From c699b2d9bed5957ccbfff13dc318713f378bc769 Mon Sep 17 00:00:00 2001
From: mikeplotean <mike@walt.id>
Date: Thu, 6 Feb 2025 18:07:24 +0200
Subject: [PATCH] fix: wallet-api encoded list decoding - consider bit order
 left-to-right

---
 .../kotlin/id/walt/webwallet/utils/Utils.kt   | 42 +++++++++++++------
 .../webwallet/utils/BitstringUtilsTest.kt     |  2 +-
 2 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/waltid-services/waltid-wallet-api/src/main/kotlin/id/walt/webwallet/utils/Utils.kt b/waltid-services/waltid-wallet-api/src/main/kotlin/id/walt/webwallet/utils/Utils.kt
index 6bdba4b59..9a4b49ccd 100644
--- a/waltid-services/waltid-wallet-api/src/main/kotlin/id/walt/webwallet/utils/Utils.kt
+++ b/waltid-services/waltid-wallet-api/src/main/kotlin/id/walt/webwallet/utils/Utils.kt
@@ -5,7 +5,6 @@ import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.jsonObject
 import java.io.InputStream
 import java.util.Base64
-import java.util.BitSet
 
 @OptIn(ExperimentalStdlibApi::class)
 object StringUtils {
@@ -37,30 +36,47 @@ object Base64Utils {
 
 object BitstringUtils {
     private val logger = KotlinLogging.logger {}
+    private const val BITS_PER_BYTE_UNSIGNED = 8u
+
     fun getBitValue(inputStream: InputStream, index: ULong, bitSize: Int): List<Char> =
         inputStream.use { stream ->
+            if (stream.markSupported()) {
+                stream.mark(Int.MAX_VALUE)
+                logger.debug { "available bytes: ${bitmap(stream.readAllBytes())}" }
+                inputStream.reset()
+            }
             //TODO: bitSize constraints
             val bitStartPosition = index * bitSize.toUInt()
-            logger.debug { "bitStartPosition: $bitStartPosition" }
-            val byteStart = bitStartPosition / 8u
+            logger.debug { "bitStartPosition overall: $bitStartPosition" }
+            val byteStart = bitStartPosition / BITS_PER_BYTE_UNSIGNED
             logger.debug { "skipping: $byteStart bytes" }
             stream.skip(byteStart.toLong())
             logger.debug { "available: ${stream.available()} bytes" }
-            val bytesToRead = (bitSize - 1) / 8 + 1
+            val bytesToRead = (bitSize - 1) / BITS_PER_BYTE_UNSIGNED.toInt() + 1
             logger.debug { "readingNext: $bytesToRead bytes" }
             extractBitValue(stream.readNBytes(bytesToRead), index, bitSize.toUInt())
         }
 
     private fun extractBitValue(bytes: ByteArray, index: ULong, bitSize: UInt): List<Char> {
-        val bitSet = BitSet.valueOf(bytes)
-        logger.debug { "bits set: ${bitSet.length()}" }
-        val bitStart = index * bitSize % 8u
-        logger.debug { "startingFromBit: $bitStart" }
-        val result = mutableListOf<Char>()
-        for (i in bitStart..<bitStart + bitSize) {
-            val b = bitSet[i.toInt()].takeIf { it }?.let { 1 } ?: 0
-            result.add(b.digitToChar())
+        logger.debug { "selected byte: ${bitmap(bytes)}" }
+        val bits = bytes.toBitSequence()
+        val bitStartPosition = index * bitSize % BITS_PER_BYTE_UNSIGNED
+        logger.debug { "bitStartPosition within byte: $bitStartPosition" }
+        val bitSet = bits.drop(bitStartPosition.toInt()).iterator()
+        val result = mutableListOf<Boolean>()
+        var b = 0u
+        while (b++ < bitSize) {
+            result.add(bitSet.next())
         }
-        return result
+        return result.map { if (it) '1' else '0' }
+    }
+
+    fun ByteArray.toBitSequence(): Sequence<Boolean> = this.fold(emptySequence<Boolean>()) { acc, byte ->
+        acc + (7 downTo 0).map { i -> (byte.toUInt() shr i) and 1u == 1u }.asSequence()
+    }
+
+    fun bitmap(byteArray: ByteArray) = byteArray.map { byte ->
+        // Convert byte to binary string
+        String.format("%8s", Integer.toBinaryString(byte.toInt() and 0xFF)).replace(' ', '0')
     }
 }
diff --git a/waltid-services/waltid-wallet-api/src/test/kotlin/id/walt/webwallet/utils/BitstringUtilsTest.kt b/waltid-services/waltid-wallet-api/src/test/kotlin/id/walt/webwallet/utils/BitstringUtilsTest.kt
index 6c2511294..4858e11da 100644
--- a/waltid-services/waltid-wallet-api/src/test/kotlin/id/walt/webwallet/utils/BitstringUtilsTest.kt
+++ b/waltid-services/waltid-wallet-api/src/test/kotlin/id/walt/webwallet/utils/BitstringUtilsTest.kt
@@ -4,7 +4,7 @@ import id.walt.webwallet.utils.StringUtils.hexToByteArray
 import kotlin.test.*
 
 class BitstringUtilsTest {
-    private val bitString = hexToByteArray("5AA5")//0b01011010_10100101
+    private val bitString = hexToByteArray("A265")//0b10100010_01100101
 
     @Test
     fun `test unit bitsize, no overflow`() {