// Copyright 2025 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package trace
import (
"fmt"
"internal/trace/tracev2"
)
// timestamp is an unprocessed timestamp.
type timestamp uint64
// batch represents a batch of trace events.
// It is unparsed except for its header.
type batch struct {
m threadID
time timestamp
data []byte
}
// threadID is the runtime-internal M structure's ID. This is unique
// for each OS thread.
type threadID int64
// readBatch copies b and parses the trace batch header inside.
// Returns the batch, the generation, bytes read, and an error.
func readBatch(b []byte) (batch, uint64, uint64, error) {
if len(b) == 0 {
return batch{}, 0, 0, fmt.Errorf("batch is empty")
}
data := make([]byte, len(b))
if nw := copy(data, b); nw != len(b) {
return batch{}, 0, 0, fmt.Errorf("unexpected error copying batch")
}
// Read batch header byte.
if typ := tracev2.EventType(b[0]); typ != tracev2.EvEventBatch && typ != tracev2.EvExperimentalBatch {
return batch{}, 0, 1, fmt.Errorf("expected batch event, got event %d", typ)
}
// Read the batch header: gen (generation), thread (M) ID, base timestamp
// for the batch.
total := 1
b = b[1:]
gen, n, err := readUvarint(b)
if err != nil {
return batch{}, gen, uint64(total + n), fmt.Errorf("error reading batch gen: %w", err)
}
total += n
b = b[n:]
m, n, err := readUvarint(b)
if err != nil {
return batch{}, gen, uint64(total + n), fmt.Errorf("error reading batch M ID: %w", err)
}
total += n
b = b[n:]
ts, n, err := readUvarint(b)
if err != nil {
return batch{}, gen, uint64(total + n), fmt.Errorf("error reading batch timestamp: %w", err)
}
total += n
b = b[n:]
// Read in the size of the batch to follow.
size, n, err := readUvarint(b)
if err != nil {
return batch{}, gen, uint64(total + n), fmt.Errorf("error reading batch size: %w", err)
}
if size > tracev2.MaxBatchSize {
return batch{}, gen, uint64(total + n), fmt.Errorf("invalid batch size %d, maximum is %d", size, tracev2.MaxBatchSize)
}
total += n
total += int(size)
data = data[:total]
// Return the batch.
return batch{
m: threadID(m),
time: timestamp(ts),
data: data,
}, gen, uint64(total), nil
}
