event.go

/*
 * Copyright 2024 CloudWeGo Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * The MIT License (MIT)
 *
 * Copyright (c) 2014 Manuel Martínez-Almeida
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package sse

import (
	"bufio"
	"bytes"
	"context"
	"io"
)

func (e *Event) hasContent() bool {
	return len(e.ID) > 0 || len(e.Data) > 0 || len(e.Event) > 0 || e.Retry > 0
}

// EventStreamReader scans an io.Reader looking for EventStream messages.
type EventStreamReader struct {
	scanner *bufio.Scanner
}

// NewEventStreamReader creates an instance of EventStreamReader.
func NewEventStreamReader(eventStream io.Reader, maxBufferSize int) *EventStreamReader {
	scanner := bufio.NewScanner(eventStream)
	initBufferSize := minPosInt(4096, maxBufferSize)
	scanner.Buffer(make([]byte, initBufferSize), maxBufferSize)

	split := func(data []byte, atEOF bool) (int, []byte, error) {
		if atEOF && len(data) == 0 {
			return 0, nil, nil
		}
		// We have a full event payload to parse.
		if i, nlen := containsDoubleNewline(data); i >= 0 {
			return i + nlen, data[0:i], nil
		}
		// If we're at EOF, we have all of the data.
		if atEOF {
			return len(data), data, nil
		}
		// Request more data.
		return 0, nil, nil
	}
	// Set the split function for the scanning operation.
	scanner.Split(split)

	return &EventStreamReader{
		scanner: scanner,
	}
}

// Returns a tuple containing the index of a double newline, and the number of bytes
// represented by that sequence. If no double newline is present, the first value
// will be negative.
func containsDoubleNewline(data []byte) (int, int) {
	// Search for each potentially valid sequence of newline characters
	crcr := bytes.Index(data, []byte("\r\r"))
	lflf := bytes.Index(data, []byte("\n\n"))
	crlflf := bytes.Index(data, []byte("\r\n\n"))
	lfcrlf := bytes.Index(data, []byte("\n\r\n"))
	crlfcrlf := bytes.Index(data, []byte("\r\n\r\n"))
	// Find the earliest position of a double newline combination
	minPos := minPosInt(crcr, minPosInt(lflf, minPosInt(crlflf, minPosInt(lfcrlf, crlfcrlf))))
	// Determine the length of the sequence
	nlen := 2
	if minPos == crlfcrlf {
		nlen = 4
	} else if minPos == crlflf || minPos == lfcrlf {
		nlen = 3
	}
	return minPos, nlen
}

// Returns the minimum non-negative value out of the two values. If both
// are negative, a negative value is returned.
func minPosInt(a, b int) int {
	if a < 0 {
		return b
	}
	if b < 0 {
		return a
	}
	if a > b {
		return b
	}
	return a
}

// ReadEvent scans the EventStream for events.
func (e *EventStreamReader) ReadEvent(ctx context.Context) ([]byte, error) {
	if e.scanner.Scan() {
		select {
		case <-ctx.Done():
			return nil, io.EOF
		default:
			event := e.scanner.Bytes()
			return event, nil
		}
	}
	if err := e.scanner.Err(); err != nil {
		return nil, err
	}
	return nil, io.EOF
}