internal/coverage: implement conforming Seek method in slicereader

Implement a real Seek() method in the slicereader helper (prior to
this it had a simplified SeekTo function), so that slicereader's will
satisfy the ReadSeeker interface (needed in a subsequent patch).

Change-Id: I832e3ec1e34d0f8c6b5edf390470f6f943c6ece0
Reviewed-on: https://go-review.googlesource.com/c/go/+/495438
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

diff --git a/src/internal/coverage/decodemeta/decode.go b/src/internal/coverage/decodemeta/decode.go
index 71f1c567ab0d0929d03409b20eeb998fb9b12f2d..fa047c780bd1d7e35001c04cbddfec6c60c67dc3 100644 (file)
--- a/src/internal/coverage/decodemeta/decode.go
+++ b/src/internal/coverage/decodemeta/decode.go
@@ -14,6 +14,7 @@ import (
        "internal/coverage"
        "internal/coverage/slicereader"
        "internal/coverage/stringtab"
+       "io"
        "os"
 )
 
@@ -55,7 +56,9 @@ func (d *CoverageMetaDataDecoder) readHeader() error {
 func (d *CoverageMetaDataDecoder) readStringTable() error {
        // Seek to the correct location to read the string table.
        stringTableLocation := int64(coverage.CovMetaHeaderSize + 4*d.hdr.NumFuncs)
-       d.r.SeekTo(stringTableLocation)
+       if _, err := d.r.Seek(stringTableLocation, io.SeekStart); err != nil {
+               return err
+       }
 
        // Read the table itself.
        d.strtab = stringtab.NewReader(d.r)
@@ -88,7 +91,9 @@ func (d *CoverageMetaDataDecoder) ReadFunc(fidx uint32, f *coverage.FuncDesc) er
 
        // Seek to the correct location to read the function offset and read it.
        funcOffsetLocation := int64(coverage.CovMetaHeaderSize + 4*fidx)
-       d.r.SeekTo(funcOffsetLocation)
+       if _, err := d.r.Seek(funcOffsetLocation, io.SeekStart); err != nil {
+               return err
+       }
        foff := d.r.ReadUint32()
 
        // Check assumptions
@@ -97,7 +102,10 @@ func (d *CoverageMetaDataDecoder) ReadFunc(fidx uint32, f *coverage.FuncDesc) er
        }
 
        // Seek to the correct location to read the function.
-       d.r.SeekTo(int64(foff))
+       floc := int64(foff)
+       if _, err := d.r.Seek(floc, io.SeekStart); err != nil {
+               return err
+       }
 
        // Preamble containing number of units, file, and function.
        numUnits := uint32(d.r.ReadULEB128())

diff --git a/src/internal/coverage/slicereader/slicereader.go b/src/internal/coverage/slicereader/slicereader.go
index 3d117bae374ebab43780ae97d1da3edceee5b520..d9f2a7eac4c13799a3451d7900393da9dcec36b7 100644 (file)
--- a/src/internal/coverage/slicereader/slicereader.go
+++ b/src/internal/coverage/slicereader/slicereader.go
@@ -6,6 +6,8 @@ package slicereader
 
 import (
        "encoding/binary"
+       "fmt"
+       "io"
        "unsafe"
 )
 
@@ -38,8 +40,31 @@ func (r *Reader) Read(b []byte) (int, error) {
        return amt, nil
 }
 
-func (r *Reader) SeekTo(off int64) {
-       r.off = off
+func (r *Reader) Seek(offset int64, whence int) (ret int64, err error) {
+       switch whence {
+       case io.SeekStart:
+               if offset < 0 || offset > int64(len(r.b)) {
+                       return 0, fmt.Errorf("invalid seek: new offset %d (out of range [0 %d]", offset, len(r.b))
+               }
+               r.off = offset
+               return offset, nil
+       case io.SeekCurrent:
+               newoff := r.off + offset
+               if newoff < 0 || newoff > int64(len(r.b)) {
+                       return 0, fmt.Errorf("invalid seek: new offset %d (out of range [0 %d]", newoff, len(r.b))
+               }
+               r.off = newoff
+               return r.off, nil
+       case io.SeekEnd:
+               newoff := int64(len(r.b)) + offset
+               if newoff < 0 || newoff > int64(len(r.b)) {
+                       return 0, fmt.Errorf("invalid seek: new offset %d (out of range [0 %d]", newoff, len(r.b))
+               }
+               r.off = newoff
+               return r.off, nil
+       }
+       // other modes are not supported
+       return 0, fmt.Errorf("unsupported seek mode %d", whence)
 }
 
 func (r *Reader) Offset() int64 {

diff --git a/src/internal/coverage/slicereader/slr_test.go b/src/internal/coverage/slicereader/slr_test.go
index 2f7cef00f80444b802df079e6edb2f14376283ee..461436d5f50c68d615353c527dea5fe66b20a306 100644 (file)
--- a/src/internal/coverage/slicereader/slr_test.go
+++ b/src/internal/coverage/slicereader/slr_test.go
@@ -6,6 +6,7 @@ package slicereader
 
 import (
        "encoding/binary"
+       "io"
        "testing"
 )
 
@@ -64,10 +65,12 @@ func TestSliceReader(t *testing.T) {
                if gs2 != s2 {
                        t.Fatalf("readStr got %s want %s", gs2, s2)
                }
-               slr.SeekTo(4)
+               if _, err := slr.Seek(4, io.SeekStart); err != nil {
+                       t.Fatal(err)
+               }
                off := slr.Offset()
                if off != 4 {
-                       t.Fatalf("Offset(0 returned %d wanted 4", off)
+                       t.Fatalf("Offset() returned %d wanted 4", off)
                }
                g64 = slr.ReadUint64()
                if g64 != e64 {