github.com/aloncn/graphics-go@v0.0.1/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  		var size int
    56  		if name, size, err = readGopackHeader(r); err != nil {
    57  			return
    58  		}
    59  
    60  		// Optional leading __.GOSYMDEF or __.SYMDEF.
    61  		// Read and discard.
    62  		if name == "__.SYMDEF" || name == "__.GOSYMDEF" {
    63  			const block = 4096
    64  			tmp := make([]byte, block)
    65  			for size > 0 {
    66  				n := size
    67  				if n > block {
    68  					n = block
    69  				}
    70  				if _, err = io.ReadFull(r, tmp[:n]); err != nil {
    71  					return
    72  				}
    73  				size -= n
    74  			}
    75  
    76  			if name, _, err = readGopackHeader(r); err != nil {
    77  				return
    78  			}
    79  		}
    80  
    81  		// First real entry should be __.PKGDEF.
    82  		if name != "__.PKGDEF" {
    83  			err = errors.New("go archive is missing __.PKGDEF")
    84  			return
    85  		}
    86  
    87  		// Read first line of __.PKGDEF data, so that line
    88  		// is once again the first line of the input.
    89  		if line, err = r.ReadSlice('\n'); err != nil {
    90  			return
    91  		}
    92  	}
    93  
    94  	// Now at __.PKGDEF in archive or still at beginning of file.
    95  	// Either way, line should begin with "go object ".
    96  	if !strings.HasPrefix(string(line), "go object ") {
    97  		err = errors.New("not a go object file")
    98  		return
    99  	}
   100  
   101  	// Skip over object header to export data.
   102  	// Begins after first line starting with $$.
   103  	for line[0] != '$' {
   104  		if line, err = r.ReadSlice('\n'); err != nil {
   105  			return
   106  		}
   107  	}
   108  	hdr = string(line)
   109  
   110  	return
   111  }