feat: Add Hex patch (#3034)

2024-04-18 21:37:46 +02:00
parent 50ddb680ed
commit 6fd46ad9b6
3 changed files with 194 additions and 0 deletions
@@ -0,0 +1,120 @@
+package app.revanced.patches.shared.misc.hex
+
+import app.revanced.patcher.data.ResourceContext
+import app.revanced.patcher.patch.PatchException
+import app.revanced.patcher.patch.RawResourcePatch
+import kotlin.math.max
+
+abstract class BaseHexPatch : RawResourcePatch() {
+    internal abstract val replacements: List<Replacement>
+
+    override fun execute(context: ResourceContext) {
+        replacements.groupBy { it.targetFilePath }.forEach { (targetFilePath, replacements) ->
+            val targetFile = try {
+                context[targetFilePath, true]
+            } catch (e: Exception) {
+                throw PatchException("Could not find target file: $targetFilePath")
+            }
+
+            // TODO: Use a file channel to read and write the file instead of reading the whole file into memory,
+            //  in order to reduce memory usage.
+            val targetFileBytes = targetFile.readBytes()
+
+            replacements.forEach { replacement ->
+                replacement.replacePattern(targetFileBytes)
+            }
+
+            targetFile.writeBytes(targetFileBytes)
+        }
+    }
+
+    /**
+     * Represents a pattern to search for and its replacement pattern.
+     *
+     * @property pattern The pattern to search for.
+     * @property replacementPattern The pattern to replace the [pattern] with.
+     * @property targetFilePath The path to the file to make the changes in relative to the APK root.
+     */
+    class Replacement(
+        private val pattern: String,
+        replacementPattern: String,
+        internal val targetFilePath: String,
+    ) {
+        private val patternBytes = pattern.toByteArrayPattern()
+        private val replacementPattern = replacementPattern.toByteArrayPattern()
+
+        init {
+            if (this.patternBytes.size != this.replacementPattern.size) {
+                throw PatchException("Pattern and replacement pattern must have the same length: $pattern")
+            }
+        }
+
+        /**
+         * Replaces the [patternBytes] with the [replacementPattern] in the [targetFileBytes].
+         *
+         * @param targetFileBytes The bytes of the file to make the changes in.
+         */
+        fun replacePattern(targetFileBytes: ByteArray) {
+            val startIndex = indexOfPatternIn(targetFileBytes)
+
+            if (startIndex == -1) {
+                throw PatchException("Pattern not found in target file: $pattern")
+            }
+
+            replacementPattern.copyInto(targetFileBytes, startIndex)
+        }
+
+        // TODO: Allow searching in a file channel instead of a byte array to reduce memory usage.
+        /**
+         * Returns the index of the first occurrence of [patternBytes] in the haystack
+         * using the Boyer-Moore algorithm.
+         *
+         * @param haystack The array to search in.
+         *
+         * @return The index of the first occurrence of the [patternBytes] in the haystack or -1
+         * if the [patternBytes] is not found.
+         */
+        private fun indexOfPatternIn(haystack: ByteArray): Int {
+            val needle = patternBytes
+
+            val haystackLength = haystack.size - 1
+            val needleLength = needle.size - 1
+            val right = IntArray(256) { -1 }
+
+            for (i in 0 until needleLength) right[needle[i].toInt().and(0xFF)] = i
+
+            var skip: Int
+            for (i in 0..haystackLength - needleLength) {
+                skip = 0
+
+                for (j in needleLength - 1 downTo 0)
+                    if (needle[j] != haystack[i + j]) {
+                        skip = max(1, j - right[haystack[i + j].toInt().and(0xFF)])
+
+                        break
+                    }
+
+                if (skip == 0) return i
+            }
+            return -1
+        }
+
+        companion object {
+            /**
+             * Convert a string representing a pattern of hexadecimal bytes to a byte array.
+             *
+             * @return The byte array representing the pattern.
+             * @throws PatchException If the pattern is invalid.
+             */
+            private fun String.toByteArrayPattern() = try {
+                split(" ").map { it.toInt(16).toByte() }.toByteArray()
+            } catch (e: NumberFormatException) {
+                throw PatchException(
+                    "Could not parse pattern: $this.  A pattern is a sequence of case insensitive strings " +
+                        "representing hexadecimal bytes separated by spaces",
+                    e,
+                )
+            }
+        }
+    }
+}