schema filereader: verify top-level size matches part sizes when reading

lib/go/camli/schema/fileread_test.go

@@ -55,6 +55,13 @@ func parts(parts ...*ContentPart) []*ContentPart {
 	return parts
 }
 
+func sizeSum(parts []*ContentPart) (s uint64) {
+	for _, p := range parts {
+		s += uint64(p.Size)
+	}
+	return
+}
+
 var readTests = []readTest{
 	{parts(all(blobA)), 0, "AAAAAaaaaa"},
 	{parts(all(blobA)), 2, "AAAaaaaa"},
@@ -78,7 +85,7 @@ func TestReader(t *testing.T) {
 		ss := new(Superset)
 		ss.Type = "file"
 		ss.Version = 1
-		// TODO: set size?
+		ss.Size = sizeSum(rt.parts)
 		ss.ContentParts = rt.parts
 		fr := ss.NewFileReader(testFetcher)
 		fr.Skip(rt.skip)

lib/go/camli/schema/filereader.go

@@ -32,9 +32,10 @@ type FileReader struct {
 	ss      *Superset
 	ci      int    // index into contentparts
 	ccon    uint64 // bytes into current chunk already consumed
+	remain  int64  // bytes remaining
 
 	cr   blobref.ReadSeekCloser // cached reader
-	crbr *blobref.BlobRef  // the blobref that cr is for
+	crbr *blobref.BlobRef       // the blobref that cr is for
 }
 
 // TODO: make this take a blobref.FetcherAt instead?
@@ -54,9 +55,9 @@ func NewFileReader(fetcher blobref.SeekFetcher, fileBlobRef *blobref.BlobRef) (*
 }
 
 func (ss *Superset) NewFileReader(fetcher blobref.SeekFetcher) *FileReader {
-	// TODO: return an error if ss isn't a Type "file" ?
-	// TODO: return some error if the redundant ss.Size field doesn't match ContentParts?
-	return &FileReader{fetcher: fetcher, ss: ss}
+	// TODO: return an error if ss isn't a Type "file"
+	//
+	return &FileReader{fetcher: fetcher, ss: ss, remain: int64(ss.Size)}
 }
 
 // FileSchema returns the reader's schema superset. Don't mutate it.
@@ -70,6 +71,7 @@ func (fr *FileReader) Skip(skipBytes uint64) {
 		thisChunkSkippable := cp.Size - fr.ccon
 		toSkip := minu64(skipBytes, thisChunkSkippable)
 		fr.ccon += toSkip
+		fr.remain -= int64(toSkip)
 		if fr.ccon == cp.Size {
 			fr.ci++
 			fr.ccon = 0
@@ -105,6 +107,9 @@ func (fr *FileReader) Read(p []byte) (n int, err os.Error) {
 	for {
 		if fr.ci >= len(fr.ss.ContentParts) {
 			fr.closeOpenBlobs()
+			if fr.remain > 0 {
+				return 0, fmt.Errorf("schema: declared file schema size was larger than sum of content parts")
+			}
 			return 0, os.EOF
 		}
 		cp = fr.ss.ContentParts[fr.ci]
@@ -117,6 +122,10 @@ func (fr *FileReader) Read(p []byte) (n int, err os.Error) {
 		break
 	}
 
+	if cp.Size == 0 {
+		return 0, fmt.Errorf("blobref content part contained illegal size 0")
+	}
+
 	br := cp.blobref()
 	if br == nil {
 		return 0, fmt.Errorf("no blobref in content part %d", fr.ci)
@@ -141,8 +150,10 @@ func (fr *FileReader) Read(p []byte) (n int, err os.Error) {
 	}
 
 	n, err = rsc.Read(p[:int(readSize)])
-	if err == nil || err == os.EOF {
-		fr.ccon += uint64(n)
+	fr.ccon += uint64(n)
+	fr.remain -= int64(n)
+	if fr.remain < 0 {
+		err = fmt.Errorf("schema: file schema was invalid; content parts sum to over declared size")
 	}
 	return
 }