Docker镜像名称如何解析？

TL; DR：主机名必须在第

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在仔细研究了代码之后，我遇到了distribution / reference /
reference.go
，内容如下：

// Grammar////  reference := name [ ":" tag ] [ "@" digest ]//  name      := [hostname '/'] component ['/' component]*//  hostname  := hostcomponent ['.' hostcomponent]* [':' port-number]//  hostcomponent        := /([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9-]*[a-zA-Z0-9])///  port-number          := /[0-9]+///  component := alpha-numeric [separator alpha-numeric]*//  alpha-numeric        := /[a-z0-9]+///  separator := /[_.]|__|[-]*/////  tag       := /[w][w.-]{0,127}/////  digest    := digest-algorithm ":" digest-hex//  digest-algorithm     := digest-algorithm-component [ digest-algorithm-separator digest-algorithm-component ]//  digest-algorithm-separator      := /[+.-_]///  digest-algorithm-component      := /[A-Za-z][A-Za-z0-9]*///  digest-hex:= /[0-9a-fA-F]{32,}/ ; At least 128 bit digest value

实际的实现是通过distribution / reference /
regexp.go中的regex实现的。

但是经过一番摸索之后，我发现除了该正则表达式外还有另一项检查（如果不包含a

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// splitDockerDomain splits a repository name to domain and remotename string.// If no valid domain is found, the default domain is used. Repository name// needs to be already validated before.func splitDockerDomain(name string) (domain, remainder string) {    i := strings.IndexRune(name, '/')    if i == -1 || (!strings.ContainsAny(name[:i], ".:") && name[:i] != "localhost") {        domain, remainder = defaultDomain, name    } else {        domain, remainder = name[:i], name[i+1:]    }    if domain == legacyDefaultDomain {        domain = defaultDomain    }    if domain == defaultDomain && !strings.ContainsRune(remainder, '/') {        remainder = officialReponame + "/" + remainder    }    return}

对我而言，重要的部分是检查if语句中的第一个

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