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mox!
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65
message/headerwriter.go
Normal file
65
message/headerwriter.go
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@ -0,0 +1,65 @@
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package message
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import (
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"fmt"
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"strings"
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)
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// HeaderWriter helps create headers, folding to the next line when it would
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// become too large. Useful for creating Received and DKIM-Signature headers.
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type HeaderWriter struct {
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b *strings.Builder
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lineLen int
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nonfirst bool
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}
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// Addf formats the string and calls Add.
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func (w *HeaderWriter) Addf(separator string, format string, args ...any) {
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w.Add(separator, fmt.Sprintf(format, args...))
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}
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// Add adds texts, each separated by separator. Individual elements in text are
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// not wrapped.
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func (w *HeaderWriter) Add(separator string, texts ...string) {
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if w.b == nil {
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w.b = &strings.Builder{}
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}
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for _, text := range texts {
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n := len(text)
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if w.nonfirst && w.lineLen > 1 && w.lineLen+len(separator)+n > 78 {
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w.b.WriteString("\r\n\t")
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w.lineLen = 1
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} else if w.nonfirst && separator != "" {
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w.b.WriteString(separator)
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w.lineLen += len(separator)
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}
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w.b.WriteString(text)
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w.lineLen += len(text)
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w.nonfirst = true
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}
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}
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// AddWrap adds data, folding anywhere in the buffer. E.g. for base64 data.
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func (w *HeaderWriter) AddWrap(buf []byte) {
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for len(buf) > 0 {
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line := buf
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n := 78 - w.lineLen
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if len(buf) > n {
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line, buf = buf[:n], buf[n:]
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} else {
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buf = nil
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n = len(buf)
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}
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w.b.Write(line)
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w.lineLen += n
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if len(buf) > 0 {
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w.b.WriteString("\r\n\t")
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w.lineLen = 1
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}
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}
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}
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// String returns the header in string form, ending with \r\n.
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func (w *HeaderWriter) String() string {
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return w.b.String() + "\r\n"
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}
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