github.com/euank/go@v0.0.0-20160829210321-495514729181/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 if name, _, err = readGopackHeader(r); err != nil { 56 return 57 } 58 59 // First entry should be __.PKGDEF. 60 if name != "__.PKGDEF" { 61 err = errors.New("go archive is missing __.PKGDEF") 62 return 63 } 64 65 // Read first line of __.PKGDEF data, so that line 66 // is once again the first line of the input. 67 if line, err = r.ReadSlice('\n'); err != nil { 68 return 69 } 70 } 71 72 // Now at __.PKGDEF in archive or still at beginning of file. 73 // Either way, line should begin with "go object ". 74 if !strings.HasPrefix(string(line), "go object ") { 75 err = errors.New("not a go object file") 76 return 77 } 78 79 // Skip over object header to export data. 80 // Begins after first line starting with $$. 81 for line[0] != '$' { 82 if line, err = r.ReadSlice('\n'); err != nil { 83 return 84 } 85 } 86 hdr = string(line) 87 88 return 89 }