error_page 指令代码分析

// 每一个错误码（code）将会对应一个这样的结构体
typedef struct {
    ngx_int_t                  status;  // code
    ngx_int_t                  overwrite; // response
    ngx_http_complex_value_t   value;  // uri
    ngx_str_t                  args; // rui的args
} ngx_http_err_page_t;


// 格式：error_page code ... [=[response]] uri;
static char *
ngx_http_core_error_page(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_core_loc_conf_t *clcf = conf;

    u_char                            *p;
    ngx_int_t                          overwrite;
    ngx_str_t                         *value, uri, args;
    ngx_uint_t                         i, n;
    ngx_http_err_page_t               *err;
    ngx_http_complex_value_t           cv;
    ngx_http_compile_complex_value_t   ccv;

    if (clcf->error_pages == NULL) {
        clcf->error_pages = ngx_array_create(cf->pool, 4,
                                             sizeof(ngx_http_err_page_t));
        if (clcf->error_pages == NULL) {
            return NGX_CONF_ERROR;
        }
    }

    value = cf->args->elts;

    i = cf->args->nelts - 2;

    if (value[i].data[0] == '=') {
        if (i == 1) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "invalid value \"%V\"", &value[i]);
            return NGX_CONF_ERROR;
        }

        if (value[i].len > 1) {
            overwrite = ngx_atoi(&value[i].data[1], value[i].len - 1);

            if (overwrite == NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "invalid value \"%V\"", &value[i]);
                return NGX_CONF_ERROR;
            }

        } else {
            overwrite = 0;
        }

        n = 2;

    } else {
        overwrite = -1;
        n = 1;
    }

    uri = value[cf->args->nelts - 1];

    ngx_memzero(&ccv, sizeof(ngx_http_compile_complex_value_t));

    ccv.cf = cf;
    ccv.value = &uri;
    ccv.complex_value = &cv;

    if (ngx_http_compile_complex_value(&ccv) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

    ngx_str_null(&args);

    if (cv.lengths == NULL && uri.len && uri.data[0] == '/') {
        p = (u_char *) ngx_strchr(uri.data, '?');

        if (p) {
            cv.value.len = p - uri.data;
            cv.value.data = uri.data;
            p++;
            args.len = (uri.data + uri.len) - p;
            args.data = p;
        }
    }

    for (i = 1; i < cf->args->nelts - n; i++) {
        err = ngx_array_push(clcf->error_pages);
        if (err == NULL) {
            return NGX_CONF_ERROR;
        }

        err->status = ngx_atoi(value[i].data, value[i].len);

        if (err->status == NGX_ERROR || err->status == 499) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "invalid value \"%V\"", &value[i]);
            return NGX_CONF_ERROR;
        }

        if (err->status < 300 || err->status > 599) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "value \"%V\" must be between 300 and 599",
                               &value[i]);
            return NGX_CONF_ERROR;
        }

        err->overwrite = overwrite;

        if (overwrite == -1) {
            switch (err->status) {
                case NGX_HTTP_TO_HTTPS:
                case NGX_HTTPS_CERT_ERROR:
                case NGX_HTTPS_NO_CERT:
                    err->overwrite = NGX_HTTP_BAD_REQUEST;
            }
        }

        err->value = cv;
        err->args = args;
    }

    return NGX_CONF_OK;
}

ngx_int_t
ngx_http_special_response_handler(ngx_http_request_t *r, ngx_int_t error)
{
    ngx_uint_t                 i, err;
    ngx_http_err_page_t       *err_page;
    ngx_http_core_loc_conf_t  *clcf;

    ngx_log_debug3(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "http special response: %i, \"%V?%V\"",
                   error, &r->uri, &r->args);

    r->err_status = error;

    if (r->keepalive) {
        switch (error) {
            case NGX_HTTP_BAD_REQUEST:
            case NGX_HTTP_REQUEST_ENTITY_TOO_LARGE:
            case NGX_HTTP_REQUEST_URI_TOO_LARGE:
            case NGX_HTTP_TO_HTTPS:
            case NGX_HTTPS_CERT_ERROR:
            case NGX_HTTPS_NO_CERT:
            case NGX_HTTP_INTERNAL_SERVER_ERROR:
            case NGX_HTTP_NOT_IMPLEMENTED:
                r->keepalive = 0;
        }
    }

    if (r->lingering_close) {
        switch (error) {
            case NGX_HTTP_BAD_REQUEST:
            case NGX_HTTP_TO_HTTPS:
            case NGX_HTTPS_CERT_ERROR:
            case NGX_HTTPS_NO_CERT:
                r->lingering_close = 0;
        }
    }

    r->headers_out.content_type.len = 0;

    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    if (!r->error_page && clcf->error_pages && r->uri_changes != 0) {

        // 是否递归解析错误页面
        if (clcf->recursive_error_pages == 0) {
            r->error_page = 1;
        }

        err_page = clcf->error_pages->elts;

        for (i = 0; i < clcf->error_pages->nelts; i++) {
            if (err_page[i].status == error) {
                return ngx_http_send_error_page(r, &err_page[i]);
            }
        }
    }

    r->expect_tested = 1;

    if (ngx_http_discard_request_body(r) != NGX_OK) {
        r->keepalive = 0;
    }

    if (clcf->msie_refresh
        && r->headers_in.msie
        && (error == NGX_HTTP_MOVED_PERMANENTLY
            || error == NGX_HTTP_MOVED_TEMPORARILY))
    {
        return ngx_http_send_refresh(r);
    }

    if (error == NGX_HTTP_CREATED) {
        /* 201 */
        err = 0;

    } else if (error == NGX_HTTP_NO_CONTENT) {
        /* 204 */
        err = 0;

    } else if (error >= NGX_HTTP_MOVED_PERMANENTLY
               && error < NGX_HTTP_LAST_3XX)
    {
        /* 3XX */
        err = error - NGX_HTTP_MOVED_PERMANENTLY + NGX_HTTP_OFF_3XX;

    } else if (error >= NGX_HTTP_BAD_REQUEST
               && error < NGX_HTTP_LAST_4XX)
    {
        /* 4XX */
        err = error - NGX_HTTP_BAD_REQUEST + NGX_HTTP_OFF_4XX;

    } else if (error >= NGX_HTTP_NGINX_CODES
               && error < NGX_HTTP_LAST_5XX)
    {
        /* 49X, 5XX */
        err = error - NGX_HTTP_NGINX_CODES + NGX_HTTP_OFF_5XX;
        switch (error) {
            case NGX_HTTP_TO_HTTPS:
            case NGX_HTTPS_CERT_ERROR:
            case NGX_HTTPS_NO_CERT:
            case NGX_HTTP_REQUEST_HEADER_TOO_LARGE:
                r->err_status = NGX_HTTP_BAD_REQUEST;
        }

    } else {
        /* unknown code, zero body */
        err = 0;
    }

    return ngx_http_send_special_response(r, clcf, err);
}


static ngx_int_t
ngx_http_send_error_page(ngx_http_request_t *r, ngx_http_err_page_t *err_page)
{
    ngx_int_t                  overwrite;
    ngx_str_t                  uri, args;
    ngx_table_elt_t           *location;
    ngx_http_core_loc_conf_t  *clcf;

    overwrite = err_page->overwrite;

    if (overwrite && overwrite != NGX_HTTP_OK) {
        r->expect_tested = 1;
    }

    // 覆盖的状态码
    if (overwrite >= 0) {
        r->err_status = overwrite;
    }

    if (ngx_http_complex_value(r, &err_page->value, &uri) != NGX_OK) {
        return NGX_ERROR;
    }

    if (uri.len && uri.data[0] == '/') {

        if (err_page->value.lengths) {
            ngx_http_split_args(r, &uri, &args);

        } else {
            args = err_page->args;
        }

        if (r->method != NGX_HTTP_HEAD) {
            r->method = NGX_HTTP_GET;
            r->method_name = ngx_http_core_get_method;
        }

        return ngx_http_internal_redirect(r, &uri, &args);
    }

    if (uri.len && uri.data[0] == '@') {
        return ngx_http_named_location(r, &uri);
    }

    location = ngx_list_push(&r->headers_out.headers);

    if (location == NULL) {
        return NGX_ERROR;
    }

    if (overwrite != NGX_HTTP_MOVED_PERMANENTLY
        && overwrite != NGX_HTTP_MOVED_TEMPORARILY
        && overwrite != NGX_HTTP_SEE_OTHER
        && overwrite != NGX_HTTP_TEMPORARY_REDIRECT
        && overwrite != NGX_HTTP_PERMANENT_REDIRECT)
    {
        r->err_status = NGX_HTTP_MOVED_TEMPORARILY;
    }

    location->hash = 1;
    ngx_str_set(&location->key, "Location");
    location->value = uri;

    ngx_http_clear_location(r);

    r->headers_out.location = location;

    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    if (clcf->msie_refresh && r->headers_in.msie) {
        return ngx_http_send_refresh(r);
    }

    return ngx_http_send_special_response(r, clcf, r->err_status
                                                   - NGX_HTTP_MOVED_PERMANENTLY
                                                   + NGX_HTTP_OFF_3XX);
}