efritz/derision-smtp

package main

import (
    "bufio"
    "fmt"
    "strings"
)

type (
    reader struct {
        addr   string
        reader *bufio.Reader
        writer *bufio.Writer
    }

    event struct {
        Recipient string `json:"recipient"`
        Subject   string `json:"subject"`
        Body      string `json:"body"`
    }
)

func newReader(addr string, r *bufio.Reader, w *bufio.Writer) *reader {
    return &reader{addr: addr, reader: r, writer: w}
}

func (r *reader) readEvent() *event {
    r.write("220 Welcome")

    r.read()
    r.write("250 Sender OK")

    recipientLine, _ := r.read()
    r.write("250 Recipient OK")

    r.read()
    r.write("250 OK")

    r.read()
    r.write("354 Data")

    payload := r.readPayload()
    r.write("250 OK")

    // Split into headers and body
    parts := strings.SplitN(payload, "\r\n\r\n", 2)

    r.read()
    r.write("221 Bye")

    return &event{
        Recipient: extractRecipient(recipientLine),
        Subject:   extractSubject(parts[0]),
        Body:      strings.TrimSpace(parts[1]),
    }
}

//
// Read/Write Helpers

func (r *reader) read() (string, bool) {
    reply, err := r.reader.ReadString('\n')
    fmt.Printf("[%s] >> %s", r.addr, reply)
    return reply, err == nil
}

func (r *reader) write(line string) {
    fmt.Printf("[%s] << %s\n", r.addr, line)
    r.writer.WriteString(line + "\r\n")
    r.writer.Flush()
}

func (r *reader) readPayload() string {
    payload := ""

    for {
        line, ok := r.read()

        if !ok || line == ".\r\n" {
            return payload
        }

        payload += line
    }
}

//
// Parsing Helpers

func extractRecipient(line string) string {
    return strings.Trim(strings.TrimSpace(strings.SplitN(line, ":", 2)[1]), "<>")
}

func extractSubject(headers string) string {
    for _, line := range strings.Split(headers, "\r\n") {
        if strings.HasPrefix(line, "Subject:") {
            return strings.TrimSpace(line[8:])
        }
    }

    return ""
}