samplingMessagesToChat converts an MCP CreateMessageParams into the host's chat.Message slice. The optional system prompt is prepended; per-message Content is mapped from the supported MCP block types. Oversized payloads and nil/unsupported entries surface as errors so the request is rejected rather
(req *mcp.CreateMessageParams)
| 101 | // Oversized payloads and nil/unsupported entries surface as errors so |
| 102 | // the request is rejected rather than silently truncated. |
| 103 | func samplingMessagesToChat(req *mcp.CreateMessageParams) ([]chat.Message, error) { |
| 104 | if len(req.Messages) == 0 { |
| 105 | return nil, errors.New("sampling request contains no messages") |
| 106 | } |
| 107 | if len(req.Messages) > maxSamplingMessages { |
| 108 | return nil, fmt.Errorf("sampling request contains %d messages (limit %d)", |
| 109 | len(req.Messages), maxSamplingMessages) |
| 110 | } |
| 111 | |
| 112 | messages := make([]chat.Message, 0, len(req.Messages)+1) |
| 113 | if req.SystemPrompt != "" { |
| 114 | if len(req.SystemPrompt) > maxSamplingTextBytes { |
| 115 | return nil, fmt.Errorf("sampling system prompt is too large (%d bytes, limit %d)", |
| 116 | len(req.SystemPrompt), maxSamplingTextBytes) |
| 117 | } |
| 118 | messages = append(messages, chat.Message{ |
| 119 | Role: chat.MessageRoleSystem, |
| 120 | Content: req.SystemPrompt, |
| 121 | }) |
| 122 | } |
| 123 | for i, m := range req.Messages { |
| 124 | if m == nil { |
| 125 | return nil, fmt.Errorf("sampling message at index %d is nil", i) |
| 126 | } |
| 127 | role, err := samplingRoleToChat(m.Role) |
| 128 | if err != nil { |
| 129 | return nil, err |
| 130 | } |
| 131 | text, parts, err := samplingContentToChat(m.Content) |
| 132 | if err != nil { |
| 133 | return nil, fmt.Errorf("sampling message at index %d: %w", i, err) |
| 134 | } |
| 135 | messages = append(messages, chat.Message{ |
| 136 | Role: role, |
| 137 | Content: text, |
| 138 | MultiContent: parts, |
| 139 | }) |
| 140 | } |
| 141 | return messages, nil |
| 142 | } |
| 143 | |
| 144 | func samplingRoleToChat(r mcp.Role) (chat.MessageRole, error) { |
| 145 | switch string(r) { |