hclpack: Body can now unmarshal from JSON

This allows us to round-trip Body to JSON and back without any loss as
long as the expression source codes are always valid UTF-8, and we require
that during expression parsing anyway so that is a fine restriction.

The JSON encoding is a little noisy to read due to the extra annotations
required to be lossless (including source ranges) but still relatively
compact due to the base64-VLQ encoding of the source location information.

hclpack/json_marshal.go

@@ -87,7 +87,18 @@ func (b *Block) forJSON(pos map[string]map[hcl.Pos]posOfs) blockJSON {
 
 // UnmarshalJSON is an implementation of Unmarshaler from encoding/json,
 // allowing bodies to be included in other types that are JSON-unmarshalable.
-func (b *Body) UnmarshalJSON([]byte) error {
+func (b *Body) UnmarshalJSON(data []byte) error {
+	var head jsonHeader
+	err := json.Unmarshal(data, &head)
+	if err != nil {
+		return err
+	}
+
+	fns := head.Sources
+	positions := head.Pos.Unpack()
+
+	*b = head.Body.decode(fns, positions)
+
 	return nil
 }
 
@@ -107,6 +118,28 @@ type bodyJSON struct {
 	Ranges rangesPacked `json:"r,omitempty"`
 }
 
+func (bj *bodyJSON) decode(fns []string, positions []position) Body {
+	var ret Body
+
+	if len(bj.Attrs) > 0 {
+		ret.Attributes = make(map[string]Attribute, len(bj.Attrs))
+		for name, aj := range bj.Attrs {
+			ret.Attributes[name] = aj.decode(fns, positions)
+		}
+	}
+
+	if len(bj.Blocks) > 0 {
+		ret.ChildBlocks = make([]Block, len(bj.Blocks))
+		for i, blj := range bj.Blocks {
+			ret.ChildBlocks[i] = blj.decode(fns, positions)
+		}
+	}
+
+	ret.MissingItemRange_ = bj.Ranges.UnpackIdx(fns, positions, 0)
+
+	return ret
+}
+
 type attrJSON struct {
 	// To keep things compact, in the JSON encoding we flatten the
 	// expression down into the attribute object, since overhead
@@ -118,6 +151,31 @@ type attrJSON struct {
 	Ranges rangesPacked `json:"r,omitempty"`
 }
 
+func (aj *attrJSON) decode(fns []string, positions []position) Attribute {
+	var ret Attribute
+
+	ret.Expr.Source = []byte(aj.Source)
+	switch aj.Syntax {
+	case 0:
+		ret.Expr.SourceType = ExprNative
+	case 1:
+		ret.Expr.SourceType = ExprTemplate
+	case 2:
+		ret.Expr.SourceType = ExprLiteralJSON
+	}
+
+	ret.Range = aj.Ranges.UnpackIdx(fns, positions, 0)
+	ret.NameRange = aj.Ranges.UnpackIdx(fns, positions, 1)
+	ret.Expr.Range_ = aj.Ranges.UnpackIdx(fns, positions, 2)
+	ret.Expr.StartRange_ = aj.Ranges.UnpackIdx(fns, positions, 3)
+	if ret.Expr.StartRange_ == (hcl.Range{}) {
+		// If the start range wasn't present then we'll just use the Range
+		ret.Expr.StartRange_ = ret.Expr.Range_
+	}
+
+	return ret
+}
+
 type blockJSON struct {
 	// Header is the type followed by any labels. We flatten this here
 	// to keep the JSON encoding compact.
@@ -128,3 +186,26 @@ type blockJSON struct {
 	// each of the label ranges in turn.
 	Ranges rangesPacked `json:"r,omitempty"`
 }
+
+func (blj *blockJSON) decode(fns []string, positions []position) Block {
+	var ret Block
+
+	if len(blj.Header) > 0 { // If the header is invalid then we'll end up with an empty type
+		ret.Type = blj.Header[0]
+	}
+	if len(blj.Header) > 1 {
+		ret.Labels = blj.Header[1:]
+	}
+	ret.Body = blj.Body.decode(fns, positions)
+
+	ret.DefRange = blj.Ranges.UnpackIdx(fns, positions, 0)
+	ret.TypeRange = blj.Ranges.UnpackIdx(fns, positions, 1)
+	if len(ret.Labels) > 0 {
+		ret.LabelRanges = make([]hcl.Range, len(ret.Labels))
+		for i := range ret.Labels {
+			ret.LabelRanges[i] = blj.Ranges.UnpackIdx(fns, positions, i+2)
+		}
+	}
+
+	return ret
+}

hclpack/json_marshal_test.go

@@ -2,8 +2,46 @@ package hclpack
 
 import (
 	"testing"
+
+	"github.com/google/go-cmp/cmp"
+
+	"github.com/hashicorp/hcl2/hcl"
 )
 
 func TestJSONRoundTrip(t *testing.T) {
-
+	src := `
+	service "example" {
+	  priority = 2
+	  platform {
+	    os   = "linux"
+	    arch = "amd64"
+	  }
+	  process "web" {
+	    exec = ["./webapp"]
+	  }
+	  process "worker" {
+	    exec = ["./worker"]
+	  }
+	}
+	`
+
+	startBody, diags := PackNativeFile([]byte(src), "example.svc", hcl.Pos{Line: 1, Column: 1})
+	if diags.HasErrors() {
+		t.Fatalf("Failed to parse: %s", diags.Error())
+	}
+
+	jb, err := startBody.MarshalJSON()
+	if err != nil {
+		t.Fatalf("Failed to marshal: %s", err)
+	}
+
+	endBody := &Body{}
+	err = endBody.UnmarshalJSON(jb)
+	if err != nil {
+		t.Fatalf("Failed to unmarshal: %s", err)
+	}
+
+	if !cmp.Equal(startBody, endBody) {
+		t.Errorf("incorrect result\n%s", cmp.Diff(startBody, endBody))
+	}
 }

hclpack/positions_packed.go

@@ -51,6 +51,48 @@ func (pp positionsPacked) MarshalText() ([]byte, error) {
 	return ret, nil
 }
 
+func (pp *positionsPacked) UnmarshalBinary(data []byte) error {
+	buf := vlqBuf(data)
+	var ret positionsPacked
+	fileIdx := 0
+	for len(buf) > 0 {
+		if buf[0] == ';' {
+			// Starting a new file, then.
+			fileIdx++
+			buf = buf[1:]
+			continue
+		}
+
+		var ppr positionPacked
+		var err error
+		ppr.LineDelta, buf, err = buf.ReadInt()
+		if err != nil {
+			return err
+		}
+		ppr.ColumnDelta, buf, err = buf.ReadInt()
+		if err != nil {
+			return err
+		}
+		ppr.ByteDelta, buf, err = buf.ReadInt()
+		if err != nil {
+			return err
+		}
+		ret = append(ret, ppr)
+	}
+	*pp = ret
+	return nil
+}
+
+func (pp *positionsPacked) UnmarshalText(data []byte) error {
+	maxL := base64.RawStdEncoding.DecodedLen(len(data))
+	into := make([]byte, maxL)
+	realL, err := base64.RawStdEncoding.Decode(into, data)
+	if err != nil {
+		return err
+	}
+	return pp.UnmarshalBinary(into[:realL])
+}
+
 type position struct {
 	FileIdx int
 	Pos     hcl.Pos
@@ -177,6 +219,39 @@ func (rp rangesPacked) MarshalText() ([]byte, error) {
 	return ret, nil
 }
 
+func (rp *rangesPacked) UnmarshalBinary(data []byte) error {
+	buf := vlqBuf(data)
+	var ret rangesPacked
+	for len(buf) > 0 {
+		var startInt, endInt int
+		var err error
+		startInt, buf, err = buf.ReadInt()
+		if err != nil {
+			return err
+		}
+		endInt, buf, err = buf.ReadInt()
+		if err != nil {
+			return err
+		}
+		ret = append(ret, rangePacked{
+			Start: posOfs(startInt), // these are stored as 1-based offsets, so safe to convert directly
+			End:   posOfs(endInt),
+		})
+	}
+	*rp = ret
+	return nil
+}
+
+func (rp *rangesPacked) UnmarshalText(data []byte) error {
+	maxL := base64.RawStdEncoding.DecodedLen(len(data))
+	into := make([]byte, maxL)
+	realL, err := base64.RawStdEncoding.Decode(into, data)
+	if err != nil {
+		return err
+	}
+	return rp.UnmarshalBinary(into[:realL])
+}
+
 func (rps rangesPacked) UnpackIdx(fns []string, poss []position, idx int) hcl.Range {
 	if idx < 0 || idx >= len(rps) {
 		return hcl.Range{} // out of bounds, so invalid

hclpack/vlq.go

@@ -1,6 +1,8 @@
 package hclpack
 
 import (
+	"errors"
+
 	"github.com/bsm/go-vlq"
 )
 
@@ -24,6 +26,21 @@ func (b vlqBuf) AppendInt(i int) vlqBuf {
 	return b
 }
 
+func (b vlqBuf) ReadInt() (int, vlqBuf, error) {
+	v, adv := vlq.Int([]byte(b))
+	if adv <= 0 {
+		if adv == 0 {
+			return 0, b, errors.New("missing expected VLQ value")
+		} else {
+			return 0, b, errors.New("invalid VLQ value")
+		}
+	}
+	if int64(int(v)) != v {
+		return 0, b, errors.New("VLQ value too big for integer on this platform")
+	}
+	return int(v), b[adv:], nil
+}
+
 func (b vlqBuf) AppendRawByte(by byte) vlqBuf {
 	return append(b, by)
 }