CODEWITHSUNDEEP
javasocketsnetwork-programminginputstream
Kshitiz Sharma
Kshitiz Sharma

Reputation: 18597

Why does input stream read data in chunks?

I am trying to read some data from a network socket using the following code - 

Socket s = new Socket(address, 502);
response = new byte[1024];
InputStream is = s.getInputStream();
int count = is.read(response, 0, 100);

The amount of data isn't large. It is 16 bytes in total. However the read() statement does not read all the data in one go. It reads only 8 bytes of data into my buffer.

I have to make multiple calls to read() like this in order to read the data - 

Socket s = new Socket(address, 502);
response = new byte[1024];
InputStream is = s.getInputStream();
int count = is.read(response, 0, 100);
count += is.read(response, count, 100-count);

Why is this happening? Why does read() not read the entire stream in one go?

Please note that the data is not arriving gradually. If I wait for 2 seconds before reading the data by making a call to Thread.sleep(2000) the behavior remains the same.

Upvotes: 2

Views: 2542

Answers (3)

helios
helios

Reputation: 13841

Maybe the data is arriving gradually not because of your reading but because of the sender.

The sender should use a BufferedOutputStream (in the middle) to make big chunks before sending (and use flush only when it's needed).

Upvotes: 0

Stephen C
Stephen C

Reputation: 718826

I understand that it blocks until data arrives. "That in turn is because the data doesn't necessarily arrive all in one go." Why not is my question.

The data doesn't necessarily all arrive in one go because the network typically breaks it up into packets. IP is a packet switching protocol.

Does TCP transmit it blocks of 8 bytes?

Possibly, but probably not. The packet size depends on the network / networks that the data has traversed, but a typical internet packet size is around 1500 bytes.

If you are getting 8 bytes at a time, either your data is either coming through a network with an unusually small packet size, or (more likely) the sender is sending the data 8 bytes at a time. The second explanation more or less jives with what your other comments say.

And since I explicitly specify 100, a number much larger than the data in buffer shouldn't it attempt to read up till atleast 100 bytes?

Well no. It is not specified to work that way, and it doesn't work that way. You need to write your code according to what the spec says.

It is possible that this has something to do with the way the device is being "polled". But without looking at the specs for the device (or even knowing what it is exactly) this is only a guess.

Upvotes: 1

user207421
user207421

Reputation: 310911

Why does read() not read the entire stream in one go?

Because it isn't specified to do so. See the Javadoc. It blocks until at least one byte is available, then returns some number between 1 and the supplied length, inclusive.

That in turn is because the data doesn't necessarily arrive all in one go. You have no control over how TCP sends and receives data. You are obliged to just treat it as a byte stream.

Upvotes: 7

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