\chapter{HTTP API}
\label{ch:api}

The setup web interface is a thin client over a typed JSON REST API
implemented in \texttt{SetupWebServer}. Request bodies are parsed into
domain types in the pure core (\texttt{components/core}) before any
persistence or driver call. Exact C++ signatures live in the generated
Doxygen output under \texttt{docs/api/}; this chapter documents the
wire protocol and behaviour as shipped in firmware~0.2.0 (Slices~1--2).

\section{Transport and reachability}

\begin{itemize}
  \item \textbf{Port:} TCP~80 on the ESP32-S3 HTTP server.
  \item \textbf{Setup mode (\texttt{NetState::SoftApSetup}):} join the
        SoftAP \texttt{DigiRadio-setup} (open network), then open
        \url{http://192.168.4.1/}. The root path serves a gzipped HTML
        page embedded from flash.
  \item \textbf{STA mode (\texttt{NetState::StaConnected}):} after
        successful provisioning and reboot, the same API is available at
        the device's DHCP address on the configured LAN.
\end{itemize}

All responses use \texttt{Content-Type: application/json} except
\texttt{GET /}, which returns gzipped HTML with
\texttt{Content-Encoding: gzip}.

\section{Endpoints}

\subsection{\texttt{GET /api/health}}
\label{sec:api-health}

Returns a health-check DTO serialised by
\texttt{core::serializeHealthStatusJson()} from a
\texttt{core::HealthStatus} value.

\begin{drnote}[Response schema]
\begin{drcode}[JSON]
{"status":"ok","fw":"0.2.0"}
\end{drcode}
\begin{itemize}
  \item \texttt{status} --- coarse indicator; \texttt{ok} when the
        firmware is running normally.
  \item \texttt{fw} --- firmware release string
        (\texttt{core::FirmwareVersion}).
\end{itemize}
\end{drnote}

HTTP status: \textbf{200 OK} on success.

\subsection{\texttt{POST /api/wifi}}
\label{sec:api-wifi}

Accepts Wi-Fi credentials for station (STA) join. The body is parsed by
\texttt{core::parseWifiProvisionJson()} into a \texttt{core::WifiCredentials}
value (SSID as \texttt{core::WifiSsid}, password as \texttt{core::Secret}).
On success the credentials are persisted through
\texttt{core::ISecureStore} (device implementation:
\texttt{secure\_store::NvsSecureStore}) and the device schedules a reboot
so the next boot can enter STA mode.

\begin{drnote}[Request schema]
\begin{drcode}[JSON]
{"ssid":"MyNetwork","password":"secret1234"}
\end{drcode}
\begin{itemize}
  \item \texttt{ssid} --- required, 1--32 characters (802.11 SSID limits).
  \item \texttt{password} --- optional for open networks; for WPA-PSK,
        8--63 characters. Validated by
        \texttt{core::WifiCredentials::isPasswordValid()}.
\end{itemize}
\end{drnote}

\begin{drnote}[Success response]
\begin{drcode}[JSON]
{"status":"saved","reboot_in_sec":3}
\end{drcode}
Serialised by \texttt{core::serializeWifiProvisionSavedJson()}. The device
reboots after the indicated delay.
\end{drnote}

\begin{drnote}[Error response]
\begin{drcode}[JSON]
{"status":"error","reason":"invalid_ssid"}
\end{drcode}
Serialised by \texttt{core::serializeWifiProvisionErrorJson()}. Reason
tokens (never include secrets): \texttt{invalid\_json},
\texttt{missing\_field}, \texttt{invalid\_ssid}, \texttt{invalid\_password},
\texttt{store\_failed}.
\end{drnote}

HTTP status: \textbf{200 OK} on save success; \textbf{400 Bad Request} for
parse/validation failures; \textbf{500 Internal Server Error} when NVS
persistence fails.

\section{Boot and network state machine}
\label{sec:api-boot-flow}

At boot, \texttt{net::NetBootstrap::start()} consults
\texttt{ISecureStore::hasWifiCredentials()}:

\begin{enumerate}
  \item \textbf{Credentials present} --- create STA netif, connect via
        \texttt{net::StaClient} (30\,s timeout). On success:
        \texttt{NetState::StaConnected} and HTTP on the LAN address.
  \item \textbf{No credentials, or STA join fails} --- fall back to
        SoftAP setup mode (\texttt{NetState::SoftApSetup}).
\end{enumerate}

This explicit \texttt{enum class NetState} replaces ad-hoc flags; see
\texttt{net/NetState.hpp} in the source tree.

\section{Credential storage (Slice~2)}
\label{sec:api-storage}

Wi-Fi credentials are stored in NVS namespace \texttt{digiradio}, keys
\texttt{wifi\_ssid} and \texttt{wifi\_pwd}. Passwords are wrapped in
\texttt{core::Secret} in RAM and are never logged or returned by the API.

\begin{drcaution}[Encryption at rest]
Development builds use plain NVS. Production should enable NVS encryption
using the reserved \texttt{nvs\_keys} partition (see
\texttt{partitions.csv} and \texttt{sdkconfig.defaults} comments) per
current ESP-IDF security guidance.
\end{drcaution}