add write operations

1 files changed, 70 insertions, 0 deletions

diff --git a/src/main/kotlin/NinePConnection.kt b/src/main/kotlin/NinePConnection.kt
index c5d330e..2a28df8 100644
--- a/src/main/kotlin/NinePConnection.kt
+++ b/src/main/kotlin/NinePConnection.kt
@@ -1,5 +1,6 @@
 import java.io.IOException
 import java.math.BigInteger
+import kotlin.math.pow
 
 /**
  * This class represents a 9P connection. It provides a practical implementation with networking to the 9P methods
@@ -114,4 +115,73 @@ class NinePConnection(netPackTrans: NetworkPacketTransporter) : NinePTranslator
         val error = readString()
         return Pair(SizedMessageField(2, tag), error)
     }
+
+    /**
+     * Write an integer number to the connection.
+     *
+     * In 9P, binary numbers (non-textual) are specified in little-endian order (least significant byte first).
+     *
+     * @param value The number's value. [SizedMessageField] defines both its actual value and its size.
+     */
+    private fun writeInteger(value: SizedMessageField) {
+        this.npt.transmit(value.value.toByteArray().toList())
+    }
+
+    /**
+     * 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 value The string.
+     * @throws IllegalArgumentException if the value of the string's size does not fit into 2 bytes.
+     */
+    private fun writeString(value: String) {
+        require(value.length <= 2.0.pow(16.0) - 1)
+        writeInteger(SizedMessageField(2, value.length.toBigInteger()))
+        this.npt.transmit(value.toByteArray().toList())
+    }
+
+    /**
+     * Write the message size and type.
+     *
+     * @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(size: Int, type: NinePMessageType) {
+        writeInteger(SizedMessageField(4, size.toBigInteger()))
+        writeInteger(SizedMessageField(1, type.value.toInt().toBigInteger()))
+    }
+
+    /**
+     * Write a message of the given fields.
+     *
+     * Important note: the field names in [fieldValuesInt] and [fieldValuesStr] (i.e. the keys of their maps) are
+     * mutually exclusive and the union of these two sets must result exactly in the set of field names listed in
+     * [fieldNames].
+     *
+     * @param type The 9P message type.
+     * @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.
+     * @throws IllegalArgumentException if [fieldNames], [fieldValuesInt], and [fieldValuesStr] are incoherent.
+     */
+    private fun writeMessage(type: NinePMessageType, fieldNames: List<String>, fieldValuesInt: Map<String, SizedMessageField>, fieldValuesStr: Map<String, String>) {
+        // shorthands
+        val insecInts = fieldNames.intersect(fieldValuesInt.keys)
+        val insecStrs = fieldNames.intersect(fieldValuesStr.keys)
+        // 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 = 4 + 1 + insecInts.sumOf { fieldValuesInt[it]!!.size } + insecStrs.sumOf { 2 + fieldValuesStr[it]!!.length }
+
+        writeMessageSizeType(totalSize, type)
+        for (field in fieldNames) {
+            if (field in insecInts) {
+                writeInteger(fieldValuesInt[field]!!)
+            } else {
+                writeString(fieldValuesStr[field]!!)
+            }
+        }
+    }
 }
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