parse.go

     1  // Copyright 2023 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 counter
     6  
     7  import (
     8  	"bytes"
     9  	"fmt"
    10  	"strings"
    11  	"unsafe"
    12  
    13  	"golang.org/x/telemetry/internal/mmap"
    14  )
    15  
    16  type File struct {
    17  	Meta  map[string]string
    18  	Count map[string]uint64
    19  }
    20  
    21  func Parse(filename string, data []byte) (*File, error) {
    22  	if !bytes.HasPrefix(data, []byte(hdrPrefix)) || len(data) < pageSize {
    23  		if len(data) < pageSize {
    24  			return nil, fmt.Errorf("%s: file too short (%d<%d)", filename, len(data), pageSize)
    25  		}
    26  		return nil, fmt.Errorf("%s: wrong hdr (not %q)", filename, hdrPrefix)
    27  	}
    28  	corrupt := func() (*File, error) {
    29  		// TODO(rfindley): return a useful error message.
    30  		return nil, fmt.Errorf("%s: corrupt counter file", filename)
    31  	}
    32  
    33  	f := &File{
    34  		Meta:  make(map[string]string),
    35  		Count: make(map[string]uint64),
    36  	}
    37  	np := round(len(hdrPrefix), 4)
    38  	hdrLen := *(*uint32)(unsafe.Pointer(&data[np]))
    39  	if hdrLen > pageSize {
    40  		return corrupt()
    41  	}
    42  	meta := data[np+4 : hdrLen]
    43  	if i := bytes.IndexByte(meta, 0); i >= 0 {
    44  		meta = meta[:i]
    45  	}
    46  	m := &mappedFile{
    47  		meta:    string(meta),
    48  		hdrLen:  hdrLen,
    49  		mapping: &mmap.Data{Data: data},
    50  	}
    51  
    52  	lines := strings.Split(m.meta, "\n")
    53  	for _, line := range lines {
    54  		if line == "" {
    55  			continue
    56  		}
    57  		k, v, ok := strings.Cut(line, ": ")
    58  		if !ok {
    59  			return corrupt()
    60  		}
    61  		f.Meta[k] = v
    62  	}
    63  
    64  	for i := uint32(0); i < numHash; i++ {
    65  		headOff := hdrLen + hashOff + i*4
    66  		head := m.load32(headOff)
    67  		off := head
    68  		for off != 0 {
    69  			ename, next, v, ok := m.entryAt(off)
    70  			if !ok {
    71  				return corrupt()
    72  			}
    73  			if _, ok := f.Count[string(ename)]; ok {
    74  				return corrupt()
    75  			}
    76  			ctrName := DecodeStack(string(ename))
    77  			f.Count[ctrName] = v.Load()
    78  			off = next
    79  		}
    80  	}
    81  	return f, nil
    82  }
    83
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