exportdata.go

Documentation: golang.org/x/tools/internal/gcimporter

     1  // Copyright 2011 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  // This file is a copy of $GOROOT/src/go/internal/gcimporter/exportdata.go.
     6  
     7  // This file implements FindExportData.
     8  
     9  package gcimporter
    10  
    11  import (
    12  	"bufio"
    13  	"fmt"
    14  	"io"
    15  	"strconv"
    16  	"strings"
    17  )
    18  
    19  func readGopackHeader(r *bufio.Reader) (name string, size int64, err error) {
    20  	// See $GOROOT/include/ar.h.
    21  	hdr := make([]byte, 16+12+6+6+8+10+2)
    22  	_, err = io.ReadFull(r, hdr)
    23  	if err != nil {
    24  		return
    25  	}
    26  	// leave for debugging
    27  	if false {
    28  		fmt.Printf("header: %s", hdr)
    29  	}
    30  	s := strings.TrimSpace(string(hdr[16+12+6+6+8:][:10]))
    31  	length, err := strconv.Atoi(s)
    32  	size = int64(length)
    33  	if err != nil || hdr[len(hdr)-2] != '`' || hdr[len(hdr)-1] != '\n' {
    34  		err = fmt.Errorf("invalid archive header")
    35  		return
    36  	}
    37  	name = strings.TrimSpace(string(hdr[:16]))
    38  	return
    39  }
    40  
    41  // FindExportData positions the reader r at the beginning of the
    42  // export data section of an underlying GC-created object/archive
    43  // file by reading from it. The reader must be positioned at the
    44  // start of the file before calling this function. The hdr result
    45  // is the string before the export data, either "$$" or "$$B".
    46  // The size result is the length of the export data in bytes, or -1 if not known.
    47  func FindExportData(r *bufio.Reader) (hdr string, size int64, err error) {
    48  	// Read first line to make sure this is an object file.
    49  	line, err := r.ReadSlice('\n')
    50  	if err != nil {
    51  		err = fmt.Errorf("can't find export data (%v)", err)
    52  		return
    53  	}
    54  
    55  	if string(line) == "!<arch>\n" {
    56  		// Archive file. Scan to __.PKGDEF.
    57  		var name string
    58  		if name, size, err = readGopackHeader(r); err != nil {
    59  			return
    60  		}
    61  
    62  		// First entry should be __.PKGDEF.
    63  		if name != "__.PKGDEF" {
    64  			err = fmt.Errorf("go archive is missing __.PKGDEF")
    65  			return
    66  		}
    67  
    68  		// Read first line of __.PKGDEF data, so that line
    69  		// is once again the first line of the input.
    70  		if line, err = r.ReadSlice('\n'); err != nil {
    71  			err = fmt.Errorf("can't find export data (%v)", err)
    72  			return
    73  		}
    74  		size -= int64(len(line))
    75  	}
    76  
    77  	// Now at __.PKGDEF in archive or still at beginning of file.
    78  	// Either way, line should begin with "go object ".
    79  	if !strings.HasPrefix(string(line), "go object ") {
    80  		err = fmt.Errorf("not a Go object file")
    81  		return
    82  	}
    83  
    84  	// Skip over object header to export data.
    85  	// Begins after first line starting with $$.
    86  	for line[0] != '$' {
    87  		if line, err = r.ReadSlice('\n'); err != nil {
    88  			err = fmt.Errorf("can't find export data (%v)", err)
    89  			return
    90  		}
    91  		size -= int64(len(line))
    92  	}
    93  	hdr = string(line)
    94  	if size < 0 {
    95  		size = -1
    96  	}
    97  
    98  	return
    99  }
   100
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