fix: optimize Gemini stream parsing to support real-time streaming of JSON arrays

internal/providers/helpers.go

@@ -523,9 +523,12 @@ func StreamGemini(ctx io.ReadCloser, model string) (<-chan *models.ChatCompletio
 		first := string(peek[:n])
 
 		if first[0] == '[' {
-			// JSON array format
-			rest, _ := io.ReadAll(ctx)
-			streamGeminiJSONArray(append([]byte(first), rest...), ch, model)
+			// JSON array format — stream parse it in real-time
+			combined := io.MultiReader(
+				strings.NewReader(string(peek[:n])),
+				ctx,
+			)
+			streamGeminiJSONArrayStream(combined, ch, model)
 			return
 		} else if strings.HasPrefix(first, "data:") || strings.HasPrefix(first, "data: ") {
 			// SSE format — pre-pend the peeked bytes then run SSE scanner
@@ -548,35 +551,48 @@ func StreamGemini(ctx io.ReadCloser, model string) (<-chan *models.ChatCompletio
 	return ch, nil
 }
 
-// readAll reads remaining bytes from a reader (keeps the function signature simple
-// for the JSON array fallback path).
-func readAll(r io.Reader) []byte {
-	b, _ := io.ReadAll(r)
-	return b
-}
+func streamGeminiJSONArrayStream(r io.Reader, ch chan<- *models.ChatCompletionStreamResponse, model string) {
+	dec := json.NewDecoder(r)
 
-func streamGeminiJSONArray(data []byte, ch chan<- *models.ChatCompletionStreamResponse, model string) {
-	var chunks []geminiStreamChunk
-	if err := json.Unmarshal(data, &chunks); err != nil {
-		fmt.Printf("[Gemini-Stream] JSON array parse error: %v\n", err)
+	// Read open bracket '['
+	t, err := dec.Token()
+	if err != nil {
+		fmt.Printf("[Gemini-Stream] JSON array token error: %v\n", err)
 		return
 	}
-	// Track the last chunk with usage for the final emission
+	delim, ok := t.(json.Delim)
+	if !ok || delim != '[' {
+		fmt.Printf("[Gemini-Stream] JSON array expected '[', got %v\n", t)
+		return
+	}
+
 	var lastUsage *geminiStreamChunk
-	for i := range chunks {
-		if chunks[i].UsageMetadata.TotalTokenCount > 0 {
-			lastUsage = &chunks[i]
+
+	// Read array elements
+	for dec.More() {
+		var chunk geminiStreamChunk
+		if err := dec.Decode(&chunk); err != nil {
+			fmt.Printf("[Gemini-Stream] JSON array decode error: %v\n", err)
+			return
+		}
+
+		if chunk.UsageMetadata.TotalTokenCount > 0 {
+			temp := chunk
+			lastUsage = &temp
+		}
+
+		// Emit content-bearing chunks immediately
+		if len(chunk.Candidates) > 0 {
+			emitGeminiChunk(ch, &chunk, model)
 		}
 	}
-	if lastUsage != nil {
-		// Emit a synthetic final chunk with usage data
-		if len(lastUsage.Candidates) == 0 && lastUsage.UsageMetadata.TotalTokenCount > 0 {
-			emitGeminiChunk(ch, lastUsage, model)
-		}
-	}
-	// Also emit each content-bearing chunk
-	for i := range chunks {
-		emitGeminiChunk(ch, &chunks[i], model)
+
+	// Read close bracket ']'
+	_, _ = dec.Token()
+
+	// Emit synthetic final chunk with usage if we collected it and it was not yet emitted
+	if lastUsage != nil && len(lastUsage.Candidates) == 0 && lastUsage.UsageMetadata.TotalTokenCount > 0 {
+		emitGeminiChunk(ch, lastUsage, model)
 	}
 }