I am writing a trie DS, json gzipped into a file trieSample.json.gz, and reading it back into the struct. Strangely, the unmarshal succeeds but the struct is not populated.
I have tried both json.Unmarshal and json.Decoder to no avail. Need help in finding what I am missing here. There is no error thrown while reading, just that the struct doesn't have any keys. If I try normal json marshal -> Write to file and Read from file -> Unmarshal, it works properly.
var charSet = "0123456789bcdefghjkmnopqrstuvwxyz"
const logTagSlice = "trie.log"
type trieSlice struct {
Children []*tNode `json:"c"`
Charset map[int32]int8 `json:"l"` // Charset is the legend of what charset is used to create the keys and how to position them in trie array
logger loggingapi.Logger `json:"-"`
capacity int `json:"-"` // capacity is the slice capacity to have enough to hold all the characters in the charset
}
type tNode struct {
Children []*tNode `json:"c"` // children represents the next valid runes AFTER the current one
IsLeaf bool `json:"e,omitempty"` // isLeaf represents if this node represents the end of a valid word
Value int16 `json:"v,omitempty"` // value holds the corresponding value for key value pair, where key is the whole tree of nodes starting from parent representing a valid word
}
// NewTrieSlice returns a Trie, charset represents how the children need to be positioned in the array
func NewTrieSlice(charset string, logger loggingapi.Logger) *trieSlice {
m := map[int32]int8{}
for index, r := range charset {
m[r] = int8(index)
}
return &trieSlice{
Charset: m,
Children: make([]*tNode, len(charset)),
logger: logger,
capacity: len(charset),
}
}
func newNode(capacity int) *tNode {
return &tNode{
Children: make([]*tNode, capacity),
}
}
// getPosition gets the array index position that the rune should be put in
func (t *trieSlice) getPosition(r int32) (index int8, found bool) {
if index, ok := t.Charset[r]; ok {
return index, true
}
return -1, false
}
// Add ...
func (t *trieSlice) Add(key string, val int16) {
if len(key) == 0 {
t.logger.Info(logTagSlice, "trying to add empty key, return with no action")
return
}
runes := []rune(key)
prefix := runes[0]
var child *tNode
var pos int
index, ok := t.getPosition(prefix)
if !ok {
t.logger.Info(logTagSlice, "key is not present in the charset %s, cannot add to trieSlice", prefix)
return
}
// trie node with same prefix doesnt exist
if child = t.Children[index]; child == nil {
child = newNode(len(t.Charset))
t.Children[index] = child
}
pos = 1
for pos <= len(runes) {
// base condition
if pos == len(key) {
child.IsLeaf = true
child.Value = val
return
}
prefix := runes[pos]
index, ok := t.getPosition(prefix)
if !ok {
t.logger.Info(logTagSlice, "key is not present in the charset %s, cannot add to trieSlice", prefix)
return
}
// repeat with child node if prefix is already present
if newChild := child.Children[index]; newChild == nil {
child.Children[index] = newNode(len(t.Charset))
child = child.Children[index]
} else {
child = newChild
}
pos++
}
}
// Test using gzip writer, reader
func TestSample(t *testing.T) {
// Create trie and add a few keys
trie := NewTrieSlice(charSet, loggingapi.NewStdOut())
trie.Add("test", 10)
trie.Add("test1", 20)
trie.Add("test2", 30)
trie.Add("test3", 40)
trie.Add("test4", 50)
// Write gzipped json to file
var network bytes.Buffer
b, err := json.Marshal(trie)
if err != nil {
fmt.Println("error in marshal ... ", err.Error())
t.Fail()
}
w := gzip.NewWriter(&network)
w.Write(b)
ioutil.WriteFile("../resources/trieSample.json.gz", []byte(network.String()), 0644)
w.Close()
// Read gzipped json from file into struct
trieUnmarshal := NewTrieSlice(charSet, loggingapi.NewStdOut())
trieDecoder := NewTrieSlice(charSet, loggingapi.NewStdOut())
// attempt via json Unmarshal
file, err := os.Open("../resources/trieSample.json.gz")
if err != nil {
fmt.Println(err.Error())
t.Fail()
}
r, err := gzip.NewReader(file)
if err != nil {
fmt.Println(err.Error())
t.Fail()
}
sc := bufio.NewScanner(r)
json.Unmarshal(sc.Bytes(), trieUnmarshal)
// attempt via json Decoder
b, err = ioutil.ReadFile("../resources/trieSample.json.gz")
if err != nil {
fmt.Println(err.Error())
t.Fail()
}
bReader := bytes.NewReader(b)
json.NewDecoder(bReader).Decode(trieDecoder)
// spew.Dump shows that object is not populated
spew.Dump(trieUnmarshal)
spew.Dump(trieDecoder)
}
spew.Dump shows that the trieSlice Children array has all nil elements
Close the compressor before using the data. Decompress the data before using it. Don't chop it up with inappropriate use of bufio.Scanner.
var network bytes.Buffer
b, err := json.Marshal(trie)
if err != nil {
fmt.Println("error in marshal ... ", err.Error())
t.Fail()
}
w := gzip.NewWriter(&network)
w.Write(b)
w.Close()
err = ioutil.WriteFile("trieSample.json.gz", network.Bytes(), 0644)
if err != nil {
log.Fatal(err)
}
trieDecoder := NewTrieSlice(charSet)
// attempt via json Unmarshal
file, err := os.Open("trieSample.json.gz")
if err != nil {
log.Fatal(err)
}
r, err := gzip.NewReader(file)
if err != nil {
log.Fatal(err)
}
err = json.NewDecoder(r).Decode(trieDecoder)
if err != nil {
log.Fatal(err)
}
spew.Dump(trieDecoder)