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A streaming MIME parser for Go. Reads emails from an io.Reader and produces a part tree containing only headers and byte offsets — body data is never buffered. This makes it efficient for indexing large messages and locating attachments or part bodies for later random access.
- Stream-based — parses from any io.Reader in a single pass
- Offset-only — stores byte positions (StartPos, BodyPos, EndPos) instead of body content
- No regexp — all parsing is done with straightforward byte/string operations
- Nested multipart — handles arbitrary nesting of multipart types
- RFC compliant — handles header folding (RFC 2822), boundary delimiters (RFC 2046), both CRLF and LF line endings
go get github.com/KarpelesLab/gomailparse
package main
import (
"fmt"
"os"
"github.com/KarpelesLab/gomailparse"
)
func main() {
f, _ := os.Open("message.eml")
defer f.Close()
part, err := gomailparse.Parse(f)
if err != nil {
panic(err)
}
// Walk all parts
for _, p := range part.Parts() {
fmt.Printf("%-30s body=[%d:%d] (%d bytes)\n",
p.ContentType, p.BodyPos, p.EndPos, p.BodySize())
// Read an attachment body using offsets
if p.ContentDisposition == "attachment" {
reader := p.BodyReader(f)
// reader is an *io.SectionReader positioned at the body
_ = reader
}
}
}Parses a MIME message and returns the root part. Only headers and byte offsets are retained.
type Part struct {
StartPos int64 // byte offset: start of part (headers)
BodyPos int64 // byte offset: start of body
EndPos int64 // byte offset: end of body
Header textproto.MIMEHeader // parsed headers (canonical key form)
ContentType string // e.g. "text/plain"
Boundary string // for multipart types
Charset string // defaults to "us-ascii"
TransferEncoding string // defaults to "7bit"
ContentDisposition string // "attachment", "inline", etc.
Name string // name= from Content-Type
Filename string // filename= from Content-Disposition (RFC 2231 supported)
Children []*Part
}Header is a standard textproto.MIMEHeader:
- Header.Get("Subject") — first value (case-insensitive)
- Header.Values("Received") — all values
- Header["Content-Type"] — direct map access with canonical key
- Walk(func(*Part) bool) bool — depth-first traversal (return false to stop)
- Parts() []*Part — flat list of all parts
- BodySize() int64 — body size in bytes
- BodyReader(ra io.ReaderAt) *io.SectionReader — positioned reader for the body
MIT — see LICENSE.