lib/utils.js

/*jshint strict: false */
/*global chrome */
var merge = require('./merge');
exports.extend = require('pouchdb-extend');
exports.ajax = require('./deps/ajax');
exports.createBlob = require('./deps/blob');
exports.uuid = require('./deps/uuid');
exports.getArguments = require('argsarray');
var buffer = require('./deps/buffer');
var errors = require('./deps/errors');
var EventEmitter = require('events').EventEmitter;
var collections = require('pouchdb-collections');
exports.Map = collections.Map;
exports.Set = collections.Set;

if (typeof global.Promise === 'function') {
  exports.Promise = global.Promise;
} else {
  exports.Promise = require('bluebird');
}
var Promise = exports.Promise;

function toObject(array) {
  return array.reduce(function (obj, item) { 
    obj[item] = true;
    return obj;
  }, {});
}
// List of top level reserved words for doc
var reservedWords = toObject([
  '_id',
  '_rev',
  '_attachments',
  '_deleted',
  '_revisions',
  '_revs_info',
  '_conflicts',
  '_deleted_conflicts',
  '_local_seq',
  '_rev_tree',
  //replication documents
  '_replication_id',
  '_replication_state',
  '_replication_state_time',
  '_replication_state_reason',
  '_replication_stats',
  // Specific to Couchbase Sync Gateway
  '_removed'
]);

// List of reserved words that should end up the document
var dataWords = toObject([
  '_attachments',
  //replication documents
  '_replication_id',
  '_replication_state',
  '_replication_state_time',
  '_replication_state_reason',
  '_replication_stats'
]);

exports.lastIndexOf = function (str, char) {
  for (var i = str.length - 1; i >= 0; i--) {
    if (str.charAt(i) === char) {
      return i;
    }
  }
  return -1;
};

exports.clone = function (obj) {
  return exports.extend(true, {}, obj);
};

// like underscore/lodash _.pick()
exports.pick = function (obj, arr) {
  var res = {};
  for (var i = 0, len = arr.length; i < len; i++) {
    var prop = arr[i];
    res[prop] = obj[prop];
  }
  return res;
};

exports.inherits = require('inherits');

// Determine id an ID is valid
//   - invalid IDs begin with an underescore that does not begin '_design' or
//     '_local'
//   - any other string value is a valid id
// Returns the specific error object for each case
exports.invalidIdError = function (id) {
  var err;
  if (!id) {
    err = errors.error(errors.MISSING_ID);
  } else if (typeof id !== 'string') {
    err = errors.error(errors.INVALID_ID);
  } else if (/^_/.test(id) && !(/^_(design|local)/).test(id)) {
    err = errors.error(errors.RESERVED_ID);
  }
  if (err) {
    throw err;
  }
};

function isChromeApp() {
  return (typeof chrome !== "undefined" &&
          typeof chrome.storage !== "undefined" &&
          typeof chrome.storage.local !== "undefined");
}

// Pretty dumb name for a function, just wraps callback calls so we dont
// to if (callback) callback() everywhere
exports.call = exports.getArguments(function (args) {
  if (!args.length) {
    return;
  }
  var fun = args.shift();
  if (typeof fun === 'function') {
    fun.apply(this, args);
  }
});

exports.isLocalId = function (id) {
  return (/^_local/).test(id);
};

// check if a specific revision of a doc has been deleted
//  - metadata: the metadata object from the doc store
//  - rev: (optional) the revision to check. defaults to winning revision
exports.isDeleted = function (metadata, rev) {
  if (!rev) {
    rev = merge.winningRev(metadata);
  }
  var dashIndex = rev.indexOf('-');
  if (dashIndex !== -1) {
    rev = rev.substring(dashIndex + 1);
  }
  var deleted = false;
  merge.traverseRevTree(metadata.rev_tree,
  function (isLeaf, pos, id, acc, opts) {
    if (id === rev) {
      deleted = !!opts.deleted;
    }
  });

  return deleted;
};

exports.revExists = function (metadata, rev) {
  var found = false;
  merge.traverseRevTree(metadata.rev_tree, function (leaf, pos, id) {
    if ((pos + '-' + id) === rev) {
      found = true;
    }
  });
  return found;
};

exports.filterChange = function filterChange(opts) {
  var req = {};
  var hasFilter = opts.filter && typeof opts.filter === 'function';
  req.query = opts.query_params;

  return function filter(change) {
    if (opts.filter && hasFilter && !opts.filter.call(this, change.doc, req)) {
      return false;
    }
    if (!opts.include_docs) {
      delete change.doc;
    } else if (!opts.attachments) {
      for (var att in change.doc._attachments) {
        if (change.doc._attachments.hasOwnProperty(att)) {
          change.doc._attachments[att].stub = true;
        }
      }
    }
    return true;
  };
};

// Preprocess documents, parse their revisions, assign an id and a
// revision for new writes that are missing them, etc
exports.parseDoc = function (doc, newEdits) {

  var nRevNum;
  var newRevId;
  var revInfo;
  var error;
  var opts = {status: 'available'};
  if (doc._deleted) {
    opts.deleted = true;
  }

  function parseRevisionInfo() {
    revInfo = /^(\d+)-(.+)$/.exec(doc._rev);
    if (!revInfo) {
      error = errors.error(errors.INVALID_REV);
      return error;
    }
    return {
      prefix: parseInt(revInfo[1], 10),
      id: revInfo[2]
    };
  }

  if (newEdits) {
    if (!doc._id) {
      doc._id = exports.uuid();
    }
    newRevId = exports.uuid(32, 16).toLowerCase();
    if (doc._rev) {
      revInfo = parseRevisionInfo(doc._rev);
      if (revInfo.error) {
        return revInfo;
      }
      doc._rev_tree = [{
        pos: revInfo.prefix,
        ids: [revInfo.id, {status: 'missing'}, [[newRevId, opts, []]]]
      }];
      nRevNum = revInfo.prefix + 1;
    } else {
      doc._rev_tree = [{
        pos: 1,
        ids : [newRevId, opts, []]
      }];
      nRevNum = 1;
    }
  } else {
    if (doc._revisions) {
      doc._rev_tree = [{
        pos: doc._revisions.start - doc._revisions.ids.length + 1,
        ids: doc._revisions.ids.reduce(function (acc, x) {
          if (acc === null) {
            return [x, opts, []];
          } else {
            return [x, {status: 'missing'}, [acc]];
          }
        }, null)
      }];
      nRevNum = doc._revisions.start;
      newRevId = doc._revisions.ids[0];
    }
    if (!doc._rev_tree) {
      revInfo = parseRevisionInfo(doc._rev);
      if (revInfo.error) {
        return revInfo;
      }
      nRevNum = revInfo.prefix;
      newRevId = revInfo.id;
      doc._rev_tree = [{
        pos: nRevNum,
        ids: [newRevId, opts, []]
      }];
    }
  }

  exports.invalidIdError(doc._id);

  doc._rev = [nRevNum, newRevId].join('-');

  var result = {metadata : {}, data : {}};
  for (var key in doc) {
    if (doc.hasOwnProperty(key)) {
      var specialKey = key[0] === '_';
      if (specialKey && !reservedWords[key]) {
        error = errors.error(errors.DOC_VALIDATION, key);
        error.message = errors.DOC_VALIDATION.message + ': ' + key;
        throw error;
      } else if (specialKey && !dataWords[key]) {
        result.metadata[key.slice(1)] = doc[key];
      } else {
        result.data[key] = doc[key];
      }
    }
  }
  return result;
};

exports.isCordova = function () {
  return (typeof cordova !== "undefined" ||
          typeof PhoneGap !== "undefined" ||
          typeof phonegap !== "undefined");
};

exports.hasLocalStorage = function () {
  if (isChromeApp()) {
    return false;
  }
  try {
    return localStorage;
  } catch (e) {
    return false;
  }
};
exports.Changes = Changes;
exports.inherits(Changes, EventEmitter);
function Changes() {
  if (!(this instanceof Changes)) {
    return new Changes();
  }
  var self = this;
  EventEmitter.call(this);
  this.isChrome = isChromeApp();
  this.listeners = {};
  this.hasLocal = false;
  if (!this.isChrome) {
    this.hasLocal = exports.hasLocalStorage();
  }
  if (this.isChrome) {
    chrome.storage.onChanged.addListener(function (e) {
      // make sure it's event addressed to us
      if (e.db_name != null) {
        //object only has oldValue, newValue members
        self.emit(e.dbName.newValue);
      }
    });
  } else if (this.hasLocal) {
    if (typeof addEventListener !== 'undefined') {
      addEventListener("storage", function (e) {
        self.emit(e.key);
      });
    } else { // old IE
      window.attachEvent("storage", function (e) {
        self.emit(e.key);
      });
    }
  }

}
Changes.prototype.addListener = function (dbName, id, db, opts) {
  if (this.listeners[id]) {
    return;
  }
  var self = this;
  var inprogress = false;
  function eventFunction() {
    if (!self.listeners[id]) {
      return;
    }
    if (inprogress) {
      inprogress = 'waiting';
      return;
    }
    inprogress = true;
    db.changes({
      include_docs: opts.include_docs,
      attachments: opts.attachments,
      conflicts: opts.conflicts,
      continuous: false,
      descending: false,
      filter: opts.filter,
      doc_ids: opts.doc_ids,
      view: opts.view,
      since: opts.since,
      query_params: opts.query_params
    }).on('change', function (c) {
      if (c.seq > opts.since && !opts.cancelled) {
        opts.since = c.seq;
        exports.call(opts.onChange, c);
      }
    }).on('complete', function () {
      if (inprogress === 'waiting') {
        process.nextTick(function () {
          self.notify(dbName);
        });
      }
      inprogress = false;
    }).on('error', function () {
      inprogress = false;
    });
  }
  this.listeners[id] = eventFunction;
  this.on(dbName, eventFunction);
};

Changes.prototype.removeListener = function (dbName, id) {
  if (!(id in this.listeners)) {
    return;
  }
  EventEmitter.prototype.removeListener.call(this, dbName,
    this.listeners[id]);
};


Changes.prototype.notifyLocalWindows = function (dbName) {
  //do a useless change on a storage thing
  //in order to get other windows's listeners to activate
  if (this.isChrome) {
    chrome.storage.local.set({dbName: dbName});
  } else if (this.hasLocal) {
    localStorage[dbName] = (localStorage[dbName] === "a") ? "b" : "a";
  }
};

Changes.prototype.notify = function (dbName) {
  this.emit(dbName);
  this.notifyLocalWindows(dbName);
};

if (typeof window === 'undefined' || typeof window.atob !== 'function') {
  exports.atob = function (str) {
    var base64 = new buffer(str, 'base64');
    // Node.js will just skip the characters it can't encode instead of
    // throwing and exception
    if (base64.toString('base64') !== str) {
      throw ("Cannot base64 encode full string");
    }
    return base64.toString('binary');
  };
} else {
  exports.atob = function (str) {
    return atob(str);
  };
}

if (typeof window === 'undefined' || typeof window.btoa !== 'function') {
  exports.btoa = function (str) {
    return new buffer(str, 'binary').toString('base64');
  };
} else {
  exports.btoa = function (str) {
    return btoa(str);
  };
}

// From http://stackoverflow.com/questions/14967647/ (continues on next line)
// encode-decode-image-with-base64-breaks-image (2013-04-21)
exports.fixBinary = function (bin) {
  if (!process.browser) {
    // don't need to do this in Node
    return bin;
  }

  var length = bin.length;
  var buf = new ArrayBuffer(length);
  var arr = new Uint8Array(buf);
  for (var i = 0; i < length; i++) {
    arr[i] = bin.charCodeAt(i);
  }
  return buf;
};

// shim for browsers that don't support it
exports.readAsBinaryString = function (blob, callback) {
  var reader = new FileReader();
  var hasBinaryString = typeof reader.readAsBinaryString === 'function';
  reader.onloadend = function (e) {
    var result = e.target.result || '';
    if (hasBinaryString) {
      return callback(result);
    }
    callback(exports.arrayBufferToBinaryString(result));
  };
  if (hasBinaryString) {
    reader.readAsBinaryString(blob);
  } else {
    reader.readAsArrayBuffer(blob);
  }
};

// simplified API. universal browser support is assumed
exports.readAsArrayBuffer = function (blob, callback) {
  var reader = new FileReader();
  reader.onloadend = function (e) {
    var result = e.target.result || new ArrayBuffer(0);
    callback(result);
  };
  reader.readAsArrayBuffer(blob);
};

exports.once = function (fun) {
  var called = false;
  return exports.getArguments(function (args) {
    if (called) {
      throw new Error('once called  more than once');
    } else {
      called = true;
      fun.apply(this, args);
    }
  });
};

exports.toPromise = function (func) {
  //create the function we will be returning
  return exports.getArguments(function (args) {
    var self = this;
    var tempCB =
      (typeof args[args.length - 1] === 'function') ? args.pop() : false;
    // if the last argument is a function, assume its a callback
    var usedCB;
    if (tempCB) {
      // if it was a callback, create a new callback which calls it,
      // but do so async so we don't trap any errors
      usedCB = function (err, resp) {
        process.nextTick(function () {
          tempCB(err, resp);
        });
      };
    }
    var promise = new Promise(function (fulfill, reject) {
      var resp;
      try {
        var callback = exports.once(function (err, mesg) {
          if (err) {
            reject(err);
          } else {
            fulfill(mesg);
          }
        });
        // create a callback for this invocation
        // apply the function in the orig context
        args.push(callback);
        resp = func.apply(self, args);
        if (resp && typeof resp.then === 'function') {
          fulfill(resp);
        }
      } catch (e) {
        reject(e);
      }
    });
    // if there is a callback, call it back
    if (usedCB) {
      promise.then(function (result) {
        usedCB(null, result);
      }, usedCB);
    }
    promise.cancel = function () {
      return this;
    };
    return promise;
  });
};

exports.adapterFun = function (name, callback) {
  var log = require('debug')('pouchdb:api');

  function logApiCall(self, name, args) {
    if (!log.enabled) {
      return;
    }
    var logArgs = [self._db_name, name];
    for (var i = 0; i < args.length - 1; i++) {
      logArgs.push(args[i]);
    }
    log.apply(null, logArgs);

    // override the callback itself to log the response
    var origCallback = args[args.length - 1];
    args[args.length - 1] = function (err, res) {
      var responseArgs = [self._db_name, name];
      responseArgs = responseArgs.concat(
        err ? ['error', err] : ['success', res]
      );
      log.apply(null, responseArgs);
      origCallback(err, res);
    };
  }


  return exports.toPromise(exports.getArguments(function (args) {
    if (this._closed) {
      return Promise.reject(new Error('database is closed'));
    }
    var self = this;
    logApiCall(self, name, args);
    if (!this.taskqueue.isReady) {
      return new exports.Promise(function (fulfill, reject) {
        self.taskqueue.addTask(function (failed) {
          if (failed) {
            reject(failed);
          } else {
            fulfill(self[name].apply(self, args));
          }
        });
      });
    }
    return callback.apply(this, args);
  }));
};

//Can't find original post, but this is close
//http://stackoverflow.com/questions/6965107/ (continues on next line)
//converting-between-strings-and-arraybuffers
exports.arrayBufferToBinaryString = function (buffer) {
  var binary = "";
  var bytes = new Uint8Array(buffer);
  var length = bytes.byteLength;
  for (var i = 0; i < length; i++) {
    binary += String.fromCharCode(bytes[i]);
  }
  return binary;
};

exports.cancellableFun = function (fun, self, opts) {

  opts = opts ? exports.clone(true, {}, opts) : {};

  var emitter = new EventEmitter();
  var oldComplete = opts.complete || function () { };
  var complete = opts.complete = exports.once(function (err, resp) {
    if (err) {
      oldComplete(err);
    } else {
      emitter.emit('end', resp);
      oldComplete(null, resp);
    }
    emitter.removeAllListeners();
  });
  var oldOnChange = opts.onChange || function () {};
  var lastChange = 0;
  self.on('destroyed', function () {
    emitter.removeAllListeners();
  });
  opts.onChange = function (change) {
    oldOnChange(change);
    if (change.seq <= lastChange) {
      return;
    }
    lastChange = change.seq;
    emitter.emit('change', change);
    if (change.deleted) {
      emitter.emit('delete', change);
    } else if (change.changes.length === 1 &&
      change.changes[0].rev.slice(0, 1) === '1-') {
      emitter.emit('create', change);
    } else {
      emitter.emit('update', change);
    }
  };
  var promise = new Promise(function (fulfill, reject) {
    opts.complete = function (err, res) {
      if (err) {
        reject(err);
      } else {
        fulfill(res);
      }
    };
  });

  promise.then(function (result) {
    complete(null, result);
  }, complete);

  // this needs to be overwridden by caller, dont fire complete until
  // the task is ready
  promise.cancel = function () {
    promise.isCancelled = true;
    if (self.taskqueue.isReady) {
      opts.complete(null, {status: 'cancelled'});
    }
  };

  if (!self.taskqueue.isReady) {
    self.taskqueue.addTask(function () {
      if (promise.isCancelled) {
        opts.complete(null, {status: 'cancelled'});
      } else {
        fun(self, opts, promise);
      }
    });
  } else {
    fun(self, opts, promise);
  }
  promise.on = emitter.on.bind(emitter);
  promise.once = emitter.once.bind(emitter);
  promise.addListener = emitter.addListener.bind(emitter);
  promise.removeListener = emitter.removeListener.bind(emitter);
  promise.removeAllListeners = emitter.removeAllListeners.bind(emitter);
  promise.setMaxListeners = emitter.setMaxListeners.bind(emitter);
  promise.listeners = emitter.listeners.bind(emitter);
  promise.emit = emitter.emit.bind(emitter);
  return promise;
};

exports.MD5 = exports.toPromise(require('./deps/md5'));

// designed to give info to browser users, who are disturbed
// when they see 404s in the console
exports.explain404 = function (str) {
  if (process.browser && 'console' in global && 'info' in console) {
    console.info('The above 404 is totally normal. ' + str);
  }
};

exports.info = function (str) {
  if (typeof console !== 'undefined' && 'info' in console) {
    console.info(str);
  }
};

exports.parseUri = require('./deps/parse-uri');

exports.compare = function (left, right) {
  return left < right ? -1 : left > right ? 1 : 0;
};

exports.updateDoc = function updateDoc(prev, docInfo, results,
                                       i, cb, writeDoc, newEdits) {

  if (exports.revExists(prev, docInfo.metadata.rev)) {
    results[i] = docInfo;
    return cb();
  }

  var previouslyDeleted = exports.isDeleted(prev);
  var deleted = exports.isDeleted(docInfo.metadata);
  var isRoot = /^1-/.test(docInfo.metadata.rev);

  if (previouslyDeleted && !deleted && newEdits && isRoot) {
    var newDoc = docInfo.data;
    newDoc._rev = merge.winningRev(prev);
    newDoc._id = docInfo.metadata.id;
    docInfo = exports.parseDoc(newDoc, newEdits);
  }

  var merged = merge.merge(prev.rev_tree, docInfo.metadata.rev_tree[0], 1000);

  var inConflict = newEdits && (((previouslyDeleted && deleted) ||
    (!previouslyDeleted && merged.conflicts !== 'new_leaf') ||
    (previouslyDeleted && !deleted && merged.conflicts === 'new_branch')));

  if (inConflict) {
    var err = errors.error(errors.REV_CONFLICT);
    results[i] = err;
    return cb();
  }

  var newRev = docInfo.metadata.rev;
  docInfo.metadata.rev_tree = merged.tree;
  if (prev.rev_map) {
    docInfo.metadata.rev_map = prev.rev_map; // used by leveldb
  }

  // recalculate
  var winningRev = merge.winningRev(docInfo.metadata);
  deleted = exports.isDeleted(docInfo.metadata, winningRev);

  var delta = 0;
  if (newEdits || winningRev === newRev) {
    // if newEdits==false and we're pushing existing revisions,
    // then the only thing that matters is whether this revision
    // is the winning one, and thus replaces an old one
    delta = (previouslyDeleted === deleted) ? 0 :
      previouslyDeleted < deleted ? -1 : 1;
  }

  writeDoc(docInfo, winningRev, deleted, cb, true, delta, i);
};

exports.processDocs = function processDocs(docInfos, api, fetchedDocs,
                                           tx, results, writeDoc, opts,
                                           overallCallback) {

  if (!docInfos.length) {
    return;
  }

  function insertDoc(docInfo, resultsIdx, callback) {
    // Cant insert new deleted documents
    var winningRev = merge.winningRev(docInfo.metadata);
    var deleted = exports.isDeleted(docInfo.metadata, winningRev);
    if ('was_delete' in opts && deleted) {
      results[resultsIdx] = errors.error(errors.MISSING_DOC, 'deleted');
      return callback();
    }

    var delta = deleted ? 0 : 1;

    writeDoc(docInfo, winningRev, deleted, callback, false, delta, resultsIdx);
  }

  var newEdits = opts.new_edits;
  var idsToDocs = new exports.Map();

  var docsDone = 0;
  var docsToDo = docInfos.length;

  function checkAllDocsDone() {
    if (++docsDone === docsToDo && overallCallback) {
      overallCallback();
    }
  }

  docInfos.forEach(function (currentDoc, resultsIdx) {

    if (currentDoc._id && exports.isLocalId(currentDoc._id)) {
      api[currentDoc._deleted ? '_removeLocal' : '_putLocal'](
        currentDoc, {ctx: tx}, function (err) {
          if (err) {
            results[resultsIdx] = err;
          } else {
            results[resultsIdx] = {ok: true};
          }
          checkAllDocsDone();
        });
      return;
    }

    var id = currentDoc.metadata.id;
    if (idsToDocs.has(id)) {
      docsToDo--; // duplicate
      idsToDocs.get(id).push([currentDoc, resultsIdx]);
    } else {
      idsToDocs.set(id, [[currentDoc, resultsIdx]]);
    }
  });

  // in the case of new_edits, the user can provide multiple docs
  // with the same id. these need to be processed sequentially
  idsToDocs.forEach(function (docs, id) {
    var numDone = 0;

    function docWritten() {
      if (++numDone < docs.length) {
        nextDoc();
      } else {
        checkAllDocsDone();
      }
    }
    function nextDoc() {
      var value = docs[numDone];
      var currentDoc = value[0];
      var resultsIdx = value[1];

      if (fetchedDocs.has(id)) {
        exports.updateDoc(fetchedDocs.get(id), currentDoc, results,
          resultsIdx, docWritten, writeDoc, newEdits);
      } else {
        insertDoc(currentDoc, resultsIdx, docWritten);
      }
    }
    nextDoc();
  });
};

exports.preprocessAttachments = function preprocessAttachments(
    docInfos, blobType, callback) {

  if (!docInfos.length) {
    return callback();
  }

  var docv = 0;

  function parseBase64(data) {
    try {
      return exports.atob(data);
    } catch (e) {
      var err = errors.error(errors.BAD_ARG,
                             'Attachments need to be base64 encoded');
      return {error: err};
    }
  }

  function preprocessAttachment(att, callback) {
    if (att.stub) {
      return callback();
    }
    if (typeof att.data === 'string') {
      // input is a base64 string

      var asBinary = parseBase64(att.data);
      if (asBinary.error) {
        return callback(asBinary.error);
      }

      att.length = asBinary.length;
      if (blobType === 'blob') {
        att.data = exports.createBlob([exports.fixBinary(asBinary)],
          {type: att.content_type});
      } else if (blobType === 'base64') {
        att.data = exports.btoa(asBinary);
      } else { // binary
        att.data = asBinary;
      }
      exports.MD5(asBinary).then(function (result) {
        att.digest = 'md5-' + result;
        callback();
      });
    } else { // input is a blob
      exports.readAsArrayBuffer(att.data, function (buff) {
        if (blobType === 'binary') {
          att.data = exports.arrayBufferToBinaryString(buff);
        } else if (blobType === 'base64') {
          att.data = exports.btoa(exports.arrayBufferToBinaryString(buff));
        }
        exports.MD5(buff).then(function (result) {
          att.digest = 'md5-' + result;
          att.length = buff.byteLength;
          callback();
        });
      });
    }
  }

  var overallErr;

  docInfos.forEach(function (docInfo) {
    var attachments = docInfo.data && docInfo.data._attachments ?
      Object.keys(docInfo.data._attachments) : [];
    var recv = 0;

    if (!attachments.length) {
      return done();
    }

    function processedAttachment(err) {
      overallErr = err;
      recv++;
      if (recv === attachments.length) {
        done();
      }
    }

    for (var key in docInfo.data._attachments) {
      if (docInfo.data._attachments.hasOwnProperty(key)) {
        preprocessAttachment(docInfo.data._attachments[key],
          processedAttachment);
      }
    }
  });

  function done() {
    docv++;
    if (docInfos.length === docv) {
      if (overallErr) {
        callback(overallErr);
      } else {
        callback();
      }
    }
  }
};

// compact a tree by marking its non-leafs as missing,
// and return a list of revs to delete
exports.compactTree = function compactTree(metadata) {
  var revs = [];
  merge.traverseRevTree(metadata.rev_tree, function (isLeaf, pos,
                                                     revHash, ctx, opts) {
    if (opts.status === 'available' && !isLeaf) {
      revs.push(pos + '-' + revHash);
      opts.status = 'missing';
    }
  });
  return revs;
};

var vuvuzela = require('vuvuzela');

exports.safeJsonParse = function safeJsonParse(str) {
  try {
    return JSON.parse(str);
  } catch (e) {
    return vuvuzela.parse(str);
  }
};

exports.safeJsonStringify = function safeJsonStringify(json) {
  try {
    return JSON.stringify(json);
  } catch (e) {
    return vuvuzela.stringify(json);
  }
};