fix fragmentation baby (#266)

app/src/main/java/com/bitchat/android/mesh/FragmentManager.kt

@@ -3,6 +3,7 @@ package com.bitchat.android.mesh
 import android.util.Log
 import com.bitchat.android.protocol.BitchatPacket
 import com.bitchat.android.protocol.MessageType
+import com.bitchat.android.protocol.MessagePadding
 import com.bitchat.android.model.FragmentPayload
 import kotlinx.coroutines.*
 import java.util.concurrent.ConcurrentHashMap
@@ -47,7 +48,10 @@ class FragmentManager {
      * Matches iOS sendFragmentedPacket() implementation exactly
      */
     fun createFragments(packet: BitchatPacket): List<BitchatPacket> {
-        val fullData = packet.toBinaryData() ?: return emptyList()
+        val encoded = packet.toBinaryData() ?: return emptyList()
+        
+        // Fragment the unpadded frame; each fragment will be encoded (and padded) independently - iOS fix
+        val fullData = MessagePadding.unpad(encoded)
         
         // iOS logic: if data.count > 512 && packet.type != MessageType.fragment.rawValue
         if (fullData.size <= FRAGMENT_SIZE_THRESHOLD) {
@@ -150,26 +154,18 @@ class FragmentManager {
                     }
                 }
                 
-                // iOS: if let metadata = fragmentMetadata[fragmentID] 
-                val metadata = fragmentMetadata[fragmentIDString]
-                if (metadata != null) {
-                    // iOS: let reassembledPacket = BitchatPacket(type: metadata.type, ...)
-                    val reassembledPacket = BitchatPacket(
-                        type = metadata.first,
-                        senderID = packet.senderID,
-                        recipientID = packet.recipientID,
-                        timestamp = packet.timestamp,
-                        payload = reassembledData.toByteArray(),
-                        signature = packet.signature,
-                        ttl = if (packet.ttl > 0u) (packet.ttl - 1u).toUByte() else 0u
-                    )
-                    
+                // Decode the original packet bytes we reassembled, so flags/compression are preserved - iOS fix
+                val originalPacket = BitchatPacket.fromBinaryData(reassembledData.toByteArray())
+                if (originalPacket != null) {
                     // iOS cleanup: incomingFragments.removeValue(forKey: fragmentID)
                     incomingFragments.remove(fragmentIDString)
                     fragmentMetadata.remove(fragmentIDString)
                     
-                    Log.d(TAG, "Successfully reassembled packet of ${reassembledData.size} bytes")
-                    return reassembledPacket
+                    Log.d(TAG, "Successfully reassembled and decoded original packet of ${reassembledData.size} bytes")
+                    return originalPacket
+                } else {
+                    val metadata = fragmentMetadata[fragmentIDString]
+                    Log.e(TAG, "Failed to decode reassembled packet (type=${metadata?.first}, total=${metadata?.second})")
                 }
             } else {
                 val received = fragmentMap?.size ?: 0

app/src/main/java/com/bitchat/android/protocol/BinaryProtocol.kt

@@ -248,13 +248,24 @@ object BinaryProtocol {
     }
     
     fun decode(data: ByteArray): BitchatPacket? {
+        // Try decode as-is first (robust when padding wasn't applied) - iOS fix
+        decodeCore(data)?.let { return it }
+        
+        // If that fails, try after removing padding
+        val unpadded = MessagePadding.unpad(data)
+        if (unpadded.contentEquals(data)) return null // No padding was removed, already failed
+        
+        return decodeCore(unpadded)
+    }
+    
+    /**
+     * Core decoding implementation used by decode() with and without padding removal - iOS fix
+     */
+    private fun decodeCore(raw: ByteArray): BitchatPacket? {
         try {
-            // Remove padding first - exactly same as iOS
-            val unpaddedData = MessagePadding.unpad(data)
+            if (raw.size < HEADER_SIZE + SENDER_ID_SIZE) return null
             
-            if (unpaddedData.size < HEADER_SIZE + SENDER_ID_SIZE) return null
-            
-            val buffer = ByteBuffer.wrap(unpaddedData).apply { order(ByteOrder.BIG_ENDIAN) }
+            val buffer = ByteBuffer.wrap(raw).apply { order(ByteOrder.BIG_ENDIAN) }
             
             // Header
             val version = buffer.get().toUByte()
@@ -280,7 +291,7 @@ object BinaryProtocol {
             if (hasRecipient) expectedSize += RECIPIENT_ID_SIZE
             if (hasSignature) expectedSize += SIGNATURE_SIZE
             
-            if (unpaddedData.size < expectedSize) return null
+            if (raw.size < expectedSize) return null
             
             // SenderID
             val senderID = ByteArray(SENDER_ID_SIZE)

app/src/main/java/com/bitchat/android/protocol/MessagePadding.kt

@@ -30,48 +30,49 @@ object MessagePadding {
     }
     
     /**
-     * Add PKCS#7-style padding to reach target size - exact same as iOS
+     * Add PKCS#7-style padding to reach target size - FIXED: proper PKCS#7 (iOS compatible)
      */
     fun pad(data: ByteArray, targetSize: Int): ByteArray {
         if (data.size >= targetSize) return data
         
         val paddingNeeded = targetSize - data.size
         
-        // PKCS#7 only supports padding up to 255 bytes
-        // If we need more padding than that, don't pad - return original data
-        if (paddingNeeded > 255) return data
+        // Constrain to 255 to fit a single-byte pad length marker
+        if (paddingNeeded <= 0 || paddingNeeded > 255) return data
         
         val result = ByteArray(targetSize)
         
         // Copy original data
         System.arraycopy(data, 0, result, 0, data.size)
         
-        // Standard PKCS#7 padding - fill with random bytes then add padding length
-        val randomBytes = ByteArray(paddingNeeded - 1)
-        SecureRandom().nextBytes(randomBytes)
-        
-        // Copy random bytes
-        System.arraycopy(randomBytes, 0, result, data.size, paddingNeeded - 1)
-        
-        // Last byte tells how much padding was added
-        result[result.size - 1] = paddingNeeded.toByte()
+        // PKCS#7: All pad bytes are equal to the pad length (iOS fix)
+        for (i in data.size until targetSize) {
+            result[i] = paddingNeeded.toByte()
+        }
         
         return result
     }
     
     /**
-     * Remove padding from data - exact same as iOS
+     * Remove padding from data - FIXED: strict PKCS#7 validation (iOS compatible)
      */
     fun unpad(data: ByteArray): ByteArray {
         if (data.isEmpty()) return data
         
-        // Last byte tells us how much padding to remove
-        val paddingLength = data[data.size - 1].toInt() and 0xFF
-        if (paddingLength <= 0 || paddingLength > data.size) {
-            // Invalid padding, return original data
-            return data
+        val last = data[data.size - 1]
+        val paddingLength = last.toInt() and 0xFF
+        
+        // Must have at least 1 pad byte and not exceed data length
+        if (paddingLength <= 0 || paddingLength > data.size) return data
+        
+        // Verify PKCS#7: all last N bytes equal to pad length (iOS fix)
+        val start = data.size - paddingLength
+        for (i in start until data.size) {
+            if (data[i] != last) {
+                return data // Invalid padding, return original
+            }
         }
         
-        return data.copyOfRange(0, data.size - paddingLength)
+        return data.copyOfRange(0, start)
     }
 }