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fix: Enforce strict JSON Schema compliance to prevent OpenAI 400 Bad Request errors #1266

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fix: Enforce strict JSON Schema compliance to prevent OpenAI 400 Bad Request errors #1266

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42 changes: 32 additions & 10 deletions core/src/main/java/com/google/adk/models/chat/ChatCompletionsCommon.java
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,10 @@ private ChatCompletionsCommon() {}

private static final ObjectMapper objectMapper = new ObjectMapper();

static final String EMPTY_JSON_OBJECT = "{}";
static final Map<String, Object> EMPTY_PARAMETERS_SCHEMA =
Map.of("type", "object", "properties", Map.of());

public static final String ROLE_ASSISTANT = "assistant";
public static final String ROLE_MODEL = "model";

Expand Down Expand Up @@ -157,6 +161,18 @@ public Part applyThoughtSignature(Part part) {
}
}

/**
* Robust defense: Function arguments and responses MUST be JSON objects. If the LLM hallucinates
* "null", "NULL", "none", or conversational text, we fallback to an empty JSON object "{}". This
* prevents OpenAI-compatible proxies (like Groq) from throwing 400 Bad Request errors.
*/
static String enforceJsonObject(String json) {
if (json == null || !json.trim().startsWith("{")) {
return EMPTY_JSON_OBJECT;
}
return json.trim();
}

/**
* See
* https://developers.openai.com/api/reference/resources/chat#(resource)%20chat.completions%20%3E%20(model)%20chat_completion_message_function_tool_call%20%3E%20(schema)
Expand All @@ -181,21 +197,27 @@ public FunctionCall toFunctionCall(@Nullable String toolCallId) {
if (name != null) {
fcBuilder.name(name);
}
if (arguments != null && !arguments.isEmpty()) {
try {
Map<String, Object> args =
objectMapper.readValue(arguments, new TypeReference<Map<String, Object>>() {});
fcBuilder.args(args);
} catch (Exception e) {
throw new IllegalArgumentException(
"Failed to parse function arguments JSON: " + arguments, e);
}
}
fcBuilder.args(parseArguments(arguments));
if (toolCallId != null) {
fcBuilder.id(toolCallId);
}
return fcBuilder.build();
}

private Map<String, Object> parseArguments(String arguments) {
if (arguments == null || arguments.trim().isEmpty()) {
return Map.of();
}
try {
String json = enforceJsonObject(arguments);
Map<String, Object> result =
objectMapper.readValue(json, new TypeReference<Map<String, Object>>() {});
return result != null ? result : Map.of();
} catch (Exception e) {
throw new IllegalArgumentException(
"Failed to parse function arguments JSON: " + arguments, e);
}
}
}

/**
Expand Down
56 changes: 47 additions & 9 deletions core/src/main/java/com/google/adk/models/chat/ChatCompletionsRequest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -21,8 +21,12 @@
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonValue;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.module.SimpleModule;
import com.google.adk.JsonBaseModel;
import com.google.adk.models.LlmRequest;
import com.google.common.collect.ImmutableList;
Expand All @@ -32,6 +36,8 @@
import com.google.genai.types.FunctionResponse;
import com.google.genai.types.GenerateContentConfig;
import com.google.genai.types.Part;
import com.google.genai.types.Type;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Base64;
import java.util.List;
Expand Down Expand Up @@ -270,7 +276,28 @@ public final class ChatCompletionsRequest {
public Map<String, Object> extraBody;

private static final Logger logger = LoggerFactory.getLogger(ChatCompletionsRequest.class);
private static final ObjectMapper objectMapper = JsonBaseModel.getMapper();

/**
* Registers a custom serializer to force JSON Schema types to lowercase (e.g., "STRING" ->
* "string"). The genai SDK uses uppercase Enums for schema types, which strict OpenAI-compatible
* endpoints reject with HTTP 400.
*/
private static SimpleModule schemaNormalizerModule() {
SimpleModule module = new SimpleModule();
module.addSerializer(
Type.class,
new JsonSerializer<Type>() {
@Override
public void serialize(Type value, JsonGenerator gen, SerializerProvider serializers)
throws IOException {
gen.writeString(value.toString().toLowerCase());
}
});
return module;
}

private static final ObjectMapper objectMapper =
JsonBaseModel.getMapper().copy().registerModule(schemaNormalizerModule());

/**
* Converts a standard {@link LlmRequest} into a {@link ChatCompletionsRequest} for
Expand Down Expand Up @@ -473,10 +500,14 @@ private static ChatCompletionsCommon.ToolCall processFunctionCallPart(Part part)
function.name = fc.name().orElse("");
if (fc.args().isPresent()) {
try {
function.arguments = objectMapper.writeValueAsString(fc.args().get());
String json = objectMapper.writeValueAsString(fc.args().get());
function.arguments = ChatCompletionsCommon.enforceJsonObject(json);
} catch (Exception e) {
logger.warn("Failed to serialize function arguments", e);
function.arguments = ChatCompletionsCommon.EMPTY_JSON_OBJECT;
}
} else {
function.arguments = ChatCompletionsCommon.EMPTY_JSON_OBJECT;
}
toolCall.function = function;
part.thoughtSignature()
Expand All @@ -502,10 +533,14 @@ private static Message processFunctionResponsePart(Part part) {
toolResp.toolCallId = fr.id().orElse("");
if (fr.response().isPresent()) {
try {
toolResp.content = new MessageContent(objectMapper.writeValueAsString(fr.response().get()));
String json = objectMapper.writeValueAsString(fr.response().get());
toolResp.content = new MessageContent(ChatCompletionsCommon.enforceJsonObject(json));
} catch (Exception e) {
logger.warn("Failed to serialize tool response", e);
toolResp.content = new MessageContent(ChatCompletionsCommon.EMPTY_JSON_OBJECT);
}
} else {
toolResp.content = new MessageContent(ChatCompletionsCommon.EMPTY_JSON_OBJECT);
}
return toolResp;
}
Expand Down Expand Up @@ -570,12 +605,15 @@ private static void handleTools(GenerateContentConfig config, ChatCompletionsReq
FunctionDefinition def = new FunctionDefinition();
def.name = fd.name().orElse("");
def.description = fd.description().orElse("");
fd.parameters()
.ifPresent(
params ->
def.parameters =
objectMapper.convertValue(
params, new TypeReference<Map<String, Object>>() {}));
if (fd.parameters().isPresent()) {
def.parameters =
objectMapper.convertValue(
fd.parameters().get(), new TypeReference<Map<String, Object>>() {});
} else {
// OpenAI-compatible APIs (like Groq) strictly require the parameters object
// to exist, even for zero-argument functions.
def.parameters = ChatCompletionsCommon.EMPTY_PARAMETERS_SCHEMA;
}
tool.function = def;
tools.add(tool);
}
Expand Down
83 changes: 81 additions & 2 deletions core/src/test/java/com/google/adk/models/chat/ChatCompletionsRequestTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,7 @@
import com.google.genai.types.FunctionResponse;
import com.google.genai.types.GenerateContentConfig;
import com.google.genai.types.Part;
import com.google.genai.types.Schema;
import com.google.genai.types.Tool;
import com.google.genai.types.ToolConfig;
import java.util.AbstractMap;
Expand Down Expand Up @@ -567,6 +568,84 @@ public void testFromLlmRequest_withFunctionCall() throws Exception {
assertThat(msg.toolCalls.get(0).function.arguments).isEqualTo("{\"location\":\"Paris\"}");
}

@Test
public void testFromLlmRequest_withAbsentFunctionArguments() throws Exception {
FunctionCall functionCall = FunctionCall.builder().id("call_123").name("get_time").build();
Part part = Part.builder().functionCall(functionCall).build();
Content content = Content.builder().role("model").parts(ImmutableList.of(part)).build();

LlmRequest llmRequest =
LlmRequest.builder().model("gemini-1.5-pro").contents(ImmutableList.of(content)).build();

ChatCompletionsRequest request = ChatCompletionsRequest.fromLlmRequest(llmRequest, false);

assertThat(request.messages).hasSize(1);
ChatCompletionsRequest.Message msg = request.messages.get(0);
assertThat(msg.role).isEqualTo("assistant");
assertThat(msg.toolCalls).hasSize(1);
assertThat(msg.toolCalls.get(0).function.name).isEqualTo("get_time");
assertThat(msg.toolCalls.get(0).function.arguments).isEqualTo("{}");
}

@Test
public void testFromLlmRequest_withAbsentParameters() throws Exception {
FunctionDeclaration function =
FunctionDeclaration.builder().name("test_func").description("A test function").build();

Tool tool = Tool.builder().functionDeclarations(ImmutableList.of(function)).build();
GenerateContentConfig config =
GenerateContentConfig.builder().tools(ImmutableList.of(tool)).build();

LlmRequest llmRequest =
LlmRequest.builder()
.model("gemini-1.5-pro")
.config(config)
.contents(ImmutableList.of())
.build();

ChatCompletionsRequest request = ChatCompletionsRequest.fromLlmRequest(llmRequest, false);

assertThat(request.tools).hasSize(1);
Map<String, Object> params = (Map<String, Object>) request.tools.get(0).function.parameters;
assertThat(params.get("type")).isEqualTo("object");
@SuppressWarnings("unchecked")
Map<String, Object> props = (Map<String, Object>) params.get("properties");
assertThat(props).isEmpty();
}

@Test
public void testFromLlmRequest_normalizesSchemaTypeToLowerCase() throws Exception {
Schema param1Schema = Schema.builder().type("STRING").build();

Schema functionSchema =
Schema.builder().type("OBJECT").properties(ImmutableMap.of("param1", param1Schema)).build();

FunctionDeclaration function =
FunctionDeclaration.builder().name("test_func").parameters(functionSchema).build();

Tool tool = Tool.builder().functionDeclarations(ImmutableList.of(function)).build();
GenerateContentConfig config =
GenerateContentConfig.builder().tools(ImmutableList.of(tool)).build();

LlmRequest llmRequest =
LlmRequest.builder()
.model("gemini-1.5-pro")
.config(config)
.contents(ImmutableList.of())
.build();

ChatCompletionsRequest request = ChatCompletionsRequest.fromLlmRequest(llmRequest, false);

assertThat(request.tools).hasSize(1);
Map<String, Object> params = (Map<String, Object>) request.tools.get(0).function.parameters;
assertThat(params.get("type")).isEqualTo("object");
@SuppressWarnings("unchecked")
Map<String, Object> props = (Map<String, Object>) params.get("properties");
@SuppressWarnings("unchecked")
Map<String, Object> param1 = (Map<String, Object>) props.get("param1");
assertThat(param1.get("type")).isEqualTo("string");
}

@Test
public void testFromLlmRequest_withStreamOptions() throws Exception {
LlmRequest llmRequest =
Expand Down Expand Up @@ -628,11 +707,11 @@ public void testFromLlmRequest_withFunctionResponse() throws Exception {

assertThat(request.messages.get(1).role).isEqualTo("tool");
assertThat(request.messages.get(1).toolCallId).isEmpty();
assertThat(request.messages.get(1).content).isNull();
assertThat(request.messages.get(1).content.getValue()).isEqualTo("{}");

assertThat(request.messages.get(2).role).isEqualTo("tool");
assertThat(request.messages.get(2).toolCallId).isEqualTo("call_faulty");
assertThat(request.messages.get(2).content).isNull();
assertThat(request.messages.get(2).content.getValue()).isEqualTo("{}");
}

@Test
Expand Down