const FilesAndRelays = require('./files_and_relays')
const fsPromises = require('fs/promises')
const fs = require('fs')
const uuid = require('../lib/uuid')
//
const MAX_LAX_CACHE_TIME = 1000*3600*4
const MAX_BYTES_ALLOWED = (1<<24)
const MAX_GROUP_STORAGE_SIZE = 256 // ?? The max length of data passed to the parent class, which will write all data to a file for restore
const DEFAULT_DB_DIR = "local/static_db"
//
/**
* Some elements of the `_storage_map` are large enough that they should be stored on disk to keep RAM available.
* A PageableMemStoreElement instance is used as a standin for the actual data record.
* The total version of the object is to be placed in a file on disk. The larger fields are replaced in the object
* with a descriptor. The resulting smaller object is allowed to stay in memory the PageableMemStoreElement instance
* makes a reference to it via its `_obj` field. The PageableMemStoreElement instance retains information about the
* name of the file holding the complete object.
*
* As the object refered to by the PageableMemStoreElement instance is used, the complete object may or may not reside in memory.
* The longer it is in memory without being used, the more likely the object will be reduced with the complete form being put out to
* disk. Several fields relate to the state of the objects storage and residence in memory.
*
* * unhooked -- the object has been stashed during the syncing interval.
* * saved -- true if the object data has been written to disk.
* * flat_object -- the string form of the storage whose length determines if the PageableMemStoreElement is appropriate
* * file -- where the object will be stored, which is the name of the `_id` field, the wide are id.
*
* @memberof DefaultDB
*/
class PageableMemStoreElement {
//
constructor(key,file,obj,flat_obj,buod) {
this.key = key
this.file = file
this.type = '.json'
this._obj = Object.assign({},obj)
this.saved = false
this.unhooked = false
this.t_stamp = Date.now()
this.back_up_on_delete = buod
this.flat_object = flat_obj
this.clip_big_fields(obj)
this.blob_dir = DEFAULT_DB_DIR
}
update(obj,flat_obj) {
this._obj = Object.assign({},obj)
this.clip_big_fields(obj)
this.t_stamp = Date.now()
this.unhooked = false
this.saved = false
this.flat_object = flat_obj
this.clip_big_fields(obj)
}
back_up(deleting) {
if ( deleting ) {
if ( !(this.back_up_on_delete) ) return;
}
// write to a file.....
}
clip_big_fields(obj) {
for ( let ky in obj ) {
let val = obj[ky]
if ( val.length > (MAX_GROUP_STORAGE_SIZE/4) ) {
obj[ky] = `@${ky}`
}
}
}
}
/**
*
* This class handles the relationship between static storage and files on disk.
*
* The object map will be stored at predefined intervals. And, some table entries will refer to larger data components
* that are better stored in files on disk.
*
* This is a local storage implementation for those applications that do not supply their own in overriding
* the general DB methods given by the class DBClass nor by configuring a replacement for this class.
*
* This class extends the FilesAndRelays class.
*
*
* @memberof DefaultDB
*/
class LocalStorageSerialization extends FilesAndRelays {
constructor(messenger,stash_interval,default_m_path) {
super(messenger,stash_interval,default_m_path)
//
this.blob_dir = false
}
/**
*
* @param {object} conf
*/
initialize(conf) {
super.initialize(conf.static_db)
this.blob_dir = conf.static_db.blob_dir
//
if ( this.blob_dir ) {
this.load_dir(this.blob_dir)
}
}
/**
*
* Synchronous file reading to a string
*
* @param {string} file
* @returns {string|boolean} - returns the contents of the file as a string - false on failure
*/
load_file(file) {
if ( !(this.blob_dir) ) return;
if ( file !== undefined ) {
try {
let fpath = this.blob_dir + '/' + file
let data = fs.readFileSync(fpath)
let str = data.toString()
return str
} catch (e) {
console.log(e)
}
}
return false
}
//
/**
* Calls on the frameworks file removale method.
* @param {string} file
*/
async remove_file(file) {
if ( !(this.blob_dir) ) return;
if ( file !== undefined ) {
try {
let fpath = this.blob_dir + '/' + file
await fsPromises.rm(fpath)
} catch (e) {}
}
}
/**
* This method is called as part of initialization.
* Take the name of the directory where the application will store blob data.
* Reads each file in the directory.
*
* Calls on `application_stash_large_data` to get the data's rerefence set up in memory.
* @param {string} blob_dir
*/
load_dir(blob_dir) {
if ( !(this.blob_dir) ) return;
try {
fs.mkdirSync(blob_dir)
} catch (e) {
}
try {
let files = fs.readdirSync(blob_dir)
files.forEach(async file => {
if ( file === '.DS_Store' ) return;
try {
let datstr = this.load_file(file)
if ( datstr ) {
let obj = JSON.parse(datstr)
this.application_stash_large_data(obj,true)
// can't do this:: this.set_key_value(whokey,datum)
}
} catch (e) {
}
});
} catch (e) {
console.log(e)
}
}
/**
* override pruning behavior
*
* Usess `max_freeloading_time` instead of `_age_out_delta` (???)
*/
prune_storage_map() {
let ctime = Date.now()
let stamps = Object.keys(this._time_to_id)
stamps.sort()
ctime -= this.max_freeloading_time
while ( stamps.length > 0 ) {
let ts = stamps.shift()
if ( ctime > ts ) {
let ids = this._time_to_id[ts]
this.remote_store_sync(ids)
if ( Object.keys(ids) == 0 ) {
delete this._time_to_id[ts]
}
}
}
}
/**
* It is up to application subsclasses to make sure that the schedule method is called.
* The interval is set to be `static_sync_interval`. At the interval, this calls `static_backup`
* immediately after calling the callers `static_backup`.
*
* @param {Function} sync_function
* @param {Number} static_sync_interval
*/
schedule(sync_function,static_sync_interval) { // sync_function this may go away, but it is here for now...
if ( static_sync_interval ) {
this.storage_interval = setInterval(() => {
if ( typeof sync_function === 'function' ) {
sync_function()
}
this.static_backup()
},static_sync_interval)
}
}
//
// static_backup
// write the larger data objects to a file.. one per object if it has not been saved
//
/**
* Write the current data tables out to files.
* If memory is getting tight, then objects that have been staying in memory too long are removed.
* (This is a very simple ... clumsy - implementation of an LRU)
*/
async static_backup() {
if ( this.blob_dir === undefined ) return;
//this.unhooked = false
for ( let hh in this._ids_to_data_rep ) {
let pmse = this._ids_to_data_rep[hh]
if ( !(pmse.saved) ) {
let string = pmse.flat_object
let file = this.blob_dir + '/' + pmse.file
await fsPromises.writeFile(file,string)
this.saved = true
// remove old data from memory if space is being used up.
if ( this.ultra_test || ((this.max_freeloading_time < (Date.now() - pmse.t_stamp))
&& (this.allocated > this.memory_allocation_preference)) ) {
this.allocated -= string.length
pmse._obj = null
pmse.unhooked = true
}
}
}
}
/// FILES AND RELAYS - called by the wide area relationship
/**
* The main goal of this method is to create an instance of PageableMemStoreElement for the object or to
* update it. It is called by the FilesAndRelays class when an object is created or when it is updated.
*
*
* @param {object} obj
* @param {boolean} check_presistence
* @returns {object} - the object passed or the reference to its storage.
*/
application_stash_large_data(obj,check_presistence) {
let flat_object = this.flat_object(obj)
if ( obj && (flat_object.length < this._max_group_storage) ) return(obj) // no concern of this method
//
if ( obj._key !== undefined && !(check_presistence) ) { // in data reps table, _ids_to_data_rep
let hh = obj._key
let pmse = this._ids_to_data_rep[hh]
if ( pmse ) {
pmse.update(obj,flat_object)
return(pmse._obj)
} else return(obj)
} else {
let hh = false
if ( check_presistence ) {
hh = obj._key
}
if ( !(hh) ) {
hh = ( obj._id !== undefined ) ? this.hash_from_persitence(obj) : this.hash(flat_object)
}
if ( !(hh) ) {
hh = this.hash(flat_object)
}
if ( obj._id == undefined ) obj._id = this.id_maker()
obj._key = hh
let whokey = obj._whokey ? obj._whokey : "lost"
obj._whokey = whokey
this._whokey_to_ids[whokey] = obj._id
this._whokey_to_hash[whokey] = obj._key
let pmse = new PageableMemStoreElement(whokey,obj._id,obj,flat_object,this.back_up_on_delete) // keep the big data here
this._ids_to_data_rep[hh] = pmse
return(pmse._obj)
}
}
/**
* Called locally. (would be protected in C++)
*
* This loads data from a file if the pmse indicates that the data is no longer in memory.
* The psme.update similar to deserialization method that will the state of the psme to indicate the state as 'datao loaded'
* The term here is `hooked` and `unhooked`.
*
* @param {object} pmse
* @returns {object} - the object managed by the psme (PageableMemStoreElement)
*/
async _load_object_pmse(pmse) {
if ( pmse.unhooked ) {
let str = await this.load_file(pmse.file)
try {
let loaded_obj = JSON.parse(str)
pmse.update(loaded_obj)
} catch (e) {
console.log("PMSE - parse error...")
}
}
return(pmse._obj)
}
/**
*
* Part of getting a piece of data. Given are representation of the data is found, the key for the psme (PageableMemStoreElement)
* is used to find information for loading the larger object from a file.
*
* Called by the ancestor FilesAndRelays. In FilesAndRelays, this method is a nooperation.
* It is assumed that the static DB will provide custom storage for certain types of obects.
*
*
* @param {object} obj
* @returns {object} - the object managed by the psme (PageableMemStoreElement)
*/
async application_large_data_from_stash(obj) {
let hh = obj._key
if ( hh !== undefined ) { // in data reps table, _ids_to_data_rep
let pmse = this._ids_to_data_rep[hh]
if ( pmse === undefined ) return(obj) // this is a problemc
let loaded_obj = await this._load_object_pmse(pmse)
loaded_obj._key = hh
return loaded_obj
}
return(obj)
}
/**
* This method is used in deleting a record.
*
* Makes use of `_ids_to_data_rep` to fetch the psme (PageableMemStoreElement)
* Calls the backup method of the for the psme and then deletes the reference from the table.
* (Data may be retrieved from disk)
*
* Called by the ancestor FilesAndRelays. In FilesAndRelays, this method is a nooperation.
* It is assumed that the static DB will provide custom storage for certain types of obects.
*
* @param {object} obj
* @returns {object} obj, which was passed in. But, it may be removed from the map holding PageableMemStoreElement instances
*/
application_clear_large_data(obj) {
let hh = obj._key
if ( hh !== undefined ) {
let pmse = this._ids_to_data_rep[hh]
if ( pmse ) {
pmse.back_up(true)
delete this._ids_to_data_rep[hh]
}
}
return(obj)
}
// the id should only be available if the object is known to the uniers...
/**
*
* @param {string} id
* @param {object} obj
* @param {object} data
*/
async load_missing_or_update(id,obj,data) {
if ( data._id ) delete data._id // remove the data id so as not to overwrite the object id
let up_obj = Object.assign(obj,data)
if ( super.missing(up_obj) ) { // this means that the general mesh never saw it either (as far as local queries can make out)
// so ask the mesh to find it (if at all possible)
// this instead of super for application overrides
let remote_obj = await this.findOne(id,true) // if we get a copy from the universe don't tell the universe that id never existed
// so it showed up (but it's more up to date than the one stored here)
if ( this.newer(remote_obj,up_obj) ) {
up_obj = Object.assign(up_obj,remote_obj) // let this be the one we know
}
}
// make a space for it in local storage -- if there are changes the universe will be told
this.update(up_obj) // use the current object -- this call will make use of this static's application stashing
}
/**
* Called by the ancestor FilesAndRelays. In FilesAndRelays, this method is a nooperation.
* It is assumed that the static DB will provide custom storage for certain types of obects.
*
*
* @param {object} obj
* @param {string} key
* @param {string} field
*/
application_fix_keys_obj(obj,key,field,match_data) { // `_id` `_key` `_whokey`
if ( obj._whokey === undefined ) {
obj._whokey_field = key
let id_chunk = obj[field]
if ( id_chunk && id_chunk.length && (typeof id_chunk === 'string') ) {
obj._whokey = id_chunk
}
if ( obj._key === undefined ) {
obj._key = this.hash(JSON.stringify(obj))
}
if ( obj._id === undefined ) { // this should not happend (but as a stopgap)
obj._id = match_data
}
}
}
}
//
// and also a pub/sub client
//
/**
*
* This is a local storage implementation for those applications that do not supply their own in overriding
* the general DB methods given by the class DBClass nor by configuring a replacement for this class.
*
* This class extends FilesAndRelays which will attempt to port stored object out to an external DB, connected
* via the message service relay.
*
* One property of this storage class is that data is updated by the last writer. There is no mechanism for consensus exposed
* by this stack. Local copies can be inconsistent with remote entries. It is possible that an intermediary process can handle
* consistency, or a derived class might handle consistency. Part of the reason for this state of affairs is that the code here
* is provided for default usage of the Copious Transitions stack; it is not provided to solve a universal problem. Yet, it might
* provide some basic logic that can be used to interface with more universal architectures.
*
* On the other hand, there is a pub/sub mechanism that may be configured. And, a subclass of this class may implement `app_subscription_handler`.
* One possibility for the implementation of that method may be to take in copies of known entries and recitfy the differences when they arive
* and also to put in new entries without much extra effort.
*
* This implementation stores data, all entries, in a file and reloads it later. Large objects, those that can be sent through
* communication channels without relying on special streaming or P2P architectures, are stored in their own files, but
* a representation of the data, including the name of the file it is in, is stored in a PageableMemStoreElement element.
*
* The handling of data persisted between runs is introduced by extending LocalStorageSerialization.
*
* In this object storage, there is an assumption made about fields in the object.
* Object are expected to have or end up with about three different fields.
*
* At least locally, the object will have a local identity or if not that some field indicating an owner of the object: `_whokey`
* Another id would be a wide area id (or univsersal id): `_id`. It is expected that objects anywhere would be stored with such
* an id. Then, the objects will have a hash (most likely a hash of the object data) stored in `_key`.
*
* This stack expects that globally the two keys `_id` and `_key` will be part of the object. And, this stack will add `_whokey` locally.
*
* However, if the object cannot be found by those two keys, then this stack may search the wider area for the object using the local key
* with the assumption that the local key is made up of some salient feature of the object. For example, it actaully might be the case
* that just one object is stored per owner, or perhaps `_whokey` and `_key` are the same universal hash. (It may be the case that all
* three fields are the same.)
*
*
* @memberof DefaultDB
*
*/
class LocalStaticDB extends LocalStorageSerialization {
//
constructor(messenger,stash_interval,default_m_path,whokey_field) {
super(messenger,stash_interval,default_m_path)
this._whokey_to_ids = {}
this._whokey_to_hash = {}
this._ids_to_data_rep = {}
this.max_freeloading_time = MAX_LAX_CACHE_TIME
this.memory_allocation_preference = MAX_BYTES_ALLOWED
this.allocated = 0
this._whokey_field = whokey_field ? whokey_field : "email"
this.back_up_on_delete = false
this._max_group_storage = MAX_GROUP_STORAGE_SIZE
}
//
/**
* Calls the initializer for FilesAndRelays and the immediate LocalStorageSerialization
*
* @param {object} conf
*/
initialize(conf) {
super.initialize(conf.static_db)
if ( conf.static_db ) {
//
this._whokey_field = conf.static_db.index_key ? conf.static_db.index_key : this._whokey_field
//
let freeloading_timeout = conf.static_db.freeloading_timeout
this.max_freeloading_time = freeloading_timeout ? freeloading_timeout : MAX_LAX_CACHE_TIME
this.memory_allocation_preference = conf.static_db.max_data_RAM
this._max_group_storage = conf.static_db.max_forwarded_storage ? conf.static_db.max_forwarded_storage : MAX_GROUP_STORAGE_SIZE
}
}
//
/**
* quite possibly another DB made fore keeping objects around for a long time will be used
* @param {*} presistence_db
*/
setPersistence(presistence_db) {
this.pdb = presistence_db // application dependent :: quite possibly another DB made fore keeping objects around for a long time will be used.
}
/**
*
* @param {string} whokey
* @returns {string|boolean} - returns fals if the elementis not in the `_whokey_to_ids` map. Otherwise, the id.
*/
has(whokey) {
let id = this._whokey_to_ids[whokey]
return ( (id !== undefined) ? id : false )
}
/**
*
* @param {string} data
* @returns {string} the hash of the data
*/
hash(data) {
let hh = Math.floor(Math.random()*data.length) // not official left to the app
return(hh)
}
/**
*
* @param {object} remote_obj
* @param {object} up_obj
* @returns {boolean}
*/
newer(remote_obj,up_obj) {
return false // application policy
}
/**
* Add up all the fields values of an object that have a length field.
* @param {object} obj
* @returns {Number} - object size
*/
flat_object_size(obj) {
let sz = 0
for ( let ky in obj ) {
let dat = obj[ky]
if ( dat.length ) {
sz += dat.length
}
}
return sz
}
/**
* Stringify the object -- some implementations might want to use some other method to turn an object into a packed array.
* @param {object} obj
* @returns {string} - the stringified object
*/
flat_object(obj) {
return (JSON.stringify(obj))
}
field_transforms(ky) { return ky } // for renaming fields if it is necessary (see descendants)
/**
*
* @param {object} obj
* @returns {string} - value in a field `_key`, which is expected to be the hash of the data
*/
application_hash_key(obj) {
return obj._key
}
/**
* Returns the intrinsic hash key
* @param {object} obj
* @returns {string} - object hash
*/
hash_from_persitence(obj) {
let id = obj._id
let hh = super.hash_from_key(id)
return hh
}
/**
*
* Searches for the id of the data object by using a local identity,
* where the id mapped by the whokey refers to a universal wide area identity of the data.
*
* If it finds a local copy of the object, it will check to see if the local persistence storage keeps a copy.
* Given there is a local copy, this method calls `get_key_value` primarily for loadging instances of PageableMemStoreElement
* as it is already established the object exists.
*
* If it does not find a local copy of the object, it will check to see if the larger world knows about it. Without a local copy,
* the object `_id` cannot be known, so it searches for the object using the `whokey` using the field `_whokey_field`, which
* is hopefully known universally. (It is expected the application has standardized some field and way of obtaining a universal
* id for the objects stored here.) The search performed is the same as in `get_key_value`, however this method attempts to update
* the object data. It calls `load_missing_or_update` to perform this operation.
*
* Once the knowledge of the object is established, it will make sure the data is updated and synced with the local disk.
*
* If the object has not been seen anywhere, this method will store it as a the definitive entry and send out to the wider area.
*
* @param {string} whokey
* @param {object} data
* @returns {boolean}
*/
async set_key_value(whokey,data) {
//
let wa_id = this.has(whokey) // can we get the wide area id given the whokey
//
if ( wa_id !== false ) { // we think we know about this object, but do we? Try to go from the key to having the object
// look in all possible places to find this object
let obj = await this.get_key_value(whokey) // maybe it's stored locally (or it can be found with get)
if ( !(obj) ) { obj = await this.findOne(wa_id) } // so just try to find it somewhere on the mesh (should be known to the universe)
if ( obj ) { // can't be found at all
// set .. in this case is update
obj._whokey = whokey // make records that this chunk of code can track
// put data into the object and rectify with what is on disk.
await this.load_missing_or_update(wa_id,obj,data) // use LocalStorageSerialization and get the objects larger data
}
} else { // never saw this (this node -- plugged into the copious-transitions relationship management)
// so we go looking for it on the mesh
// -----------------search_one--------> using the *field* parameter
let obj = await this.search_one(whokey,this._whokey_field,data[this._whokey_field]) // going to try to find an object with a local ownership field being used here
if ( obj ) { // there it is from the universe
obj._whokey = whokey // the local identity will be stored with the object
wa_id = delete data._id // get the wide area id
await this.load_missing_or_update(wa_id,obj,data) // use LocalStorageSerialization and get the objects larger data
//
} else { // OK -- don't have local record -- can't find it (very likey this node is the creator)
obj = {
"key_field" : "file",
"file" : uuid()
}
obj._whokey = whokey
obj = Object.assign(obj,data) // add the data being stored to the object (hence other keys)
// CREATE
this.update(obj,false,'create') // store a persistence representation, but send any amount of data to the backend
// -- this call will make use of this static's application stashing
}
this._whokey_to_ids[whokey] = obj._id // by not setting the id, the parent class is allowed to set it
this._whokey_to_hash[whokey] = obj._key
}
return(true)
}
/**
* Returns the object that can be found by the key.
*
* Searches for the id of the data object by using a local identity,
* where the id mapped by the whokey refers to a universal wide area identity of the data.
*
* If a local copy cannot be found it searches the wide area using the application defined field and the
* `whokey` as its value.
*
* Otherwise, it finds one and tries to load its psme (PageableMemStoreElement). The object returned to the application will be
* stored with the psme. If the object is not large, it should be in the storage map, `_storage_map`. The method `findOne`
* will return the object from `_storage_map` which is defined in the super class. Also, it `_storage_map` is out of sync,
* then `findOne` will bring it back to sync (and take longer).
*
* @param {string} whokey
* @returns {object} - the value stored
*/
async get_key_value(whokey) {
let id = this.has(whokey)
let obj = null
if ( !(id) ) { // never saw this object (but someone seems to know its key)
obj = await this.search_one(whokey,this._whokey_field)
} else {
let hh = this._whokey_to_hash[whokey] // the object is here and known
let pmse = this._ids_to_data_rep[hh] // maybe load it.
if ( pmse ) {
let obj = pmse._obj
if ( !obj ) {
let loaded_obj = await this._load_object_pmse(pmse)
if ( loaded_obj) {
return loaded_obj
}
}
return obj
}
obj = await this.findOne(id) // by calling findOne, the object is pulled from `_storage_map`
}
if ( obj !== false ) {
this._whokey_to_ids[whokey] = obj._id // by not setting the id, the parent class is allowed to set it
this._whokey_to_hash[whokey] = obj._key
}
return obj
}
/**
*
* Clear out the local knowledge of this object. Requests the wider area to forget the object.
* Removes any files associated with the object.
*
* The call to *delete*
*
* @param {string} whokey - named this to emphasize that this stack is usually used just for user objects.
* @returns {boolean}
*/
del_key_value(whokey) {
let id = this.has(whokey)
if ( !(id) ) return(false) // never saw this object (but someone seems to know its key)
// call files and relays delete, which will call out to remotes for delete, also it will clear the `_storage_map`.
this.delete(id) // delete does not return a useful value
let hh = this._whokey_to_hash[whokey] // if the object is here and known
if ( hh ) { // The key to larger storage
let pmse = this._ids_to_data_rep[hh] // it might be a large object
if ( pmse ) {
let local_data = pmse.data // the stored data
this.allocated -= local_data.string.length // keep track of how much memory is being used up
let file = pmse.file
delete this._ids_to_data_rep[hh] // remove the record of this file based data
this.remove_file(file) // destroy the file containing the data
}
}
delete this._whokey_to_ids[whokey] // remove other references
delete this._whokey_to_hash[whokey]
return true
}
}
module.exports = LocalStaticDB