exportdata.go

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