Struct Host 

#[repr(C)]
pub struct Host {
    pub ctx: *mut c_void,
    pub query: Option<extern "C" fn(ctx: *mut c_void, request_json: *const c_char) -> *mut c_char>,
    pub log: Option<extern "C" fn(ctx: *mut c_void, level: i32, message: *const c_char)>,
    pub config: Option<extern "C" fn(ctx: *mut c_void) -> *mut c_char>,
    pub principal_id: Option<extern "C" fn(ctx: *mut c_void) -> *mut c_char>,
    pub hook: Option<extern "C" fn(ctx: *mut c_void) -> *mut c_char>,
    pub free_string: Option<extern "C" fn(ctx: *mut c_void, string: *mut c_char)>,
    pub send_email: Option<extern "C" fn(ctx: *mut c_void, request_json: *const c_char) -> *mut c_char>,
    pub cache: Option<extern "C" fn(ctx: *mut c_void, request_json: *const c_char) -> *mut c_char>,
    pub payments: Option<extern "C" fn(ctx: *mut c_void, request_json: *const c_char) -> *mut c_char>,
    pub ai: Option<extern "C" fn(ctx: *mut c_void, request_json: *const c_char) -> *mut c_char>,
    pub emit: Option<extern "C" fn(ctx: *mut c_void, chunk: *const c_char) -> i32>,
}

Services the host lends to a C function for the duration of one call.

The host fills this in and passes a pointer that is valid only until apiplant_invoke returns; ctx must be handed back to every callback untouched. Each char * the host returns is owned by the callee and must be released with free_string.

Fields

ctx: *mut c_void

Opaque host state. Pass it back to every callback; never dereference it.

query: Option<extern "C" fn(ctx: *mut c_void, request_json: *const c_char) -> *mut c_char>

Run a query. request_json is {"sql": "…", "params": [ … ]}. Returns a JSON array of rows, {"rows_affected": n}, or {"error": "…"} when the query failed — the shape distinguishes them, so there is no out-param.

log: Option<extern "C" fn(ctx: *mut c_void, level: i32, message: *const c_char)>

Emit a log line through the host’s tracing subscriber. level is one of log_level; anything else is treated as INFO.

config: Option<extern "C" fn(ctx: *mut c_void) -> *mut c_char>

The function’s resolved configuration, as a JSON object.

principal_id: Option<extern "C" fn(ctx: *mut c_void) -> *mut c_char>

Id of the authenticated caller, or an empty string when anonymous.

hook: Option<extern "C" fn(ctx: *mut c_void) -> *mut c_char>

Lifecycle-hook context as JSON, or an empty string for a plain HTTP call. See HostApi::hook for the shape.

free_string: Option<extern "C" fn(ctx: *mut c_void, string: *mut c_char)>

Release a string one of the callbacks above returned.

send_email: Option<extern "C" fn(ctx: *mut c_void, request_json: *const c_char) -> *mut c_char>

Send an email. request_json is the message ({"to":…,"subject":…,"text":…}); returns the receipt {"provider":…,"id":…,"recipients":n} or {"error":"…"}. As with query the shape distinguishes them. See HostApi::send_email.

cache: Option<extern "C" fn(ctx: *mut c_void, request_json: *const c_char) -> *mut c_char>

Run one cache operation. request_json is {"op":"get","key":"…"} and friends; returns the operation’s reply or {"error":"…"}. See HostApi::cache.

payments: Option<extern "C" fn(ctx: *mut c_void, request_json: *const c_char) -> *mut c_char>

Run one payment operation. request_json is {"op":"checkout","stripe_price_id":"…"} and friends; returns the operation’s reply or {"error":"…"}. See HostApi::payments.

ai: Option<extern "C" fn(ctx: *mut c_void, request_json: *const c_char) -> *mut c_char>

Ask the AI assistant. request_json is a conversation ({"messages":[{"role":"user","content":"…"}]}); returns the answer {"text":…,"provider":…,"model":…} or {"error":"…"}. See HostApi::ai.

emit: Option<extern "C" fn(ctx: *mut c_void, chunk: *const c_char) -> i32>

Push a chunk of the response to the caller before the call returns. Returns non-zero while it is still worth producing more, and zero once the caller has hung up. See HostApi::emit.