feat: enhance ensureDataURIPrefix to detect MIME types and trim whitespace

Author: ilopezluna

pkg/ollama/http_handler.go

@@ -724,17 +724,33 @@ func (h *HTTPHandler) mapOllamaOptionsToOpenAI(ollamaOpts map[string]interface{}
 // OpenWebUI may send raw base64 data without prefix, but llama.cpp requires it.
 // This function:
 // - Returns data as-is if it already starts with "data:", "http://", or "https://"
-// - Prepends "data:image/jpeg;base64," to raw base64 strings
+// - Detects MIME type from base64 prefix and prepends appropriate data URI
 func ensureDataURIPrefix(imageData string) string {
+	// Trim whitespace that might come from UIs
+	imageData = strings.TrimSpace(imageData)
+
 	// Check if already has a URI scheme
 	if strings.HasPrefix(imageData, "data:") ||
 		strings.HasPrefix(imageData, "http://") ||
 		strings.HasPrefix(imageData, "https://") {
 		return imageData
 	}
 
-	// Assume raw base64 data - add data URI prefix
-	return "data:image/jpeg;base64," + imageData
+	// Detect MIME type from base64 prefix
+	var mimeType string
+	if strings.HasPrefix(imageData, "/9j/") {
+		mimeType = "image/jpeg"
+	} else if strings.HasPrefix(imageData, "iVBOR") {
+		mimeType = "image/png"
+	} else if strings.HasPrefix(imageData, "R0lG") {
+		mimeType = "image/gif"
+	} else {
+		// Default to jpeg for unknown formats
+		mimeType = "image/jpeg"
+	}
+
+	// Assume raw base64 data - add data URI prefix with detected MIME type
+	return "data:" + mimeType + ";base64," + imageData
 }
 
 // convertMessages converts Ollama messages to OpenAI format
@@ -748,7 +764,11 @@ func convertMessages(messages []Message) []map[string]interface{} {
 		// Handle multimodal content (text + images)
 		if len(msg.Images) > 0 {
 			// Convert to OpenAI multimodal format: content is an array of content objects
-			var contentArray []map[string]interface{}
+			contentArraySize := len(msg.Images)
+			if msg.Content != "" {
+				contentArraySize++
+			}
+			contentArray := make([]map[string]interface{}, 0, contentArraySize)
 
 			// Add text content if present
 			if msg.Content != "" {

pkg/ollama/http_handler_test.go

@@ -91,6 +91,32 @@ func TestConvertMessages_Multimodal(t *testing.T) {
 			// Note: JSON field order follows struct definition
 			expected: `[{"content":"Let me call a function","role":"assistant","tool_calls":[{"id":"call_123","type":"function","function":{"name":"get_weather","arguments":"{\"location\":\"San Francisco\"}"}}]}]`,
 		},
+		{
+			name: "tool result message with tool_call_id",
+			messages: []Message{
+				{
+					Role:       "tool",
+					Content:    "The weather in San Francisco is sunny, 72°F",
+					ToolCallID: "call_123",
+				},
+			},
+			expected: `[{"content":"The weather in San Francisco is sunny, 72°F","role":"tool","tool_call_id":"call_123"}]`,
+		},
+		{
+			name: "multiple raw base64 images without prefix",
+			messages: []Message{
+				{
+					Role:    "user",
+					Content: "Compare these two images",
+					Images: []string{
+						"/9j/4AAQSkZJRgABAQEBLA...",
+						"iVBORw0KGgoAAAANSUhEUgAAA...",
+					},
+				},
+			},
+			// Should auto-detect MIME types and add appropriate prefixes
+			expected: `[{"content":[{"text":"Compare these two images","type":"text"},{"image_url":{"url":"data:image/jpeg;base64,/9j/4AAQSkZJRgABAQEBLA..."},"type":"image_url"},{"image_url":{"url":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAA..."},"type":"image_url"}],"role":"user"}]`,
+		},
 	}
 
 	for _, tt := range tests {
@@ -118,10 +144,20 @@ func TestEnsureDataURIPrefix(t *testing.T) {
 		expected string
 	}{
 		{
-			name:     "raw base64 without prefix",
+			name:     "raw JPEG base64 without prefix",
 			input:    "/9j/4AAQSkZJRgABAQEBLA...",
 			expected: "data:image/jpeg;base64,/9j/4AAQSkZJRgABAQEBLA...",
 		},
+		{
+			name:     "raw PNG base64 without prefix",
+			input:    "iVBORw0KGgoAAAANSUhEUgAAA...",
+			expected: "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAA...",
+		},
+		{
+			name:     "raw GIF base64 without prefix",
+			input:    "R0lGODlhAQABAIAAAAAAAP...",
+			expected: "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP...",
+		},
 		{
 			name:     "already has data URI prefix",
 			input:    "data:image/jpeg;base64,/9j/4AAQSkZJRgABAQEBLA...",
@@ -142,6 +178,16 @@ func TestEnsureDataURIPrefix(t *testing.T) {
 			input:    "https://example.com/image.jpg",
 			expected: "https://example.com/image.jpg",
 		},
+		{
+			name:     "empty string",
+			input:    "",
+			expected: "data:image/jpeg;base64,",
+		},
+		{
+			name:     "whitespace with base64",
+			input:    "  /9j/4AAQSkZJRgABAQEBLA...  ",
+			expected: "data:image/jpeg;base64,/9j/4AAQSkZJRgABAQEBLA...",
+		},
 	}
 
 	for _, tt := range tests {