Provide fallback for broken AES/GCM streaming implementation on Andro…

…id (#1096)

Co-authored-by: Martin Devillers <[email protected]>

okio/src/jvmMain/kotlin/okio/CipherSink.kt

@@ -50,7 +50,13 @@ class CipherSink(
     // Shorten input until output is guaranteed to fit within a segment
     var outputSize = cipher.getOutputSize(size)
     while (outputSize > Segment.SIZE) {
-      check(size > blockSize) { "Unexpected output size $outputSize for input size $size" }
+      if (size <= blockSize) {
+        // Bug: For AES-GCM on Android `update` method never outputs any data
+        // As a consequence, `getOutputSize` just keeps increasing indefinitely after each update
+        // When that happens, the fallback is to perform the update operation without using a pre-allocated segment
+        sink.write(cipher.update(source.readByteArray(remaining)))
+        return remaining.toInt()
+      }
       size -= blockSize
       outputSize = cipher.getOutputSize(size)
     }
@@ -104,6 +110,18 @@ class CipherSink(
     val outputSize = cipher.getOutputSize(0)
     if (outputSize == 0) return null
 
+    if (outputSize > Segment.SIZE) {
+      // Bug: For AES-GCM on Android `update` method never outputs any data
+      // As a consequence, `doFinal` returns the fully encrypted data, which may be arbitrarily large
+      // When that happens, the fallback is to perform the `doFinal` operation without using a pre-allocated segment
+      try {
+        sink.write(cipher.doFinal())
+      } catch (t: Throwable) {
+        return t
+      }
+      return null
+    }
+
     var thrown: Throwable? = null
     val buffer = sink.buffer
 

okio/src/jvmMain/kotlin/okio/CipherSource.kt

@@ -37,15 +37,14 @@ class CipherSource(
     require(byteCount >= 0L) { "byteCount < 0: $byteCount" }
     check(!closed) { "closed" }
     if (byteCount == 0L) return 0L
-    if (final) return buffer.read(sink, byteCount)
 
     refill()
 
     return buffer.read(sink, byteCount)
   }
 
   private fun refill() {
-    while (buffer.size == 0L) {
+    while (buffer.size == 0L && !final) {
       if (source.exhausted()) {
         final = true
         doFinal()
@@ -63,7 +62,14 @@ class CipherSource(
     // Shorten input until output is guaranteed to fit within a segment
     var outputSize = cipher.getOutputSize(size)
     while (outputSize > Segment.SIZE) {
-      check(size > blockSize) { "Unexpected output size $outputSize for input size $size" }
+      if (size <= blockSize) {
+        // Bug: For AES-GCM on Android `update` method never outputs any data
+        // As a consequence, `getOutputSize` just keeps increasing indefinitely after each update
+        // When that happens, the fallback is to break the streaming implementation and just cipher the rest of the data all at once
+        final = true
+        buffer.write(cipher.doFinal(source.readByteArray()))
+        return
+      }
       size -= blockSize
       outputSize = cipher.getOutputSize(size)
     }