Fix NPE in Gson when serializing request headers on cold start (#1603)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: faraz152

library/src/main/kotlin/com/chuckerteam/chucker/internal/data/entity/HttpTransaction.kt

@@ -13,6 +13,7 @@ import androidx.room.Ignore
 import androidx.room.PrimaryKey
 import com.chuckerteam.chucker.internal.support.FormatUtils
 import com.chuckerteam.chucker.internal.support.FormattedUrl
+import com.chuckerteam.chucker.internal.support.HttpHeaderSerializer
 import com.chuckerteam.chucker.internal.support.JsonConverter
 import com.chuckerteam.chucker.internal.support.SpanTextUtil
 import com.google.gson.reflect.TypeToken
@@ -161,7 +162,7 @@ internal class HttpTransaction(
     }
 
     fun setRequestHeaders(headers: List<HttpHeader>) {
-        requestHeaders = JsonConverter.instance.toJson(headers)
+        requestHeaders = HttpHeaderSerializer.toJson(headers)
     }
 
     fun setGraphQlOperationName(headers: Headers) {
@@ -194,7 +195,7 @@ internal class HttpTransaction(
     }
 
     fun setResponseHeaders(headers: List<HttpHeader>) {
-        responseHeaders = JsonConverter.instance.toJson(headers)
+        responseHeaders = HttpHeaderSerializer.toJson(headers)
     }
 
     fun getResponseHeadersString(withMarkup: Boolean): String =

library/src/main/kotlin/com/chuckerteam/chucker/internal/support/HttpHeaderSerializer.kt

@@ -0,0 +1,31 @@
+package com.chuckerteam.chucker.internal.support
+
+import com.chuckerteam.chucker.internal.data.entity.HttpHeader
+import com.google.gson.JsonArray
+import com.google.gson.JsonObject
+
+internal object HttpHeaderSerializer {
+    fun toJson(headers: List<HttpHeader>): String =
+        try {
+            JsonConverter.instance.toJson(headers)
+        } catch (
+            @Suppress("TooGenericExceptionCaught", "SwallowedException") e: Exception,
+        ) {
+            // Gson's default path resolves the List<HttpHeader> element type
+            // reflectively, which occasionally throws NPE on cold start (issue
+            // #1602). Build the JSON tree explicitly so callers still get a
+            // valid string that fromJson<List<HttpHeader>> can round-trip.
+            buildHeadersJson(headers)
+        }
+
+    private fun buildHeadersJson(headers: List<HttpHeader>): String {
+        val array = JsonArray(headers.size)
+        headers.forEach { header ->
+            val obj = JsonObject()
+            obj.addProperty("name", header.name)
+            obj.addProperty("value", header.value)
+            array.add(obj)
+        }
+        return array.toString()
+    }
+}

library/src/test/kotlin/com/chuckerteam/chucker/internal/support/HttpHeaderSerializerTest.kt

@@ -0,0 +1,62 @@
+package com.chuckerteam.chucker.internal.support
+
+import com.chuckerteam.chucker.internal.data.entity.HttpHeader
+import com.google.common.truth.Truth.assertThat
+import com.google.gson.reflect.TypeToken
+import org.junit.jupiter.api.Test
+
+internal class HttpHeaderSerializerTest {
+    private val sampleHeaders =
+        listOf(
+            HttpHeader("Content-Type", "application/json"),
+            HttpHeader("X-Trace", "abc\"123\n"),
+        )
+
+    private val headerListType =
+        TypeToken.getParameterized(List::class.java, HttpHeader::class.java).type
+
+    @Test
+    fun `empty list serializes to an empty JSON array`() {
+        val json = HttpHeaderSerializer.toJson(emptyList())
+
+        val parsed: List<HttpHeader> = JsonConverter.instance.fromJson(json, headerListType)
+        assertThat(parsed).isEmpty()
+    }
+
+    @Test
+    fun `round-trips headers through the default Gson path`() {
+        val json = HttpHeaderSerializer.toJson(sampleHeaders)
+
+        val parsed: List<HttpHeader> = JsonConverter.instance.fromJson(json, headerListType)
+        assertThat(parsed).containsExactlyElementsIn(sampleHeaders).inOrder()
+    }
+
+    @Test
+    fun `fallback path produces JSON that round-trips back to the same headers`() {
+        val fallbackJson = invokePrivateFallback(sampleHeaders)
+
+        val parsed: List<HttpHeader> = JsonConverter.instance.fromJson(fallbackJson, headerListType)
+        assertThat(parsed).containsExactlyElementsIn(sampleHeaders).inOrder()
+    }
+
+    @Test
+    fun `fallback escapes control characters and quotes into valid JSON`() {
+        val awkward =
+            listOf(
+                HttpHeader("k\"ey", "line1\nline2\tend"),
+            )
+
+        val fallbackJson = invokePrivateFallback(awkward)
+
+        val parsed: List<HttpHeader> = JsonConverter.instance.fromJson(fallbackJson, headerListType)
+        assertThat(parsed).containsExactlyElementsIn(awkward).inOrder()
+    }
+
+    private fun invokePrivateFallback(headers: List<HttpHeader>): String {
+        val method =
+            HttpHeaderSerializer::class.java.getDeclaredMethod("buildHeadersJson", List::class.java).apply {
+                isAccessible = true
+            }
+        return method.invoke(HttpHeaderSerializer, headers) as String
+    }
+}