edge_fetch.h

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// Copyright (C) 2026 Douglas Quigg (dstroy0) <dquigg123@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-or-later
 
/**
 * @file edge_fetch.h
 * @brief CDN edge-cache tier - async origin-fetch engine (DETWS_ENABLE_EDGE_CACHE).
 *
 * A non-blocking origin fetch: open + send a request over a transport seam, accumulate the response
 * across poll loops into a bounded buffer, detect completion (Content-Length / chunked / connection
 * close), then parse it with the proven http_client codec. Pumped from the server poll loop so a miss
 * or revalidation never stalls the worker; the transport seam is det_client on the device and a mock in
 * host tests. Zero heap; the buffer is fixed (`DETWS_EDGE_FETCH_BUF`).
 *
 * @author  Douglas Quigg (dstroy0)
 * @date    2026
 */
 
#ifndef DETERMINISTICESPASYNCWEBSERVER_EDGE_FETCH_H
#define DETERMINISTICESPASYNCWEBSERVER_EDGE_FETCH_H
 
#include "ServerConfig.h"
 
#if DETWS_ENABLE_EDGE_CACHE
 
#include <stddef.h>
#include <stdint.h>
 
/** @brief The origin transport, bound to det_client on the device and a mock in host tests. */
struct EdgeFetchTransport
{
    int (*open)(void *ctx, const char *host, uint16_t port, uint32_t timeout_ms); ///< cid >= 0, or < 0 on failure
    bool (*send)(void *ctx, int cid, const void *data, size_t len);
    size_t (*read)(void *ctx, int cid, uint8_t *buf, size_t cap); ///< 0 = nothing available right now
    bool (*closed)(void *ctx, int cid);                           ///< true once the origin closed its side
    void (*close)(void *ctx, int cid);
    void *ctx;
};
 
/** @brief Fetch progress. */
enum class EdgeFetchStatus : uint8_t
{
    PENDING,  ///< still receiving
    DONE,     ///< a complete response is parsed (status / body_off / body_len valid)
    OVERSIZE, ///< response exceeded the buffer - not cacheable (caller passes through / fails open)
    FAILED,   ///< connect / send / timeout / closed-before-complete
};
 
/** @brief One in-flight origin fetch (fixed-size, zero-heap). */
struct EdgeFetch
{
    EdgeFetchStatus st;
    int cid;
    uint32_t start_ms;
    uint32_t got; ///< bytes accumulated
    int status;   ///< HTTP status (valid when DONE)
    size_t head_len;
    size_t body_off, body_len;
    uint8_t buf[DETWS_EDGE_FETCH_BUF];
};
 
/** @brief Open + send @p request; begin receiving. Sets @p st to PENDING, or FAILED on open/send error. */
void edge_fetch_begin(EdgeFetch *f, const EdgeFetchTransport *t, const char *host, uint16_t port, const void *request,
                      size_t req_len, uint32_t now_ms);
 
/**
 * @brief Drain available bytes and advance. On DONE the response is parsed (chunked bodies decoded in
 *        place); honors `DETWS_EDGE_FETCH_TIMEOUT_MS`. @return the current status.
 */
EdgeFetchStatus edge_fetch_pump(EdgeFetch *f, const EdgeFetchTransport *t, uint32_t now_ms);
 
/** @brief Release the transport connection (idempotent). */
void edge_fetch_end(EdgeFetch *f, const EdgeFetchTransport *t);
 
/**
 * @brief Is the accumulated response complete? (headers terminated + body per Content-Length / chunked
 *        terminator / connection close). Sets @p head_len to the header-block length (0 if not yet whole).
 *        Pure - host-testable without a transport.
 */
bool edge_resp_complete(const uint8_t *buf, size_t len, bool conn_closed, size_t *head_len);
 
#endif // DETWS_ENABLE_EDGE_CACHE
 
#endif // DETERMINISTICESPASYNCWEBSERVER_EDGE_FETCH_H