do not fail if input contains some garbage, still try to parse json

Author: anna239

acp-model/build.gradle.kts

@@ -12,5 +12,13 @@ kotlin {
                 api(libs.kotlinx.collections.immutable)
             }
         }
+
+        commonTest {
+            dependencies {
+                implementation(kotlin("test"))
+                implementation(libs.kotlinx.coroutines.test)
+            }
+        }
+
     }
 }

acp-model/src/commonMain/kotlin/com/agentclientprotocol/rpc/JsonRpc.kt

@@ -4,6 +4,7 @@ package com.agentclientprotocol.rpc
 
 import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.Serializable
+import kotlinx.serialization.SerializationException
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.JsonObject
@@ -103,7 +104,17 @@ public val ACPJson: Json by lazy {
  * - Notification: has "method" but no "id"
  */
 public fun decodeJsonRpcMessage(jsonString: String): JsonRpcMessage {
-    val element = ACPJson.parseToJsonElement(jsonString)
+    val element = try {
+        ACPJson.parseToJsonElement(jsonString)
+    } catch (e: SerializationException) {
+        // maybe there is some garbage output at the beginning of the like, try to find where JSON starts
+        val jsonStart = jsonString.indexOfFirst { it == '{' }
+        if (jsonStart == -1) {
+            throw e
+        }
+        val jsonStartTrimmed = jsonString.substring(jsonStart)
+        ACPJson.parseToJsonElement(jsonStartTrimmed)
+    }
     require(element is JsonObject) { "Expected JSON object" }
 
     val hasId = element.containsKey("id")

acp-model/src/commonTest/kotlin/com/agentclientprotocol/rpc/JsonDecodeTest.kt

@@ -0,0 +1,68 @@
+package com.agentclientprotocol.rpc
+
+import kotlinx.serialization.SerializationException
+import kotlinx.serialization.json.jsonObject
+import kotlinx.serialization.json.jsonPrimitive
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+import kotlin.test.fail
+
+class JsonDecodeTest {
+
+    @Test
+    fun testDecode() {
+        val result = decodeJsonRpcMessage(
+            """
+            {
+              "jsonrpc": "2.0",
+              "id": 5,
+              "result": {
+                "outcome": {
+                  "outcome": "selected",
+                  "optionId": "allow-once"
+                }
+              }
+            }
+        """.trimIndent()
+        )
+        assertTrue(result is JsonRpcResponse)
+    }
+
+    @Test
+    fun testDecodeWithPrefix() {
+        val result = decodeJsonRpcMessage(
+            """
+            asdfasdfasdf(){
+              "jsonrpc": "2.0",
+              "id": 5,
+              "result": {
+                "outcome": {
+                  "outcome": "selected",
+                  "optionId": "allow-once"
+                }
+              }
+            }
+        """.trimIndent()
+        )
+        assertTrue(result is JsonRpcResponse)
+        assertEquals("selected", result.result!!.jsonObject["outcome"]!!.jsonObject["outcome"]!!.jsonPrimitive.content)
+    }
+
+    @Test
+    fun testDecodeError() {
+        try {
+            decodeJsonRpcMessage("""
+            asdfasdfas
+                "outcome": {
+                  "outcome": "selected",
+                  "optionId": "allow-once"
+                }
+              }
+            }
+        """.trimIndent())
+            fail("Exception expected")
+        } catch (_: SerializationException) {}
+    }
+
+}

acp/src/commonMain/kotlin/com/agentclientprotocol/transport/StdioTransport.kt

@@ -60,7 +60,6 @@ public class StdioTransport(
                             decodeJsonRpcMessage(line)
                         } catch (t: Throwable) {
                             logger.trace(t) { "Failed to decode JSON message: $line" }
-                            fireError(t)
                             continue
                         }
                         logger.trace { "Sending message to channel: $jsonRpcMessage" }