variable-length-quantity: create test case generator

exercises/variable-length-quantity/.meta/gen.go

@@ -0,0 +1,113 @@
+package main
+
+import (
+	"log"
+	"text/template"
+
+	"../../../gen"
+)
+
+func main() {
+	t := template.New("").Funcs(template.FuncMap{
+		"GroupComment": GroupComment,
+		"byteSlice":    byteSlice,
+		"lengthSlice":  lengthSlice,
+	})
+	t, err := t.Parse(tmpl)
+	if err != nil {
+		log.Fatal(err)
+	}
+	var j js
+	if err := gen.Gen("variable-length-quantity", &j, t); err != nil {
+		log.Fatal(err)
+	}
+}
+
+// byteSlice converts a slice of uint32 to a byte slice.
+func byteSlice(ns []uint32) []byte {
+	b := make([]byte, len(ns))
+	for i, n := range ns {
+		b[i] = byte(n)
+	}
+	return b
+}
+
+// lengthSlice returns the length of given slice.
+func lengthSlice(ns []uint32) int {
+	return len(ns)
+}
+
+// The JSON structure we expect to be able to unmarshal into
+type js struct {
+	Groups []TestGroup `json:"Cases"`
+}
+
+type TestGroup struct {
+	Description string
+	Cases       []OneCase
+}
+
+type OneCase struct {
+	Description string
+	Property    string   // "encode" or "decode"
+	Input       []uint32 // supports both []byte and []uint32 in JSON.
+	Expected    []uint32 // supports []byte, []uint32, or null in JSON.
+}
+
+// PropertyMatch returns true when given test case c has .Property field matching property;
+// this serves as a filter to put test cases with "like" property into the same group.
+func (c OneCase) PropertyMatch(property string) bool { return c.Property == property }
+
+// GroupComment looks in each of the test case groups to find the
+// group for which every test case has the .Property matching given property;
+// it returns the .Description field for the matching property group,
+// or a 'Note: ...' if no test group consistently matches given property.
+func GroupComment(groups []TestGroup, property string) string {
+	for _, group := range groups {
+		propertyGroupMatch := true
+		for _, testcase := range group.Cases {
+			if !testcase.PropertyMatch(property) {
+				propertyGroupMatch = false
+				break
+			}
+		}
+		if propertyGroupMatch {
+			return group.Description
+		}
+	}
+	return "Note: Apparent inconsistent use of \"property\": \"" + property + "\" within test case group!"
+}
+
+// template applied to above data structure generates the Go test cases
+var tmpl = `package variablelengthquantity
+
+{{.Header}}
+
+// {{GroupComment .J.Groups "encode"}}
+var encodeTestCases = []struct {
+	description string
+	input	[]uint32
+	output	[]byte
+}{ {{range .J.Groups}} {{range .Cases}}
+	{{if .PropertyMatch "encode"}} {
+		{{printf "%q" .Description}},
+		{{printf "%#v" .Input }},
+		{{byteSlice .Expected | printf "%#v" }},
+	},{{- end}}{{end}}{{end}}
+}
+
+// {{GroupComment .J.Groups "decode"}}
+var decodeTestCases = []struct {
+	description string
+	input	[]byte
+	output	[]uint32 // nil slice indicates error expected.
+	size int
+}{ {{range .J.Groups}} {{range .Cases}}
+	{{if .PropertyMatch "decode"}} {
+		{{printf "%q" .Description}},
+		{{byteSlice .Input | printf "%#v" }},
+		{{printf "%#v" .Expected }},
+		{{lengthSlice .Input}},
+	},{{- end}}{{end}}{{end}}
+}
+`

exercises/variable-length-quantity/cases_test.go

@@ -0,0 +1,161 @@
+package variablelengthquantity
+
+// Source: exercism/x-common
+// Commit: d6a62f7 variable-length-quantity: Fix canonical-data.json formatting
+// x-common version: 1.0.0
+
+// Encode a series of integers, producing a series of bytes.
+var encodeTestCases = []struct {
+	description string
+	input       []uint32
+	output      []byte
+}{
+	{
+		"zero",
+		[]uint32{0x0},
+		[]byte{0x0},
+	},
+	{
+		"arbitrary single byte",
+		[]uint32{0x40},
+		[]byte{0x40},
+	},
+	{
+		"largest single byte",
+		[]uint32{0x7f},
+		[]byte{0x7f},
+	},
+	{
+		"smallest double byte",
+		[]uint32{0x80},
+		[]byte{0x81, 0x0},
+	},
+	{
+		"arbitrary double byte",
+		[]uint32{0x2000},
+		[]byte{0xc0, 0x0},
+	},
+	{
+		"largest double byte",
+		[]uint32{0x3fff},
+		[]byte{0xff, 0x7f},
+	},
+	{
+		"smallest triple byte",
+		[]uint32{0x4000},
+		[]byte{0x81, 0x80, 0x0},
+	},
+	{
+		"arbitrary triple byte",
+		[]uint32{0x100000},
+		[]byte{0xc0, 0x80, 0x0},
+	},
+	{
+		"largest triple byte",
+		[]uint32{0x1fffff},
+		[]byte{0xff, 0xff, 0x7f},
+	},
+	{
+		"smallest quadruple byte",
+		[]uint32{0x200000},
+		[]byte{0x81, 0x80, 0x80, 0x0},
+	},
+	{
+		"arbitrary quadruple byte",
+		[]uint32{0x8000000},
+		[]byte{0xc0, 0x80, 0x80, 0x0},
+	},
+	{
+		"largest quadruple byte",
+		[]uint32{0xfffffff},
+		[]byte{0xff, 0xff, 0xff, 0x7f},
+	},
+	{
+		"smallest quintuple byte",
+		[]uint32{0x10000000},
+		[]byte{0x81, 0x80, 0x80, 0x80, 0x0},
+	},
+	{
+		"arbitrary quintuple byte",
+		[]uint32{0xff000000},
+		[]byte{0x8f, 0xf8, 0x80, 0x80, 0x0},
+	},
+	{
+		"maximum 32-bit integer input",
+		[]uint32{0xffffffff},
+		[]byte{0x8f, 0xff, 0xff, 0xff, 0x7f},
+	},
+	{
+		"two single-byte values",
+		[]uint32{0x40, 0x7f},
+		[]byte{0x40, 0x7f},
+	},
+	{
+		"two multi-byte values",
+		[]uint32{0x4000, 0x123456},
+		[]byte{0x81, 0x80, 0x0, 0xc8, 0xe8, 0x56},
+	},
+	{
+		"many multi-byte values",
+		[]uint32{0x2000, 0x123456, 0xfffffff, 0x0, 0x3fff, 0x4000},
+		[]byte{0xc0, 0x0, 0xc8, 0xe8, 0x56, 0xff, 0xff, 0xff, 0x7f, 0x0, 0xff, 0x7f, 0x81, 0x80, 0x0},
+	},
+}
+
+// Decode a series of bytes, producing a series of integers.
+var decodeTestCases = []struct {
+	description string
+	input       []byte
+	output      []uint32 // nil slice indicates error expected.
+	size        int
+}{
+
+	{
+		"one byte",
+		[]byte{0x7f},
+		[]uint32{0x7f},
+		1,
+	},
+	{
+		"two bytes",
+		[]byte{0xc0, 0x0},
+		[]uint32{0x2000},
+		2,
+	},
+	{
+		"three bytes",
+		[]byte{0xff, 0xff, 0x7f},
+		[]uint32{0x1fffff},
+		3,
+	},
+	{
+		"four bytes",
+		[]byte{0x81, 0x80, 0x80, 0x0},
+		[]uint32{0x200000},
+		4,
+	},
+	{
+		"maximum 32-bit integer",
+		[]byte{0x8f, 0xff, 0xff, 0xff, 0x7f},
+		[]uint32{0xffffffff},
+		5,
+	},
+	{
+		"incomplete sequence causes error",
+		[]byte{0xff},
+		[]uint32(nil),
+		1,
+	},
+	{
+		"incomplete sequence causes error, even if value is zero",
+		[]byte{0x80},
+		[]uint32(nil),
+		1,
+	},
+	{
+		"multiple values",
+		[]byte{0xc0, 0x0, 0xc8, 0xe8, 0x56, 0xff, 0xff, 0xff, 0x7f, 0x0, 0xff, 0x7f, 0x81, 0x80, 0x0},
+		[]uint32{0x2000, 0x123456, 0xfffffff, 0x0, 0x3fff, 0x4000},
+		15,
+	},
+}

exercises/variable-length-quantity/example.go

@@ -1,9 +1,13 @@
 package variablelengthquantity
 
-const testVersion = 2
+import "errors"
 
-// EncodeVarint returns the varint encoding of x.
-func EncodeVarint(x uint32) []byte {
+const testVersion = 3
+
+var ErrUnterminatedSequence = errors.New("unterminated sequence")
+
+// encodeInt returns the varint encoding of x.
+func encodeInt(x uint32) []byte {
 	if x>>7 == 0 {
 		return []byte{
 			byte(x),
@@ -25,34 +29,73 @@ func EncodeVarint(x uint32) []byte {
 		}
 	}
 
+	if x>>28 == 0 {
+		return []byte{
+			byte(0x80 | x>>21),
+			byte(0x80 | x>>14),
+			byte(0x80 | x>>6),
+			byte(127 & x),
+		}
+	}
+
 	return []byte{
+		byte(0x80 | x>>28),
 		byte(0x80 | x>>21),
 		byte(0x80 | x>>14),
 		byte(0x80 | x>>7),
 		byte(127 & x),
 	}
 }
 
-// DecodeVarint reads a varint-encoded integer from the slice.
+// decodeInt reads a varint-encoded integer from the slice.
 // It returns the integer and the number of bytes consumed, or
 // zero if there is not enough.
-func DecodeVarint(buf []byte) (x uint32, n int) {
+func decodeInt(buf []byte) (x uint32, n int, err error) {
 	if len(buf) < 1 {
-		return 0, 0
+		return 0, 0, nil
 	}
 
-	if buf[0] <= 0x80 {
-		return uint32(buf[0]), 1
+	if buf[0] < 0x80 {
+		return uint32(buf[0]), 1, nil
 	}
 
 	var b byte
 	for n, b = range buf {
 		x = x << 7
-		x |= uint32(b) & 0x7F
+		x |= uint32(b) & 0x7f
 		if (b & 0x80) == 0 {
-			return x, n + 1
+			return x, n + 1, nil
 		}
 	}
 
-	return x, 0
+	return x, 0, ErrUnterminatedSequence
+}
+
+// EncodeVarint encodes a slice of uint32 into a var-int encoded bytes.
+func EncodeVarint(xa []uint32) []byte {
+	result := make([]byte, 0)
+	for _, x := range xa {
+		result = append(result, encodeInt(x)...)
+	}
+	return result
+}
+
+// DecodeVarint decodes a buffer of var-int encoded values into
+// a slice of uint32 values; an error is returned if buf doesn't
+// decode var-int successfully.
+func DecodeVarint(buf []byte) (ra []uint32, n int, err error) {
+	if len(buf) == 0 {
+		return []uint32{0}, 1, nil
+	}
+	usedBytes := 0
+	ra = make([]uint32, 0)
+	for usedBytes < len(buf) {
+		r, nUsed, err := decodeInt(buf[usedBytes:])
+		if err != nil {
+			return nil, usedBytes, err
+		}
+		ra = append(ra, r)
+		usedBytes += nUsed
+	}
+	return ra, usedBytes, nil
 }