// 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 (
	
	
	
	
	
)

func readGopackHeader( *bufio.Reader) ( string,  int,  error) {
	// See $GOROOT/include/ar.h.
	 := make([]byte, 16+12+6+6+8+10+2)
	_,  = io.ReadFull(, )
	if  != nil {
		return
	}
	// leave for debugging
	if false {
		fmt.Printf("header: %s", )
	}
	 := strings.TrimSpace(string([16+12+6+6+8:][:10]))
	,  = strconv.Atoi()
	if  != nil || [len()-2] != '`' || [len()-1] != '\n' {
		 = fmt.Errorf("invalid archive header")
		return
	}
	 = strings.TrimSpace(string([: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 ( *bufio.Reader) ( string,  error) {
	// Read first line to make sure this is an object file.
	,  := .ReadSlice('\n')
	if  != nil {
		 = fmt.Errorf("can't find export data (%v)", )
		return
	}

	if string() == "!<arch>\n" {
		// Archive file. Scan to __.PKGDEF.
		var  string
		if , _,  = readGopackHeader();  != nil {
			return
		}

		// First entry should be __.PKGDEF.
		if  != "__.PKGDEF" {
			 = 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 ,  = .ReadSlice('\n');  != nil {
			 = fmt.Errorf("can't find export data (%v)", )
			return
		}
	}

	// Now at __.PKGDEF in archive or still at beginning of file.
	// Either way, line should begin with "go object ".
	if !strings.HasPrefix(string(), "go object ") {
		 = fmt.Errorf("not a Go object file")
		return
	}

	// Skip over object header to export data.
	// Begins after first line starting with $$.
	for [0] != '$' {
		if ,  = .ReadSlice('\n');  != nil {
			 = fmt.Errorf("can't find export data (%v)", )
			return
		}
	}
	 = string()

	return
}