change Message class to OutMessage

1 files changed, 104 insertions, 0 deletions

diff --git a/src/main/kotlin/OutMessage.kt b/src/main/kotlin/OutMessage.kt
new file mode 100644
index 0000000..dcb3705
--- /dev/null
+++ b/src/main/kotlin/OutMessage.kt
@@ -0,0 +1,104 @@
+import java.math.BigInteger
+import kotlin.math.pow
+
+/**
+ * An outgoing 9P message with the given type, tag, and fields. The message size is calculated automatically.
+ *
+ * Important note: the field names in [fieldValuesInt] and [fieldValuesStr] (i.e. the keys of their maps) must be
+ * mutually exclusive and the union of these two maps' keys must result in a subset of (or a set equal to) [fieldNames].
+ * Calling [write] when these conditions are not met throws an exception.
+ *
+ * @param type The 9P message type.
+ * @param tag The tag given to the message.
+ * @param fieldNames The names of the message fields, in the same order they are expected to be sent.
+ * @param fieldValuesInt A map of each field name into its value. This map only stores integer values.
+ * @param fieldValuesStr A map of each field name into its value. This map only stores string values.
+ */
+class OutMessage(val type: NinePMessageType, val tag: UShort, val fieldNames: List<String>, val fieldValuesInt: Map<String, BigInteger>, val fieldValuesStr: Map<String, String>, val maxSize: UInt) {
+    /**
+     * Intersection between [fieldNames] and [fieldValuesInt]. In other words: the amount of integer fields that are
+     * going to be used when writing the message.
+     */
+    private val insecInts = fieldNames.intersect(fieldValuesInt.keys)
+    /**
+     * Intersection between [fieldNames] and [fieldValuesStr]. In other words: the amount of string fields that are
+     * going to be used when writing the message.
+     */
+    private val insecStrs = fieldNames.intersect(fieldValuesStr.keys)
+
+    /**
+     * Send the message using the given networking API.
+     *
+     * @param tl The networking API.
+     * @throws IllegalArgumentException if [fieldNames], [fieldValuesInt], and [fieldValuesStr] are incoherent or the
+     *         final size of the message exceeds the negotiated value.
+     */
+    fun write(tl: TransportLayer) {
+        // check that names in fieldNames exist as keys in either fieldValuesInt or fieldValuesStr but not both
+        require(insecInts.size == fieldNames.size - insecStrs.size)
+
+        val totalSize = size()
+        if (totalSize > this.maxSize) {
+            throw IllegalArgumentException("Message size exceeded.")
+        }
+        writeMessageSizeType(tl, totalSize, type)
+        writeInteger(tl, tag.toInt().toBigInteger())
+        for (field in fieldNames) {
+            if (field in insecInts) {
+                writeInteger(tl, fieldValuesInt[field]!!)
+            } else {
+                writeString(tl, fieldValuesStr[field]!!)
+            }
+        }
+    }
+
+    // TODO: Add size that the value is required to fit in
+    /**
+     * Write an integer number to the connection.
+     *
+     * In 9P, binary numbers (non-textual) are specified in little-endian order (least significant byte first).
+     *
+     * @param tl The networking API.
+     * @param value The number's value.
+     */
+    private fun writeInteger(tl: TransportLayer, value: BigInteger) {
+        val bytes = value.toByteArray()
+        tl.transmit(Array(bytes.size) { i -> bytes[i].toUByte() })
+    }
+
+    /**
+     * Write a string to 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.
+     *
+     * @param tl The networking API.
+     * @param value The string.
+     * @throws IllegalArgumentException if the value of the string's size does not fit into 2 bytes.
+     */
+    private fun writeString(tl: TransportLayer, value: String) {
+        require(value.length <= 2.0.pow(16.0) - 1)
+        writeInteger(tl, value.length.toBigInteger())
+        val bytes = value.toByteArray()
+        tl.transmit(Array(bytes.size) { i -> bytes[i].toUByte() })
+    }
+
+    /**
+     * Write the message size and type.
+     *
+     * @param tl The networking API.
+     * @param size The total message size, including the 4 bytes of this parameter and the type's byte.
+     * @param type The 9P message type as a [NinePMessageType] constant.
+     */
+    private fun writeMessageSizeType(tl: TransportLayer, size: UInt, type: NinePMessageType) {
+        writeInteger(tl, size.toInt().toBigInteger())
+        writeInteger(tl, type.value.toInt().toBigInteger())
+    }
+
+    /**
+     * Calculate the expected size of the message.
+     */
+    fun size(): UInt {
+        return 4u + 1u + 2u + this.insecInts.sumOf { this.fieldValuesInt[it]!!.bitLength().toUInt() } + this.insecStrs.sumOf { 2u + this.fieldValuesStr[it]!!.length.toUInt() }
+    }
+}
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