httpcache.cpp

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// Copyright (C) 2026 Douglas Quigg (dstroy0) <dquigg123@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-or-later
 
/**
 * @file httpcache.cpp
 * @brief Cache-Control builder / parser / freshness implementation (see httpcache.h).
 */
 
#include "httpcache.h"
 
#if DETWS_ENABLE_HTTP_CACHE
 
#include <string.h>
 
static const size_t CC_SENT = (size_t)-1; // overflow sentinel threaded through the emitters
 
void cache_control_init(DetwsCacheControl *cc)
{
    cc->cc_public = false;
    cc->cc_private = false;
    cc->no_store = false;
    cc->no_cache = false;
    cc->no_transform = false;
    cc->must_revalidate = false;
    cc->proxy_revalidate = false;
    cc->must_understand = false;
    cc->cc_immutable = false;
    cc->only_if_cached = false;
    cc->max_age = -1;
    cc->s_maxage = -1;
    cc->stale_while_revalidate = -1;
    cc->stale_if_error = -1;
    cc->max_stale = -1;
    cc->min_fresh = -1;
}
 
// --- build -----------------------------------------------------------------
 
static size_t cc_emit_uint(char *buf, size_t cap, size_t n, unsigned v)
{
    char rev[10];
    int ri = 0;
    if (v == 0)
        rev[ri++] = '0';
    else
        while (v)
        {
            rev[ri++] = (char)('0' + (v % 10));
            v /= 10;
        }
    if (n + (size_t)ri > cap)
        return CC_SENT;
    for (int k = 0; k < ri; k++)
        buf[n + k] = rev[ri - 1 - k];
    return n + (size_t)ri;
}
 
// Emit one bare token (with the ", " separator before all but the first).
static size_t cc_tok(char *buf, size_t cap, size_t n, bool *first, const char *tok)
{
    if (n == CC_SENT)
        return CC_SENT;
    size_t tlen = strnlen(tok, cap);
    size_t need = (*first ? 0 : 2) + tlen;
    if (n + need > cap)
        return CC_SENT;
    if (!*first)
    {
        buf[n++] = ',';
        buf[n++] = ' ';
    }
    memcpy(buf + n, tok, tlen);
    *first = false;
    return n + tlen;
}
 
// Emit "key=value".
static size_t cc_kv(char *buf, size_t cap, size_t n, bool *first, const char *key, long v)
{
    n = cc_tok(buf, cap, n, first, key);
    if (n == CC_SENT || n >= cap)
        return CC_SENT;
    buf[n++] = '=';
    return cc_emit_uint(buf, cap, n, (unsigned)v);
}
 
size_t cache_control_build(char *buf, size_t cap, const DetwsCacheControl *cc)
{
    if (!buf || !cc || cap == 0)
        return 0;
    size_t n = 0;
    bool first = true;
 
    if (cc->cc_public)
        n = cc_tok(buf, cap, n, &first, "public");
    if (cc->cc_private)
        n = cc_tok(buf, cap, n, &first, "private");
    if (cc->no_store)
        n = cc_tok(buf, cap, n, &first, "no-store");
    if (cc->no_cache)
        n = cc_tok(buf, cap, n, &first, "no-cache");
    if (cc->max_age >= 0)
        n = cc_kv(buf, cap, n, &first, "max-age", cc->max_age);
    if (cc->s_maxage >= 0)
        n = cc_kv(buf, cap, n, &first, "s-maxage", cc->s_maxage);
    if (cc->must_revalidate)
        n = cc_tok(buf, cap, n, &first, "must-revalidate");
    if (cc->proxy_revalidate)
        n = cc_tok(buf, cap, n, &first, "proxy-revalidate");
    if (cc->no_transform)
        n = cc_tok(buf, cap, n, &first, "no-transform");
    if (cc->must_understand)
        n = cc_tok(buf, cap, n, &first, "must-understand");
    if (cc->cc_immutable)
        n = cc_tok(buf, cap, n, &first, "immutable");
    if (cc->stale_while_revalidate >= 0)
        n = cc_kv(buf, cap, n, &first, "stale-while-revalidate", cc->stale_while_revalidate);
    if (cc->stale_if_error >= 0)
        n = cc_kv(buf, cap, n, &first, "stale-if-error", cc->stale_if_error);
    if (cc->only_if_cached)
        n = cc_tok(buf, cap, n, &first, "only-if-cached");
    if (cc->max_stale == -2)
        n = cc_tok(buf, cap, n, &first, "max-stale");
    else if (cc->max_stale >= 0)
        n = cc_kv(buf, cap, n, &first, "max-stale", cc->max_stale);
    if (cc->min_fresh >= 0)
        n = cc_kv(buf, cap, n, &first, "min-fresh", cc->min_fresh);
 
    if (n == CC_SENT || first || n + 1 > cap)
        return 0; // overflow, or nothing was emitted, or no room for the NUL
    buf[n] = 0;
    return n;
}
 
// --- parse -----------------------------------------------------------------
 
// Case-insensitive compare of [s,s+len) to the (lowercase) NUL-terminated @p target.
static bool cc_ci_eq(const char *s, size_t len, const char *target)
{
    size_t i = 0;
    for (; i < len && target[i]; i++)
    {
        char c = s[i];
        if (c >= 'A' && c <= 'Z')
            c = (char)(c + 32);
        if (c != target[i])
            return false;
    }
    return i == len && target[i] == 0;
}
 
// Parse a non-negative delta-seconds from [v,v+vlen) (tolerates surrounding quotes / spaces).
// Returns the value clamped to INT32_MAX, or -1 if no digits are present.
static int32_t cc_parse_delta(const char *v, size_t vlen)
{
    if (!v)
        return -1;
    size_t i = 0;
    while (i < vlen && (v[i] == ' ' || v[i] == '\t' || v[i] == '"'))
        i++;
    long val = -1;
    bool any = false;
    while (i < vlen && v[i] >= '0' && v[i] <= '9')
    {
        if (!any)
        {
            val = 0;
            any = true;
        }
        val = val * 10 + (v[i] - '0');
        if (val > 2147483647L)
            val = 2147483647L;
        i++;
    }
    return any ? (int32_t)val : -1;
}
 
static bool cc_match(DetwsCacheControl *cc, const char *name, size_t nlen, const char *val, size_t vlen)
{
    if (cc_ci_eq(name, nlen, "public"))
        cc->cc_public = true;
    else if (cc_ci_eq(name, nlen, "private"))
        cc->cc_private = true;
    else if (cc_ci_eq(name, nlen, "no-store"))
        cc->no_store = true;
    else if (cc_ci_eq(name, nlen, "no-cache"))
        cc->no_cache = true;
    else if (cc_ci_eq(name, nlen, "no-transform"))
        cc->no_transform = true;
    else if (cc_ci_eq(name, nlen, "must-revalidate"))
        cc->must_revalidate = true;
    else if (cc_ci_eq(name, nlen, "proxy-revalidate"))
        cc->proxy_revalidate = true;
    else if (cc_ci_eq(name, nlen, "must-understand"))
        cc->must_understand = true;
    else if (cc_ci_eq(name, nlen, "immutable"))
        cc->cc_immutable = true;
    else if (cc_ci_eq(name, nlen, "only-if-cached"))
        cc->only_if_cached = true;
    else if (cc_ci_eq(name, nlen, "max-age"))
        cc->max_age = cc_parse_delta(val, vlen);
    else if (cc_ci_eq(name, nlen, "s-maxage"))
        cc->s_maxage = cc_parse_delta(val, vlen);
    else if (cc_ci_eq(name, nlen, "stale-while-revalidate"))
        cc->stale_while_revalidate = cc_parse_delta(val, vlen);
    else if (cc_ci_eq(name, nlen, "stale-if-error"))
        cc->stale_if_error = cc_parse_delta(val, vlen);
    else if (cc_ci_eq(name, nlen, "max-stale"))
        cc->max_stale = val ? cc_parse_delta(val, vlen) : -2; // present with no value = "any"
    else if (cc_ci_eq(name, nlen, "min-fresh"))
        cc->min_fresh = cc_parse_delta(val, vlen);
    else
        return false; // unknown directive - ignored
    return true;
}
 
// Parse one comma-separated directive starting at *i (advancing past it) and apply it; returns true
// if a known directive matched.
static bool cache_parse_one_directive(const char *s, size_t len, size_t *i, DetwsCacheControl *cc)
{
    while (*i < len && (s[*i] == ',' || s[*i] == ' ' || s[*i] == '\t'))
        (*i)++; // skip separators / OWS
    if (*i >= len)
        return false;
    size_t start = *i;
    while (*i < len && s[*i] != ',')
        (*i)++; // to the next comma
    size_t end = *i;
    while (end > start && (s[end - 1] == ' ' || s[end - 1] == '\t'))
        end--; // trim trailing OWS
    size_t eq = start;
    while (eq < end && s[eq] != '=')
        eq++;
    size_t nlen = (eq < end ? eq : end) - start;
    while (nlen > 0 && (s[start + nlen - 1] == ' ' || s[start + nlen - 1] == '\t'))
        nlen--; // trim trailing OWS from name
    const char *val = (eq < end) ? s + eq + 1 : nullptr;
    size_t vlen = (eq < end) ? end - (eq + 1) : 0;
    return nlen && cc_match(cc, s + start, nlen, val, vlen);
}
 
bool cache_control_parse(const char *s, size_t len, DetwsCacheControl *cc)
{
    cache_control_init(cc);
    if (!s)
        return false;
    bool found = false;
    size_t i = 0;
    while (i < len)
    {
        if (cache_parse_one_directive(s, len, &i, cc))
            found = true;
    }
    return found;
}
 
// --- presets + freshness ---------------------------------------------------
 
void cache_immutable_asset(DetwsCacheControl *cc, uint32_t max_age)
{
    cache_control_init(cc);
    cc->cc_public = true;
    cc->max_age = (int32_t)(max_age > 2147483647u ? 2147483647u : max_age);
    cc->cc_immutable = true;
}
 
void cache_revalidatable(DetwsCacheControl *cc, uint32_t max_age, int32_t stale_while_revalidate)
{
    cache_control_init(cc);
    cc->cc_public = true;
    cc->max_age = (int32_t)(max_age > 2147483647u ? 2147483647u : max_age);
    if (stale_while_revalidate >= 0)
        cc->stale_while_revalidate = stale_while_revalidate;
}
 
void cache_no_store(DetwsCacheControl *cc)
{
    cache_control_init(cc);
    cc->no_store = true;
}
 
void cache_shared(DetwsCacheControl *cc, uint32_t max_age, uint32_t s_maxage)
{
    cache_control_init(cc);
    cc->cc_public = true;
    cc->max_age = (int32_t)(max_age > 2147483647u ? 2147483647u : max_age);
    cc->s_maxage = (int32_t)(s_maxage > 2147483647u ? 2147483647u : s_maxage);
}
 
long cache_freshness_lifetime(const DetwsCacheControl *cc, bool shared, long expires_minus_date)
{
    if (shared && cc->s_maxage >= 0)
        return cc->s_maxage;
    if (cc->max_age >= 0)
        return cc->max_age;
    if (expires_minus_date >= 0)
        return expires_minus_date;
    return -1; // no explicit expiration - the caller applies a heuristic
}
 
#endif // DETWS_ENABLE_HTTP_CACHE