Use XML encoding when present while parsing the feed

core/network/src/commonMain/kotlin/dev/sasikanth/rss/reader/core/network/parser/FeedParser.kt

@@ -23,6 +23,7 @@ import io.ktor.http.set
 import io.ktor.utils.io.ByteReadChannel
 import io.ktor.utils.io.core.readBytes
 import korlibs.io.lang.Charset
+import korlibs.io.lang.Charsets
 import kotlin.coroutines.CoroutineContext
 import kotlin.coroutines.EmptyCoroutineContext
 import kotlinx.coroutines.runBlocking
@@ -124,6 +125,7 @@ private fun ByteReadChannel.toCharIterator(
 
     private val DEFAULT_BUFFER_SIZE = 1024L
 
+    private var encodingCharset: Charset? = null
     private var currentIndex = 0
     private var currentBuffer = String()
 
@@ -132,13 +134,34 @@ private fun ByteReadChannel.toCharIterator(
       if (this@toCharIterator.isClosedForRead) return false
 
       val packet = runBlocking(context) { this@toCharIterator.readRemaining(DEFAULT_BUFFER_SIZE) }
-      currentBuffer = buildString { charset.decode(this, packet.readBytes()) }
+      val bytes = packet.readBytes()
+      val encodingRegex = """<?xml.*encoding=["']([^"']+)["'].*?>""".toRegex()
+      if (encodingCharset == null) {
+        val encodingContent = buildString { Charsets.UTF8.decode(this, bytes) }
+        encodingCharset = findEncodingCharset(encodingRegex, encodingContent, charset)
+      }
+
+      currentBuffer = buildString { (encodingCharset ?: charset).decode(this, bytes) }
 
       packet.release()
       currentIndex = 0
       return currentBuffer.isNotEmpty()
     }
 
+    private fun findEncodingCharset(
+      encodingRegex: Regex,
+      encodingContent: String,
+      fallbackCharset: Charset,
+    ) =
+      (encodingRegex.find(encodingContent)?.groupValues?.get(1)?.let { encoding ->
+        try {
+          Charset.forName(encoding)
+        } catch (e: Exception) {
+          null
+        }
+      }
+        ?: fallbackCharset)
+
     override fun nextChar(): Char {
       if (!hasNext()) throw NoSuchElementException()
       return currentBuffer[currentIndex++]