level-stream-access

Write and read stream values from leveldb database

Installation

Install level-stream-access from npm. You also need levelup to be installed.

npm install level-stream-access level

Setup

Create a level-stream-access instance by providing a levelup object that is used for storage.

const levelup = require('levelup');
const levelStreamAccess = require('level-stream-access');
const levelStream = levelStreamAccess(levelup('./mydb'));

createWriteStream()

Write a large stream into leveldb database

let writer = levelStream.createWriteStream('keyname');

Example

fs.createReadStream('file.txt').
    pipe(levelStream.createWriteStream('keyname'));

createReadStream()

Read a stream from leveldb database

let reader = levelStream.createReadStream('keyname');

Example

levelStream.createReadStream('keyname').
    pipe(process.stdout);

createStoreStream()

Write a large stream into leveldb database and immediatelly read the stored data. Use it if you want to pass on data but you need to make sure that data gets stored.

let store = levelStream.createStoreStream('keyname');

Example

fs.createReadStream('file.txt').
    pipe(levelStream.createStoreStream('keyname')).
    pipe(process.stdout);

prepend()

Prepend data to the beginning of the stored stream. This is mostly useful if the stream is an email message and you want to add new headers to it

levelStream.prepend(keyname, value, callback);

Where

• keyname is the stream key to prepend data to
• value is a Buffer or string data to be prepended to the stream
• callback is the function to run once data is prepended

Example

levelStream.delete('keyname', 'new first line\n' function(err, prepended){
    if(err){
        console.log(err);
    }else if(!prepended){
        console.log('Stream was not found');
    }else{
        console.log('data prepended to the stream');
    }
});

setMeta()

Attach JSON metadata to the stored stream. This value gets removed when you delete the stream. If there already was metadata set, it gets overwritten. If the stream does not exists, then metadata is not stored and callback returns false, otherwise it returns true

levelStream.setMeta(keyname, data, callback);

Where

• keyname is the stream key to add metadata to
• data is an object that can be converted to JSON
• callback is the function to run once data is stored

Example

levelStream.setMeta('keyname', {
    filename: 'some-file.txt'
}, function(err, stored){
    if(err){
        console.log(err);
    }else if(!stored){
        console.log('Stream was not found');
    }else{
        console.log('metadata was stored');
    }
});

getMeta()

Get JSON metadata for the stored stream. This value combines both the user defined metadata using setMeta and system metadata (eg. created with creation timestamp).

levelStream.getMeta(keyname, callback);

Where

• keyname is the stream key to get metadata for
• callback is the function to run once data is stored

Example

levelStream.setMeta('keyname', function(err, meta){
    if(err){
        console.log(err);
    }
    if(!meta){
        console.log('Stream was not found!');
    }else{
        // user defined metadata
        console.log(meta.filename); // 'some-file.txt'
        // system provided metadata
        console.log(meta.created); // 1470901349281
    }
});

delete()

Delete streamed data from leveldb

levelStream.delete('keyname', callback);

Example

levelStream.delete('keyname', function(err, deleted){
    if(err){
        console.log(err);
    }else{
        console.log('%s chunks deleted', deleted);
    }
});

License

MIT