Function HandleCached

engine/dlib/src/dlib/http_client.cpp:822–905

#if !defined(DM_NO_HTTP_CACHE)
    static Result HandleCached(HClient client, const char* path, Response* response, bool method_is_head)
    {
        client->m_Statistics.m_CachedResponses++;
        if (client->m_IgnoreCache)
        {
            return RESULT_OK;
        }

        if (client->m_HttpCache == 0)
        {
            dmLogWarning("Got HTTP response NOT MODIFIED (304) but no cache present");
            return RESULT_OK;
        }
        dmHttpCache::Result cache_result;

        char cache_etag[dmHttpCache::MAX_TAG_LEN];
        cache_etag[0] = '\0';
        cache_result = dmHttpCache::GetETag(client->m_HttpCache, client->m_CacheKey, cache_etag, sizeof(cache_etag));

        if (cache_result != dmHttpCache::RESULT_OK)
        {
            dmLogWarning("Got HTTP response NOT MODIFIED (304) but no ETag present. Returning no cached data.");
            return RESULT_OK;
        }

        if (response->m_ETag[0] != '\0')
        {
            // The Entity Tag (ETag) is optional in HTTP 1.1.
            // It is the servers responsibility to verify the ETag in case it is included. The
            // ETag is a mechanism to reduce the bandwidth required by the server, not
            // by the client. There is no guarantee that an ETag will be included in a
            // 403 response even though it's been sent with a previous 200 response.
            // Even though it might be possible at times, the client has no formal responsibility
            // to perform this verification.
            if (strcmp(cache_etag, response->m_ETag) != 0)
            {
                dmLogError("ETag mismatch (%s vs %s)", cache_etag, response->m_ETag);
                return RESULT_IO_ERROR;
            }
        }

        FILE* file = 0;
        uint32_t file_size = 0;
        uint64_t checksum;
        uint32_t range_start;
        uint32_t range_end;
        uint32_t document_size;
        cache_result = dmHttpCache::Get(client->m_HttpCache, client->m_CacheKey, cache_etag, &file, &file_size, &checksum,
                                        &range_start, &range_end, &document_size);
        if (cache_result == dmHttpCache::RESULT_OK)
        {
            // If the request is a "HEAD" request, and the URI is cached (i.e the file exists),
            // then we should return the meta-data about the file (including triggering the progress callback).
            if (method_is_head)
            {
                client->m_HttpContent(response, client->m_Userdata, response->m_Status, 0, 0, file_size,
                                        range_start, range_end, document_size,
                                        "HEAD");