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package sse
import (
"bufio"
"fmt"
"io"
"strings"
)
// Event represents a server-sent event. Name and ID are optional fields.
type Event struct {
Name string
ID string
Data string
}
// Decoder reads and decodes a server-sent event from an input stream.
type Decoder struct {
scanner *bufio.Scanner
}
// Decode reads and decodes the next event from the underlying reader.
func (d *Decoder) Decode() (*Event, error) {
// https://www.rfc-editor.org/rfc/rfc8895.html#name-server-push-server-sent-eve
var (
event Event
data strings.Builder
lastRead string
gotName bool
gotID bool
gotData bool
decoding bool
)
for d.scanner.Scan() {
line := strings.TrimSpace(d.scanner.Text())
if line == "" {
if decoding {
break // Done with event
} else {
continue // Waiting for first non-empty line
}
}
lastRead = line
decoding = true
parts := strings.SplitN(line, ": ", 2)
if len(parts) < 2 || parts[0] == "" {
continue
}
switch parts[0] {
case "event":
if gotName {
return nil, fmt.Errorf("got more than one event line: last read %q", lastRead)
}
event.Name = parts[1]
gotName = true
case "id":
if gotID {
return nil, fmt.Errorf("got more than one id line: last read %q", lastRead)
}
event.ID = parts[1]
gotID = true
case "data":
if data.Len() > 0 {
data.WriteString(" ")
}
data.WriteString(parts[1])
gotData = true
default:
return nil, fmt.Errorf("invalid field name %q: last read %q", parts[0], lastRead)
}
}
if err := d.scanner.Err(); err != nil {
return nil, err
}
if !decoding {
return nil, io.EOF
}
if !event.IsEnd() && !gotData {
return nil, fmt.Errorf("no data line found for event: last read %q", lastRead)
}
event.Data = data.String()
return &event, nil
}
// NewDecoder creates a new Decoder that reads from r.
func NewDecoder(r io.Reader) *Decoder { return &Decoder{scanner: bufio.NewScanner(r)} }
// IsEnd returns whether this event indicates that the stream has ended.
func (e Event) IsEnd() bool { return e.Name == "end" }
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