95 lines
2.5 KiB
Go
95 lines
2.5 KiB
Go
// Package mailutil provides utilities for email processing:
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// charset conversion and RFC 2047 address formatting.
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package mailutil
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import (
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"fmt"
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"io"
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"mime"
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"strings"
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"unicode/utf8"
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asgomail "github.com/emersion/go-message/mail"
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"golang.org/x/text/encoding/htmlindex"
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)
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// DecodeCharset converts bytes from the given charset to a UTF-8 string.
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// If charset is empty, "utf-8", or "us-ascii", it returns string(buf) directly.
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// If the bytes are already valid UTF-8, no conversion is attempted.
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func DecodeCharset(buf []byte, charset string) string {
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cs := strings.ToLower(strings.Trim(charset, `"'`))
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if cs == "" || cs == "utf-8" || cs == "us-ascii" {
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return string(buf)
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}
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// 已是合法 UTF-8，无需转换
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if utf8.Valid(buf) {
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return string(buf)
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}
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enc, err := htmlindex.Get(cs)
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if err != nil {
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// 未知字符集，原样返回
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return string(buf)
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}
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decoded, err := enc.NewDecoder().Bytes(buf)
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if err != nil {
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// 解码失败，原样返回
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return string(buf)
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}
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return string(decoded)
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}
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// DecodeRFC2047 解码邮件头中的 RFC 2047 encoded-word。
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func DecodeRFC2047(value string) string {
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decoder := mime.WordDecoder{
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CharsetReader: func(charset string, input io.Reader) (io.Reader, error) {
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data, err := io.ReadAll(input)
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if err != nil {
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return nil, err
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}
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return strings.NewReader(DecodeCharset(data, charset)), nil
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},
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}
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decoded, err := decoder.DecodeHeader(value)
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if err != nil {
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return value
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}
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return decoded
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}
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// FormatAddressList 解析 RFC 2047 编码的地址列表头并格式化为可读字符串。
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// 例如: "=?gb2312?B?zuIgzsS35Q==?= <a@b.com>" → "吴文锋 <a@b.com>"
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func FormatAddressList(header *asgomail.Header, key string) string {
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addrs, err := header.AddressList(key)
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if err != nil || len(addrs) == 0 {
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// 降级：返回解码后的原始值
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return DecodeRFC2047(header.Get(key))
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}
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var parts []string
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for _, addr := range addrs {
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if addr.Name != "" {
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parts = append(parts, fmt.Sprintf("%s <%s>", addr.Name, addr.Address))
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} else {
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parts = append(parts, addr.Address)
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}
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}
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return strings.Join(parts, ", ")
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}
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// ExtractCharset 从 Content-Type 头值中提取 charset 参数。
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// 例如: "text/plain; charset=gb2312" → "gb2312"
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func ExtractCharset(contentType string) string {
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parts := strings.Split(contentType, ";")
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for _, part := range parts[1:] {
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part = strings.TrimSpace(part)
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if strings.HasPrefix(strings.ToLower(part), "charset=") {
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return strings.Trim(strings.TrimPrefix(part, "charset="), `"'`)
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}
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}
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return ""
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}
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