codec: ensure that byte descriptor is read before calling ContainerType, Read(Map|Array)Start

This should allow calls to Codec(En|De)codeSelf to work directly, without going through
(en|de)coder (En|De)code methods

Updates #199

codec/binc.go

@@ -356,6 +356,9 @@ func (d *bincDecDriver) uncacheRead() {
 }
 
 func (d *bincDecDriver) ContainerType() (vt valueType) {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	if d.vd == bincVdSpecial && d.vs == bincSpNil {
 		return valueTypeNil
 	} else if d.vd == bincVdByteArray {
@@ -580,6 +583,9 @@ func (d *bincDecDriver) DecodeBool() (b bool) {
 }
 
 func (d *bincDecDriver) ReadMapStart() (length int) {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	if d.vd != bincVdMap {
 		d.d.errorf("Invalid d.vd for map. Expecting 0x%x. Got: 0x%x", bincVdMap, d.vd)
 		return
@@ -590,6 +596,9 @@ func (d *bincDecDriver) ReadMapStart() (length int) {
 }
 
 func (d *bincDecDriver) ReadArrayStart() (length int) {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	if d.vd != bincVdArray {
 		d.d.errorf("Invalid d.vd for array. Expecting 0x%x. Got: 0x%x", bincVdArray, d.vd)
 		return

codec/cbor.go

@@ -196,6 +196,9 @@ func (d *cborDecDriver) uncacheRead() {
 }
 
 func (d *cborDecDriver) ContainerType() (vt valueType) {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	if d.bd == cborBdNil {
 		return valueTypeNil
 	} else if d.bd == cborBdIndefiniteBytes || (d.bd >= cborBaseBytes && d.bd < cborBaseString) {
@@ -351,6 +354,9 @@ func (d *cborDecDriver) DecodeBool() (b bool) {
 }
 
 func (d *cborDecDriver) ReadMapStart() (length int) {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	d.bdRead = false
 	if d.bd == cborBdIndefiniteMap {
 		return -1
@@ -359,6 +365,9 @@ func (d *cborDecDriver) ReadMapStart() (length int) {
 }
 
 func (d *cborDecDriver) ReadArrayStart() (length int) {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	d.bdRead = false
 	if d.bd == cborBdIndefiniteArray {
 		return -1

codec/msgpack.go

@@ -569,6 +569,9 @@ func (d *msgpackDecDriver) uncacheRead() {
 }
 
 func (d *msgpackDecDriver) ContainerType() (vt valueType) {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	bd := d.bd
 	if bd == mpNil {
 		return valueTypeNil
@@ -621,10 +624,16 @@ func (d *msgpackDecDriver) readContainerLen(ct msgpackContainerType) (clen int)
 }
 
 func (d *msgpackDecDriver) ReadMapStart() int {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	return d.readContainerLen(msgpackContainerMap)
 }
 
 func (d *msgpackDecDriver) ReadArrayStart() int {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	return d.readContainerLen(msgpackContainerList)
 }
 

codec/simple.go

@@ -174,6 +174,9 @@ func (d *simpleDecDriver) uncacheRead() {
 }
 
 func (d *simpleDecDriver) ContainerType() (vt valueType) {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	if d.bd == simpleVdNil {
 		return valueTypeNil
 	} else if d.bd == simpleVdByteArray || d.bd == simpleVdByteArray+1 ||
@@ -315,11 +318,17 @@ func (d *simpleDecDriver) DecodeBool() (b bool) {
 }
 
 func (d *simpleDecDriver) ReadMapStart() (length int) {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	d.bdRead = false
 	return d.decLen()
 }
 
 func (d *simpleDecDriver) ReadArrayStart() (length int) {
+	if !d.bdRead {
+		d.readNextBd()
+	}
 	d.bdRead = false
 	return d.decLen()
 }