管道连接Gulp流file.contents到服务器（连接，表达或http）响应

Question

I suspect this comes from a limited understanding of streams but I've looked everywhere and cannot get it to work. In short, I want to take a Gulp stream and pass the concatenated contents of the stream to an express response directly without writing to the file system.

This is how I got the idea (which works fine):

app.get('*', function(req, res){
    var stream = fs.createReadStream(__dirname + '/app/index.html');
    stream.pipe(res);
});

But I want to apply the same concept using a Gulp stream:

app.get('/app/js/concatenated-js-files.js', function(req, res){
    gulp.src('app/js/**/*.js')
        .pipe(concat())
        .pipe(res);
});
app.listen(5555, function() {
    console.log('Listening on port 5555');
});

Which does not work and yields the following when requesting /app/js/concatenated-js-files.js from the browser:

[gulp] Error in plugin 'gulp-concat': Missing fileName option for gulp-concat
    at module.exports (/Users/lgomez/Projects/index-packager/node_modules/gulp-concat/index.js:10:24)
    at Object.handle (/Users/lgomez/Projects/index-packager/index.js:83:15)
    at next_layer (/Users/lgomez/Projects/index-packager/node_modules/express/lib/router/route.js:103:13)
    at Route.dispatch (/Users/lgomez/Projects/index-packager/node_modules/express/lib/router/route.js:107:5)
    at /Users/lgomez/Projects/index-packager/node_modules/express/lib/router/index.js:213:24
    at Function.proto.process_params (/Users/lgomez/Projects/index-packager/node_modules/express/lib/router/index.js:284:12)
    at next (/Users/lgomez/Projects/index-packager/node_modules/express/lib/router/index.js:207:19)
    at Layer.expressInit [as handle] (/Users/lgomez/Projects/index-packager/node_modules/express/lib/middleware/init.js:23:5)
    at trim_prefix (/Users/lgomez/Projects/index-packager/node_modules/express/lib/router/index.js:255:15)
    at /Users/lgomez/Projects/index-packager/node_modules/express/lib/router/index.js:216:9

That error is expected. gulp-concat was written to output to file.

I'd like to avoid writing a gulp plugin that would be very similar to gulp-concat. I may fork and suggest it but, for now, is there another way to achieve this?

Thank you!

Here's the complete code if you'd like to try it.

var express = require('express');
var gulp    = require('gulp');
var concat  = require('gulp-concat');
var app     = express();
app.get('/app/js/concatenated-js-files.js', function(req, res){
    gulp.src('app/js/**/*.js')
        .pipe(concat())
        .pipe(res);
});
app.listen(5555, function() {
    console.log('Listening on port 5555');
});
// http://localhost:5555/app/js/concatenated-js-files.js

Answer 1

gulp works on streams of virtual File objects, not physical files. As such, gulp-concat doesn't write to the file system no matter what name you give it. However, you will still have a problem because you cannot send these file objects directly to the res response.

You need to write the contents of the virtual file(s) to res . An easy way to do this is to use through to make a stream that reads the gulp input and writes the files' contents to res . If your stream handles multiple files, then you don't need concat .

var through = require('through');

// create a stream that reads gulp File objects and outputs their contents
function sendTo(res) {   
    return through(
        function write(data) {    // this will be called once for each file
            res.write(data.contents);
        },
        function end() {    // this will be called when there are no more files
            res.end()
        }
    );
}

app.get('/app/js/concatenated-js-files.js', function(req, res){
    gulp.src('app/js/**/*.js')
        .pipe(sendTo(res));
});

Also, gulp internally uses vinyl-fs to read the files, so you can use vinyl-fs directly if have no other need for gulp .