From 06408157dfde2f40c6368c5ab03e46479428f566 Mon Sep 17 00:00:00 2001
From: Allan Wang <me@allanwang.ca>
Date: Tue, 13 Aug 2019 23:49:04 -0700
Subject: Use one stringbuilder per tag creation and add test

---
 .../com/pitchedapps/frost/injectors/JsInjector.kt  | 37 ++++++++++------------
 .../frost/injectors/TagObfuscatorTest.kt           | 22 +++++++++++++
 2 files changed, 38 insertions(+), 21 deletions(-)
 create mode 100644 app/src/test/kotlin/com/pitchedapps/frost/injectors/TagObfuscatorTest.kt

diff --git a/app/src/main/kotlin/com/pitchedapps/frost/injectors/JsInjector.kt b/app/src/main/kotlin/com/pitchedapps/frost/injectors/JsInjector.kt
index 5d8c55e6..eed2f819 100644
--- a/app/src/main/kotlin/com/pitchedapps/frost/injectors/JsInjector.kt
+++ b/app/src/main/kotlin/com/pitchedapps/frost/injectors/JsInjector.kt
@@ -16,13 +16,11 @@
  */
 package com.pitchedapps.frost.injectors
 
-import android.util.Log
 import android.webkit.WebView
-import com.pitchedapps.frost.BuildConfig
+import androidx.annotation.VisibleForTesting
 import com.pitchedapps.frost.utils.L
 import com.pitchedapps.frost.web.FrostWebViewClient
 import org.apache.commons.text.StringEscapeUtils
-import java.util.Locale
 import kotlin.random.Random
 
 class JsBuilder {
@@ -115,33 +113,30 @@ class JsInjector(val function: String) : InjectorContract {
 /**
  * Helper object to obfuscate window tags for JS injection.
  */
-private object TagObfuscator {
+@VisibleForTesting
+internal object TagObfuscator {
 
-    fun obfuscateTag(tag: String) : String {
+    fun obfuscateTag(tag: String): String {
         val rnd = Random(tag.hashCode() + salt)
-        val obfuscated = StringBuilder()
-            .append(prefix)
-            .append(randomChars(rnd, tag.length))
-        L._d { "TagObfuscator: Obfuscating tag '$tag' to '$obfuscated'" }
-        //if (BuildConfig.DEBUG) {
-        //    return "_frost_${tag.toLowerCase(Locale.CANADA)}"
-        //} else
-        return obfuscated.toString()
+        val obfuscated = buildString {
+            append(prefix)
+            append('_')
+            appendRandomChars(rnd, 16)
+        }
+        L.v { "TagObfuscator: Obfuscating tag '$tag' to '$obfuscated'" }
+        return obfuscated
     }
 
-    private val salt by lazy { System.currentTimeMillis() }
+    private val salt: Long = System.currentTimeMillis()
 
-    private val prefix by lazy {
+    private val prefix: String by lazy {
         val rnd = Random(System.currentTimeMillis())
-        val length = rnd.nextInt(10, 16)
-        randomChars(rnd, length)
+        buildString { appendRandomChars(rnd, 8) }
     }
 
-    private fun randomChars(random: Random, count: Int) : String {
-        val result = StringBuilder()
+    private fun Appendable.appendRandomChars(random: Random, count: Int) {
         for (i in 1..count) {
-            result.append('a' + random.nextInt(0, 26))
+            append('a' + random.nextInt(26))
         }
-        return result.toString()
     }
 }
\ No newline at end of file
diff --git a/app/src/test/kotlin/com/pitchedapps/frost/injectors/TagObfuscatorTest.kt b/app/src/test/kotlin/com/pitchedapps/frost/injectors/TagObfuscatorTest.kt
new file mode 100644
index 00000000..5c316a4a
--- /dev/null
+++ b/app/src/test/kotlin/com/pitchedapps/frost/injectors/TagObfuscatorTest.kt
@@ -0,0 +1,22 @@
+package com.pitchedapps.frost.injectors
+
+import java.util.UUID
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class TagObfuscatorTest {
+
+    /**
+     * The same key should result in the same tag per session
+     */
+    @Test
+    fun consistentTags() {
+        val keys = generateSequence { UUID.randomUUID().toString() }.take(10).toSet()
+        val tags = keys.map {
+            val tag = generateSequence { TagObfuscator.obfuscateTag(it) }.take(10).toSet()
+            assertEquals(1, tag.size, "Key $it produced multiple tags: $tag")
+            tag.first()
+        }
+        assertEquals(keys.size, tags.size, "Key set and tag set have different sizes")
+    }
+}
-- 
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