Reading lines and raw bytes from the same source in scala - scala

Question

I need to write code that does the following:
Connect to a tcp socket
Read a line ending in "\r\n" that contains a number N
Read N bytes
Use those N bytes
I am currently using the following code:
val socket = new Socket(InetAddress.getByName(host), port)
val in = socket.getInputStream;
val out = new PrintStream(socket.getOutputStream)
val reader = new DataInputStream(in)
val baos = new ByteArrayOutputStream
val buffer = new Array[Byte](1024)
out.print(cmd + "\r\n")
out.flush
val firstLine = reader.readLine.split("\\s")
if(firstLine(0) == "OK") {
def read(written: Int, max: Int, baos: ByteArrayOutputStream): Array[Byte] = {
if(written >= max) baos.toByteArray
else {
val count = reader.read(buffer, 0, buffer.length)
baos.write(buffer, 0, count)
read(written + count, max, baos)
}
}
read(0, firstLine(1).toInt, baos)
} else {
// RAISE something
}
baos.toByteArray()
The problem with this code is that the use of DataInputStream#readLine raises a deprecation warning, but I can't find a class that implements both read(...) and readLine(...). BufferedReader for example, implements read but it reads Chars and not Bytes. I could cast those chars to bytes but I don't think it's safe.
Any other ways to write something like this in scala?
Thank you

Answer 1

be aware that on the JVM a char has 2 bytes, so "\r\n" is 4 bytes. This is generally not true for Strings stored outside of the JVM.
I think the safest way would be to read your file in raw bytes until you reache your Binary representation of "\r\n", now you can create a Reader (makes bytes into JVM compatible chars) on the first bytes, where you can be shure that there is Text only, parse it, and contiue safely with the rest of the binary data.

Answer 2

You can achive the goal to use read(...) and readLine(...) in one class. The idea is use BufferedReader.read():Int. The BufferedReader class has buffered the content so you can read one byte a time without performance decrease.
The change can be: (without scala style optimization)
import java.io.BufferedInputStream
import java.io.BufferedReader
import java.io.ByteArrayOutputStream
import java.io.PrintStream
import java.net.InetAddress
import java.net.Socket
import java.io.InputStreamReader
object ReadLines extends App {
val host = "127.0.0.1"
val port = 9090
val socket = new Socket(InetAddress.getByName(host), port)
val in = socket.getInputStream;
val out = new PrintStream(socket.getOutputStream)
// val reader = new DataInputStream(in)
val bufIns = new BufferedInputStream(in)
val reader = new BufferedReader(new InputStreamReader(bufIns, "utf8"));
val baos = new ByteArrayOutputStream
val buffer = new Array[Byte](1024)
val cmd = "get:"
out.print(cmd + "\r\n")
out.flush
val firstLine = reader.readLine.split("\\s")
if (firstLine(0) == "OK") {
def read(written: Int, max: Int, baos: ByteArrayOutputStream): Array[Byte] = {
if (written >= max) {
println("get: " + new String(baos.toByteArray))
baos.toByteArray()
} else {
// val count = reader.read(buffer, 0, buffer.length)
var count = 0
var b = reader.read()
while(b != -1){
buffer(count) = b.toByte
count += 1
if (count < max){
b = reader.read()
}else{
b = -1
}
}
baos.write(buffer, 0, count)
read(written + count, max, baos)
}
}
read(0, firstLine(1).toInt, baos)
} else {
// RAISE something
}
baos.toByteArray()
}
for test, below is a server code:
object ReadLinesServer extends App {
val serverSocket = new ServerSocket(9090)
while(true){
println("accepted a connection.")
val socket = serverSocket.accept()
val ops = socket.getOutputStream()
val printStream = new PrintStream(ops, true, "utf8")
printStream.print("OK 2\r\n") // 1 byte for alpha-number char
printStream.print("ab")
}
}

Answer 3

Seems this is the best solution I can find:
val reader = new BufferedReader(new InputStreamReader(in))
val buffer = new Array[Char](1024)
out.print(cmd + "\r\n")
out.flush
val firstLine = reader.readLine.split("\\s")
if(firstLine(0) == "OK") {
def read(readCount: Int, acc: List[Byte]): Array[Byte] = {
if(readCount <= 0) acc.toArray
else {
val count = reader.read(buffer, 0, buffer.length)
val asBytes = buffer.slice(0, count).map(_.toByte)
read(readCount - count, acc ++ asBytes)
}
}
read(firstLine(1).toInt, List[Byte]())
} else {
// RAISE
}
That is, use buffer.map(_.toByte).toArray to transform a char Array into a Byte Array without caring about the encoding.