[Go] Streaming responses contain empty content parts that break OpenAI serialization #3606
Description
Describe the bug
When using ai.WithStreaming(), response messages contain empty content parts that cause OpenAI API failures when used as conversation history with ai.WithMessages(). The empty parts get serialized as null content fields, resulting in: Invalid value for 'content': expected a string, got null errors.
To Reproduce
package main
import (
"context"
"os"
"github.com/firebase/genkit/go/ai"
"github.com/firebase/genkit/go/genkit"
"github.com/firebase/genkit/go/plugins/compat_oai/openai"
)
func main() {
g := genkit.Init(context.Background(),
genkit.WithPlugins(&openai.OpenAI{APIKey: os.Getenv("OPENAI_API_KEY")}),
genkit.WithDefaultModel("openai/gpt-4o-mini"),
)
// Step 1: Streaming request (works fine)
resp, _ := genkit.Generate(context.Background(), g,
ai.WithMessages(ai.NewUserTextMessage("My favorite color is blue")),
ai.WithStreaming(func(ctx context.Context, chunk *ai.ModelResponseChunk) error {
return nil
}),
)
// resp.Message.Content now contains empty parts at [0] and [last]
// Step 2: Use response in conversation history (fails)
history := []*ai.Message{
ai.NewUserTextMessage("My favorite color is blue"),
resp.Message, // Contains empty content parts
}
// This fails with 400 Bad Request
_, err := genkit.Generate(context.Background(), g,
ai.WithMessages(history...),
ai.WithPrompt("What is my favorite color?"),
)
// Error: "Invalid value for 'content': expected a string, got null."
}Expected behavior
Streaming responses should not contain empty content parts, or the OpenAI compatibility layer should handle them properly. Using streaming response messages as
conversation history should work seamlessly.
Screenshots
N /A
Runtime (please complete the following information):
- OS: MacOS
- Version Sequoia 15.6.1
** Go version
go version go1.25.1 darwin/arm64
Additional context
This affects a common use case - storing LLM responses for conversation history in chatbots/agents. Workaround is to filter empty parts before storing:
var cleanParts []*ai.Part
for _, part := range resp.Message.Content {
if part.Text != "" {
cleanParts = append(cleanParts, part)
}
}