fix: sanitize tool call arguments JSON on interrupted streaming to prevent 400 errors by flystar32 · Pull Request #1148 · agentscope-ai/agentscope-java

flystar32 · 2026-04-07T02:19:26Z

Summary

When streaming tool call responses are interrupted mid-arguments, the partially accumulated JSON (e.g. {"query": "hello wor) was saved to memory and sent as-is in subsequent API requests, causing DashScope (百炼) to reject with HTTP 400 due to invalid JSON in tool call arguments.
This fix adds JSON validation at two layers: (1) ToolCallsAccumulator.build() now falls back to "{}" when raw content is not valid JSON, and (2) both DashScopeToolsHelper and OpenAIMessageConverter validate content before using it as arguments, falling back to serializing the input map.

Test plan

Verify streaming tool call completes normally (no regression)
Simulate interrupt during streaming tool call and verify the saved message contains valid JSON arguments ("{}" instead of broken JSON)
After interrupt, verify next model request succeeds without 400 error
Test with DashScope API (qwen3.5/qwen3.6) specifically

Made with Cursor

…event 400 errors When streaming tool call responses are interrupted, the partially accumulated arguments (incomplete JSON) were saved to memory as-is. On subsequent requests, this malformed JSON was sent to the model API as tool call arguments, causing DashScope/OpenAI to reject with 400. Fixes agentscope-ai#1147 Change-Id: I23701960b5d4fa0962f872fb48a6252b13c3dc0b Co-developed-by: Cursor <noreply@cursor.com>

Copilot

Pull request overview

This PR hardens tool-call argument handling during streaming so that interrupted tool-call argument accumulation doesn’t persist malformed JSON into conversation history and subsequent provider requests (addressing #1147).

Changes:

Sanitize accumulated tool-call argument JSON in ToolCallsAccumulator to avoid keeping malformed/incomplete JSON strings.
Add defensive validation in both DashScope and OpenAI formatters to only use ToolUseBlock.content when it is valid JSON, otherwise serialize input.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 7 comments.

File	Description
agentscope-core/src/main/java/io/agentscope/core/formatter/openai/OpenAIMessageConverter.java	Routes tool-call argument resolution through a validating helper to avoid sending malformed JSON to OpenAI-compatible APIs.
agentscope-core/src/main/java/io/agentscope/core/formatter/dashscope/DashScopeToolsHelper.java	Adds validated tool-call argument resolution before building DashScope tool-call DTOs.
agentscope-core/src/main/java/io/agentscope/core/agent/accumulator/ToolCallsAccumulator.java	Adjusts tool-call accumulation/build logic to avoid persisting malformed JSON argument fragments on interrupted streams.

Copilot · 2026-04-07T02:23:40Z

agentscope-core/src/main/java/io/agentscope/core/agent/accumulator/ToolCallsAccumulator.java

+            // Use raw content only if it was successfully parsed or args were
+            // already populated (meaning the content matches the parsed input).
+            // Otherwise fall back to "{}" to avoid sending malformed JSON
+            // (e.g. when streaming was interrupted mid-arguments).
+            String contentStr;
+            if (rawContentStr.isEmpty()) {
+                contentStr = "{}";
+            } else if (!finalArgs.isEmpty() || rawContentParsed) {
+                contentStr = rawContentStr;
+            } else if (isValidJson(rawContentStr)) {
+                contentStr = rawContentStr;
+            } else {
+                contentStr = "{}";


In ToolCallBuilder.build(), contentStr is set to rawContentStr whenever finalArgs is non-empty, but finalArgs being populated doesn’t guarantee rawContentStr is valid JSON (e.g., interrupted streaming could leave a partial rawContent while some args were already merged from input). This can still persist malformed JSON in memory. Consider validating rawContentStr (and ensuring it’s a JSON object) before using it; otherwise fall back to serializing finalArgs or "{}".

Copilot · 2026-04-07T02:23:40Z

agentscope-core/src/main/java/io/agentscope/core/formatter/openai/OpenAIMessageConverter.java

+    private String resolveArgsJson(ToolUseBlock toolUse) {
+        String content = toolUse.getContent();
+        if (content != null && !content.isEmpty()) {
+            if (isValidJson(content)) {
+                return content;
+            }
+            log.warn(
+                    "Invalid JSON in tool call content for '{}', falling back to input"
+                            + " serialization",
+                    toolUse.getName());
+        }
+
+        try {
+            return JsonUtils.getJsonCodec().toJson(toolUse.getInput());
+        } catch (Exception e) {
+            String errorMsg =
+                    e.getMessage() != null ? e.getMessage() : e.getClass().getSimpleName();
+            log.warn("Failed to serialize tool call arguments: {}", errorMsg);
+            return "{}";
+        }
+    }
+
+    private boolean isValidJson(String str) {
+        try {
+            JsonUtils.getJsonCodec().fromJson(str, Object.class);
+            return true;
+        } catch (Exception e) {
+            return false;
+        }
+    }


isValidJson() currently treats any JSON value as valid (e.g. null, [], or a quoted string). Tool call arguments are expected to be a JSON object, so accepting non-object JSON can still lead to downstream 400s. Consider validating that parsing yields a Map/object node rather than just “parsable JSON”.

Copilot · 2026-04-07T02:23:41Z

agentscope-core/src/main/java/io/agentscope/core/formatter/dashscope/DashScopeToolsHelper.java

+    private String resolveArgsJson(ToolUseBlock toolUse) {
+        String content = toolUse.getContent();
+        if (content != null && !content.isEmpty()) {
+            if (isValidJson(content)) {
+                return content;
+            }
+            log.warn(
+                    "Invalid JSON in tool call content for '{}', falling back to input"
+                            + " serialization",
+                    toolUse.getName());
+        }
+
+        try {
+            return JsonUtils.getJsonCodec().toJson(toolUse.getInput());
+        } catch (Exception e) {
+            log.warn("Failed to serialize tool call arguments: {}", e.getMessage());
+            return "{}";
+        }
+    }
+
+    private boolean isValidJson(String str) {
+        try {
+            JsonUtils.getJsonCodec().fromJson(str, Object.class);
+            return true;
+        } catch (Exception e) {
+            return false;
+        }
+    }


isValidJson() validates only that the string is parseable JSON, but tool call arguments should be a JSON object. Values like null/arrays would pass validation and still be rejected by providers expecting an object. Consider validating the parsed value is a Map/object node before returning content as arguments.

Copilot · 2026-04-07T02:23:41Z

agentscope-core/src/main/java/io/agentscope/core/agent/accumulator/ToolCallsAccumulator.java

        ToolUseBlock build() {
            Map<String, Object> finalArgs = new HashMap<>(args);
            String rawContentStr = this.rawContent.toString();
+            boolean rawContentParsed = false;

            // If no parsed arguments but has raw JSON content, try to parse
            if (finalArgs.isEmpty() && rawContentStr.length() > 0) {
                try {
                    @SuppressWarnings("unchecked")
                    Map<String, Object> parsed =
                            JsonUtils.getJsonCodec().fromJson(rawContentStr, Map.class);
                    if (parsed != null) {
                        finalArgs.putAll(parsed);
+                        rawContentParsed = true;
                    }
                } catch (Exception ignored) {
                    // Parsing failed, keep empty args
                }
            }

+            // Use raw content only if it was successfully parsed or args were
+            // already populated (meaning the content matches the parsed input).
+            // Otherwise fall back to "{}" to avoid sending malformed JSON
+            // (e.g. when streaming was interrupted mid-arguments).
+            String contentStr;
+            if (rawContentStr.isEmpty()) {
+                contentStr = "{}";
+            } else if (!finalArgs.isEmpty() || rawContentParsed) {
+                contentStr = rawContentStr;
+            } else if (isValidJson(rawContentStr)) {
+                contentStr = rawContentStr;
+            } else {
+                contentStr = "{}";
+            }
+
            return ToolUseBlock.builder()
                    .id(toolId != null ? toolId : generateId())
                    .name(name)
                    .input(finalArgs)
-                    .content(rawContentStr.isEmpty() ? "{}" : rawContentStr)
+                    .content(contentStr)
                    .metadata(metadata.isEmpty() ? null : metadata)


This change adds new fallback behavior for malformed/partial tool arguments, but there are no unit tests covering the interrupted/invalid JSON cases (e.g. content like {"query":"hel should produce "{}" or serialized input). Adding a test for this scenario would help prevent regressions in the next streaming/tool-call refactor.

Copilot · 2026-04-07T02:23:41Z

agentscope-core/src/main/java/io/agentscope/core/formatter/openai/OpenAIMessageConverter.java

+                String argsJson = resolveArgsJson(toolUse);



resolveArgsJson() introduces a new behavior change (ignore invalid content and fall back to input serialization), but OpenAIMessageConverter’s tests currently cover only the content present/null/empty cases—not malformed JSON. Adding a unit test where ToolUseBlock.content is incomplete JSON would lock in the intended behavior and prevent reintroducing 400s.

Copilot · 2026-04-07T02:23:41Z

agentscope-core/src/main/java/io/agentscope/core/formatter/dashscope/DashScopeToolsHelper.java

+            String argsJson = resolveArgsJson(toolUse);

            DashScopeFunction function = DashScopeFunction.of(toolUse.getName(), argsJson);
            DashScopeToolCall toolCall =


resolveArgsJson() changes how tool-call arguments are chosen (validate content before using it), but DashScopeToolsHelper tests only cover input-based arguments today. Adding a test case with malformed content (and a valid input map) would ensure this guardrail stays effective against interrupted streaming.

Copilot · 2026-04-07T02:23:41Z

agentscope-core/src/main/java/io/agentscope/core/formatter/openai/OpenAIMessageConverter.java

+    /**
+     * Resolve the arguments JSON string from a ToolUseBlock, with validation
+     * to prevent sending malformed JSON (e.g. from interrupted streaming).
+     */
+    private String resolveArgsJson(ToolUseBlock toolUse) {
+        String content = toolUse.getContent();
+        if (content != null && !content.isEmpty()) {
+            if (isValidJson(content)) {
+                return content;
+            }
+            log.warn(
+                    "Invalid JSON in tool call content for '{}', falling back to input"
+                            + " serialization",
+                    toolUse.getName());
+        }
+
+        try {
+            return JsonUtils.getJsonCodec().toJson(toolUse.getInput());
+        } catch (Exception e) {
+            String errorMsg =
+                    e.getMessage() != null ? e.getMessage() : e.getClass().getSimpleName();
+            log.warn("Failed to serialize tool call arguments: {}", errorMsg);
+            return "{}";
+        }
+    }
+
+    private boolean isValidJson(String str) {
+        try {
+            JsonUtils.getJsonCodec().fromJson(str, Object.class);
+            return true;
+        } catch (Exception e) {
+            return false;
+        }
+    }


resolveArgsJson()/isValidJson() are now duplicated in both OpenAIMessageConverter and DashScopeToolsHelper (and there’s similar JSON validation in ToolCallsAccumulator). Consider extracting a small shared helper (e.g., in JsonUtils or a formatter utility) so validation rules don’t drift across providers over time.

codecov · 2026-04-07T02:29:15Z

Codecov Report

❌ Patch coverage is 88.00000% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...c/main/java/io/agentscope/core/util/JsonUtils.java	82.35%	3 Missing ⚠️

📢 Thoughts on this report? Let us know!

…idation, add tests Address PR review feedback: - Extract duplicated resolveArgsJson/isValidJson into JsonUtils as shared isValidJsonObject() and resolveToolCallArgsJson() methods - Strengthen validation to reject non-object JSON (arrays, null, strings) since tool call arguments must be JSON objects - Fix edge case in ToolCallsAccumulator where finalArgs being non-empty didn't guarantee rawContent was valid JSON - Add comprehensive unit tests for all affected components Change-Id: I05640215b1de0a802434750a94804dd18e01605e Co-developed-by: Cursor <noreply@cursor.com>

Jackson's fromJson("null", Map.class) returns null instead of throwing, so isValidJsonObject("null") incorrectly returned true. Added null check on the parsed result to properly reject JSON null values. Change-Id: I411e6305aa90b06eb3bc906745a66b13fa133e66 Co-developed-by: Cursor <noreply@cursor.com>

flystar32 requested review from a team and Copilot April 7, 2026 02:19

Copilot started reviewing on behalf of flystar32 April 7, 2026 02:20 View session

Copilot AI reviewed Apr 7, 2026

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flystar32 added 2 commits April 7, 2026 13:39

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fix: sanitize tool call arguments JSON on interrupted streaming to prevent 400 errors#1148

fix: sanitize tool call arguments JSON on interrupted streaming to prevent 400 errors#1148
flystar32 wants to merge 3 commits intoagentscope-ai:mainfrom
flystar32:fix/invalid-json-tool-call-on-interrupt

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flystar32 commented Apr 7, 2026

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