batch.go

     1  // Copyright 2025 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package trace
     6  
     7  import (
     8  	"fmt"
     9  	"internal/trace/tracev2"
    10  )
    11  
    12  // timestamp is an unprocessed timestamp.
    13  type timestamp uint64
    14  
    15  type batch struct {
    16  	time timestamp
    17  	gen  uint64
    18  	data []byte
    19  }
    20  
    21  // readBatch copies b and parses the trace batch header inside.
    22  // Returns the batch, bytes read, and an error.
    23  func readBatch(b []byte) (batch, uint64, error) {
    24  	if len(b) == 0 {
    25  		return batch{}, 0, fmt.Errorf("batch is empty")
    26  	}
    27  	data := make([]byte, len(b))
    28  	copy(data, b)
    29  
    30  	// Read batch header byte.
    31  	if typ := tracev2.EventType(b[0]); typ == tracev2.EvEndOfGeneration {
    32  		if len(b) != 1 {
    33  			return batch{}, 1, fmt.Errorf("unexpected end of generation in batch of size >1")
    34  		}
    35  		return batch{data: data}, 1, nil
    36  	}
    37  	if typ := tracev2.EventType(b[0]); typ != tracev2.EvEventBatch && typ != tracev2.EvExperimentalBatch {
    38  		return batch{}, 1, fmt.Errorf("expected batch event, got event %d", typ)
    39  	}
    40  	total := 1
    41  	b = b[1:]
    42  
    43  	// Read the generation
    44  	gen, n, err := readUvarint(b)
    45  	if err != nil {
    46  		return batch{}, uint64(total + n), fmt.Errorf("error reading batch gen: %w", err)
    47  	}
    48  	total += n
    49  	b = b[n:]
    50  
    51  	// Read the M (discard it).
    52  	_, n, err = readUvarint(b)
    53  	if err != nil {
    54  		return batch{}, uint64(total + n), fmt.Errorf("error reading batch M ID: %w", err)
    55  	}
    56  	total += n
    57  	b = b[n:]
    58  
    59  	// Read the timestamp.
    60  	ts, n, err := readUvarint(b)
    61  	if err != nil {
    62  		return batch{}, uint64(total + n), fmt.Errorf("error reading batch timestamp: %w", err)
    63  	}
    64  	total += n
    65  	b = b[n:]
    66  
    67  	// Read the size of the batch to follow.
    68  	size, n, err := readUvarint(b)
    69  	if err != nil {
    70  		return batch{}, uint64(total + n), fmt.Errorf("error reading batch size: %w", err)
    71  	}
    72  	if size > tracev2.MaxBatchSize {
    73  		return batch{}, uint64(total + n), fmt.Errorf("invalid batch size %d, maximum is %d", size, tracev2.MaxBatchSize)
    74  	}
    75  	total += n
    76  	total += int(size)
    77  	if total != len(data) {
    78  		return batch{}, uint64(total), fmt.Errorf("expected complete batch")
    79  	}
    80  	data = data[:total]
    81  
    82  	// Return the batch.
    83  	return batch{
    84  		gen:  gen,
    85  		time: timestamp(ts),
    86  		data: data,
    87  	}, uint64(total), nil
    88  }
    89
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