Struct Message 

pub struct Message {
    pub role: String,
    pub name: Option<String>,
    pub content: Option<String>,
    pub tool_calls: Option<Vec<ToolCall>>,
    pub tool_call_id: Option<String>,
    pub image_base64: Option<String>,
}

One message in an OpenAI Chat Completions conversation. Spec: https://platform.openai.com/docs/api-reference/chat/create#chat/create-messages

One struct, four roles (system / user / assistant / tool); each role uses a different subset of the optional fields. skip_serializing_if on every Option prunes irrelevant fields at serialization, so the wire JSON for each role only carries what OpenAI expects:

system → role + content user → role + content (+ optional name for multi-user) assistant → role + content (may be null when only tool_calls are emitted) + optional tool_calls[] tool → role + content + tool_call_id (must match an id in the preceding assistant.tool_calls)

We use a flat struct with optional fields rather than a tagged enum because the planner does a lot of generic Vec manipulation (trim, sanitize, sliding-window slicing) that’s awkward to express through match on every access. Type-safety for “tool messages must have tool_call_id” is delegated to runtime checks (history::sanitize_for_vlm) and the OpenAI server’s own validation.

image_base64 is a robonix-side simplification, NOT part of the OpenAI wire format. Callers set it on a user message; build_openai_messages in this file repackages content + image into OpenAI’s multimodal content array ([{type:"text",...}, {type:"image_url",...}]) at request time.

Fields

role: String

“system” / “user” / “assistant” / “tool”. Determines which other fields are meaningful; OpenAI rejects mismatched combinations.

name: Option<String>

Optional sender name. Used by user/assistant for multi-user disambiguation; rare in practice. Robonix doesn’t set it today.

content: Option<String>

Message text. Always present except on assistant messages whose only output is tool calls (then None / null on the wire).

tool_calls: Option<Vec<ToolCall>>

Tool calls the LLM decided to make. Present only on assistant messages. Each entry carries id + function.{name, arguments}; the corresponding tool message links back via tool_call_id.

tool_call_id: Option<String>

Correlates a tool result back to the assistant.tool_calls[].id that produced it. Required on tool messages; absent on others.

image_base64: Option<String>

Inline image attached to a user message (base64-encoded JPEG bytes). Robonix-only field; rewritten into OpenAI’s multimodal content array at serialize time by build_openai_messages.

Implementations

impl Message

pub fn system(content: &str) -> Self

pub fn user(content: &str) -> Self

pub fn user_with_image(content: &str, image_base64: String) -> Self

pub fn assistant(content: &str) -> Self

pub fn tool_result(id: &str, content: &str) -> Self

Trait Implementations

impl Clone for Message

fn clone(&self) -> Message

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'de> Deserialize<'de> for Message

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for Message

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.