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import java.io.IOException
import java.math.BigInteger
/**
* This class represents a 9P connection. It provides a practical implementation with networking to the 9P methods
* described in [NinePTranslator]. Details about methods related to 9P can be found in [NinePTranslator]. Remember to
* disconnect using [disconnect] after use.
*
* Details about network-related topics can be found in [NetworkPacketTransporter] and the implementation of choice.
*
* Details about 9P messages and methods can be found in [NinePTranslator].
*
* @param netPackTrans The networking API backend of choice.
*
* @throws UnresolvableHostException if the host resolution made by [netPackTrans] failed.
*/
class NinePConnection(netPackTrans: NetworkPacketTransporter) : NinePTranslator {
/**
* Networking API.
*/
val npt: NetworkPacketTransporter = netPackTrans
/**
* Disconnect from the remote host,
*
* @throws IOException if an I/O error occurred while closing the socket.
*/
fun disconnect() {
this.npt.close()
}
/**
* Read an [nBytes]-long unsigned integer number from the connection.
*
* In 9P, binary numbers (non-textual) are specified in little-endian order (least significant byte first).
*
* @param nBytes The length of the integer number in bytes. It only works with unsigned numbers strictly greater
* than zero (zero is excluded).
* @return The number's value.
* @throws IllegalArgumentException if [nBytes] is zero or negative.
*/
private fun readInteger(nBytes: Int): BigInteger {
require(nBytes > 0)
val bytes = this.npt.receiveFixed(nBytes.toULong())
var number: BigInteger = BigInteger.valueOf(0)
for (i in 0..<bytes.size) {
number += bytes[i].toInt().toBigInteger().shl(i)
}
return number
}
/**
* Read a string from the connection.
*
* In 9P, strings are represented as a 2-byte integer (the string's size) followed by the actual UTF-8 string. The
* null terminator is forbidden in 9P messages.
*
* @return The string.
*/
private fun readString(): String {
val length = readInteger(2).toInt()
return String(this.npt.receiveFixed(length.toULong()).toByteArray())
}
/**
* Read a message size, type, and tag.
*
* @return A triple in which the first element is the message size in bytes, the second is the message type as a
* [NinePMessageType] constant, and the third element is the message tag.
*/
private fun readSizeTypeTag(): Triple<UInt, NinePMessageType, UInt> {
return Triple(
readInteger(4).toInt().toUInt(),
NinePMessageType.fromByte(readInteger(1).toByte()),
readInteger(2).toInt().toUInt()
)
}
// TODO: implement methods from NinePTranslator
/**
* Wait for a 9P message with the same tag from the server.
*
* All messages prior to the returned one are discarded.
*
* @param tag The tag to wait for.
* @return A pair of (1) the size and (2) the type of the message that matches the given tag.
*/
private fun waitForTag(tag: UInt): Pair<UInt, NinePMessageType> {
var s = 0u
var ty: NinePMessageType? = null
var ta = 0u
var found = false
while (!found) {
val stt = readSizeTypeTag()
s = stt.first
ty = stt.second
ta = stt.third
if (ta == tag) {
found = true
}
}
return Pair(s, ty ?: NinePMessageType.RERROR)
}
/**
* Read a 9P message of type Rerror, after the message size and type have already been read.
*
* @return A pair of: (1) the message tag and (2) the error message
*/
private fun readError(): Pair<SizedMessageField, String> {
val tag = readInteger(2)
val error = readString()
return Pair(SizedMessageField(2, tag), error)
}
}
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