fix(openai): handle mixed content and tool call stream chunks

providers/openai/language_model.go

@@ -349,8 +349,7 @@ func (o languageModel) Stream(ctx context.Context, call fantasy.Call) (fantasy.S
 				if choice.FinishReason != "" {
 					finishReason = choice.FinishReason
 				}
-				switch {
-				case choice.Delta.Content != "":
+				if choice.Delta.Content != "" {
 					if !isActiveText {
 						isActiveText = true
 						if !yield(fantasy.StreamPart{
@@ -367,7 +366,8 @@ func (o languageModel) Stream(ctx context.Context, call fantasy.Call) (fantasy.S
 					}) {
 						return
 					}
-				case len(choice.Delta.ToolCalls) > 0:
+				}
+				if len(choice.Delta.ToolCalls) > 0 {
 					if isActiveText {
 						isActiveText = false
 						if !yield(fantasy.StreamPart{

providers/openai/openai_test.go

@@ -2288,6 +2288,16 @@ func (sms *streamingMockServer) prepareToolStreamResponse() {
 	sms.chunks = chunks
 }
 
+func (sms *streamingMockServer) prepareMixedContentToolStreamResponse() {
+	chunks := []string{
+		`data: {"id":"chatcmpl-mixed","object":"chat.completion.chunk","created":1711357598,"model":"gpt-3.5-turbo-0125","system_fingerprint":"fp_3bc1b5746c","choices":[{"index":0,"delta":{"role":"assistant","content":"thinking before tool","tool_calls":[{"index":0,"id":"call_mixed_content","type":"function","function":{"name":"test-tool","arguments":"{\"value\":\"mixed\"}"}}]},"logprobs":null,"finish_reason":null}]}` + "\n\n",
+		`data: {"id":"chatcmpl-mixed","object":"chat.completion.chunk","created":1711357598,"model":"gpt-3.5-turbo-0125","system_fingerprint":"fp_3bc1b5746c","choices":[{"index":0,"delta":{},"logprobs":null,"finish_reason":"tool_calls"}]}` + "\n\n",
+		`data: {"id":"chatcmpl-mixed","object":"chat.completion.chunk","created":1711357598,"model":"gpt-3.5-turbo-0125","system_fingerprint":"fp_3bc1b5746c","choices":[],"usage":{"prompt_tokens":53,"completion_tokens":17,"total_tokens":70}}` + "\n\n",
+		"data: [DONE]\n\n",
+	}
+	sms.chunks = chunks
+}
+
 func (sms *streamingMockServer) prepareErrorStreamResponse() {
 	chunks := []string{
 		`data: {"error":{"message": "The server had an error processing your request. Sorry about that! You can retry your request, or contact us through our help center at help.openai.com if you keep seeing this error.","type":"server_error","param":null,"code":null}}` + "\n\n",
@@ -2566,6 +2576,74 @@ func TestDoStream(t *testing.T) {
 		require.Equal(t, `{"value":"Sparkle Day"}`, fullInput.String())
 	})
 
+	t.Run("should handle content and tool call deltas in the same chunk", func(t *testing.T) {
+		t.Parallel()
+
+		server := newStreamingMockServer()
+		defer server.close()
+
+		server.prepareMixedContentToolStreamResponse()
+
+		provider, err := New(
+			WithAPIKey("test-api-key"),
+			WithBaseURL(server.server.URL),
+		)
+		require.NoError(t, err)
+		model, _ := provider.LanguageModel(t.Context(), "gpt-3.5-turbo")
+
+		stream, err := model.Stream(context.Background(), fantasy.Call{
+			Prompt: testPrompt,
+			Tools: []fantasy.Tool{
+				fantasy.FunctionTool{
+					Name: "test-tool",
+					InputSchema: map[string]any{
+						"type": "object",
+						"properties": map[string]any{
+							"value": map[string]any{
+								"type": "string",
+							},
+						},
+						"required":             []string{"value"},
+						"additionalProperties": false,
+						"$schema":              "http://json-schema.org/draft-07/schema#",
+					},
+				},
+			},
+		})
+		require.NoError(t, err)
+
+		parts, err := collectStreamParts(stream)
+		require.NoError(t, err)
+
+		var textDeltas []string
+		toolInputStart, toolInputEnd, toolCall := -1, -1, -1
+		for i, part := range parts {
+			switch part.Type {
+			case fantasy.StreamPartTypeTextDelta:
+				textDeltas = append(textDeltas, part.Delta)
+			case fantasy.StreamPartTypeToolInputStart:
+				toolInputStart = i
+				require.Equal(t, "call_mixed_content", part.ID)
+				require.Equal(t, "test-tool", part.ToolCallName)
+			case fantasy.StreamPartTypeToolInputEnd:
+				toolInputEnd = i
+				require.Equal(t, "call_mixed_content", part.ID)
+			case fantasy.StreamPartTypeToolCall:
+				toolCall = i
+				require.Equal(t, "call_mixed_content", part.ID)
+				require.Equal(t, "test-tool", part.ToolCallName)
+				require.Equal(t, `{"value":"mixed"}`, part.ToolCallInput)
+			}
+		}
+
+		require.Equal(t, []string{"thinking before tool"}, textDeltas)
+		require.NotEqual(t, -1, toolInputStart, "expected ToolInputStart part")
+		require.NotEqual(t, -1, toolInputEnd, "expected ToolInputEnd part")
+		require.NotEqual(t, -1, toolCall, "expected ToolCall part")
+		require.Less(t, toolInputStart, toolInputEnd)
+		require.Less(t, toolInputEnd, toolCall)
+	})
+
 	t.Run("should handle tool calls with empty arguments", func(t *testing.T) {
 		t.Parallel()