Bound pre-auth compressed payload expansion

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

@@ -324,21 +324,36 @@ object BinaryProtocol {
         }
     }
     
-    fun decode(data: ByteArray): BitchatPacket? {
+    fun decode(data: ByteArray): BitchatPacket? =
+        decode(data, CompressionUtil::decompress)
+
+    /** Test seam used to prove rejected expansion sizes never reach inflation. */
+    internal fun decodeForTesting(
+        data: ByteArray,
+        decompress: (ByteArray, Int) -> ByteArray?
+    ): BitchatPacket? = decode(data, decompress)
+
+    private fun decode(
+        data: ByteArray,
+        decompress: (ByteArray, Int) -> ByteArray?
+    ): BitchatPacket? {
         // Try decode as-is first (robust when padding wasn't applied) - iOS fix
-        decodeCore(data)?.let { return it }
+        decodeCore(data, decompress)?.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)
+        return decodeCore(unpadded, decompress)
     }
     
     /**
      * Core decoding implementation used by decode() with and without padding removal - iOS fix
      */
-    private fun decodeCore(raw: ByteArray): BitchatPacket? {
+    private fun decodeCore(
+        raw: ByteArray,
+        decompress: (ByteArray, Int) -> ByteArray?
+    ): BitchatPacket? {
         try {
             if (raw.size < HEADER_SIZE_V1 + SENDER_ID_SIZE) return null
 
@@ -435,23 +450,42 @@ object BinaryProtocol {
                 } else {
                     buffer.getShort().toUShort().toInt()
                 }
+
+                val maxExpandedSize = com.bitchat.android.util.AppConstants.Protocol.MAX_PAYLOAD_LENGTH
+                if (originalSize <= 0 || originalSize > maxExpandedSize) {
+                    Log.w(
+                        "BinaryProtocol",
+                        "Expanded payload size $originalSize is outside the allowed range 1..$maxExpandedSize"
+                    )
+                    return null
+                }
                 
                 // Compressed payload
                 val compressedSize = payloadLength.toInt() - lengthFieldBytes
+                if (compressedSize == 0) {
+                    Log.w("BinaryProtocol", "Compressed payload has no deflate bytes")
+                    return null
+                }
                 val compressedPayload = ByteArray(compressedSize)
                 buffer.get(compressedPayload)
 
                 // Security check: Compression bomb protection
-                if (compressedSize > 0) {
-                    val ratio = originalSize.toDouble() / compressedSize.toDouble()
-                    if (ratio > 50_000.0) {
-                        Log.w("BinaryProtocol", "🚫 Suspicious compression ratio: ${ratio}:1")
-                        return null
-                    }
+                val ratio = originalSize.toDouble() / compressedSize.toDouble()
+                if (ratio > 50_000.0) {
+                    Log.w("BinaryProtocol", "🚫 Suspicious compression ratio: ${ratio}:1")
+                    return null
                 }
                 
                 // Decompress
-                CompressionUtil.decompress(compressedPayload, originalSize) ?: return null
+                val expandedPayload = decompress(compressedPayload, originalSize) ?: return null
+                if (expandedPayload.size != originalSize) {
+                    Log.w(
+                        "BinaryProtocol",
+                        "Expanded payload size ${expandedPayload.size} did not match declared size $originalSize"
+                    )
+                    return null
+                }
+                expandedPayload
             } else {
                 val payloadBytes = ByteArray(payloadLength.toInt())
                 buffer.get(payloadBytes)

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

@@ -2,6 +2,7 @@ package com.bitchat.android.protocol
 
 import android.util.Log
 import java.io.ByteArrayOutputStream
+import java.util.zip.DataFormatException
 import java.util.zip.Deflater
 import java.util.zip.Inflater
 
@@ -11,6 +12,10 @@ import java.util.zip.Inflater
  */
 object CompressionUtil {
     private const val COMPRESSION_THRESHOLD = com.bitchat.android.util.AppConstants.Protocol.COMPRESSION_THRESHOLD_BYTES  // bytes - same as iOS
+
+    // Inflation allocates the full declared output buffer. Keep that allocation single-flight so
+    // concurrent packets cannot multiply the bounded per-packet memory cost.
+    private val decompressionLock = Any()
     
     /**
      * Helper to check if compression is worth it - exact same logic as iOS
@@ -73,49 +78,93 @@ object CompressionUtil {
      * iOS COMPRESSION_ZLIB produces raw deflate data (no headers)
      */
     fun decompress(compressedData: ByteArray, originalSize: Int): ByteArray? {
-        // iOS COMPRESSION_ZLIB produces raw deflate format (no headers)
-        try {
-            val inflater = Inflater(true) // true = raw deflate, no headers
-            inflater.setInput(compressedData)
-            
-            val decompressedBuffer = ByteArray(originalSize)
-            val actualSize = inflater.inflate(decompressedBuffer)
-            inflater.end()
-            
-            // Verify decompressed size matches expected (same validation as iOS)
-            return if (actualSize == originalSize) {
-                decompressedBuffer
-            } else if (actualSize > 0) {
-                // Handle case where actual size is different
-                decompressedBuffer.copyOfRange(0, actualSize)
-            } else {
+        val maxExpandedSize = com.bitchat.android.util.AppConstants.Protocol.MAX_PAYLOAD_LENGTH
+        if (compressedData.isEmpty()) {
+            Log.w("CompressionUtil", "Refusing an empty compressed payload")
+            return null
+        }
+        if (originalSize <= 0 || originalSize > maxExpandedSize) {
+            Log.w(
+                "CompressionUtil",
+                "Refusing expanded payload size $originalSize outside 1..$maxExpandedSize"
+            )
+            return null
+        }
+
+        return synchronized(decompressionLock) {
+            // iOS COMPRESSION_ZLIB produces raw deflate format (no headers).
+            val rawResult = try {
+                inflateExact(compressedData, originalSize, nowrap = true)
+            } catch (e: Exception) {
+                Log.d(
+                    "CompressionUtil",
+                    "Raw deflate decompression failed: ${e.message}"
+                )
                 null
             }
-        } catch (e: Exception) {
-            Log.d("CompressionUtil", "Raw deflate decompression failed: ${e.message}, trying with zlib headers...")
-            
-            // Fallback: try with zlib headers in case of mixed usage
-            try {
-                val inflater = Inflater(false) // false = expect zlib headers
-                inflater.setInput(compressedData)
-                
-                val decompressedBuffer = ByteArray(originalSize)
-                val actualSize = inflater.inflate(decompressedBuffer)
-                inflater.end()
-                
-                return if (actualSize == originalSize) {
-                    decompressedBuffer
-                } else if (actualSize > 0) {
-                    decompressedBuffer.copyOfRange(0, actualSize)
-                } else {
+
+            if (rawResult != null) {
+                rawResult
+            } else {
+                // Fallback after either a format error or an incomplete/wrong-sized raw stream:
+                // accept the zlib-wrapped form used by some older/mixed clients, but only when it
+                // independently satisfies the same exact-size and complete-stream checks.
+                try {
+                    inflateExact(compressedData, originalSize, nowrap = false)
+                } catch (fallbackException: Exception) {
+                    Log.e(
+                        "CompressionUtil",
+                        "Both raw deflate and zlib decompression failed: ${fallbackException.message}"
+                    )
                     null
                 }
-            } catch (fallbackException: Exception) {
-                Log.e("CompressionUtil", "Both raw deflate and zlib decompression failed: ${fallbackException.message}")
-                return null
             }
         }
     }
+
+    /**
+     * Inflate one complete stream into exactly [originalSize] bytes.
+     *
+     * A full output buffer alone is not success: an attacker can under-declare a larger stream so
+     * the first inflate call fills the buffer while [Inflater.finished] remains false. Conversely,
+     * a truncated or over-declared stream can produce a non-empty prefix. Both forms are rejected,
+     * as are trailing bytes after the compressed stream.
+     *
+     * [DataFormatException] is deliberately allowed to escape so the caller can try the legacy
+     * zlib-wrapped format. Size/completion mismatches return null; the fallback must then prove the
+     * same bytes are a complete, exact-sized zlib stream before they can be accepted.
+     */
+    @Throws(DataFormatException::class)
+    private fun inflateExact(
+        compressedData: ByteArray,
+        originalSize: Int,
+        nowrap: Boolean
+    ): ByteArray? {
+        val inflater = Inflater(nowrap)
+        return try {
+            inflater.setInput(compressedData)
+            val output = ByteArray(originalSize)
+            var written = 0
+
+            while (written < originalSize) {
+                val count = inflater.inflate(output, written, originalSize - written)
+                if (count == 0) break
+                written += count
+            }
+
+            if (written != originalSize) return null
+
+            // Give Inflater one byte of room to consume the end marker. Any produced byte proves
+            // the declared size was smaller than the actual expansion.
+            val overflowProbe = ByteArray(1)
+            if (inflater.inflate(overflowProbe) != 0) return null
+
+            if (!inflater.finished() || inflater.remaining != 0) return null
+            output
+        } finally {
+            inflater.end()
+        }
+    }
     
     /**
      * Test function to verify deflate compression works correctly

app/src/test/java/com/bitchat/android/protocol/BinaryProtocolTest.kt

@@ -1,5 +1,6 @@
 package com.bitchat.android.protocol
 
+import com.bitchat.android.model.BitchatFilePacket
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertArrayEquals
 import org.junit.Assert.assertFalse
@@ -7,9 +8,11 @@ import org.junit.Assert.assertNotNull
 import org.junit.Assert.assertNull
 import org.junit.Assert.assertTrue
 import org.junit.Test
+import java.io.ByteArrayOutputStream
 import java.nio.ByteBuffer
 import java.nio.ByteOrder
 import java.util.Random
+import java.util.zip.Deflater
 
 class BinaryProtocolTest {
 
@@ -987,6 +990,309 @@ class BinaryProtocolTest {
         assertNull("v2 compression bomb (ratio > 50,000:1) must be rejected", result)
     }
 
+    @Test
+    fun `v2 expanded payload at exact maximum passes bound without allocating output`() {
+        val max = com.bitchat.android.util.AppConstants.Protocol.MAX_PAYLOAD_LENGTH
+        val raw = compressedPacket(
+            version = 2u,
+            originalSize = max,
+            compressedData = ByteArray(256) { it.toByte() }
+        )
+        var calls = 0
+
+        val result = BinaryProtocol.decodeForTesting(raw) { _, requestedSize ->
+            calls += 1
+            assertEquals(max, requestedSize)
+            null // Prove the boundary reached this seam without allocating a 10 MiB result.
+        }
+
+        assertNull("The test decompressor deliberately returns no payload", result)
+        assertEquals(1, calls)
+    }
+
+    @Test
+    fun `v2 expanded payload above maximum never reaches decompressor`() {
+        val max = com.bitchat.android.util.AppConstants.Protocol.MAX_PAYLOAD_LENGTH
+        val raw = compressedPacket(
+            version = 2u,
+            originalSize = max + 1,
+            compressedData = ByteArray(256) { it.toByte() }
+        )
+        var calls = 0
+
+        val result = BinaryProtocol.decodeForTesting(raw) { _, _ ->
+            calls += 1
+            byteArrayOf(0x42)
+        }
+
+        assertNull("An oversized expansion must be rejected before inflation", result)
+        assertEquals("The decompressor must not be invoked", 0, calls)
+    }
+
+    @Test
+    fun `v2 negative expanded payload never reaches decompressor`() {
+        val raw = compressedPacket(
+            version = 2u,
+            originalSize = -1,
+            compressedData = byteArrayOf(0x03)
+        )
+        var calls = 0
+
+        val result = BinaryProtocol.decodeForTesting(raw) { _, _ ->
+            calls += 1
+            byteArrayOf(0x42)
+        }
+
+        assertNull("A negative expansion must be rejected before inflation", result)
+        assertEquals("The decompressor must not be invoked", 0, calls)
+    }
+
+    @Test
+    fun `zero expanded payload never reaches decompressor`() {
+        val raw = compressedPacket(
+            version = 2u,
+            originalSize = 0,
+            compressedData = rawDeflate(ByteArray(0))
+        )
+        var calls = 0
+
+        val result = BinaryProtocol.decodeForTesting(raw) { _, _ ->
+            calls += 1
+            ByteArray(0)
+        }
+
+        assertNull("Compressed zero-length payloads are non-canonical and must be rejected", result)
+        assertEquals("The decompressor must not be invoked", 0, calls)
+    }
+
+    @Test
+    fun `empty compressed body never reaches decompressor`() {
+        val raw = compressedPacket(
+            version = 2u,
+            originalSize = 128,
+            compressedData = ByteArray(0)
+        )
+        var calls = 0
+
+        val result = BinaryProtocol.decodeForTesting(raw) { _, _ ->
+            calls += 1
+            ByteArray(128)
+        }
+
+        assertNull("A compressed payload must contain deflate bytes", result)
+        assertEquals("The decompressor must not be invoked", 0, calls)
+    }
+
+    @Test
+    fun `v1 unsigned maximum expanded size reaches decompressor`() {
+        val originalSize = 0xFFFF
+        val raw = compressedPacket(
+            version = 1u,
+            originalSize = originalSize,
+            compressedData = byteArrayOf(0x01, 0x02)
+        )
+        var calls = 0
+
+        val result = BinaryProtocol.decodeForTesting(raw) { _, requestedSize ->
+            calls += 1
+            assertEquals(originalSize, requestedSize)
+            null
+        }
+
+        assertNull("The test decompressor deliberately returns no payload", result)
+        assertEquals(1, calls)
+    }
+
+    @Test
+    fun `compression utility rejects invalid expansion sizes directly`() {
+        val max = com.bitchat.android.util.AppConstants.Protocol.MAX_PAYLOAD_LENGTH
+
+        assertNull(CompressionUtil.decompress(ByteArray(0), 1))
+        assertNull(CompressionUtil.decompress(rawDeflate(ByteArray(0)), 0))
+        assertNull(CompressionUtil.decompress(byteArrayOf(0x03), -1))
+        assertNull(CompressionUtil.decompress(byteArrayOf(0x03), max + 1))
+    }
+
+    @Test
+    fun `raw deflate expands only when size and stream completion are exact`() {
+        val payload = ByteArray(4_096) { index -> (index % 17).toByte() }
+        val compressed = rawDeflate(payload)
+
+        val decoded = BinaryProtocol.decode(
+            compressedPacket(version = 2u, originalSize = payload.size, compressedData = compressed)
+        )
+
+        assertNotNull(decoded)
+        assertArrayEquals(payload, decoded!!.payload)
+    }
+
+    @Test
+    fun `zlib wrapped payload remains compatible when size and stream completion are exact`() {
+        val payload = ByteArray(4_096) { index -> (index % 23).toByte() }
+        val compressed = zlibDeflate(payload)
+
+        val decoded = BinaryProtocol.decode(
+            compressedPacket(version = 2u, originalSize = payload.size, compressedData = compressed)
+        )
+
+        assertNotNull(decoded)
+        assertArrayEquals(payload, decoded!!.payload)
+    }
+
+    @Test
+    fun `under-declared zlib expansion is rejected by fallback`() {
+        val payload = ByteArray(4_096) { 0x51 }
+        val compressed = zlibDeflate(payload)
+
+        val decoded = BinaryProtocol.decode(
+            compressedPacket(version = 2u, originalSize = 128, compressedData = compressed)
+        )
+
+        assertNull("Zlib fallback must reject output beyond the declaration", decoded)
+    }
+
+    @Test
+    fun `over-declared zlib expansion is rejected by fallback`() {
+        val payload = ByteArray(128) { 0x52 }
+        val compressed = zlibDeflate(payload)
+
+        val decoded = BinaryProtocol.decode(
+            compressedPacket(version = 2u, originalSize = 256, compressedData = compressed)
+        )
+
+        assertNull("Zlib fallback must reject output shorter than the declaration", decoded)
+    }
+
+    @Test
+    fun `truncated zlib stream is rejected by fallback`() {
+        val payload = ByteArray(4_096) { index -> (index % 29).toByte() }
+        val compressed = zlibDeflate(payload)
+        val truncated = compressed.copyOf(compressed.size - 1)
+
+        val decoded = BinaryProtocol.decode(
+            compressedPacket(version = 2u, originalSize = payload.size, compressedData = truncated)
+        )
+
+        assertNull("Zlib fallback must require the stream end marker and checksum", decoded)
+    }
+
+    @Test
+    fun `zlib stream with trailing bytes is rejected by fallback`() {
+        val payload = ByteArray(4_096) { index -> (index % 13).toByte() }
+        val compressedWithTrailingByte = zlibDeflate(payload) + byteArrayOf(0x00)
+
+        val decoded = BinaryProtocol.decode(
+            compressedPacket(
+                version = 2u,
+                originalSize = payload.size,
+                compressedData = compressedWithTrailingByte
+            )
+        )
+
+        assertNull("Zlib fallback must consume the complete input and nothing more", decoded)
+    }
+
+    @Test
+    fun `under-declared raw expansion is rejected even when output buffer fills`() {
+        val payload = ByteArray(4_096) { 0x41 }
+        val compressed = rawDeflate(payload)
+
+        val decoded = BinaryProtocol.decode(
+            compressedPacket(version = 2u, originalSize = 128, compressedData = compressed)
+        )
+
+        assertNull("Inflater must be finished, not merely fill the declared buffer", decoded)
+    }
+
+    @Test
+    fun `over-declared raw expansion is rejected instead of returning a prefix`() {
+        val payload = ByteArray(128) { 0x42 }
+        val compressed = rawDeflate(payload)
+
+        val decoded = BinaryProtocol.decode(
+            compressedPacket(version = 2u, originalSize = 256, compressedData = compressed)
+        )
+
+        assertNull("The expanded byte count must equal the declaration", decoded)
+    }
+
+    @Test
+    fun `truncated raw stream is rejected even if all declared bytes were emitted`() {
+        val payload = ByteArray(4_096) { index -> (index % 31).toByte() }
+        val compressed = rawDeflate(payload)
+        val truncated = compressed.copyOf(compressed.size - 1)
+
+        val decoded = BinaryProtocol.decode(
+            compressedPacket(version = 2u, originalSize = payload.size, compressedData = truncated)
+        )
+
+        assertNull("A stream without its end marker must not be accepted", decoded)
+    }
+
+    @Test
+    fun `raw stream with trailing bytes is rejected`() {
+        val payload = ByteArray(4_096) { index -> (index % 19).toByte() }
+        val compressedWithTrailingByte = rawDeflate(payload) + byteArrayOf(0x00)
+
+        val decoded = BinaryProtocol.decode(
+            compressedPacket(
+                version = 2u,
+                originalSize = payload.size,
+                compressedData = compressedWithTrailingByte
+            )
+        )
+
+        assertNull("Trailing bytes after a complete stream must not be accepted", decoded)
+    }
+
+    @Test
+    fun `decoder rejects a decompressor result shorter than its declaration`() {
+        val raw = compressedPacket(
+            version = 2u,
+            originalSize = 128,
+            compressedData = ByteArray(16) { it.toByte() }
+        )
+
+        val decoded = BinaryProtocol.decodeForTesting(raw) { _, _ -> byteArrayOf(0x01) }
+
+        assertNull("BinaryProtocol must independently enforce the declared expanded size", decoded)
+    }
+
+    @Test
+    fun `legacy 11 MiB public file transfer is explicitly rejected by bounded decoder`() {
+        val content = ByteArray(11 * 1024 * 1024) { 0x41 }
+        val filePayload = BitchatFilePacket(
+            fileName = "legacy-11m.bin",
+            fileSize = content.size.toLong(),
+            mimeType = "application/octet-stream",
+            content = content
+        ).encode()
+        assertNotNull(filePayload)
+
+        val encoded = BinaryProtocol.encode(
+            BitchatPacket(
+                version = 2u,
+                type = MessageType.FILE_TRANSFER.value,
+                senderID = hexToBytes(senderHex),
+                recipientID = SpecialRecipients.BROADCAST,
+                timestamp = fixedTimestamp,
+                payload = filePayload!!,
+                ttl = 5u
+            ),
+            padding = false
+        )
+        assertNotNull("A legacy sender can produce the highly-compressible wire packet", encoded)
+        assertTrue(
+            "The compressed wire body remains below the normal 10 MiB input cap",
+            encoded!!.size < com.bitchat.android.util.AppConstants.Protocol.MAX_PAYLOAD_LENGTH
+        )
+
+        assertNull(
+            "The uniform bound intentionally rejects this legacy expansion until streaming admission exists",
+            BinaryProtocol.decode(encoded)
+        )
+    }
+
     /**
      * Compression bomb is rejected
      *
@@ -1163,6 +1469,59 @@ class BinaryProtocolTest {
         return result
     }
 
+    private fun compressedPacket(
+        version: UByte,
+        originalSize: Int,
+        compressedData: ByteArray,
+        type: UByte = MessageType.MESSAGE.value
+    ): ByteArray {
+        val originalSizeFieldBytes = if (version >= 2u.toUByte()) 4 else 2
+        val payloadLength = originalSizeFieldBytes + compressedData.size
+        val headerSize = if (version >= 2u.toUByte()) 16 else 14
+        val buffer = ByteBuffer.allocate(headerSize + 8 + payloadLength).apply {
+            order(ByteOrder.BIG_ENDIAN)
+            put(version.toByte())
+            put(type.toByte())
+            put(5.toByte())
+            putLong(fixedTimestamp.toLong())
+            put(BinaryProtocol.Flags.IS_COMPRESSED.toByte())
+            if (version >= 2u.toUByte()) {
+                putInt(payloadLength)
+            } else {
+                putShort(payloadLength.toShort())
+            }
+            put(hexToBytes(senderHex))
+            if (version >= 2u.toUByte()) {
+                putInt(originalSize)
+            } else {
+                putShort(originalSize.toShort())
+            }
+            put(compressedData)
+        }
+        return buffer.array()
+    }
+
+    private fun rawDeflate(data: ByteArray): ByteArray = deflate(data, nowrap = true)
+
+    private fun zlibDeflate(data: ByteArray): ByteArray = deflate(data, nowrap = false)
+
+    private fun deflate(data: ByteArray, nowrap: Boolean): ByteArray {
+        val deflater = Deflater(Deflater.DEFAULT_COMPRESSION, nowrap)
+        return try {
+            deflater.setInput(data)
+            deflater.finish()
+            val output = ByteArrayOutputStream()
+            val buffer = ByteArray(1_024)
+            while (!deflater.finished()) {
+                val count = deflater.deflate(buffer)
+                output.write(buffer, 0, count)
+            }
+            output.toByteArray()
+        } finally {
+            deflater.end()
+        }
+    }
+
     private fun makePacket(
         version: UByte = 1u,
         type: UByte = MessageType.MESSAGE.value,

docs/file_transfer.md

@@ -91,6 +91,26 @@ PayloadLength: 4 bytes (big-endian, max ~4 GiB)
 - Clients sending file transfers should preferentially use v2 format.
 - Fragmentation still applies: large files are split into fragments that fit within BLE MTU constraints (~128 KiB per fragment).
 
+#### Compressed expansion rollout gate (draft/HOLD)
+
+Android's bounded decoder applies the same 10 MiB expanded-payload ceiling to every outer
+message type. It also requires a non-empty compressed body, an exact declared output size, and a
+complete deflate stream. The `FILE_TRANSFER (0x22)` byte cannot safely grant a larger ceiling: it is
+attacker-controlled before packet signature verification, and the current receive pipeline must
+inflate before it can perform that verification.
+
+This intentionally means a legacy Android sender can produce a highly compressible public file
+between 10 MiB and the UI's 50 MiB send limit that the bounded decoder rejects. The hardening must
+therefore remain a rollout HOLD rather than silently ship as backward compatible. Grandfathering
+50 MiB also is not safe after only a type check: inflation allocates the declared payload and
+`BitchatFilePacket.decode` currently copies the content again, creating a greater than 100 MiB peak
+for a maximum-size transfer.
+
+Before enabling that legacy range, receive processing needs an authenticated admission decision
+made before large allocation plus streaming inflation/TLV parsing into a bounded temporary file (or
+another ownership-preserving design that avoids the second full-size copy). The sender limit and a
+wire capability/version transition must then be coordinated so old and new clients fail predictably.
+
 ### 1.3 File Transfer TLV payload (BitchatFilePacket)
 
 The file payload is a TLV structure with mixed length field sizes to support large contents efficiently.