更新
下载之前更新一下源就没那么多事了
go env -w GOPROXY=https://goproxy.cn,direct
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版本
go 1.13
过程
一开始直接go go get gopkg.in/gomail.v2时提示:
go get gopkg.in/gomail.v2: module gopkg.in/gomail.v2: Get
https://proxy.golang.org/gopkg.in/gomail.v2/@v/list: dial tcp 216.58.200.49:443:
connectex: A connection attempt failed because the connected party did not
properly respond after a period of time, or established connection failed because
connected host has failed to respond.
后面直接用gopm get -g gopkg.in/gomail.v2，安装成功了，自动安装到/$GOPATH/src/gopkg.in下，因为项目用的是go.mod的方式，就把包复制到了 $GOPATH/pkg/mod/gopkg.in下，然后再项目里 直接 import "gopkg.in/gomail.v2"
结果也找到包了，但是还是下载失败
go: finding gopkg.in/gomail.v2 latest
go: downloading gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df
verifying gopkg.in/gomail.v2@v2.0.0-20160411212932-81ebce5c23df:
gopkg.in/gomail.v2@v2.0.0-20160411212932-81ebce5c23df: Get
https://sum.golang.org/lookup/gopkg.in/gomail.v2@v2.0.0-20160411212932-
81ebce5c23df: dial tcp 172.217.24.17:443: connectex: A connection attempt
failed because the connected party did not properly respond after a period of
time, or established connection failed because connected host has failed to
respond.
解决方案
后来才知道, go 1.13之后默认会用sum校验,就是go.sum，由于刚刚下载的包虽然下载成功了，但是目录名是gomail.v2，所以module还是认为在你这里找不到包，于是会自动去下载，后面的就清除了，因为大陆访问不了gopkg.in，所以下载失败。。
现在只需要将 GOPROXY设置一下就好了
go env -w GOPROXY=https://goproxy.cn
然后运行项目
go run ./main.go
go: finding gopkg.in/gomail.v2 latest
go: downloading gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df
go: extracting gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df
成功，然后可以看到go.sum添加了如下信息
gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df h1:n7WqCuqOuCbNr617RXOY0AWRXxgwEyPp2z+p0+hgMuE=
gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df/go.mod h1:LRQQ+SO6ZHR7tOkpBDuZnXENFzX8qRjMDMyPD6BRkCw=
总结
有时候gopm get下载下来之后，发生上面的情况，可以按照报错的提示，将目录名修改一下就可以了，例如 提示 verifying gopkg.in/[email protected]:，直接把刚刚gopm安装的包名改一下[email protected]:就可以了
