android [nfc]: Pull guts off React module in TextCompression

This will let us straightforwardly re-use this logic from
within the Android-side code.

Author: gnprice

android/app/src/main/java/com/zulipmobile/TextCompression.kt

@@ -20,6 +20,47 @@ private const val bufferSize = 8192
 
 private const val header = "z|zlib base64|"
 
+internal fun compress(input: String): String {
+    val outputStream = ByteArrayOutputStream()
+    val deflater = Deflater()
+    deflater.setInput(input.toByteArray(charset("UTF-8")))
+    deflater.finish()
+    val buffer = ByteArray(bufferSize)
+    while (!deflater.finished()) {
+        val byteCount = deflater.deflate(buffer)
+        outputStream.write(buffer, 0, byteCount)
+    }
+    deflater.end()
+    outputStream.close()
+    // The RN bridge currently doesn't support sending byte strings, so we
+    // have to encode the compressed output as a `String`.  To avoid any
+    // trouble, we use base64 to keep things inside ASCII.
+    //
+    // Ultimately our ASCII data seems to end up going to SQLite with size
+    // no more than about 1 byte/char (presumably the string gets encoded
+    // as UTF-8 and it's exactly 1 byte/char), so this is pretty OK.
+    return header + Base64.encodeToString(outputStream.toByteArray(),
+        Base64.DEFAULT)
+}
+
+internal fun decompress(input: String): String {
+    val inflater = Inflater()
+    val inputBytes = input.toByteArray(charset("ISO-8859-1"))
+    inflater.setInput(Base64.decode(inputBytes,
+        header.length,
+        inputBytes.size - header.length,
+        Base64.DEFAULT))
+    val outputStream = ByteArrayOutputStream()
+    val buffer = ByteArray(bufferSize)
+    while (inflater.remaining != 0) {
+        val byteCount = inflater.inflate(buffer)
+        outputStream.write(buffer, 0, byteCount)
+    }
+    inflater.end()
+    outputStream.close()
+    return outputStream.toString("UTF-8")
+}
+
 internal class TextCompressionModule(reactContext: ReactApplicationContext?) :
         ReactContextBaseJavaModule(reactContext) {
     override fun getName(): String = "TextCompressionModule"
@@ -29,26 +70,7 @@ internal class TextCompressionModule(reactContext: ReactApplicationContext?) :
     @ReactMethod
     fun compress(input: String, promise: Promise) {
         try {
-            val outputStream = ByteArrayOutputStream()
-            val deflater = Deflater()
-            deflater.setInput(input.toByteArray(charset("UTF-8")))
-            deflater.finish()
-            val buffer = ByteArray(bufferSize)
-            while (!deflater.finished()) {
-                val byteCount = deflater.deflate(buffer)
-                outputStream.write(buffer, 0, byteCount)
-            }
-            deflater.end()
-            outputStream.close()
-            // The RN bridge currently doesn't support sending byte strings, so we
-            // have to encode the compressed output as a `String`.  To avoid any
-            // trouble, we use base64 to keep things inside ASCII.
-            //
-            // Ultimately our ASCII data seems to end up going to SQLite with size
-            // no more than about 1 byte/char (presumably the string gets encoded
-            // as UTF-8 and it's exactly 1 byte/char), so this is pretty OK.
-            promise.resolve(header + Base64.encodeToString(outputStream.toByteArray(),
-                Base64.DEFAULT))
+            promise.resolve(compress(input))
         } catch (e: UnsupportedEncodingException) {
             promise.reject("UNSUPPORTED_ENCODING_EXCEPTION", e)
         } catch (e: IOException) {
@@ -59,21 +81,7 @@ internal class TextCompressionModule(reactContext: ReactApplicationContext?) :
     @ReactMethod
     fun decompress(input: String, promise: Promise) {
         try {
-            val inflater = Inflater()
-            val inputBytes = input.toByteArray(charset("ISO-8859-1"))
-            inflater.setInput(Base64.decode(inputBytes,
-                header.length,
-                inputBytes.size - header.length,
-                Base64.DEFAULT))
-            val outputStream = ByteArrayOutputStream()
-            val buffer = ByteArray(bufferSize)
-            while (inflater.remaining != 0) {
-                val byteCount = inflater.inflate(buffer)
-                outputStream.write(buffer, 0, byteCount)
-            }
-            inflater.end()
-            outputStream.close()
-            promise.resolve(outputStream.toString("UTF-8"))
+            promise.resolve(decompress(input))
         } catch (e: UnsupportedEncodingException) {
             promise.reject("UNSUPPORTED_ENCODING_EXCEPTION", e)
         } catch (e: IOException) {
@@ -82,4 +90,4 @@ internal class TextCompressionModule(reactContext: ReactApplicationContext?) :
             promise.reject("DATA_FORMAT_EXCEPTION", e)
         }
     }
-}
+}