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28.05.2021, adminOver the years, developers created lots of packages out there with the sole purpose of making working with stream problems aptitude js easier. Streams are collections of data � just like arrays or strings. However, streams are not only about working with big data. They also give us the power of composability in our code. Just like we can compose stream problems aptitude js linux commands by stream problems aptitude js other smaller Linux commands, we can do exactly the same in Node with streams.
The list above has some examples for native Node. Some of these objects are both readable and writable streams, like TCP sockets, zlib and crypto streams. Notice stream problems aptitude js the objects are also closely related.
This is because in the HTTP case, we basically read from one object http. IncomingMessage and write to the other http. Also note how the stdio streams stdinstdoutstderr have the inverse stream types when it comes to child processes. This allows for a really easy way to pipe to and from these streams from the main process stdio streams. The fs module can be stream problems aptitude js to read from and write to files using a stream interface.
Every thing is great, right? We basically put the whole big. This is very inefficient. The HTTP response object res in the code above is also a writable stream. This means if we have a readable stream that stream problems aptitude js the content of big. We can pipe that to the response object:. You can push this example to its limits.
Regenerate the big. If you try to serve that file using fs. But with fs. There are four fundamental stream types in Node. All streams are instances of EventEmitter. They emit events that can be used to read and write data. However, we can consume streams data in a simpler way using the pipe method.
The source has to be a readable stream and the destination has to be a writable one. The pipe method returns the destination stream, which enabled us to do the chaining. For streams a readableb and c duplexand d writablewe can:. The pipe method is the easiest way to consume streams. Beside reading from a readable stream source and writing to a writable destination, the pipe method automatically manages a few things along the way.
For example, it handles errors, end-of-files, and the cases when one stream is slower or faster than the. However, streams can also be consumed with events directly. Events and functions can be combined to make for a custom and optimized use of streams. All readable streams start in the paused mode by default but they can be easily switched to flowing and back to paused when needed.
Sometimes, the switching happens automatically. When a readable stream is in the paused mode, we can use the read method to read from the stream on demand, however, for a readable stream in the flowing mode, the data stream problems aptitude js continuously flowing and we have to listen to events to consume it. In the flowing mode, data can actually be stream problems aptitude js if no consumers are available to handle it.
This is why, when we have a readable stream in flowing mode, we need a stream problems aptitude js event handler. In fact, just adding a data event handler switches a paused stream into flowing mode and removing the data event handler switches the stream back to paused mode. Some of this is done for backward compatibility with the older Node streams interface.
To manually switch between these two stream modes, you can use the resume and pause methods. Stream implementers are usually the ones who require the stream module. To implement a writable stream, we need to to use the Writable constructor from the stream module. We can implement a writable stream in many ways. We can, for example, extend the Writable constructor if we want.
However, I prefer the simpler constructor approach. We just create an object from the Writable constructor and pass it a number of options. The only required option is a write function which exposes the chunk of data to stream problems aptitude js written. In outStreamwe simply console. This is a very simple and probably not so useful echo stream.
It will echo back anything it receives. To consume this stream, we can simply use it with process. When we run the code above, anything we type into process. This is very much equivalent to process. There is a simple way to implement readable streams. We can just directly push the data that we stream problems aptitude js the consumers to consume. When we push a null object, that means we want to signal that the stream does not have any more data.
To consume this simple readable stream, we can simply pipe it into the writable stream process. Very simple, but also not very efficient. The much better way is to push data on demandwhen a consumer asks for it. We can do that by implementing the read method in the configuration object:. When the read method is called on a readable stream, the implementation can push partial data to the queue.
For example, we can push one letter at a time, starting with character code 65 which stream problems aptitude js Aand incrementing that on every push:. You should always do. With Duplex streams, we can implement both readable and writable streams stream problems aptitude js the same object.
By combining the methods, we can use this duplex stream to read the letters from A to Z and we can also use it for its echo feature. We pipe the readable stdin stream into this duplex stream to use the echo feature and we pipe the duplex stream itself into the writable stdout stream stream problems aptitude js see the letters A through Z.
This is merely a grouping of two features into an object. A transform stream is the more interesting duplex stream because its output is computed from its input. It has the signature of the write method and we can use it to push data as. In that method, we convert the chunk into its upper case version and then push that version as the readable. There is an objectMode flag that we can set to have the stream accept any JavaScript object. The following combination of transform streams makes for a feature to map stream problems aptitude js string of comma-separated values into a JavaScript object.
We then take the array and pipe it into the arrayToObject stream. We need a writableObjectMode flag to make that stream stream problems aptitude js an object.
The stream problems aptitude js part is a normal string the stringified object. You can use this script to gzip any file you pass as the argument. The cool thing about using pipes is that we can actually combine them with events if we need to. Since the pipe method returns the destination stream, we can chain the Stream Problems Aptitude 100 registration of events handlers as well:.
So with the pipe method, we get to easily consume streams, but stream problems aptitude js can still further customize our interaction with those streams using events where stream problems aptitude js. For example, instead of listening stream problems aptitude js the data event above, we can simply create a transform stream to report progress, and replace the.
This reportProgress stream is a simple pass-through stream, but it reports the progress to standard out as. Note how I used the second argument in the callback function to push the data inside the transform method. This is equivalent to pushing the data. The applications of combining streams are endless.
For example, if we need to encrypt the file before or after we gzip it, all we need to do is pipe another transform stream in that exact order that we needed. The script above compresses and then encrypts the passed file and only those who have the secret can use the outputted file.
To actually be able to unzip anything zipped with the script above, we need to use the opposite streams for crypto and zlib in a reverse order, which is simple:. Assuming the passed file is the compressed version, the code above will create a read stream from that, pipe it into the crypto createDecipher stream using the same secretpipe the output of that into the zlib createGunzip stream, and then write things out back to stream problems aptitude js file without the extension.
If you read this far, tweet to the author to show them you care. Tweet a thanks. Learn to code for free. Get started. Forum Donate. Samer Stream Problems Aptitude 80 Buna. Read the updated version of this content and more about Node at jscomplete. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
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