// hash_sha1.go
package main
​
import (
    "fmt"
    "crypto/sha1"
    "io"
    "log"
)
​
func main() {
    hasher := sha1.New()
    io.WriteString(hasher, "test")
    b := []byte{}
    fmt.Printf("Result: %x\n", hasher.Sum(b))
    fmt.Printf("Result: %d\n", hasher.Sum(b))
    //
    hasher.Reset()
    data := []byte("We shall overcome!")
    n, err := hasher.Write(data)
    if n!=len(data) || err!=nil {
        log.Printf("Hash write error: %v / %v", n, err)
    }
    checksum := hasher.Sum(b)
    fmt.Printf("Result: %x\n", checksum)
}

Result: a94a8fe5ccb19ba61c4c0873d391e987982fbbd3
Result: [169 74 143 229 204 177 155 166 28 76 8 115 211 145 233 135 152 47 187 211]
Result: e2222bfc59850bbb00a722e764a555603bb59b2a

type Hash interface {
    // Write (via the embedded io.Writer interface) adds more data to the running hash.
    // It never returns an error.
    io.Writer
​
    // Sum appends the current hash to b and returns the resulting slice.
    // It does not change the underlying hash state.
    Sum(b []byte) []byte
​
    // Reset resets the Hash to its initial state.
    Reset()
​
    // Size returns the number of bytes Sum will return.
    Size() int
​
    // BlockSize returns the hash's underlying block size.
    // The Write method must be able to accept any amount
    // of data, but it may operate more efficiently if all writes
    // are a multiple of the block size.
    BlockSize() int
}