cmd/internal/bio: rename Reader.Seek to MustSeek

Renaming the method makes clear, both to readers and to vet,
that this method is not the implementation of io.Seeker:
it cannot fail.

Working toward making the tree vet-safe instead of having
so many exceptions in cmd/vet/all/whitelist.

For #31916.

Change-Id: I3e6ad7264cb0121b4b76935450cccb71d533e96b
Reviewed-on: https://go-review.googlesource.com/c/go/+/176108
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/iimport.go

@@ -117,7 +117,7 @@ func iimport(pkg *types.Pkg, in *bio.Reader) {
 	stringData := data[:sLen]
 	declData := data[sLen:]
 
-	in.Seek(int64(sLen+dLen), os.SEEK_CUR)
+	in.MustSeek(int64(sLen+dLen), os.SEEK_CUR)
 
 	p := &iimporter{
 		ipkg: pkg,

src/cmd/compile/internal/gc/obj.go

@@ -97,13 +97,13 @@ func finishArchiveEntry(bout *bio.Writer, start int64, name string) {
 	if size&1 != 0 {
 		bout.WriteByte(0)
 	}
-	bout.Seek(start-ArhdrSize, 0)
+	bout.MustSeek(start-ArhdrSize, 0)
 
 	var arhdr [ArhdrSize]byte
 	formathdr(arhdr[:], name, size)
 	bout.Write(arhdr[:])
 	bout.Flush()
-	bout.Seek(start+size+(size&1), 0)
+	bout.MustSeek(start+size+(size&1), 0)
 }
 
 func dumpCompilerObj(bout *bio.Writer) {

src/cmd/internal/bio/buf.go

@@ -43,7 +43,7 @@ func Open(name string) (*Reader, error) {
 	return &Reader{f: f, Reader: bufio.NewReader(f)}, nil
 }
 
-func (r *Reader) Seek(offset int64, whence int) int64 {
+func (r *Reader) MustSeek(offset int64, whence int) int64 {
 	if whence == 1 {
 		offset -= int64(r.Buffered())
 	}
@@ -55,7 +55,7 @@ func (r *Reader) Seek(offset int64, whence int) int64 {
 	return off
 }
 
-func (w *Writer) Seek(offset int64, whence int) int64 {
+func (w *Writer) MustSeek(offset int64, whence int) int64 {
 	if err := w.Flush(); err != nil {
 		log.Fatalf("writing output: %v", err)
 	}

src/cmd/internal/bio/buf_mmap.go

@@ -57,6 +57,6 @@ func (r *Reader) sliceOS(length uint64) ([]byte, bool) {
 	}
 
 	data = data[off-aoff:]
-	r.Seek(int64(length), 1)
+	r.MustSeek(int64(length), 1)
 	return data, true
 }

src/cmd/link/internal/ld/ar.go

@@ -126,7 +126,7 @@ func hostArchive(ctxt *Link, name string) {
 
 			libgcc := sym.Library{Pkg: "libgcc"}
 			h := ldobj(ctxt, f, &libgcc, l, pname, name)
-			f.Seek(h.off, 0)
+			f.MustSeek(h.off, 0)
 			h.ld(ctxt, f, h.pkg, h.length, h.pn)
 		}
 

src/cmd/link/internal/ld/lib.go

@@ -741,7 +741,7 @@ func nextar(bp *bio.Reader, off int64, a *ArHdr) int64 {
 	if off&1 != 0 {
 		off++
 	}
-	bp.Seek(off, 0)
+	bp.MustSeek(off, 0)
 	var buf [SAR_HDR]byte
 	if n, err := io.ReadFull(bp, buf[:]); err != nil {
 		if n == 0 && err != io.EOF {
@@ -864,8 +864,8 @@ func loadobjfile(ctxt *Link, lib *sym.Library) {
 		}
 
 		/* load it as a regular file */
-		l := f.Seek(0, 2)
-		f.Seek(0, 0)
+		l := f.MustSeek(0, 2)
+		f.MustSeek(0, 0)
 		ldobj(ctxt, f, lib, l, lib.File, lib.File)
 		return
 	}
@@ -985,7 +985,7 @@ func hostobjs(ctxt *Link) {
 			Exitf("cannot reopen %s: %v", h.pn, err)
 		}
 
-		f.Seek(h.off, 0)
+		f.MustSeek(h.off, 0)
 		h.ld(ctxt, f, h.pkg, h.length, h.pn)
 		f.Close()
 	}
@@ -1607,7 +1607,7 @@ func ldobj(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, pn string,
 	c2 := bgetc(f)
 	c3 := bgetc(f)
 	c4 := bgetc(f)
-	f.Seek(start, 0)
+	f.MustSeek(start, 0)
 
 	magic := uint32(c1)<<24 | uint32(c2)<<16 | uint32(c3)<<8 | uint32(c4)
 	if magic == 0x7f454c46 { // \x7F E L F
@@ -1740,9 +1740,9 @@ func ldobj(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, pn string,
 
 	import1 := f.Offset()
 
-	f.Seek(import0, 0)
+	f.MustSeek(import0, 0)
 	ldpkg(ctxt, f, lib, import1-import0-2, pn) // -2 for !\n
-	f.Seek(import1, 0)
+	f.MustSeek(import1, 0)
 
 	flags := 0
 	switch *FlagStrictDups {

src/cmd/link/internal/loadelf/ldelf.go

@@ -590,9 +590,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length i
 
 	elfobj.nsect = uint(elfobj.shnum)
 	for i := 0; uint(i) < elfobj.nsect; i++ {
-		if f.Seek(int64(uint64(base)+elfobj.shoff+uint64(int64(i)*int64(elfobj.shentsize))), 0) < 0 {
-			return errorf("malformed elf file: negative seek")
-		}
+		f.MustSeek(int64(uint64(base)+elfobj.shoff+uint64(int64(i)*int64(elfobj.shentsize))), 0)
 		sect := &elfobj.sect[i]
 		if is64 != 0 {
 			var b ElfSectBytes64
@@ -996,9 +994,7 @@ func elfmap(elfobj *ElfObj, sect *ElfSect) (err error) {
 	}
 
 	sect.base = make([]byte, sect.size)
-	if elfobj.f.Seek(int64(uint64(elfobj.base)+sect.off), 0) < 0 {
-		return fmt.Errorf("short read: seek not successful")
-	}
+	elfobj.f.MustSeek(int64(uint64(elfobj.base)+sect.off), 0)
 	if _, err := io.ReadFull(elfobj.f, sect.base); err != nil {
 		return fmt.Errorf("short read: %v", err)
 	}

src/cmd/link/internal/loadmacho/ldmacho.go

@@ -321,9 +321,7 @@ func macholoadrel(m *ldMachoObj, sect *ldMachoSect) int {
 	rel := make([]ldMachoRel, sect.nreloc)
 	n := int(sect.nreloc * 8)
 	buf := make([]byte, n)
-	if m.f.Seek(m.base+int64(sect.reloff), 0) < 0 {
-		return -1
-	}
+	m.f.MustSeek(m.base+int64(sect.reloff), 0)
 	if _, err := io.ReadFull(m.f, buf); err != nil {
 		return -1
 	}
@@ -367,9 +365,7 @@ func macholoaddsym(m *ldMachoObj, d *ldMachoDysymtab) int {
 	n := int(d.nindirectsyms)
 
 	p := make([]byte, n*4)
-	if m.f.Seek(m.base+int64(d.indirectsymoff), 0) < 0 {
-		return -1
-	}
+	m.f.MustSeek(m.base+int64(d.indirectsymoff), 0)
 	if _, err := io.ReadFull(m.f, p); err != nil {
 		return -1
 	}
@@ -387,9 +383,7 @@ func macholoadsym(m *ldMachoObj, symtab *ldMachoSymtab) int {
 	}
 
 	strbuf := make([]byte, symtab.strsize)
-	if m.f.Seek(m.base+int64(symtab.stroff), 0) < 0 {
-		return -1
-	}
+	m.f.MustSeek(m.base+int64(symtab.stroff), 0)
 	if _, err := io.ReadFull(m.f, strbuf); err != nil {
 		return -1
 	}
@@ -400,9 +394,7 @@ func macholoadsym(m *ldMachoObj, symtab *ldMachoSymtab) int {
 	}
 	n := int(symtab.nsym * uint32(symsize))
 	symbuf := make([]byte, n)
-	if m.f.Seek(m.base+int64(symtab.symoff), 0) < 0 {
-		return -1
-	}
+	m.f.MustSeek(m.base+int64(symtab.symoff), 0)
 	if _, err := io.ReadFull(m.f, symbuf); err != nil {
 		return -1
 	}
@@ -463,7 +455,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length i
 	}
 
 	if is64 {
-		f.Seek(4, 1) // skip reserved word in header
+		f.MustSeek(4, 1) // skip reserved word in header
 	}
 
 	m := &ldMachoObj{
@@ -555,9 +547,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length i
 		return errorf("load segment out of range")
 	}
 
-	if f.Seek(m.base+int64(c.seg.fileoff), 0) < 0 {
-		return errorf("cannot load object data: seek failed")
-	}
+	f.MustSeek(m.base+int64(c.seg.fileoff), 0)
 	dat := make([]byte, c.seg.filesz)
 	if _, err := io.ReadFull(f, dat); err != nil {
 		return errorf("cannot load object data: %v", err)

src/cmd/link/internal/loadpe/ldpe.go

@@ -133,7 +133,7 @@ const (
 type peBiobuf bio.Reader
 
 func (f *peBiobuf) ReadAt(p []byte, off int64) (int, error) {
-	ret := ((*bio.Reader)(f)).Seek(off, 0)
+	ret := ((*bio.Reader)(f)).MustSeek(off, 0)
 	if ret < 0 {
 		return 0, errors.New("fail to seek")
 	}

src/cmd/link/internal/loadxcoff/ldxcoff.go

@@ -27,7 +27,7 @@ type ldSection struct {
 type xcoffBiobuf bio.Reader
 
 func (f *xcoffBiobuf) ReadAt(p []byte, off int64) (int, error) {
-	ret := ((*bio.Reader)(f)).Seek(off, 0)
+	ret := ((*bio.Reader)(f)).MustSeek(off, 0)
 	if ret < 0 {
 		return 0, errors.New("fail to seek")
 	}

src/cmd/link/internal/objfile/objfile.go

@@ -85,7 +85,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, lib *sym.Library, le
 	start := f.Offset()
 	roObject := f.SliceRO(uint64(length))
 	if roObject != nil {
-		f.Seek(int64(-length), os.SEEK_CUR)
+		f.MustSeek(int64(-length), os.SEEK_CUR)
 	}
 	r := &objReader{
 		rd:              f,
@@ -104,7 +104,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, lib *sym.Library, le
 		if r.roOffset != length {
 			log.Fatalf("%s: unexpected end at %d, want %d", pn, r.roOffset, start+length)
 		}
-		r.rd.Seek(int64(length), os.SEEK_CUR)
+		r.rd.MustSeek(int64(length), os.SEEK_CUR)
 	} else if f.Offset() != start+length {
 		log.Fatalf("%s: unexpected end at %d, want %d", pn, f.Offset(), start+length)
 	}

src/cmd/vet/all/whitelist/all.txt

@@ -23,8 +23,6 @@ cmd/compile/internal/gc/testdata/short_test.go: unreachable code
 // These cases are basically ok.
 // Errors are handled reasonably and there's no clear need for interface satisfaction.
 // Except for the runtime/pprof case, the API is not exported.
-cmd/internal/bio/buf.go: method Seek(offset int64, whence int) int64 should have signature Seek(int64, int) (int64, error)
-cmd/internal/bio/buf.go: method Seek(offset int64, whence int) int64 should have signature Seek(int64, int) (int64, error)
 fmt/print.go: method WriteByte(c byte) should have signature WriteByte(byte) error
 
 // Also non-standard, but this method is on an unexported type, so it's