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Pipe node.js streams safely with Promises


Safely pipe node.js streams while capturing all errors to a single promise.

promisePipe(<readable stream>, [transform streams...], <writeable stream>)

It returns a promise. On success the resolved value will be an array of the streams passed in. When rejected an error object is created with following keys:

  • source: The stream that caused the error
  • originalError: Original error from the stream
  • message: The error message from original error
var promisePipe = require("promisepipe");
    new UpcaseTransform(),
    console.log("Yay, all streams are now closed/ended/finished!");
}, function(err) {
    console.log("This stream failed:", err.source);
    console.log("Original error was:", err.originalError);
npm instal promisepipe

Stream piping in node.js is cool, but error handling is not because streams do not bubble to the target streams.

For example if the previous example is written like this:

.pipe(new UpcaseTransform())

It might crash your program at any time. You must handle the errors from each stream manually like this:

fs.createReadStream(INPUT_FILE).on("error", function(err) {
    // handle the error 
}).pipe(new UpcaseTransform()).on("error", function(err) {
    // handle the error 
}).pipe(fs.createReadStream(OUTPUT_FILE)).on("error", function(err) {
    // handle the error 

Which is imo repeative and cumbersome (at least when you want to use promises).