Struct BackendSection 

pub struct BackendSection {
    pub base_url: String,
    pub auth: AuthConfig,
    pub http: HttpConfig,
}

[backend] section — the OpenAPI/REST HTTP backend declaration (D-06).

This is the HTTP analog of DatabaseSection: it identifies the upstream REST API the synthesized tools call. base_url is the API root; the optional [backend.auth] sub-table selects an AuthConfig variant (type = "...") and [backend.http] carries HttpConfig tuning (timeout / retries / …).

Gated behind the http feature — the whole section (and the ServerConfig::backend field) is absent in a no-http build so there is no dead stub type. AuthConfig and HttpConfig are DEFINED in crate::http (Plan 90-01) and re-exported here, not redefined (H3).

Strict-parse discipline (D-13) is preserved: #[serde(deny_unknown_fields)] rejects a typo’d key under [backend] or [backend.http].

Secrets posture (T-90-02-02): inline token fields under [backend.auth] hold operator references (${ENV} / env:VAR) resolved upstream by the Phase 83 secrets machinery — config parsing stores the string verbatim and never the resolved value.

Fields

base_url: String

REST API root URL (e.g. "https://api.tfl.gov.uk"). Single-call tools concatenate their path onto this (an empty per-tool base_url inherits this value).

auth: AuthConfig

[backend.auth] — outgoing authentication (AuthConfig, six modes). Defaults to AuthConfig::None when the sub-table is omitted.

http: HttpConfig

[backend.http] — client tuning (HttpConfig: timeout / retries / backoff / user-agent / default headers). Defaults to HttpConfig’s defaults when the sub-table is omitted.

Implementations

impl BackendSection

pub fn resolved_base_url(&self) -> Result<String, ToolkitError>

Resolve Self::base_url, expanding a ${VAR} / env:VAR reference from the process environment. Callers MUST use this rather than reading base_url directly — the raw field may hold an unresolved placeholder.

A Shape A server’s endpoint is frequently a slot the target environment fills, so the config records base_url = "${TFL_BASE_URL}" and the package digest stays environment-independent. Without expansion that literal ${...} parses, VALIDATES (it is non-empty, so the emptiness rule passes) and is then sent as the request URL.

Resolution rules — the grammar is crate::env_ref::parse_env_ref, the single toolkit-wide chokepoint:

• a plain literal (no ${...} / env: prefix) is returned VERBATIM;
• ${VAR} / env:VAR reads VAR from the process environment;
• a MALFORMED reference — the empty ${}, or a multi-placeholder composition like ${A}://${B} (a brace reference names exactly ONE variable) — is an error;
• an UNSET variable, or one set to an empty / whitespace-only value, is an error.

Deliberate divergence from credential resolution

A credential resolves an unset reference to the empty string so an optional credential is OMITTED (see crate::http::auth). An endpoint does NOT get that treatment: an empty credential yields a degraded request, but an empty endpoint yields a broken one, and ServerConfig::validate only checks emptiness at parse time — an empty resolution would sail through and then break every request. This uses the error-on-unset semantics of code_mode’s token_secret resolution instead.

Errors

Returns ToolkitError::UnresolvedBaseUrlRef when the reference cannot be resolved. Per T-120-17 the error names the FIELD and the environment-variable NAME only — never a resolved URL or credential.

Examples

use pmcp_server_toolkit::config::ServerConfig;

let cfg = ServerConfig::from_toml_strict_validated(
    "[server]\nname = \"demo\"\nversion = \"0.1.0\"\n\
     [backend]\nbase_url = \"https://api.example.com\"\n",
)
.expect("valid config");
let backend = cfg.backend.as_ref().expect("[backend] present");
// A plain literal is used verbatim.
assert_eq!(backend.resolved_base_url().unwrap(), "https://api.example.com");

Trait Implementations

impl Clone for BackendSection

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for BackendSection

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for BackendSection

fn default() -> Self

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for BackendSection

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

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Eq for BackendSection

impl PartialEq for BackendSection

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl Serialize for BackendSection

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

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for BackendSection