github.com/insionng/yougam@v0.0.0-20170714101924-2bc18d833463/libraries/x/tools/go/gcimporter15/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  // +build go1.5
     6  
     7  // This file is a copy of $GOROOT/src/go/internal/gcimporter/exportdata.go, tagged for go1.5.
     8  
     9  // This file implements FindExportData.
    10  
    11  package gcimporter
    12  
    13  import (
    14  	"bufio"
    15  	"errors"
    16  	"fmt"
    17  	"io"
    18  	"strconv"
    19  	"strings"
    20  )
    21  
    22  func readGopackHeader(r *bufio.Reader) (name string, size int, err error) {
    23  	// See $GOROOT/include/ar.h.
    24  	hdr := make([]byte, 16+12+6+6+8+10+2)
    25  	_, err = io.ReadFull(r, hdr)
    26  	if err != nil {
    27  		return
    28  	}
    29  	// leave for debugging
    30  	if false {
    31  		fmt.Printf("header: %s", hdr)
    32  	}
    33  	s := strings.TrimSpace(string(hdr[16+12+6+6+8:][:10]))
    34  	size, err = strconv.Atoi(s)
    35  	if err != nil || hdr[len(hdr)-2] != '`' || hdr[len(hdr)-1] != '\n' {
    36  		err = errors.New("invalid archive header")
    37  		return
    38  	}
    39  	name = strings.TrimSpace(string(hdr[:16]))
    40  	return
    41  }
    42  
    43  // FindExportData positions the reader r at the beginning of the
    44  // export data section of an underlying GC-created object/archive
    45  // file by reading from it. The reader must be positioned at the
    46  // start of the file before calling this function. The hdr result
    47  // is the string before the export data, either "$$" or "$$B".
    48  //
    49  func FindExportData(r *bufio.Reader) (hdr string, err error) {
    50  	// Read first line to make sure this is an object file.
    51  	line, err := r.ReadSlice('\n')
    52  	if err != nil {
    53  		return
    54  	}
    55  
    56  	if string(line) == "!<arch>\n" {
    57  		// Archive file. Scan to __.PKGDEF.
    58  		var name string
    59  		var size int
    60  		if name, size, err = readGopackHeader(r); err != nil {
    61  			return
    62  		}
    63  
    64  		// Optional leading __.GOSYMDEF or __.SYMDEF.
    65  		// Read and discard.
    66  		if name == "__.SYMDEF" || name == "__.GOSYMDEF" {
    67  			const block = 4096
    68  			tmp := make([]byte, block)
    69  			for size > 0 {
    70  				n := size
    71  				if n > block {
    72  					n = block
    73  				}
    74  				if _, err = io.ReadFull(r, tmp[:n]); err != nil {
    75  					return
    76  				}
    77  				size -= n
    78  			}
    79  
    80  			if name, _, err = readGopackHeader(r); err != nil {
    81  				return
    82  			}
    83  		}
    84  
    85  		// First real entry should be __.PKGDEF.
    86  		if name != "__.PKGDEF" {
    87  			err = errors.New("go archive is missing __.PKGDEF")
    88  			return
    89  		}
    90  
    91  		// Read first line of __.PKGDEF data, so that line
    92  		// is once again the first line of the input.
    93  		if line, err = r.ReadSlice('\n'); err != nil {
    94  			return
    95  		}
    96  	}
    97  
    98  	// Now at __.PKGDEF in archive or still at beginning of file.
    99  	// Either way, line should begin with "go object ".
   100  	if !strings.HasPrefix(string(line), "go object ") {
   101  		err = errors.New("not a go object file")
   102  		return
   103  	}
   104  
   105  	// Skip over object header to export data.
   106  	// Begins after first line starting with $$.
   107  	for line[0] != '$' {
   108  		if line, err = r.ReadSlice('\n'); err != nil {
   109  			return
   110  		}
   111  	}
   112  	hdr = string(line)
   113  
   114  	return
   115  }