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fix(lwip): Document DNS limitation in lwIP
* Add a note that DNS server config is global in lwIP * Add a section about defining LWIP config macros from CMake * Mention the DNS limitation in ESP-IDF additions to lwIP * Update CN for lwIP DNS limitation Co-Authored-By: Wang Ziyan <wangziyan@espressif.com>
This commit is contained in:
David Cermak
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c8243465e4
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1f6a927e33
@ -13,6 +13,8 @@ ESP-IDF supports the following lwIP TCP/IP stack functions:
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- `BSD Sockets API`_
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- `Netconn API`_ is enabled but not officially supported for ESP-IDF applications
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.. _lwip-dns-limitation:
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Adapted APIs
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^^^^^^^^^^^^
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@ -23,6 +25,12 @@ Adapted APIs
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Some common lwIP app APIs are supported indirectly by ESP-IDF:
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- Dynamic Host Configuration Protocol (DHCP) Server & Client are supported indirectly via the :doc:`/api-reference/network/esp_netif` functionality.
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- Domain Name System (DNS) is supported in lwIP; DNS servers could be assigned automatically when acquiring a DHCP address, or manually configured using the :doc:`/api-reference/network/esp_netif` API.
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.. note::
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DNS server configuration in lwIP is global, not interface-specific. If you are using multiple network interfaces with distinct DNS servers, exercise caution to prevent inadvertent overwrites of one interface's DNS settings when acquiring a DHCP lease from another interface.
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- Simple Network Time Protocol (SNTP) is also supported via the :doc:`/api-reference/network/esp_netif`, or directly via the :component_file:`lwip/include/apps/esp_sntp.h` functions, which also provide thread-safe API to :component_file:`lwip/lwip/src/include/lwip/apps/sntp.h` functions, see also :ref:`system-time-sntp-sync`.
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- ICMP Ping is supported using a variation on the lwIP ping API, see :doc:`/api-reference/protocols/icmp_echo`.
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- ICMPv6 Ping, supported by lwIP's ICMPv6 Echo API, is used to test IPv6 network connectivity. For more information, see :example:`protocols/sockets/icmpv6_ping`.
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@ -411,6 +419,8 @@ IP Layer Features
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- IPV4-mapped IPV6 addresses are supported
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.. _lwip-custom-hooks:
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Customized lwIP Hooks
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+++++++++++++++++++++
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@ -422,10 +432,25 @@ The original lwIP supports implementing custom compile-time modifications via ``
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target_compile_options(${lwip} PRIVATE "-I${PROJECT_DIR}/main")
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target_compile_definitions(${lwip} PRIVATE "-DESP_IDF_LWIP_HOOK_FILENAME=\"my_hook.h\"")
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Customized lwIP Options From ESP-IDF Build System
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++++++++++++++++++++++++++++++++++++++++++++++++++
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The most common lwIP options are configurable through the component configuration menu. However, certain definitions need to be injected from the command line. The CMake function ``target_compile_definitions()`` can be employed to define macros, as illustrated below:
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.. code-block:: cmake
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idf_component_get_property(lwip lwip COMPONENT_LIB)
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target_compile_definitions(${lwip} PRIVATE "-DETHARP_SUPPORT_VLAN=1")
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This approach may not work for function-like macros, as there is no guarantee that the definition will be accepted by all compilers, although it is supported in GCC. To address this limitation, the ``add_definitions()`` function can be utilized to define the macro for the entire project, for example: ``add_definitions("-DFALLBACK_DNS_SERVER_ADDRESS(addr)=\"IP_ADDR4((addr), 8,8,8,8)\"")``.
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Alternatively, you can define your function-like macro in a header file which will be pre-included as an lwIP hook file, see :ref:`lwip-custom-hooks`.
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Limitations
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^^^^^^^^^^^
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ESP-IDF additions to lwIP still suffer from the global DNS limitation, described in :ref:`lwip-dns-limitation`. To address this limitation from application code, the ``FALLBACK_DNS_SERVER_ADDRESS()`` macro can be utilized to define a global DNS fallback server accessible from all interfaces. Alternatively, you have the option to maintain per-interface DNS servers and reconfigure them whenever the default interface changes.
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Calling ``send()`` or ``sendto()`` repeatedly on a UDP socket may eventually fail with ``errno`` equal to ``ENOMEM``. This failure occurs due to the limitations of buffer sizes in the lower-layer network interface drivers. If all driver transmit buffers are full, the UDP transmission will fail. For applications that transmit a high volume of UDP datagrams and aim to avoid any dropped datagrams by the sender, it is advisable to implement error code checking and employ a retransmission mechanism with a short delay.
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.. only:: esp32
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@ -13,6 +13,8 @@ ESP-IDF 支持以下 lwIP TCP/IP 协议栈功能：
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- `BSD 套接字 API`_
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- `Netconn API`_ 已启用，但暂无对 ESP-IDF 应用程序的官方支持
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.. _lwip-dns-limitation:
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适配的 API
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^^^^^^^^^^^^
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@ -23,6 +25,12 @@ ESP-IDF 支持以下 lwIP TCP/IP 协议栈功能：
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ESP-IDF 间接支持以下常见的 lwIP 应用程序 API：
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- 动态主机设置协议 (DHCP) 服务器和客户端，由 :doc:`/api-reference/network/esp_netif` 功能间接支持。
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- 域名系统 (DNS)；获取 DHCP 地址时，可以自动分配 DNS 服务器，也可以通过 :doc:`/api-reference/network/esp_netif` API 手动配置。
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.. note::
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lwIP 中的 DNS 服务器配置为全局配置，而非针对特定接口的配置。如需同时使用不同 DNS 服务器的多个网络接口，在从一个接口获取 DHCP 租约时，请注意避免意外覆盖另一个接口的 DNS 设置。
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- 简单网络时间协议 (SNTP)，由 :doc:`/api-reference/network/esp_netif` 功能间接支持，或通过 :component_file:`lwip/include/apps/esp_sntp.h` 中的函数直接支持。该函数还为 :component_file:`lwip/lwip/src/include/lwip/apps/sntp.h` 函数提供了线程安全的 API，请参阅 :ref:`system-time-sntp-sync`。
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- ICMP Ping，由 lwIP ping API 的变体支持，请参阅 :doc:`/api-reference/protocols/icmp_echo`。
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- ICMPv6 Ping，由 lwIP 的 ICMPv6 Echo API 支持，用于测试 IPv6 网络连接情况。有关详细信息，请参阅 :example:`protocols/sockets/icmpv6_ping`。
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@ -411,6 +419,8 @@ IP 层特性
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- 支持 IPV4 映射 IPV6 地址
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.. _lwip-custom-hooks:
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自定义 lwIP 钩子
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+++++++++++++++++++++
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@ -422,10 +432,25 @@ IP 层特性
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target_compile_options(${lwip} PRIVATE "-I${PROJECT_DIR}/main")
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target_compile_definitions(${lwip} PRIVATE "-DESP_IDF_LWIP_HOOK_FILENAME=\"my_hook.h\"")
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使用 ESP-IDF 构建系统自定义 lwIP 选项
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++++++++++++++++++++++++++++++++++++++++++++++++++
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组件配置菜单可以配置常见的 lwIP 选项，但是一些自定义选项需要通过命令行添加。CMake 函数 ``target_compile_definitions()`` 可以用于定义宏，示例如下：
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.. code-block:: cmake
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idf_component_get_property(lwip lwip COMPONENT_LIB)
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target_compile_definitions(${lwip} PRIVATE "-DETHARP_SUPPORT_VLAN=1")
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使用这种方法可能无法定义函数式宏。虽然 GCC 支持此类定义，但是未必所有编译器都会接受。为了解决这一限制，可以使用 ``add_definitions()`` 函数为整个项目定义宏，例如 ``add_definitions("-DFALLBACK_DNS_SERVER_ADDRESS(addr)=\"IP_ADDR4((addr), 8,8,8,8)\"")``。
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另一种方法是在头文件中定义函数式宏，该头文件将预先包含在 lwIP 钩子文件中，请参考 :ref:`lwip-custom-hooks`。
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限制
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^^^^^^^^^^^
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如 :ref:`lwip-dns-limitation` 所述，ESP-IDF 中的 lwIP 扩展功能仍然受到全局 DNS 限制的影响。为了在应用程序代码中解决这一限制，可以使用 ``FALLBACK_DNS_SERVER_ADDRESS()`` 宏定义所有接口能够访问的全局 DNS 备用服务器，或者单独维护每个接口的 DNS 服务器，并在默认接口更改时重新配置。
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在 UDP 套接字上重复调用 ``send()`` 或 ``sendto()`` 最终可能会导致错误。此时 ``errno`` 报错为 ``ENOMEM``，错误原因是底层网络接口驱动程序中的 buffer 大小有限。当所有驱动程序的传输 buffer 已满时，UDP 传输事务失败。如果应用程序需要发送大量 UDP 数据报，且不希望发送方丢弃数据报，建议检查错误代码，采用短延迟的重传机制。
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.. only:: esp32
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