Add regression tests for SSE comment lines from OpenRouter (#2349)

The OpenAI Go SDK (v3.30.0) already handles SSE comment lines correctly,
so no code fix is needed. Add regression tests for both ChatCompletions
and Responses API paths to ensure SSE comments (e.g. ': OPENROUTER
PROCESSING') don't cause 'unexpected end of JSON input' errors.

Closes #2349

Assisted-By: docker-agent

Author: dgageot

pkg/model/provider/openai/sse_comment_test.go

@@ -0,0 +1,195 @@
+package openai
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/docker/docker-agent/pkg/chat"
+	"github.com/docker/docker-agent/pkg/config/latest"
+	"github.com/docker/docker-agent/pkg/environment"
+)
+
+// writeSSEWithComments writes an SSE response prefixed with comment lines
+// (starting with ':'), as sent by providers like OpenRouter during initial
+// processing. Per the SSE spec, comment lines must be ignored by clients.
+// This is used to verify the fix for https://github.com/docker/docker-agent/issues/2349.
+func writeSSEWithComments(w http.ResponseWriter, sseLines []string) {
+	w.Header().Set("Content-Type", "text/event-stream")
+	flusher, _ := w.(http.Flusher)
+
+	// Comment lines like OpenRouter sends during processing
+	_, _ = fmt.Fprint(w, ": OPENROUTER PROCESSING\n")
+	_, _ = fmt.Fprint(w, ": OPENROUTER PROCESSING\n")
+
+	for _, line := range sseLines {
+		_, _ = fmt.Fprint(w, line+"\n")
+	}
+	flusher.Flush()
+}
+
+// TestCustomProvider_SSECommentLines_ChatCompletions is a regression test for
+// https://github.com/docker/docker-agent/issues/2349
+//
+// OpenRouter sends SSE comment lines (": OPENROUTER PROCESSING") before the
+// actual data events. This test verifies those comments don't cause
+// "unexpected end of JSON input" errors during streaming.
+func TestCustomProvider_SSECommentLines_ChatCompletions(t *testing.T) {
+	t.Parallel()
+
+	chunks := []map[string]any{
+		{
+			"id": "gen-123", "object": "chat.completion.chunk", "model": "test",
+			"choices": []map[string]any{{"index": 0, "delta": map[string]any{"role": "assistant", "content": ""}, "finish_reason": nil}},
+		},
+		{
+			"id": "gen-123", "object": "chat.completion.chunk", "model": "test",
+			"choices": []map[string]any{{"index": 0, "delta": map[string]any{"content": "hello"}, "finish_reason": nil}},
+		},
+		{
+			"id": "gen-123", "object": "chat.completion.chunk", "model": "test",
+			"choices": []map[string]any{{"index": 0, "delta": map[string]any{}, "finish_reason": "stop"}},
+		},
+		{
+			"id": "gen-123", "object": "chat.completion.chunk", "model": "test",
+			"choices": []map[string]any{}, "usage": map[string]any{"prompt_tokens": 10, "completion_tokens": 1, "total_tokens": 11},
+		},
+	}
+
+	var sseLines []string
+	for _, chunk := range chunks {
+		data, _ := json.Marshal(chunk)
+		sseLines = append(sseLines, "data: "+string(data), "")
+	}
+	sseLines = append(sseLines, "data: [DONE]", "")
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		writeSSEWithComments(w, sseLines)
+	}))
+	defer server.Close()
+
+	cfg := &latest.ModelConfig{
+		Provider: "openrouter",
+		Model:    "test-model",
+		BaseURL:  server.URL,
+		TokenKey: "OPENROUTER_API_KEY",
+		ProviderOpts: map[string]any{
+			"api_type": "openai_chatcompletions",
+		},
+	}
+	env := environment.NewMapEnvProvider(map[string]string{
+		"OPENROUTER_API_KEY": "test-key",
+	})
+
+	client, err := NewClient(t.Context(), cfg, env)
+	require.NoError(t, err)
+
+	stream, err := client.CreateChatCompletionStream(
+		t.Context(),
+		[]chat.Message{{Role: chat.MessageRoleUser, Content: "hello"}},
+		nil,
+	)
+	require.NoError(t, err)
+	defer stream.Close()
+
+	var content strings.Builder
+	for {
+		chunk, err := stream.Recv()
+		if err != nil {
+			break
+		}
+		for _, choice := range chunk.Choices {
+			content.WriteString(choice.Delta.Content)
+		}
+	}
+
+	assert.Equal(t, "hello", content.String())
+}
+
+// TestCustomProvider_SSECommentLines_Responses is a regression test for
+// https://github.com/docker/docker-agent/issues/2349 using the Responses API
+// path (api_type: openai_responses), which is exactly what the issue reporter
+// was using with OpenRouter.
+func TestCustomProvider_SSECommentLines_Responses(t *testing.T) {
+	t.Parallel()
+
+	events := []map[string]any{
+		{"type": "response.output_text.delta", "delta": "hello", "item_id": "item-1"},
+		{
+			"type": "response.completed",
+			"response": map[string]any{
+				"id":     "resp-123",
+				"status": "completed",
+				"output": []map[string]any{
+					{"type": "message", "id": "item-1"},
+				},
+				"usage": map[string]any{
+					"input_tokens":  10,
+					"output_tokens": 1,
+					"total_tokens":  11,
+					"input_tokens_details": map[string]any{
+						"cached_tokens": 0,
+					},
+					"output_tokens_details": map[string]any{
+						"reasoning_tokens": 0,
+					},
+				},
+			},
+		},
+	}
+
+	var sseLines []string
+	for _, event := range events {
+		data, _ := json.Marshal(event)
+		eventType := event["type"].(string)
+		sseLines = append(sseLines, "event: "+eventType, "data: "+string(data), "")
+	}
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		writeSSEWithComments(w, sseLines)
+	}))
+	defer server.Close()
+
+	cfg := &latest.ModelConfig{
+		Provider: "openrouter",
+		Model:    "test-model",
+		BaseURL:  server.URL,
+		TokenKey: "OPENROUTER_API_KEY",
+		ProviderOpts: map[string]any{
+			"api_type": "openai_responses",
+		},
+	}
+	env := environment.NewMapEnvProvider(map[string]string{
+		"OPENROUTER_API_KEY": "test-key",
+	})
+
+	client, err := NewClient(t.Context(), cfg, env)
+	require.NoError(t, err)
+
+	stream, err := client.CreateChatCompletionStream(
+		t.Context(),
+		[]chat.Message{{Role: chat.MessageRoleUser, Content: "hello"}},
+		nil,
+	)
+	require.NoError(t, err)
+	defer stream.Close()
+
+	var content strings.Builder
+	for {
+		chunk, err := stream.Recv()
+		if err != nil {
+			break
+		}
+		for _, choice := range chunk.Choices {
+			content.WriteString(choice.Delta.Content)
+		}
+	}
+
+	assert.Equal(t, "hello", content.String())
+}