gocql can not unmarshal blob into *[20]uint8

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)

}