vom: move magicbyte handling into encode/decode.

  * move magicbyte handling into encode/decode and change
   New{Encoder,Decoder} API to no return error any more.

MultiPart: 2/3
Change-Id: I9ceef311128c4b422494d4cd7929bfc1e420508f
diff --git a/lib/security/serialization/signing_writer.go b/lib/security/serialization/signing_writer.go
index 840f6cb..93245d7 100644
--- a/lib/security/serialization/signing_writer.go
+++ b/lib/security/serialization/signing_writer.go
@@ -17,9 +17,8 @@
 )
 
 var (
-	errCantBeNilSigner   = verror.Register(pkgPath+".errCantBeNilSigner", verror.NoRetry, "{1:}{2:} data:{3} signature:{4} signer:{5} cannot be nil{:_}")
-	errCantCreateEncoder = verror.Register(pkgPath+".errCantCreateEncoder", verror.NoRetry, "{1:}{2:} failed to create new encoder{:_}")
-	errCantSign          = verror.Register(pkgPath+".errCantSign", verror.NoRetry, "{1:}{2:} signing failed{:_}")
+	errCantBeNilSigner = verror.Register(pkgPath+".errCantBeNilSigner", verror.NoRetry, "{1:}{2:} data:{3} signature:{4} signer:{5} cannot be nil{:_}")
+	errCantSign        = verror.Register(pkgPath+".errCantSign", verror.NoRetry, "{1:}{2:} signing failed{:_}")
 )
 
 const defaultChunkSizeBytes = 1 << 20
@@ -98,10 +97,7 @@
 	if (data == nil) || (signature == nil) || (s == nil) {
 		return nil, verror.New(errCantBeNilSigner, nil, data, signature, s)
 	}
-	enc, err := vom.NewEncoder(signature)
-	if err != nil {
-		return nil, verror.New(errCantCreateEncoder, nil, err)
-	}
+	enc := vom.NewEncoder(signature)
 	w := &signingWriter{data: data, signature: signature, signer: s, signatureHash: sha256.New(), chunkSizeBytes: defaultChunkSizeBytes, sigEnc: enc}
 
 	if opts != nil {
diff --git a/lib/security/serialization/verifying_reader.go b/lib/security/serialization/verifying_reader.go
index 28c736a..5427009 100644
--- a/lib/security/serialization/verifying_reader.go
+++ b/lib/security/serialization/verifying_reader.go
@@ -21,7 +21,6 @@
 var (
 	errCantBeNilVerifier      = verror.Register(pkgPath+".errCantBeNilVerifier", verror.NoRetry, "{1:}{2:} data:{3} signature:{4} key:{5} cannot be nil{:_}")
 	errModifiedSinceWritten   = verror.Register(pkgPath+".errModifiedSinceWritten", verror.NoRetry, "{1:}{2:} data has been modified since being written{:_}")
-	errCantCreateDecoder      = verror.Register(pkgPath+".errCantCreateDecoder", verror.NoRetry, "{1:}{2:} failed to create new decoder{:_}")
 	errCantDecodeHeader       = verror.Register(pkgPath+".errCantDecodeHeader", verror.NoRetry, "{1:}{2:} failed to decode header{:_}")
 	errCantVerifySig          = verror.Register(pkgPath+".errCantVerifySig", verror.NoRetry, "{1:}{2:} signature verification failed{:_}")
 	errBadTypeFromSigReader   = verror.Register(pkgPath+".errBadTypeFromSigReader", verror.NoRetry, "{1:}{2:} invalid data of type: {3} read from signature Reader{:_}")
@@ -93,10 +92,7 @@
 
 func (r *verifyingReader) verifySignature(signature io.Reader, key security.PublicKey) error {
 	signatureHash := sha256.New()
-	dec, err := vom.NewDecoder(signature)
-	if err != nil {
-		return verror.New(errCantCreateDecoder, nil, err)
-	}
+	dec := vom.NewDecoder(signature)
 	var h SignedHeader
 	if err := dec.Decode(&h); err != nil {
 		return verror.New(errCantDecodeHeader, nil, err)
diff --git a/lib/security/storage.go b/lib/security/storage.go
index 1690c91..07058f3 100644
--- a/lib/security/storage.go
+++ b/lib/security/storage.go
@@ -25,11 +25,7 @@
 	if err != nil {
 		return err
 	}
-	enc, err := vom.NewEncoder(swc)
-	if err != nil {
-		swc.Close()
-		return err
-	}
+	enc := vom.NewEncoder(swc)
 	if err := enc.Encode(obj); err != nil {
 		swc.Close()
 		return err
@@ -47,9 +43,6 @@
 	if err != nil {
 		return err
 	}
-	dec, err := vom.NewDecoder(vr)
-	if err != nil {
-		return err
-	}
+	dec := vom.NewDecoder(vr)
 	return dec.Decode(obj)
 }