`lte` key limits in LevelDB and Unicode

fill-and-read-db.js

// Generated by CoffeeScript 1.8.0
(function() {
  var $, D, db, db_route, feed, fs, gte, keys, log, new_db, read, rmrf, rpr, through2;

  fs = require('fs');

  log = console.log;

  rpr = (require('util')).inspect;

  new_db = require('level');

  through2 = require('through2');

  rmrf = require('rimraf');

  D = require('pipedreams2');

  $ = D.remit.bind(D);

  feed = function(db, keys, handler) {
    var input, key, output, _i, _len;
    output = db.createWriteStream();
    input = through2.obj();
    input.pipe($(function(key, send) {
      return send({
        key: key,
        value: 1
      });
    })).pipe(output).on('close', function() {
      return handler();
    });
    for (_i = 0, _len = keys.length; _i < _len; _i++) {
      key = keys[_i];
      input.write(key);
    }
    return input.end();
  };

  read = function(db, lte, gte, handler) {
    var input;
    log("listing keys up to LTE: " + (rpr(lte)) + " " + (rpr(new Buffer(lte))));
    input = db.createKeyStream({
      gte: gte,
      lte: lte
    });
    return input.pipe($(function(key, send, end) {
      log(rpr(key));
      if (end != null) {
        end();
        return handler();
      }
    }));
  };

  if (module.parent == null) {
    keys = ['a', 'abcdef', 'aäöü', 'aΔ', 'a中', 'a𠁩', '~', 'äöü', 'ÿ', 'Δ', '中', '𠁩', '\uffff', '\xff'];
    db_route = '/tmp/level';
    if (fs.existsSync(db_route)) {
      rmrf.sync(db_route);
    }
    db = new_db(db_route);
    gte = 'a';
    feed(db, keys, function() {
      var lte;
      log('--------');
      lte = 'a~';
      return read(db, lte, gte, function() {
        log('--------');
        lte = 'a\xff';
        return read(db, lte, gte, function() {
          log('--------');
          lte = 'a\uffff';
          return read(db, lte, gte, function() {
            log('--------');
            lte = new Buffer([0x61, 0xff]);
            return read(db, lte, gte, function() {
              return log('--------');
            });
          });
        });
      });
    });
  }

}).call(this);

fille-and-read-db.coffee

############################################################################################################
fs                        = require 'fs'
log                       = console.log
rpr                       = ( require 'util' ).inspect
new_db                    = require 'level'
through2                  = require 'through2'
rmrf                      = require 'rimraf'
D                         = require 'pipedreams2'
$                         = D.remit.bind D

#-----------------------------------------------------------------------------------------------------------
feed = ( db, keys, handler ) ->
  output    = db.createWriteStream()
  input     = through2.obj()
  #.........................................................................................................
  input
    .pipe $ ( key, send ) -> send { key, value: 1, }
    .pipe output
    .on 'close', -> handler()
  #.........................................................................................................
  input.write key for key in keys
  input.end()

#-----------------------------------------------------------------------------------------------------------
read = ( db, lte, gte, handler ) ->
  log "listing keys up to LTE: #{rpr lte} #{rpr new Buffer lte}"
  input   = db.createKeyStream { gte, lte, }
  input
    .pipe $ ( key, send, end ) ->
      log rpr key
      if end?
        end()
        handler()

############################################################################################################
unless module.parent?
  keys = [
    'a'
    'abcdef'
    'aäöü'
    'aΔ'
    'a中'
    'a𠁩'
    '~'
    'äöü'
    'ÿ'
    'Δ'
    '中'
    '𠁩'
    '\uffff'
    '\xff'
    ]
  #---------------------------------------------------------------------------------------------------------
  db_route  = '/tmp/level'
  rmrf.sync db_route if fs.existsSync db_route
  db        = new_db db_route
  gte       = 'a'
  #---------------------------------------------------------------------------------------------------------
  feed db, keys, ->
    log '--------'
    lte = 'a~'
    read db, lte, gte, ->
      log '--------'
      lte = 'a\xff'
      read db, lte, gte, ->
        log '--------'
        lte = 'a\uffff'
        read db, lte, gte, ->
          log '--------'
          lte = new Buffer [ 0x61, 0xff, ]
          read db, lte, gte, ->
            log '--------'

output

--------
listing keys up to LTE: 'a~' <Buffer 61 7e>
'a'
'abcdef'
--------
listing keys up to LTE: 'aÿ' <Buffer 61 c3 bf>
'a'
'abcdef'
'aäöü'
--------
listing keys up to LTE: 'a￿' <Buffer 61 ef bf bf>
'a'
'abcdef'
'aäöü'
'aΔ'
'a中'
--------
listing keys up to LTE: <Buffer 61 ff> <Buffer 61 ff>
'a'
'abcdef'
'aäöü'
'aΔ'
'a中'
'a𠁩'
--------

quick demo to demonstrate that you should not use any of ~, ÿ, or even \uFFFF in your LevelDB when you want 'all possible keys with this prefix'.