无法克隆socket.io子模块，多次尝试仍失败求助

问题详情 #

执行git clone --recursive -j8 https://github.com/saikat/DrawTogether.git克隆DrawTogether仓库时，主仓库克隆成功，但socket.io子模块无法克隆，错误输出如下：

C:\Users\raj\Desktop>git clone --recursive -j8 https://github.com/saikat/DrawTogether.git
Cloning into 'DrawTogether'...
remote: Enumerating objects: 505, done.
remote: Total 505 (delta 0), reused 0 (delta 0), pack-reused 505
Receiving objects: 100% (505/505), 1.04 MiB | 2.10 MiB/s, done.
Resolving deltas: 100% (75/75), done.
Submodule 'lib/socket.io' (git://github.com/LearnBoost/Socket.IO-node.git) registered for path 'lib/socket.io'
Cloning into 'C:/Users/raj/Desktop/DrawTogether/lib/socket.io'...
fatal: unable to connect to github.com:
github.com[0: 20.205.243.166]: errno=Unknown error

fatal: clone of 'git://github.com/LearnBoost/Socket.IO-node.git' into submodule path 'C:/Users/raj/Desktop/DrawTogether/lib/socket.io' failed
Failed to clone 'lib/socket.io'. Retry scheduled
Cloning into 'C:/Users/raj/Desktop/DrawTogether/lib/socket.io'...
fatal: unable to connect to github.com:
github.com[0: 20.205.243.166]: errno=Unknown error

fatal: clone of 'git://github.com/LearnBoost/Socket.IO-node.git' into submodule path 'C:/Users/raj/Desktop/DrawTogether/lib/socket.io' failed
Failed to clone 'lib/socket.io' a second time, aborting

尝试执行以下命令重试：

git submodule init
git submodule update

但仍出现相同错误：

Cloning into 'C:/Users/raj/Desktop/DrawTogether/lib/socket.io'...    fatal: unable to connect to github.com: github.com[0:
   20.205.243.166]: errno=Unknown error
       fatal: clone of 'git://github.com/LearnBoost/Socket.IO-node.git' into    submodule path 'C:/Users/raj/Desktop/DrawTogether/lib/socket.io'    failed Failed to clone 'lib/socket.io'. Retry scheduled Cloning into    'C:/Users/raj/Desktop/DrawTogether/lib/socket.io'... fatal: unable to    connect to github.com: github.com[0: 20.205.243.166]: errno=Unknown    error
       fatal: clone of 'git://github.com/LearnBoost/Socket.IO-node.git' into    submodule path 'C:/Users/raj/Desktop/DrawTogether/lib/socket.io'    failed Failed to clone 'lib/socket.io' a second time, aborting

解决方法 #

1. 单独修改子模块协议为HTTPS #

进入已克隆的主仓库目录，修改子模块的远程URL为HTTPS后重新更新：

cd DrawTogether
git config submodule.lib/socket.io.url https://github.com/LearnBoost/Socket.IO-node.git
git submodule update --init

2. 全局配置Git自动转换协议 #

若经常遇到git://协议被限制的问题，可全局设置Git将所有GitHub的git://请求转换为HTTPS：

git config --global url."https://github.com/".insteadOf git://github.com/

配置完成后，直接执行git submodule update --init即可自动使用HTTPS克隆子模块。

3. 手动克隆子模块到指定路径 #

如果上述方法无效，可手动克隆子模块到对应目录：

# 进入主仓库目录
cd DrawTogether
# 删除已创建的空目录（如果存在）
rmdir /s lib/socket.io
# 用HTTPS克隆子模块到指定路径
git clone https://github.com/LearnBoost/Socket.IO-node.git lib/socket.io
# 同步子模块状态
git submodule sync

内容的提问来源于stack exchange，提问作者Ritu Raj