fix(replay): Fix network detail response body size being unknown for gzip-compressed responses (#5592)

* fix(replay): Derive response body size from peeked bytes when contentLength is unknown

For gzip-compressed responses, OkHttp strips the Content-Length header
during transparent decompression, so response.body.contentLength() returns
-1. This caused NetworkRequestData.responseBodySize to be unknown for
replay network details.

Add originalByteCount to NetworkBody, set it from the actual byte array
in NetworkBodyParser.fromBytes, and use it as a fallback in
NetworkDetailCaptureUtils when the passed bodySize is null or -1. This
piggybacks on the existing peekBody call with no additional I/O.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* changelog

* Changelog

* fix(replay): make NetworkBody 3-arg constructor package-private

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: romtsn

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## 8.46.0
 
+### Fixes
+
+- Session Replay: Fix network detail response body size being unknown for gzip-compressed responses ([#5592](https://github.com/getsentry/sentry-java/pull/5592))
+
 ### Behavioral Changes
 
 - Collections returned by scope (e.g. `getBreadcrumbs`, `getTags`, `getAttachments`) are shared state and should not be mutated. ([#5541](https://github.com/getsentry/sentry-java/pull/5541))

sentry/src/main/java/io/sentry/util/network/NetworkBody.java

@@ -16,15 +16,24 @@ public final class NetworkBody {
 
   private final @Nullable Object body;
   private final @Nullable List<NetworkBodyWarning> warnings;
+  private final long originalByteCount;
 
   public NetworkBody(final @Nullable Object body) {
-    this(body, null);
+    this(body, null, -1);
   }
 
   public NetworkBody(
       final @Nullable Object body, final @Nullable List<NetworkBodyWarning> warnings) {
+    this(body, warnings, -1);
+  }
+
+  NetworkBody(
+      final @Nullable Object body,
+      final @Nullable List<NetworkBodyWarning> warnings,
+      final long originalByteCount) {
     this.body = body;
     this.warnings = warnings;
+    this.originalByteCount = originalByteCount;
   }
 
   public @Nullable Object getBody() {
@@ -35,6 +44,10 @@ public NetworkBody(
     return warnings;
   }
 
+  long getOriginalByteCount() {
+    return originalByteCount;
+  }
+
   // Based on
   // https://github.com/getsentry/sentry/blob/ccb61aa9b0f33e1333830093a5ce3bd5db88ef33/static/app/utils/replays/replay.tsx#L5-L12
   public enum NetworkBodyWarning {

sentry/src/main/java/io/sentry/util/network/NetworkBodyParser.java

@@ -45,24 +45,33 @@ private NetworkBodyParser() {}
       return null;
     }
 
+    final boolean isTruncated = bytes.length > maxSizeBytes;
+    final long originalByteCount = bytes.length;
+
     if (contentType != null && isBinaryContentType(contentType)) {
       // For binary content, return a description instead of the actual content
       return new NetworkBody(
-          "[Binary data, " + bytes.length + " bytes, type: " + contentType + "]");
+          "[Binary data, " + bytes.length + " bytes, type: " + contentType + "]",
+          null,
+          originalByteCount);
     }
 
     // Convert to string and parse
     try {
       final String effectiveCharset = charset != null ? charset : "UTF-8";
       final int size = Math.min(bytes.length, maxSizeBytes);
-      final boolean isPartial = bytes.length > maxSizeBytes;
       final String content = new String(bytes, 0, size, effectiveCharset);
-      return parse(content, contentType, isPartial, logger);
+      final NetworkBody parsed = parse(content, contentType, isTruncated, logger);
+      if (parsed == null) {
+        return null;
+      }
+      return new NetworkBody(parsed.getBody(), parsed.getWarnings(), originalByteCount);
     } catch (UnsupportedEncodingException e) {
       logger.log(SentryLevel.WARNING, "Failed to decode bytes: " + e.getMessage());
       return new NetworkBody(
           "[Failed to decode bytes, " + bytes.length + " bytes]",
-          Collections.singletonList(NetworkBody.NetworkBodyWarning.BODY_PARSE_ERROR));
+          Collections.singletonList(NetworkBody.NetworkBodyWarning.BODY_PARSE_ERROR),
+          originalByteCount);
     }
   }
 

sentry/src/main/java/io/sentry/util/network/NetworkDetailCaptureUtils.java

@@ -160,9 +160,15 @@ private static boolean shouldCaptureUrl(
       body = bodyExtractor.extract(httpObject);
     }
 
+    // When contentLength is unknown (-1), use the actual byte count from body extraction
+    Long effectiveBodySize = bodySize;
+    if ((bodySize == null || bodySize == -1L) && body != null && body.getOriginalByteCount() >= 0) {
+      effectiveBodySize = body.getOriginalByteCount();
+    }
+
     Map<String, String> headers =
         getCaptureHeaders(headerExtractor.extract(httpObject), allowedHeaders);
 
-    return new ReplayNetworkRequestOrResponse(bodySize, body, headers);
+    return new ReplayNetworkRequestOrResponse(effectiveBodySize, body, headers);
   }
 }

sentry/src/test/java/io/sentry/util/network/NetworkBodyParserTest.kt

@@ -341,6 +341,27 @@ class NetworkBodyParserTest {
     val body = NetworkBodyParser.fromBytes(bytes, "image/png", null, bytes.size, logger)
     assertNotNull(body)
     assertEquals("[Binary data, 100 bytes, type: image/png]", body.body)
+    assertEquals(100, body.originalByteCount)
+  }
+
+  @Test
+  fun `originalByteCount is set when body fits within limit`() {
+    val logger = mock<ILogger>()
+    val bytes = """{"key":"value"}""".toByteArray()
+
+    val body = NetworkBodyParser.fromBytes(bytes, "application/json", null, bytes.size, logger)
+    assertNotNull(body)
+    assertEquals(bytes.size.toLong(), body.originalByteCount)
+  }
+
+  @Test
+  fun `originalByteCount is set to capped size when body is truncated`() {
+    val logger = mock<ILogger>()
+    val bytes = """{"key":"value"}""".toByteArray()
+
+    val body = NetworkBodyParser.fromBytes(bytes, "application/json", null, bytes.size - 1, logger)
+    assertNotNull(body)
+    assertEquals(bytes.size.toLong(), body.originalByteCount)
   }
 
   @Test

sentry/src/test/java/io/sentry/util/network/NetworkDetailCaptureUtilsTest.kt

@@ -1,12 +1,70 @@
 package io.sentry.util.network
 
+import io.sentry.ILogger
 import java.util.LinkedHashMap
 import kotlin.test.assertEquals
+import kotlin.test.assertNull
 import kotlin.test.assertTrue
 import org.junit.Test
+import org.mockito.kotlin.mock
 
 class NetworkDetailCaptureUtilsTest {
 
+  @Test
+  fun `createResponse uses originalByteCount when bodySize is unknown`() {
+    val logger = mock<ILogger>()
+    val jsonBytes = """{"key":"value"}""".toByteArray()
+
+    val result =
+      NetworkDetailCaptureUtils.createResponse(
+        jsonBytes,
+        -1L,
+        true,
+        { bytes ->
+          NetworkBodyParser.fromBytes(bytes, "application/json", null, bytes.size, logger)
+        },
+        emptyList(),
+        { emptyMap() },
+      )
+
+    assertEquals(jsonBytes.size.toLong(), result.size)
+  }
+
+  @Test
+  fun `createResponse keeps explicit bodySize when available`() {
+    val logger = mock<ILogger>()
+    val jsonBytes = """{"key":"value"}""".toByteArray()
+
+    val result =
+      NetworkDetailCaptureUtils.createResponse(
+        jsonBytes,
+        42L,
+        true,
+        { bytes ->
+          NetworkBodyParser.fromBytes(bytes, "application/json", null, bytes.size, logger)
+        },
+        emptyList(),
+        { emptyMap() },
+      )
+
+    assertEquals(42L, result.size)
+  }
+
+  @Test
+  fun `createResponse keeps null bodySize when body capture is off`() {
+    val result =
+      NetworkDetailCaptureUtils.createResponse(
+        "unused",
+        null,
+        false,
+        { null },
+        emptyList(),
+        { emptyMap() },
+      )
+
+    assertNull(result.size)
+  }
+
   @Test
   fun `getCaptureHeaders should match headers case-insensitively`() {
     // Setup: allHeaders with mixed case keys