ps:下面操作是Linux系统，针对win操作系统也适合

问题现象

在运行conan install时，本地没有对应的库的缓存，conan会自动从conan center下载，可能会出现以下情况，重试多次，仍然是报错。

libssh2/1.11.0: Calling source() in /root/.conan2/p/libss767f7ba6d9ff3/s/src
libssh2/1.11.0: ERROR: Error downloading file https://github.com/libssh2/libssh2/releases/download/libssh2-1.11.0/libssh2-1.11.0.tar.xz: 'HTTPSConnectionPool(host='github.com', port=443): Max retries exceeded with url: /libssh2/libssh2/releases/download/libssh2-1.11.0/libssh2-1.11.0.tar.xz (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x7f2ed1abbe10>: Failed to establish a new connection: [Errno -2] Name or service not known',))'
libssh2/1.11.0: Waiting 5 seconds to retry...
libssh2/1.11.0: ERROR: Error downloading file https://github.com/libssh2/libssh2/releases/download/libssh2-1.11.0/libssh2-1.11.0.tar.xz: 'HTTPSConnectionPool(host='github.com', port=443): Max retries exceeded with url: /libssh2/libssh2/releases/download/libssh2-1.11.0/libssh2-1.11.0.tar.xz (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x7f2ed0b61c18>: Failed to establish a new connection: [Errno -2] Name or service not known',))'
libssh2/1.11.0: Waiting 5 seconds to retry...
ERROR: libssh2/1.11.0: Error in source() method, line 94
        get(self, **self.conan_data["sources"][self.version], strip_root=True)
        ConanException: Error downloading file https://github.com/libssh2/libssh2/releases/download/libssh2-1.11.0/libssh2-1.11.0.tar.xz: 'HTTPSConnectionPool(host='github.com', port=443): Max retries exceeded with url: /libssh2/libssh2/releases/download/libssh2-1.11.0/libssh2-1.11.0.tar.xz (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x7f2ed0b75208>: Failed to establish a new connection: [Errno -2] Name or service not known',))'

手动下载解决

1、将日志中的url复制到浏览器，https://github.com/libssh2/libssh2/releases/download/libssh2-1.11.0/libssh2-1.11.0.tar.xz，进行手动下载。（可以开代理，或者IDM多线程下载）

2、修改conanfile.py

aii@debian:~/.conan2/p/libss767f7ba6d9ff3/e$ vi conanfile.py

    def source(self):
        # 将下载解压操作注释了
        # get(self, **self.conan_data["sources"][self.version], strip_root=True)
        apply_conandata_patches(self)

3、运行一下conan install操作，这时会有报错：CMake Error: The source directory "/home/aii/.conan2/p/b/libss572bb9f56ef42/b/src" does not appear to contain CMakeLists.txt.没有关系，目的是跳过状态。删除新生产的目录rm -rf /home/aii/.conan2/p/b/libss572bb9f56ef42

4、将下载成功后，将libssh2-1.11.0.tar.xz文件解压到对应目录/root/.conan2/p/libss767f7ba6d9ff3/s/src，注意src下是libssh2-1.11.0目录下的文件

5、再次运行conan install操作，就正常了，直接编译，安装对应的库