Fix reading ranges of obfuscated EPUB resources (#82)

Author: mickael-menu

CHANGELOG.md

@@ -47,6 +47,7 @@ All notable changes to this project will be documented in this file. Take a look
 #### Streamer
 
 * Fixed the rendering of PDF covers in some edge cases.
+* Fixed reading ranges of obfuscated EPUB resources.
 
 #### Navigator
 

readium/streamer/src/main/java/org/readium/r2/streamer/parser/epub/EpubDeobfuscator.kt

@@ -1,62 +1,49 @@
 /*
- * Module: r2-streamer-kotlin
- * Developers: Aferdita Muriqi, Clément Baumannn, Quentin Gliosca
- *
- * Copyright (c) 2020. Readium Foundation. All rights reserved.
- * Use of this source code is governed by a BSD-style license which is detailed in the
- * LICENSE file present in the project repository where this source code is maintained.
+ * Copyright 2020 Readium Foundation. All rights reserved.
+ * Use of this source code is governed by the BSD-style license
+ * available in the top-level LICENSE file of the project.
  */
 
 package org.readium.r2.streamer.parser.epub
 
 import com.mcxiaoke.koi.HASH
 import com.mcxiaoke.koi.ext.toHexBytes
-import org.readium.r2.shared.fetcher.ProxyResource
-import org.readium.r2.shared.fetcher.Resource
-import org.readium.r2.shared.fetcher.ResourceTry
-import org.readium.r2.shared.fetcher.mapCatching
+import org.readium.r2.shared.fetcher.*
 import org.readium.r2.shared.publication.encryption.encryption
 import kotlin.experimental.xor
 
 internal class EpubDeobfuscator(private val pubId: String) {
 
     fun transform(resource: Resource): Resource = DeobfuscatingResource(resource)
 
-    inner class DeobfuscatingResource(resource: Resource): ProxyResource(resource) {
+    inner class DeobfuscatingResource(resource: Resource): TransformingResource(resource, cacheBytes = true) {
 
-        override suspend fun read(range: LongRange?): ResourceTry<ByteArray> {
-            val algorithm = resource.link().properties.encryption?.algorithm
+        override suspend fun transform(data: ResourceTry<ByteArray>): ResourceTry<ByteArray> =
+            data.map { bytes ->
+                val algorithm = resource.link().properties.encryption?.algorithm
 
-            if (algorithm !in algorithm2length.keys)
-                return resource.read(range)
+                val obfuscationLength: Int = algorithm2length[algorithm]
+                    ?: return@map bytes
 
-            return resource.read(range).mapCatching {
-                val obfuscationLength: Int = algorithm2length[algorithm]!!
                 val obfuscationKey: ByteArray = when (algorithm) {
                     "http://ns.adobe.com/pdf/enc#RC" -> getHashKeyAdobe(pubId)
                     else -> HASH.sha1(pubId).toHexBytes()
                 }
 
-                deobfuscate(it, range, obfuscationKey, obfuscationLength)
-                it
+                deobfuscate(bytes = bytes, obfuscationKey = obfuscationKey, obfuscationLength = obfuscationLength)
+                bytes
             }
-        }
     }
 
     private val algorithm2length: Map<String, Int> = mapOf(
         "http://www.idpf.org/2008/embedding" to 1040,
         "http://ns.adobe.com/pdf/enc#RC" to 1024
     )
 
-    private fun deobfuscate(bytes: ByteArray, range: LongRange?, obfuscationKey: ByteArray, obfuscationLength: Int) {
+    private fun deobfuscate(bytes: ByteArray, obfuscationKey: ByteArray, obfuscationLength: Int) {
         @Suppress("NAME_SHADOWING")
-        val range = range ?: (0L until bytes.size)
-        if (range.first >= obfuscationLength) {
-            return
-        }
-
-        val toDeobfuscate = Math.max(range.first, 0L)..Math.min(range.last, obfuscationLength - 1L)
-        for (i in toDeobfuscate.map { it.toInt() })
+        val toDeobfuscate = 0 until obfuscationLength
+        for (i in toDeobfuscate)
             bytes[i] = bytes[i].xor(obfuscationKey[i % obfuscationKey.size])
     }
 

readium/streamer/src/test/java/org/readium/r2/streamer/parser/epub/EpubDeobfuscatorTest.kt

@@ -9,6 +9,7 @@
 
 package org.readium.r2.streamer.parser.epub
 
+import kotlinx.coroutines.runBlocking
 import org.assertj.core.api.Assertions.assertThat
 import org.junit.Test
 import org.junit.runner.RunWith
@@ -73,6 +74,17 @@ class EpubDeobfuscatorTest {
         assertThat(deobfuscatedRes).isEqualTo(font)
     }
 
+    @Test
+    fun testIdpfDeobfuscationWithRange() {
+        runBlocking {
+            val deobfuscatedRes = deobfuscate(
+                "/deobfuscation/cut-cut.obf.woff",
+                "http://www.idpf.org/2008/embedding"
+            ).read(20L until 40L).getOrThrow()
+            assertThat(deobfuscatedRes).isEqualTo(font.copyOfRange(20, 40))
+        }
+    }
+
     @Test
     fun testAdobeDeobfuscation() {
         val deobfuscatedRes = deobfuscate(