gocql can not unmarshal blob into *[20]uint8 - go

Question

I have a question related to using blob type as partition key.
I use it, as I need to save hash value.
(hash value returns binary data. usually as hexadecimal.)
I tried a select query with gocql, however it failed with following error.
Is there any way to get a successful result for this kind of query?
Your advice highly appreciated!!
-- result
hash_value: [208 61 222 22 16 214 223 135 169 6 25 65 44 237 166 229 50 5 40 221]
/ hash_value: ?=??߇?A,???2(?
/ hash_value: 0xd03dde1610d6df87a90619412ceda6e5320528dd
string
2018/03/22 10:03:17 can not unmarshal blob into *[20]uint8
-- select.go
package main
import (
"fmt"
"log"
"crypto/sha1"
"reflect"
"github.com/gocql/gocql"
)
func main() {
cluster := gocql.NewCluster("10.0.0.1")
cluster.Keyspace = "ks"
cluster.Consistency = gocql.Quorum
cluster.ProtoVersion = 4
cluster.Authenticator = gocql.PasswordAuthenticator{
Username: "cassandra",
Password: "cassandra",
}
session, _ := cluster.CreateSession()
defer session.Close()
text := "text before hashed"
data := []byte(text)
hash_value := sha1.Sum(data)
hexa_string := fmt.Sprintf("0x%x", hash_value)
fmt.Println("hash_value: ", hash_value)
fmt.Println(" / string: ", string(hash_value[:]))
fmt.Println(" / column1: ", hexa_string)
fmt.Println(reflect.TypeOf(hexa_string))
// *** select ***
var column1 int
returned_hash := sha1.Sum(data)
//if err := session.Query(`SELECT hash_value, column1 FROM sample WHERE hash_value= ? LIMIT 1`,
// hexa_string).Consistency(gocql.One).Scan(&returned_hash, &column1); err != nil {
if err := session.Query(`SELECT hash_value, column1 FROM sample WHERE hash_value=0xd03dde1610d6df87a90619412ceda6e5320528dd`).Consistency(gocql.One).Scan(&returned_hash, &column1); err != nil {
//fmt.Println(err)
log.Fatal(err)
}
fmt.Println("comment: ", returned_hash, user_id)
}
-- table definition --
CREATE TABLE IF NOT EXISTS ks.samle (
hash_value blob,
column1 int,
...
PRIMARY KEY((hash_value), column1)
) WITH CLUSTERING ORDER BY (column1 DESC);

Answer 1

I fixed the problem by changing the type of variable: returned_hash.
returned_hash (var to store returned result) should be []byte.
I understands as follows.
marshal: convert the data given in the code to a type cassandra can handle.
unmarshal: convert the data cassandra returned back to a type golang-code can handle.
the original error means latter pattern doesn't go well. so the type of returned_hash must be wrong.
Correct me if I'm wrong. thanks.
package main
import (
"fmt"
"log"
"crypto/sha1"
"reflect"
"github.com/gocql/gocql"
)
func main() {
cluster := gocql.NewCluster("127.0.0.1")
cluster.Keyspace = "browser"
cluster.Consistency = gocql.Quorum
//cluster.ProtoVersion = 4
//cluster.Authenticator = gocql.PasswordAuthenticator{
// Username: "cassandra",
// Password: "cassandra",
//}
session, _ := cluster.CreateSession()
defer session.Close()
text := "text before hashed"
data := []byte(text)
hash_value := sha1.Sum(data)
hexa_string := fmt.Sprintf("0x%x", hash_value)
fmt.Println("hash_value: ", hash_value)
fmt.Println(" / string(hash_value): ", string(hash_value[:]))
fmt.Println(" / hexa(hash_value): ", hexa_string)
fmt.Println(reflect.TypeOf(hexa_string))
// *** select ***
var column1 int
//returned_hash := sha1.Sum(data)
//var returned_hash *[20]uint8
var returned_hash []byte
if err := session.Query(`SELECT hash_value, column1 FROM sample WHERE hash_value=? LIMIT 1`,
hash_value[:]).Consistency(gocql.One).Scan(&returned_hash, &column1); err != nil {
//if err := session.Query(`SELECT hash_value, column1 FROM sample WHERE hash_value=0xd03dde1610d6df87a90619412ceda6e5320528dd`).Consistency(gocql.One).Scan(&returned_hash, &column1); err != nil {
log.Fatal(err)
}
fmt.Printf("Returned: %#x %d \n", returned_hash, column1)
}