returns an array of all the string values in the database.
 */
static VALUE
fdbm_values(VALUE obj)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;
    VALUE ary;

    GetDBM2(obj, dbmp, dbm);
    ary = rb_ary_new();
    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        val = dbm_fetch(dbm, key);
        rb_ary_push(ary, rb_tainted_str_new(val.dptr, val.dsize));
    }

    return ary;
}

/*
 * call-seq:
 *   dbm.has_key?(key) -> boolean
 *
 * Returns true if the database contains the specified key, false otherwise.
 */
static VALUE
fdbm_has_key(VALUE obj, VALUE keystr)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;

    ExportStringValue(keystr);
    key.dptr = RSTRING_PTR(keystr);
    key.dsize = (int)RSTRING_LEN(keystr);

    GetDBM2(obj, dbmp, dbm);
    val = dbm_fetch(dbm, key);
    if (val.dptr) return Qtrue;
    return Qfalse;
}

/*
 * call-seq:
 *   dbm.has_value?(value) -> boolean
 *
 * Returns true if the database contains the specified string value, false
 * otherwise.
 */
static VALUE
fdbm_has_value(VALUE obj, VALUE valstr)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;

    ExportStringValue(valstr);
    val.dptr = RSTRING_PTR(valstr);
    val.dsize = (int)RSTRING_LEN(valstr);

    GetDBM2(obj, dbmp, dbm);
    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        val = dbm_fetch(dbm, key);
        if (val.dsize == (int)RSTRING_LEN(valstr) &&
            memcmp(val.dptr, RSTRING_PTR(valstr), val.dsize) == 0)
            return Qtrue;
    }
    return Qfalse;
}

/*
 * call-seq:
 *   dbm.to_a -> array
 *
 * Converts the contents of the database to an array of [key, value] arrays,
 * and returns it.
 */
static VALUE
fdbm_to_a(VALUE obj)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;
    VALUE ary;

    GetDBM2(obj, dbmp, dbm);
    ary = rb_ary_new();
    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        val = dbm_fetch(dbm, key);
        rb_ary_push(ary, rb_assoc_new(rb_tainted_str_new(key.dptr, key.dsize),
                                      rb_tainted_str_new(val.dptr, val.dsize)));
    }

    return ary;
}

/*
 * call-seq:
 *   dbm.to_hash -> hash
 *
 * Converts the contents of the database to an in-memory Hash object, and
 * returns it.
 */
static VALUE
fdbm_to_hash(VALUE obj)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;
    VALUE hash;

    GetDBM2(obj, dbmp, dbm);
    hash = rb_hash_new();
    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        val = dbm_fetch(dbm, key);
        rb_hash_aset(hash, rb_tainted_str_new(key.dptr, key.dsize),
                           rb_tainted_str_new(val.dptr, val.dsize));
    }

    return hash;
}

/*
 * call-seq:
 *   dbm.reject {|key,value| block} -> Hash
 *
 * Converts the contents of the database to an in-memory Hash, then calls
 * Hash#reject with the specified code block, returning a new Hash.
 */
static VALUE
fdbm_reject(VALUE obj)
{
    return rb_hash_delete_if(fdbm_to_hash(obj));
}

/*
 * Documented by mathew meta@pobox.com.
 * = Introduction
 *
 * The DBM class provides a wrapper to a Unix-style
 * {dbm}[http://en.wikipedia.org/wiki/Dbm] or Database Manager library.
 *
 * Dbm databases do not have tables or columns; they are simple key-value
 * data stores, like a Ruby Hash except not resident in RAM. Keys and values
 * must be strings.
 *
 * The exact library used depends on how Ruby was compiled. It could be any
 * of the following:
 *
 * - The original ndbm library is released in 4.3BSD.
 *   It is based on dbm library in Unix Version 7 but has different API to
 *   support multiple databases in a process.
 * - {Berkeley DB}[http://en.wikipedia.org/wiki/Berkeley_DB] versions
 *   1 thru 5, also known as BDB and Sleepycat DB, now owned by Oracle
 *   Corporation.
 * - Berkeley DB 1.x, still found in FreeBSD and OpenBSD.
 * - {gdbm}[http://www.gnu.org/software/gdbm/], the GNU implementation of dbm.
 * - {qdbm}[http://fallabs.com/qdbm/index.html], another open source
 *   reimplementation of dbm.
 *
 * All of these dbm implementations have their own Ruby interfaces
 * available, which provide richer (but varying) APIs.
 *
 * = Cautions
 *
 * Before you decide to use DBM, there are some issues you should consider:
 *
 * - Each implementation of dbm has its own file format. Generally, dbm
 *   libraries will not read each other's files. This makes dbm files
 *   a bad choice for data exchange.
 *
 * - Even running the same OS and the same dbm implementation, the database
 *   file format may depend on the CPU architecture. For example, files may
 *   not be portable between PowerPC and 386, or between 32 and 64 bit Linux.
 *
 * - Different versions of Berkeley DB use different file formats. A change to
 *   the OS may therefore break DBM access to existing files.
 *
 * - Data size limits vary between implementations. Original Berkeley DB was
 *   limited to 2GB of data. Dbm libraries also sometimes limit the total
 *   size of a key/value pair, and the total size of all the keys that hash
 *   to the same value. These limits can be as little as 512 bytes. That said,
 *   gdbm and recent versions of Berkeley DB do away with these limits.
 *
 * Given the above cautions, DBM is not a good choice for long term storage of
 * important data. It is probably best used as a fast and easy alternative
 * to a Hash for processing large amounts of data.
 *
 * = Example
 *
 *  require 'dbm'
 *  db = DBM.open('rfcs', 666, DBM::CREATRW)
 *  db['822'] = 'Standard for the Format of ARPA Internet Text Messages'
 *  db['1123'] = 'Requirements for Internet Hosts - Application and Support'
 *  db['3068'] = 'An Anycast Prefix for 6to4 Relay Routers'
 *  puts db['822']
 */
void
Init_dbm(void)
{
    rb_cDBM = rb_define_class("DBM", rb_cObject);
    /* Document-class: DBMError
     * Exception class used to return errors from the dbm library.
     */
    rb_eDBMError = rb_define_class("DBMError", rb_eStandardError);
    rb_include_module(rb_cDBM, rb_mEnumerable);

    rb_define_alloc_func(rb_cDBM, fdbm_alloc);
    rb_define_singleton_method(rb_cDBM, "open", fdbm_s_open, -1);

    rb_define_method(rb_cDBM, "initialize", fdbm_initialize, -1);
    rb_define_method(rb_cDBM, "close", fdbm_close, 0);
    rb_define_method(rb_cDBM, "closed?", fdbm_closed, 0);
    rb_define_method(rb_cDBM, "[]", fdbm_aref, 1);
    rb_define_method(rb_cDBM, "fetch", fdbm_fetch_m, -1);
    rb_define_method(rb_cDBM, "[]=", fdbm_store, 2);
    rb_define_method(rb_cDBM, "store", fdbm_store, 2);
    rb_define_method(rb_cDBM, "index",  fdbm_index, 1);
    rb_define_method(rb_cDBM, "key",  fdbm_key, 1);
    rb_define_method(rb_cDBM, "select",  fdbm_select, 0);
    rb_define_method(rb_cDBM, "values_at", fdbm_values_at, -1);
    rb_define_method(rb_cDBM, "length", fdbm_length, 0);
    rb_define_method(rb_cDBM, "size", fdbm_length, 0);
    rb_define_method(rb_cDBM, "empty?", fdbm_empty_p, 0);
    rb_define_method(rb_cDBM, "each", fdbm_each_pair, 0);
    rb_define_method(rb_cDBM, "each_value", fdbm_each_value, 0);
    rb_define_method(rb_cDBM, "each_key", fdbm_each_key, 0);
    rb_define_method(rb_cDBM, "each_pair", fdbm_each_pair, 0);
    rb_define_method(rb_cDBM, "keys", fdbm_keys, 0);
    rb_define_method(rb_cDBM, "values", fdbm_values, 0);
    rb_define_method(rb_cDBM, "shift", fdbm_shift, 0);
    rb_define_method(rb_cDBM, "delete", fdbm_delete, 1);
    rb_define_method(rb_cDBM, "delete_if", fdbm_delete_if, 0);
    rb_define_method(rb_cDBM, "reject!", fdbm_delete_if, 0);
    rb_define_method(rb_cDBM, "reject", fdbm_reject, 0);
    rb_define_method(rb_cDBM, "clear", fdbm_clear, 0);
    rb_define_method(rb_cDBM,"invert", fdbm_invert, 0);
    rb_define_method(rb_cDBM,"update", fdbm_update, 1);
    rb_define_method(rb_cDBM,"replace", fdbm_replace, 1);

    rb_define_method(rb_cDBM, "include?", fdbm_has_key, 1);
    rb_define_method(rb_cDBM, "has_key?", fdbm_has_key, 1);
    rb_define_method(rb_cDBM, "member?", fdbm_has_key, 1);
    rb_define_method(rb_cDBM, "has_value?", fdbm_has_value, 1);
    rb_define_method(rb_cDBM, "key?", fdbm_has_key, 1);
    rb_define_method(rb_cDBM, "value?", fdbm_has_value, 1);

    rb_define_method(rb_cDBM, "to_a", fdbm_to_a, 0);
    rb_define_method(rb_cDBM, "to_hash", fdbm_to_hash, 0);

    /* Indicates that dbm_open() should open the database in read-only mode */
    rb_define_const(rb_cDBM, "READER",  INT2FIX(O_RDONLY|RUBY_DBM_RW_BIT));

    /* Indicates that dbm_open() should open the database in read/write mode */
    rb_define_const(rb_cDBM, "WRITER",  INT2FIX(O_RDWR|RUBY_DBM_RW_BIT));

    /* Indicates that dbm_open() should open the database in read/write mode,
     * and create it if it does not already exist
     */
    rb_define_const(rb_cDBM, "WRCREAT", INT2FIX(O_RDWR|O_CREAT|RUBY_DBM_RW_BIT));

    /* Indicates that dbm_open() should open the database in read/write mode,
     * create it if it does not already exist, and delete all contents if it
     * does already exist.
     */
    rb_define_const(rb_cDBM, "NEWDB",   INT2FIX(O_RDWR|O_CREAT|O_TRUNC|RUBY_DBM_RW_BIT));

#if defined(HAVE_DB_VERSION)
    /* The version of the dbm library, if using Berkeley DB */
    rb_define_const(rb_cDBM, "VERSION",  rb_str_new2(db_version(NULL, NULL, NULL)));
#elif defined(HAVE_GDBM_VERSION)
    /* since gdbm 1.9 */
    rb_define_const(rb_cDBM, "VERSION",  rb_str_new2(gdbm_version));
#elif defined(HAVE_LIBVAR_GDBM_VERSION)
    /* ndbm.h doesn't declare gdbm_version until gdbm 1.8.3.
     * See extconf.rb for more information. */
    {
        RUBY_EXTERN char *gdbm_version;
        rb_define_const(rb_cDBM, "VERSION",  rb_str_new2(gdbm_version));
    }
#elif defined(HAVE_DPVERSION)
    rb_define_const(rb_cDBM, "VERSION",  rb_sprintf("QDBM %s", dpversion));
#elif defined(_DB_H_)
    rb_define_const(rb_cDBM, "VERSION",  rb_str_new2("Berkeley DB (unknown)"));
#else
    rb_define_const(rb_cDBM, "VERSION",  rb_str_new2("unknown"));
#endif
}

---