2. Reading from a Stream<\/strong><\/p>\nI have created a file named testinput.txt. The content is as follows:
\n<\/p>\n
Find all tutorial in kindsonthegenius.com\r\nAlso watch the video lessons.\r\n<\/pre>\nThen, in VS Code, write and run the following program:<\/p>\n
var<\/span> fs =<\/span> require(\"fs\"<\/span>);\r\nvar<\/span> data =<\/span> ''<\/span>;\r\n\r\n\/\/ Create a readable stream object<\/span>\r\nvar<\/span> readStream =<\/span> fs.createReadStream('D:\/nodefiles\/testinput.txt'<\/span>);\r\n\r\n\/\/ Set the character encoding to be utf8. <\/span>\r\nreadStream.setEncoding('UTF8'<\/span>);\r\n\r\n\/\/ Handle stream data event<\/span>\r\nreadStream.on('data'<\/span>, function<\/span>(chunk) {\r\n data +=<\/span> chunk;\r\n});\r\n\r\n\/\/ Handle the end event<\/span>\r\nreadStream.on('end'<\/span>,function<\/span>() {\r\n console.log(data);\r\n});\r\n\r\n\/\/Handle the error event<\/span>\r\nreadStream.on('error'<\/span>, function<\/span>(err) {\r\n console.log(err.stack);\r\n});\r\n\r\nconsole.log(\"End of Program\"<\/span>);\r\n<\/pre>\n <\/p>\n
In the program above we created and stream. Then we read from the stream.<\/p>\n
<\/p>\n
3. Writing to a Stream<\/strong><\/p>\nNow, we are going write to a stream. The code below create a writable stream. The it writes some text into it.<\/p>\n
var<\/span> fs =<\/span> require(\"fs\"<\/span>);\r\nvar<\/span> data =<\/span> 'kindsonthegenius.com is the best place to learn'<\/span>;\r\n\r\n\/\/ Create a writable stream<\/span>\r\nvar<\/span> writeStream =<\/span> fs.createWriteStream('D:\/nodefiles\/testoutput.txt'<\/span>);\r\n\r\n\/\/ Write the data to the stream with character encoding to be utf8<\/span>\r\nwriteStream.write(data,'UTF8'<\/span>);\r\n\r\n\/\/ Indicate the end of file<\/span>\r\nwriteStream.end();\r\n\r\n\/\/ Handle stream finis event<\/span>\r\nwriteStream.on('finish'<\/span>, function<\/span>() {\r\n console.log(\"Data was written succesfully.\"<\/span>);\r\n});\r\n\r\n\/\/ Handle the Error event<\/span>\r\nwriteStream.on('error'<\/span>, function<\/span>(err) {\r\n console.log('Error Occured: '<\/span> +<\/span> err.stack);\r\n});\r\n\r\nconsole.log(\"End of Program\"<\/span>);\r\n<\/pre>\n <\/p>\n
This program creates the file specified. Then open it and writes into it. So run this code, then check the directory to see that a new file was created.<\/p>\n
Also introduce some error, just to make it fire the error event.<\/p>\n
<\/p>\n
4. Piping a Stream to another Stream<\/strong><\/p>\nSometimes a pipe and a stream works together. You use a pipe to connect an output of a stream as input to another stream. This called piping. Now, you can pipe as many streams as you want. In the code below, we would read data from a readable stream and write it into another stream.<\/p>\n
In the code below, we create two streams: readStream and writeStream. Then we pipe the readStream into the writeStream.<\/p>\n
\/\/ Program to demonstrate Piping operation<\/span>\r\nvar<\/span> fs =<\/span> require(\"fs\"<\/span>);\r\n\r\n\/\/ Create a readable stream object<\/span>\r\nvar<\/span> readerStream =<\/span> fs.createReadStream('D:\/nodefiles\/testinput.txt'<\/span>);\r\n\r\n\/\/ Create a writable stream object<\/span>\r\nvar<\/span> writerStream =<\/span> fs.createWriteStream('D:\/nodefiles\/testoutput.txt'<\/span>);\r\n\r\n\/\/ Pipe the readstream into the writeStream<\/span>\r\nreaderStream.pipe(writerStream);\r\n\r\nconsole.log(\"End of Program\"<\/span>);\r\n<\/pre>\n <\/p>\n
5. Chaining Streams<\/strong><\/p>\nSimilar to piping, is another mechanism called chaining.<\/p>\n
Chaining allows you to connect the output of a stream to another stream. Therefore, you can chain multiple stream operations. Oftentimes, chaining is used along with piping.<\/p>\n
For example, we are going to use piping and chaining to first compress a file. Then we decompress the same file.<\/p>\n
<\/p>\n
The code is given below:
\n<\/p>\n
var<\/span> fs =<\/span> require(\"fs\"<\/span>);\r\nvar<\/span> zlib =<\/span> require('zlib'<\/span>); \/\/compression module<\/span>\r\n\r\n\/\/ Compress the file testinput.txt to testinput.txt.gz<\/span>\r\nfs.createReadStream('D:\/nodefiles\/testinput.txt'<\/span>)\r\n .pipe(zlib.createGzip())\r\n .pipe(fs.createWriteStream('D:\/nodefiles\/testinput.txt.gz'<\/span>));\r\n \r\nconsole.log(\"File was Compressed.\"<\/span>);\r\n<\/pre>\n <\/p>\n
If you run the code above succefully, then it would compress the specified file. Now you can check the directory. You’ll notice that a compressed file has been created. The folder in my system is shown below.<\/p>\n
![\"Streams](\"https:\/\/kindsonthegenius.com\/nodejs\/wp-content\/uploads\/2019\/09\/Streams-in-Node.jpg\")
<\/a><\/p>\n <\/p>\n
Now, we would run a code to decompress the same file. The code is given below:<\/p>\n
var<\/span> fs =<\/span> require(\"fs\"<\/span>);\r\nvar<\/span> zlib =<\/span> require('zlib'<\/span>);\r\n\r\n\/\/ Decompress the file testinput.txt.gz to testinput.txt<\/span>\r\nfs.createReadStream('D:\/nodefiles\/testinput.txt.gz'<\/span>)\r\n .pipe(zlib.createGunzip())\r\n .pipe(fs.createWriteStream('D:\/nodefiles\/testinput.txt'<\/span>));\r\n \r\nconsole.log(\"File was Decompressed.\"<\/span>);\r\n<\/pre>\n <\/p>\n","protected":false},"excerpt":{"rendered":"
We would cover Streams in Node.js under the following sub-topics: Introduction to Streams in Node.js Reading from Streams Writing to Streams Piping a Stream Chaining … <\/p>\n","protected":false},"author":1,"featured_media":86,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-83","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/kindsonthegenius.com\/nodejs\/wp-json\/wp\/v2\/posts\/83","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/kindsonthegenius.com\/nodejs\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kindsonthegenius.com\/nodejs\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kindsonthegenius.com\/nodejs\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/kindsonthegenius.com\/nodejs\/wp-json\/wp\/v2\/comments?post=83"}],"version-history":[{"count":3,"href":"https:\/\/kindsonthegenius.com\/nodejs\/wp-json\/wp\/v2\/posts\/83\/revisions"}],"predecessor-version":[{"id":123,"href":"https:\/\/kindsonthegenius.com\/nodejs\/wp-json\/wp\/v2\/posts\/83\/revisions\/123"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/kindsonthegenius.com\/nodejs\/wp-json\/wp\/v2\/media\/86"}],"wp:attachment":[{"href":"https:\/\/kindsonthegenius.com\/nodejs\/wp-json\/wp\/v2\/media?parent=83"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kindsonthegenius.com\/nodejs\/wp-json\/wp\/v2\/categories?post=83"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kindsonthegenius.com\/nodejs\/wp-json\/wp\/v2\/tags?post=83"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}