github.com/mh-cbon/go@v0.0.0-20160603070303-9e112a3fe4c0/src/go/internal/gcimporter/exportdata.go (about)

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