Fix #347: escape JS bridge callback payloads

sample/shared/src/commonMain/kotlin/com/kevinnzou/sample/jsbridge/GreetJsMessageHandler.kt

@@ -27,7 +27,7 @@ class GreetJsMessageHandler : IJsMessageHandler {
         }
         val param = processParams<GreetModel>(message)
         val data = GreetModel("KMP Received ${param.message}")
-        callback(dataToJsonString(data))
+        navigator?.coroutineScope?.launch { callback(dataToJsonString(data)) }
 //        EventBus.post(NavigationEvent())
         navigator?.coroutineScope?.launch {
             FlowEventBus.publishEvent(NavigationEvent())

webview/build.gradle.kts

@@ -67,6 +67,10 @@ kotlin {
             implementation(libs.kotlin.serialization.json)
         }
 
+        commonTest.dependencies {
+            implementation(libs.kotlin.test)
+        }
+
         androidMain.dependencies {
             api(libs.android.activity.compose)
             api(libs.android.webkit)

webview/src/commonMain/kotlin/com/multiplatform/webview/jsbridge/WebViewJsBridge.kt

@@ -5,6 +5,8 @@ import androidx.compose.runtime.Immutable
 import androidx.compose.runtime.remember
 import com.multiplatform.webview.web.IWebView
 import com.multiplatform.webview.web.WebViewNavigator
+import kotlinx.serialization.encodeToString
+import kotlinx.serialization.json.Json
 
 /**
  * Created By Kevin Zou On 2023/10/31
@@ -39,9 +41,35 @@ open class WebViewJsBridge(
     private fun onCallback(
         data: String,
         callbackId: Int,
-    ) = webView?.evaluateJavaScript("window.$jsBridgeName.onCallback($callbackId, '$data')")
+    ) = webView?.evaluateJavaScript(callbackScript(jsBridgeName, callbackId, data))
 }
 
+/**
+ * The script that hands [data] to the web side's pending callback [callbackId].
+ *
+ * [data] is spliced in as a JavaScript string literal rather than pasted between quotes, so
+ * quotes, backslashes and line breaks in the payload reach the callback unchanged instead of
+ * breaking the script.
+ */
+internal fun callbackScript(
+    jsBridgeName: String,
+    callbackId: Int,
+    data: String,
+): String = "window.$jsBridgeName.onCallback($callbackId, ${data.toJsStringLiteral()})"
+
+/**
+ * Renders this string as a JavaScript string literal.
+ *
+ * JSON string escaping is a subset of JavaScript's, so the JSON encoding is a valid
+ * double-quoted literal. U+2028 and U+2029 are escaped as well: JSON allows them raw, but
+ * JavaScript treated them as line terminators before ES2019.
+ */
+internal fun String.toJsStringLiteral(): String =
+    Json
+        .encodeToString(this)
+        .replace("\u2028", "\\u2028")
+        .replace("\u2029", "\\u2029")
+
 /**
  * Create a [WebViewJsBridge] that is remembered across Compositions.
  */

webview/src/commonTest/kotlin/com/multiplatform/webview/jsbridge/WebViewJsBridgeTest.kt

@@ -0,0 +1,44 @@
+package com.multiplatform.webview.jsbridge
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+
+class WebViewJsBridgeTest {
+    @Test
+    fun plainTextIsQuoted() {
+        assertEquals("\"hello\"", "hello".toJsStringLiteral())
+    }
+
+    @Test
+    fun quotesAndBackslashesAreEscaped() {
+        assertEquals(
+            "\"it's \\\"quoted\\\" and \\\\ escaped\"",
+            "it's \"quoted\" and \\ escaped".toJsStringLiteral(),
+        )
+    }
+
+    @Test
+    fun lineTerminatorsAreEscaped() {
+        val literal = "line 1\nline 2\r\n\u2028\u2029".toJsStringLiteral()
+        assertEquals("\"line 1\\nline 2\\r\\n\\u2028\\u2029\"", literal)
+        assertFalse(literal.any { it == '\n' || it == '\r' || it == '\u2028' || it == '\u2029' })
+    }
+
+    @Test
+    fun jsonPayloadKeepsItsOwnEscapes() {
+        // #347: a JSON payload whose string field holds a newline. The encoder wrote that
+        // newline as the two characters `\n`; the literal must carry both so JSON.parse on
+        // the web side sees an escape sequence rather than a raw control character.
+        val payload = """{"text":"line 1\nline 2"}"""
+        assertEquals("\"{\\\"text\\\":\\\"line 1\\\\nline 2\\\"}\"", payload.toJsStringLiteral())
+    }
+
+    @Test
+    fun callbackScriptSplicesTheLiteral() {
+        assertEquals(
+            "window.kmpJsBridge.onCallback(7, \"it's\\ndone\")",
+            callbackScript("kmpJsBridge", 7, "it's\ndone"),
+        )
+    }
+}