参考cJSON进行编译mosquito，三方库源码位置；third_party，先查看已存在的三方库

ls third_party/
EGL                       brotli            dav1d           glslang      jsoncpp        libnl           ltp            musl            openmax             sane-airscan   v4l2-ctl
FatFs                     bzip2             decimal.js      gn           lame           libphonenumber  lwip           ncurses         openssl             selinux        vixl
FreeBSD                   cJSON             e2fsprogs       googletest   libabigail     libpng          lz4            nghttp2         optimized-routines  skia           vk-gl-cts
NuttX                     cangjie_compiler  elfio           gptfdisk     libbpf         libtiff         lzma           ninja           parse5              sonic          vulkan-headers
PyYAML                    cangjie_runtime   elfutils        grpc         libcoap        libunwind       markupsafe     node            pcre2               spirv-headers  vulkan-loader
abseil-cpp                cangjie_tools     exfatprogs      harfbuzz     libdrm         liburing        mbedtls        noto-cjk        popt                spirv-tools    weex-loader
alsa-lib                  cares             f2fs-tools      icu          libedit        libusb          media-ctl      notofonts       protobuf            sqlite         wpa_supplicant
alsa-utils                cmsis             ffmpeg          iptables     libevdev       libuv           mesa3d         ntfs-3g         pulseaudio          tex-hyphen     zlib
astc-encoder              css-what          flatbuffers     jerryscript  libexif        libvpx          meshoptimizer  openGLES        python              toybox
backends                  cups              freetype        jinja2       libfuse        libwebsockets   mindspore      openSLES        qrcodegen           typescript
benchmark                 cups-filters      fsverity-utils  jsframework  libinput       libxml2         mksh           opencl-headers  re2                 tzdata
bounds_checking_function  curl              glfw            json         libjpeg-turbo  littlefs        mtdev          openhitls       rust                unity

源码下载位置：https://mosquitto.org/files/source/，当前使用版本为2.0.9

下载mosquito源码，解压至third_party,修改名为mosquito，并创建编译规则BUILD.gn与bundle.json

ls third_party/mosquitto/
BUILD.gn         LICENSE.txt            README-windows.txt  apps         config.h   epl-v20    lib                   man             plugins          service
CMakeLists.txt   Makefile               README.md           bundle.json  config.mk  examples   libmosquitto.pc.in    misc            pskfile.example  snap
CONTRIBUTING.md  README-compiling.md    about.html          client       deps       include    libmosquittopp.pc.in  mosquitto.conf  pwfile.example   src
ChangeLog.txt    README-letsencrypt.md  aclfile.example     cmake        edl-v10    installer  logo                  notice.html     security         test

 third_party/mosquitto/bundle.json内容如下：

{
    "name": "@ohos/mosquitto",
    "description": "Third-party mosquitto MQTT library",
    "version": "2.0.9",
    "license": "MIT",
    "publishAs": "code-segment",
    "segment": {
        "destPath": "third_party/mosquitto"
    },
    "dirs": {},
    "scripts": {},
    "component": {
        "name": "mosquitto",
        "subsystem": "thirdparty",
        "syscap": [],
        "features": [],
        "adapted_system_type": [ "mini", "small", "standard" ],
        "rom": "",
        "ram": "",
        "deps": {
            "components": [],
            "third_party": []
        },
        "build": {
            "sub_component": [],
            "inner_kits": [
                {
                    "header": {
                        "header_base": "//third_party/mosquitto",
                        "header_files": []
                    },
                    "name": "//third_party/mosquitto:mosquitto"
                },
                {
                    "name": "//third_party/mosquitto:mosquitto_static"
                }
            ],
            "test": []
        }
    }
}

 third_party/mosquitto/BUILD.gn

#Copyright (c) 2019-2021 Huawei Device Co., Ltd.
#Licensed under the Apache License, Version 2.0 (the "License");
#you may not use this file except in compliance with the License.
#You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
#Unless required by applicable law or agreed to in writing, software
#distributed under the License is distributed on an "AS IS" BASIS,
#WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#See the License for the specific language governing permissions and
#limitations under the License.
{
  config("mosquitto_config") {
    #头文件
    include_dirs = [
        "//third_party/mosquitto",
        "//third_party/mosquitto/deps",
        "//third_party/mosquitto/src",
        "//third_party/mosquitto/lib",
        "//third_party/mosquitto/include" ]
    ldflags = [ "-lm","-lpthread" ]
    #宏
    #defines = [ "CJSON_NESTING_LIMIT=(128)" ]

    defines = [
        #"WITH_BROKER",
        "WITH_PERSISTENCE",
        "VERSION=\"2.0.18\""
        ]
  }
  #源文件
  mosquitto_sources = [   
    lib/actions.c
    lib/handle_publish.c
    lib/messages_mosq.c
    lib/read_handle.c
    lib/strings_mosq.c
    lib/alias_mosq.c
    lib/handle_pubrec.c
    lib/misc_mosq.c
    lib/send_connect.c
    lib/thread_mosq.c
    lib/callbacks.c
    lib/handle_pubrel.c
    lib/mosquitto.c
    lib/send_disconnect.c
    lib/time_mosq.c
    lib/connect.c
    lib/handle_suback.c
    lib/net_mosq.c
    lib/send_mosq.c
    lib/tls_mosq.c
    lib/handle_auth.c
    lib/handle_unsuback.c
    lib/net_mosq_ocsp.c
    lib/send_publish.c
    lib/utf8_mosq.c
    lib/handle_connack.c
    lib/helpers.c
    lib/options.c
    lib/send_subscribe.c
    lib/util_mosq.c
    lib/handle_disconnect.c
    lib/logging_mosq.c
    lib/packet_datatypes.c
    lib/send_unsubscribe.c
    lib/util_topic.c
    lib/handle_ping.c
    lib/loop.c
    lib/packet_mosq.c
    lib/socks_mosq.c
    lib/will_mosq.c
    lib/handle_pubackcomp.c
    lib/memory_mosq.c
    lib/property_mosq.c
    lib/srv_mosq.c
  ]

  if (defined(board_toolchain_type) && board_toolchain_type == "iccarm") {
    cflags = [
      "--diag_suppress",
      "Pe513",
    ]
    cflags_cc = cflags
  }
  static_library("mosquitto_static") {
    sources = mosquitto_sources
    public_configs = [ ":mosquitto_config" ]
  }

  shared_library("mosquitto_shared") {
    sources = mosquitto_sources
    public_configs = [ ":mosquitto_config" ]
  }
}

在build/lite/config/component/目录下创建mosquito文件夹，并在build/lite/config/component/mosquitto/目录下创建BUILD.gn

#
# Copyright (c) 2020 Huawei Device Co., Ltd.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

import("//build/lite/config/component/lite_component.gni")
import("//build/lite/ndk/ndk.gni")

config("mosquitto_config") {
  include_dirs = [
        "//third_party/mosquitto",
        "//third_party/mosquitto/deps",
        "//third_party/mosquitto/src",
        "//third_party/mosquitto/lib",
        "//third_party/mosquitto/include"
  ]
  ldflags = [ "-lm" ]
  #defines = [ "WITH_BROKER=1" ]
  defines = [
    #"WITH_BROKER",
    "WITH_PERSISTENCE",
    "VERSION=\"2.0.18\""
  ]
  if (board_toolchain_type == "iccarm") {
    cflags = [
      "--diag_suppress",
      "Pa084",
    ]
  }
}

mosquitto_sources = [
  "//third_party/mosquitto/lib/actions.c",
  "//third_party/mosquitto/lib/handle_publish.c",
  "//third_party/mosquitto/lib/messages_mosq.c",
  "//third_party/mosquitto/lib/read_handle.c",
  "//third_party/mosquitto/lib/strings_mosq.c",
  "//third_party/mosquitto/lib/alias_mosq.c",
  "//third_party/mosquitto/lib/handle_pubrec.c",
  "//third_party/mosquitto/lib/misc_mosq.c",
  "//third_party/mosquitto/lib/send_connect.c",
  "//third_party/mosquitto/lib/thread_mosq.c",
  "//third_party/mosquitto/lib/callbacks.c",
  "//third_party/mosquitto/lib/handle_pubrel.c",
  "//third_party/mosquitto/lib/mosquitto.c",
  "//third_party/mosquitto/lib/send_disconnect.c",
  "//third_party/mosquitto/lib/time_mosq.c",
  "//third_party/mosquitto/lib/connect.c",
  "//third_party/mosquitto/lib/handle_suback.c",
  "//third_party/mosquitto/lib/net_mosq.c",
  "//third_party/mosquitto/lib/send_mosq.c",
  "//third_party/mosquitto/lib/tls_mosq.c",
  "//third_party/mosquitto/lib/handle_auth.c",
  "//third_party/mosquitto/lib/handle_unsuback.c",
  "//third_party/mosquitto/lib/net_mosq_ocsp.c",
  "//third_party/mosquitto/lib/send_publish.c",
  "//third_party/mosquitto/lib/utf8_mosq.c",
  "//third_party/mosquitto/lib/handle_connack.c",
  "//third_party/mosquitto/lib/helpers.c",
  "//third_party/mosquitto/lib/options.c",
  "//third_party/mosquitto/lib/send_subscribe.c",
  "//third_party/mosquitto/lib/util_mosq.c",
  "//third_party/mosquitto/lib/handle_disconnect.c",
  "//third_party/mosquitto/lib/logging_mosq.c",
  "//third_party/mosquitto/lib/packet_datatypes.c",
  "//third_party/mosquitto/lib/send_unsubscribe.c",
  "//third_party/mosquitto/lib/util_topic.c",
  "//third_party/mosquitto/lib/handle_ping.c",
  "//third_party/mosquitto/lib/loop.c",
  "//third_party/mosquitto/lib/packet_mosq.c",
  "//third_party/mosquitto/lib/socks_mosq.c",
  "//third_party/mosquitto/lib/will_mosq.c",
  "//third_party/mosquitto/lib/handle_pubackcomp.c",
  "//third_party/mosquitto/lib/memory_mosq.c",
  "//third_party/mosquitto/lib/property_mosq.c",
  "//third_party/mosquitto/lib/srv_mosq.c"

]

lite_library("mosquitto_static") {
  target_type = "static_library"
  sources = mosquitto_sources
  public_configs = [ ":mosquitto_config" ]
}

lite_library("mosquitto_shared") {
  target_type = "shared_library"
  sources = mosquitto_sources
  public_configs = [ ":mosquitto_config" ]
}

ndk_lib("mosquitto_ndk") {
  if (board_name != "hispark_pegasus") {
    lib_extension = ".so"
    deps = [ ":mosquitto_shared" ]
  } else {
    deps = [ ":mosquitto_static" ]
  }
  head_files = [
    "//third_party/mosquitto/include/mosquitto.h",
    "//third_party/mosquitto/include/mosquitto_plugin.h",
    "//third_party/mosquitto/include/mosquitto_broker.h",
    "//third_party/mosquitto/include/mqtt_protocol.h"
  ]
}

单独编译三方库
./build.sh --product-name rk3506 --vendor rockchip --ccache   --gn-args enable_notice_collection=false   linux_kernel_version="linux-6.1" --build-target=mosquitto_shared

生成文件路径：out/rk3506/rk3506/
ls out/rk3506/rk3506/libmosquitto_shared.so -l
-rwxr-xr-x 1 root root 79976 May 18 15:36 out/rk3506/rk3506/libmosquitto_shared.so

如果想要编译进系统，必须让其他组件依赖，才会触发编译，可以修改foundation/arkui/ui_lite/BUILD.gn文件，找到cJSON相关，再其下方添加如下内容

在cjson_static下一行添加
"//build/lite/config/component/mosquitto:mosquitto_static",

在cjson_shared下一行添加
"//build/lite/config/component/mosquitto:mosquitto_shared",

这样修改之后重新编译系统，就会触发编译mosquito,并生成libmosquitto_shared.so了，生成位置为：out/rk3506/rk3506/usr/lib/libmosquitto_shared.so