I'm mucking about with node.js and have discovered two ways of reading a file and sending it down the wire, once I've established that it exists and have sent the proper MIME type with writeHead:
// read the entire file into memory and then spit it out fs.readFile(filename, function(err, data){ if (err) throw err; response.write(data, 'utf8'); response.end(); }); // read and pass the file as a stream of chunks fs.createReadStream(filename, { 'flags': 'r', 'encoding': 'binary', 'mode': 0666, 'bufferSize': 4 * 1024 }).addListener( "data", function(chunk) { response.write(chunk, 'binary'); }).addListener( "close",function() { response.end(); });
Am I correct in assuming that fs.createReadStream might provide a better user experience if the file in question was something large, like a video? It feels like it might be less block-ish; is this true? Are there other pros, cons, caveats, or gotchas I need to know?
readFileSync() is synchronous and blocks execution until finished. These return their results as return values. readFile() are asynchronous and return immediately while they function in the background.
The function fs. createReadStream() allows you to open up a readable stream in a very simple manner. All you have to do is pass the path of the file to start streaming in. It turns out that the response (as well as the request) objects are streams.
It starts reading the file and simultaneously executes the code. The function will be called once the file has been read meanwhile the 'readFile called' statement is printed then the contents of the file are printed.
A better approach, if you are just going to hook up "data" to "write()" and "close" to "end()":
// 0.3.x style fs.createReadStream(filename, { 'bufferSize': 4 * 1024 }).pipe(response) // 0.2.x style sys.pump(fs.createReadStream(filename, { 'bufferSize': 4 * 1024 }), response)
The read.pipe(write)
or sys.pump(read, write)
approach has the benefit of also adding flow control. So, if the write stream cannot accept data as quickly, it'll tell the read stream to back off, so as to minimize the amount of data getting buffered in memory.
The flags:"r"
and mode:0666
are implied by the fact that it is a FileReadStream
. The binary
encoding is deprecated -- if an encoding is not specified, it'll just work with the raw data buffers.
Also, you could add some other goodies that will make your file serving a whole lot slicker:
req.headers.range
and see if it matches a string like /bytes=([0-9]+)-([0-9]+)/
. If so, you want to just stream from that start to end location. (Missing number means 0 or "the end".)304 Not Modified
.if-modified-since
header against the mtime
date on the stat object. 304 if it wasn't modified since the date provided.Also, in general, if you can, send a Content-Length
header. (You're stat
-ing the file, so you should have this.)
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