fix: skip empty-content assistant messages in Bedrock translator

internal/translator/openai_awsbedrock.go

@@ -521,7 +521,11 @@ func (o *openAIToAWSBedrockTranslatorV1ChatCompletion) openAIMessageToBedrockMes
 			if err != nil {
 				return err
 			}
-			bedrockReq.Messages = append(bedrockReq.Messages, bedrockMessage)
+			// Some clients, like OpenCode, can send assistant messages with nil or empty string content and no tool calls,
+			// which would translate to an empty content array that Bedrock Converse rejects.
+			if len(bedrockMessage.Content) > 0 {
+				bedrockReq.Messages = append(bedrockReq.Messages, bedrockMessage)
+			}
 		case msg.OfSystem != nil:
 			if bedrockReq.System == nil {
 				bedrockReq.System = make([]*awsbedrock.SystemContentBlock, 0)

internal/translator/openai_awsbedrock_test.go

@@ -225,10 +225,6 @@ func TestOpenAIToAWSBedrockTranslatorV1ChatCompletion_RequestBody(t *testing.T)
 							},
 						},
 					},
-					{
-						Role:    openai.ChatMessageRoleAssistant,
-						Content: []*awsbedrock.ContentBlock{},
-					},
 				},
 			},
 		},
@@ -2582,3 +2578,110 @@ func TestCacheControlHelpers(t *testing.T) {
 		require.Nil(t, cachePoint3)
 	})
 }
+
+func TestOpenAIToAWSBedrockTranslator_EmptyContentMessages(t *testing.T) {
+	t.Run("empty assistant message without tool calls is dropped", func(t *testing.T) {
+		for _, name := range []string{"empty string", "nil content"} {
+			t.Run(name, func(t *testing.T) {
+				assistantMsg := &openai.ChatCompletionAssistantMessageParam{
+					Role: openai.ChatMessageRoleAssistant,
+				}
+				if name == "empty string" {
+					assistantMsg.Content = openai.StringOrAssistantRoleContentUnion{Value: ""}
+				}
+
+				o := &openAIToAWSBedrockTranslatorV1ChatCompletion{}
+				req := openai.ChatCompletionRequest{
+					Model: "anthropic.claude-3-5-sonnet-20241022-v2:0",
+					Messages: []openai.ChatCompletionMessageParamUnion{
+						{OfUser: &openai.ChatCompletionUserMessageParam{Role: openai.ChatMessageRoleUser, Content: openai.StringOrUserRoleContentUnion{Value: "Hello"}}},
+						{OfAssistant: assistantMsg},
+						{OfUser: &openai.ChatCompletionUserMessageParam{Role: openai.ChatMessageRoleUser, Content: openai.StringOrUserRoleContentUnion{Value: "Can you help?"}}},
+					},
+				}
+
+				_, newBody, err := o.RequestBody(nil, &req, false)
+				require.NoError(t, err)
+
+				var awsReq awsbedrock.ConverseInput
+				require.NoError(t, json.Unmarshal(newBody, &awsReq))
+				requireNoEmptyAssistantContent(t, awsReq.Messages)
+			})
+		}
+	})
+
+	t.Run("assistant message with only tool calls and no content should work", func(t *testing.T) {
+		o := &openAIToAWSBedrockTranslatorV1ChatCompletion{}
+		req := openai.ChatCompletionRequest{
+			Model: "anthropic.claude-3-5-sonnet-20241022-v2:0",
+			Messages: []openai.ChatCompletionMessageParamUnion{
+				{OfUser: &openai.ChatCompletionUserMessageParam{Role: openai.ChatMessageRoleUser, Content: openai.StringOrUserRoleContentUnion{Value: "What is the weather?"}}},
+				{OfAssistant: &openai.ChatCompletionAssistantMessageParam{
+					Role: openai.ChatMessageRoleAssistant,
+					ToolCalls: []openai.ChatCompletionMessageToolCallParam{
+						{ID: ptr.To("call_abc123"), Type: openai.ChatCompletionMessageToolCallTypeFunction, Function: openai.ChatCompletionMessageToolCallFunctionParam{Name: "get_weather", Arguments: `{"location":"NYC"}`}},
+					},
+				}},
+				{OfTool: &openai.ChatCompletionToolMessageParam{Role: openai.ChatMessageRoleTool, ToolCallID: "call_abc123", Content: openai.ContentUnion{Value: `{"temp":72}`}}},
+			},
+		}
+
+		_, newBody, err := o.RequestBody(nil, &req, false)
+		require.NoError(t, err)
+
+		var awsReq awsbedrock.ConverseInput
+		require.NoError(t, json.Unmarshal(newBody, &awsReq))
+
+		var foundAssistant bool
+		for _, msg := range awsReq.Messages {
+			if msg.Role == openai.ChatMessageRoleAssistant {
+				foundAssistant = true
+				require.NotEmpty(t, msg.Content, "assistant message with tool calls should have non-empty content")
+				require.NotNil(t, msg.Content[0].ToolUse, "expected a ToolUse block")
+				require.Equal(t, "get_weather", msg.Content[0].ToolUse.Name)
+			}
+		}
+		require.True(t, foundAssistant, "should have found an assistant message")
+	})
+
+	t.Run("mixed messages with some empty assistant messages should handle correctly", func(t *testing.T) {
+		o := &openAIToAWSBedrockTranslatorV1ChatCompletion{}
+		req := openai.ChatCompletionRequest{
+			Model: "anthropic.claude-3-5-sonnet-20241022-v2:0",
+			Messages: []openai.ChatCompletionMessageParamUnion{
+				{OfUser: &openai.ChatCompletionUserMessageParam{Role: openai.ChatMessageRoleUser, Content: openai.StringOrUserRoleContentUnion{Value: "Hello"}}},
+				{OfAssistant: &openai.ChatCompletionAssistantMessageParam{Role: openai.ChatMessageRoleAssistant, Content: openai.StringOrAssistantRoleContentUnion{Value: ""}}},
+				{OfUser: &openai.ChatCompletionUserMessageParam{Role: openai.ChatMessageRoleUser, Content: openai.StringOrUserRoleContentUnion{Value: "Tell me more"}}},
+				{OfAssistant: &openai.ChatCompletionAssistantMessageParam{Role: openai.ChatMessageRoleAssistant, Content: openai.StringOrAssistantRoleContentUnion{Value: "Here is the info"}}},
+			},
+		}
+
+		_, newBody, err := o.RequestBody(nil, &req, false)
+		require.NoError(t, err)
+
+		var awsReq awsbedrock.ConverseInput
+		require.NoError(t, json.Unmarshal(newBody, &awsReq))
+		requireNoEmptyAssistantContent(t, awsReq.Messages)
+
+		var assistantWithContent bool
+		for _, msg := range awsReq.Messages {
+			if msg.Role == openai.ChatMessageRoleAssistant {
+				for _, block := range msg.Content {
+					if block.Text != nil && *block.Text == "Here is the info" {
+						assistantWithContent = true
+					}
+				}
+			}
+		}
+		require.True(t, assistantWithContent, "should preserve assistant message with actual content")
+	})
+}
+
+func requireNoEmptyAssistantContent(t *testing.T, messages []*awsbedrock.Message) {
+	t.Helper()
+	for i, msg := range messages {
+		if msg.Role == openai.ChatMessageRoleAssistant && len(msg.Content) == 0 {
+			t.Errorf("message at index %d is an assistant message with empty content array, which Bedrock will reject", i)
+		}
+	}
+}