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Source file src/go/internal/gcimporter/exportdata.go

Documentation: go/internal/gcimporter

  // Copyright 2011 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // This file implements FindExportData.
  
  package gcimporter
  
  import (
  	"bufio"
  	"fmt"
  	"io"
  	"strconv"
  	"strings"
  )
  
  func readGopackHeader(r *bufio.Reader) (name string, size int, err error) {
  	// See $GOROOT/include/ar.h.
  	hdr := make([]byte, 16+12+6+6+8+10+2)
  	_, err = io.ReadFull(r, hdr)
  	if err != nil {
  		return
  	}
  	// leave for debugging
  	if false {
  		fmt.Printf("header: %s", hdr)
  	}
  	s := strings.TrimSpace(string(hdr[16+12+6+6+8:][:10]))
  	size, err = strconv.Atoi(s)
  	if err != nil || hdr[len(hdr)-2] != '`' || hdr[len(hdr)-1] != '\n' {
  		err = fmt.Errorf("invalid archive header")
  		return
  	}
  	name = strings.TrimSpace(string(hdr[:16]))
  	return
  }
  
  // FindExportData positions the reader r at the beginning of the
  // export data section of an underlying GC-created object/archive
  // file by reading from it. The reader must be positioned at the
  // start of the file before calling this function. The hdr result
  // is the string before the export data, either "$$" or "$$B".
  //
  func FindExportData(r *bufio.Reader) (hdr string, err error) {
  	// Read first line to make sure this is an object file.
  	line, err := r.ReadSlice('\n')
  	if err != nil {
  		err = fmt.Errorf("can't find export data (%v)", err)
  		return
  	}
  
  	if string(line) == "!<arch>\n" {
  		// Archive file. Scan to __.PKGDEF.
  		var name string
  		if name, _, err = readGopackHeader(r); err != nil {
  			return
  		}
  
  		// First entry should be __.PKGDEF.
  		if name != "__.PKGDEF" {
  			err = fmt.Errorf("go archive is missing __.PKGDEF")
  			return
  		}
  
  		// Read first line of __.PKGDEF data, so that line
  		// is once again the first line of the input.
  		if line, err = r.ReadSlice('\n'); err != nil {
  			err = fmt.Errorf("can't find export data (%v)", err)
  			return
  		}
  	}
  
  	// Now at __.PKGDEF in archive or still at beginning of file.
  	// Either way, line should begin with "go object ".
  	if !strings.HasPrefix(string(line), "go object ") {
  		err = fmt.Errorf("not a Go object file")
  		return
  	}
  
  	// Skip over object header to export data.
  	// Begins after first line starting with $$.
  	for line[0] != '$' {
  		if line, err = r.ReadSlice('\n'); err != nil {
  			err = fmt.Errorf("can't find export data (%v)", err)
  			return
  		}
  	}
  	hdr = string(line)
  
  	return
  }
  

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