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 7package importer 8 9import ( 10 "bufio" 11 "fmt" 12 "io" 13 "strconv" 14 "strings" 15) 16 17func 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. 46func 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