From 97408589e18ecebef7fa380e019c43f5a24e1be7 Mon Sep 17 00:00:00 2001
From: Edoardo La Greca
Date: Fri, 8 Aug 2025 16:38:42 +0200
Subject: change walk to use exceptions instead of error strings

---
 src/main/kotlin/Connection.kt         | 12 ++++--------
 src/main/kotlin/ProtocolTranslator.kt |  6 ++++--
 2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/src/main/kotlin/Connection.kt b/src/main/kotlin/Connection.kt
index 659dd41..cb93533 100644
--- a/src/main/kotlin/Connection.kt
+++ b/src/main/kotlin/Connection.kt
@@ -1,5 +1,6 @@
 import except.MsizeValueTooBigException
 import except.RErrorException
+import except.UnaccessibleFileException
 import except.UnknownVersionException
 import java.io.IOException
 import java.math.BigInteger
@@ -141,7 +142,7 @@ class Connection(transLay: TransportLayer) : ProtocolTranslator {
         this.pathInfo.addPath(PathInfo.Path(aname.split("/"), fid, qid))
     }
 
-    override fun walk(fid: UInt, newfid: UInt, wname: List<String>): String? {
+    override fun walk(fid: UInt, newfid: UInt, wname: List<String>) {
         val nwname = wname.size
         val omsg = OutMessage(NinePMessageType.TWALK, this.tagGen.generate(), listOf("fid", "newfid", "nwname"),
             mapOf(
@@ -157,16 +158,12 @@ class Connection(transLay: TransportLayer) : ProtocolTranslator {
         for (wn in wname) { // write wname elements
             OutMessage.writeString(this.tl, wn)
         }
-        val checkErr = checkedInMessage(omsg.tag)
-        if (checkErr.first != null) {
-            return checkErr.first
-        }
-        val imsg = checkErr.second!!
+        val imsg = checkedInMessage(omsg.tag)
 
         imsg.applyField(InMessage.Field("nwqid", InMessage.Field.Type.INTEGER, 2u))
         val nwqid = imsg.fieldsInt["nwqid"]!!.toInt()
         if (nwqid < nwname) {
-            return "cannot access ${wname.slice(0..nwqid).joinToString(separator = "/")}"
+            throw UnaccessibleFileException(wname.slice(0..nwqid).joinToString(separator = "/"))
         }
         imsg.applyField(InMessage.Field("qids", InMessage.Field.Type.RAW, (nwqid * 13).toUInt()))
         val rawQids = imsg.fieldsRaw["qids"]!!
@@ -183,7 +180,6 @@ class Connection(transLay: TransportLayer) : ProtocolTranslator {
         }
         this.pathInfo.removeFID(fid)
         this.pathInfo.addPath(PathInfo.Path(wname, newfid, qids.last()))
-        return null
     }
 
     override fun open(path: String) {
diff --git a/src/main/kotlin/ProtocolTranslator.kt b/src/main/kotlin/ProtocolTranslator.kt
index 1b45252..bf29131 100644
--- a/src/main/kotlin/ProtocolTranslator.kt
+++ b/src/main/kotlin/ProtocolTranslator.kt
@@ -67,9 +67,11 @@ interface ProtocolTranslator {
      * @param newfid The proposed FID, which is going to be associated with the result of walking the hierarchy. It must
      * be not in use, unless it is the same as [fid].
      * @param wname The successive path name elements which describe the file to walk to.
-     * @return a possible error.
+     * @throws except.InvalidMessageException if the received message is invalid.
+     * @throws except.RErrorException if the received message is an R-error message.
+     * @throws except.UnaccessibleFileException if [wname] contains one or more files that do not exist.
      */
-    fun walk(fid: UInt, newfid: UInt, wname: List<String>): String?
+    fun walk(fid: UInt, newfid: UInt, wname: List<String>)
 
     /**
      * Prepare an FID for I/O on an existing file.
-- 
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