How to return hash and bytes in one step in Go?

golang hash
golang md5
golang md5 file

I'm trying to understand how I can read content of the file, calculate its hash and return its bytes in one Go. So far, I'm doing this in two steps, e.g.

// calculate file checksum
hasher := sha256.New()
f, err := os.Open(fname)
if err != nil {
    msg := fmt.Sprintf("Unable to open file %s, %v", fname, err)
    panic(msg)
}
defer f.Close()
b, err := io.Copy(hasher, f)
if err != nil {
    panic(err)
}
cksum := hex.EncodeToString(hasher.Sum(nil))

// read again (!!!) to get data as bytes array
data, err := ioutil.ReadFile(fname)

Obviously it is not the most efficient way to do this, since read happens twice, once in copy to pass to hasher and another in ioutil to read file and return list of bytes. I'm struggling to understand how I can combine these steps together and do in one go, read data once, calculate any hash and return it along with list of bytes to another layer.


If you want to read a file, without creating a copy of the entire file in memory, and at the same time calculate its hash, you can do so with a TeeReader:

hasher := sha256.New()
f, err := os.Open(fname)
data := io.TeeReader(f, hasher)
// Now read from data as usual, which is still a stream.

What happens here is that any bytes that are read from data (which is a Reader just like the file object f is) will be pushed to hasheras well.

Note, however, that hasher will produce the correct hash only once you have read the entire file through data, and not until then. So if you need the hash before you decide whether or not you want to read the file, you are left with the options of either doing it in two passes (for example like you are now), or to always read the file but discard the result if the hash check failed.

If you do read the file in two passes, you could of course buffer the entire file data in a byte buffer in memory. However, the operating system will typically cache the file you just read in RAM anyway (if possible), so the performance benefit of doing a buffered two-pass solution yourself rather than just doing two passes over the file is probably negligible.

file: How to return hash and bytes in one step in Go?, I can read content of the file, calculate its hash and return its bytes in one Go. So far, I'm doing this in two steps, e.g.// calculate file checksumhasher := sha256. A minimal perfect hash function goes one step further. It maps the N keys to exactly the integers 0..N-1, with each key getting precisely one value. We can rank hash functions on a few different criteria: speed to construct, speed to evaluate, and space used.


You can write bytes directly to the hasher. For example:

package main

import (
    "crypto/sha256"
    "encoding/hex"
    "io/ioutil"
)

func main() {
    hasher := sha256.New()

    data, err := ioutil.ReadFile("foo.txt")
    if err != nil {
        panic(err)
    }

    hasher.Write(data)
    cksum := hex.EncodeToString(hasher.Sum(nil))

    println(cksum)
}

As the Hash interface embeds io.Writer. This allows you to read the bytes from the file once, write them into the hasher then also return them out.

How to return hash and bytes in one step in Go? - file, I can read content of the file, calculate its hash and return its bytes in one Go. So far, I'm doing this in two steps, e.g. // calculate file checksum hasher := sha256​  Select and open the file you want to know the checksum hash in the dialog box prompted. Then go to Tool menu and select Compute Hash (keyboard shortcut key is Ctrl+F2), and then choose SHA-1 (160 bit) or MD5 or any other hash function algorithm that you need. Get the has by hit OK.


Do data, err := ioutil.ReadFile(fname) first. You'll have your slice of bytes. Then create your hasher, and do hasher.Write(data).

SHA1 Hashes, func main() { s := "sha1 this string". The pattern for generating a hash is sha1.New​() , sha1.Write(bytes) , then sha1.Sum([]byte{}) . Here we start with a new hash. c. create a new byte array consisting of the XML payload bytes from step b, appended with the salt bytes from step a. d. perform a SHA512 hash on the concatenated byte array from step c, which results in a hashed byte array. e. create a new byte array consisting of the hashed bytes from step d, appended with the salt bytes from step a.


If you plan on hashing files you shouldn't read the whole file into memory because... there are large files that don't fit into RAM. Yes, in practice you very rarely will run into such out-of-memory issues but you can easily prevent them. The Hash interface is an io.Writer. Usually, the Hash packages have a New function that return a Hash. This allows you to read the file in blocks and continuously feed it to the Write method of the Hash you have. You may also use methods like io.Copy to do this:

h := sha256.New()
data := &bytes.Buffer{}
data.Write([]byte("hi there"))
data.Write([]byte("folks"))
io.Copy(h, data)
fmt.Printf("%x", h.Sum(nil))

io.Copy uses a bufer of 32KiB internally so using it requires around 32KiB of memory max.

Password Hash & Salt Using Golang - James Cox, Once we've done this, I'll go… Step Two — Hash & Salt The User Password We then return the byte slice as a string so that we can store the salted hash in  You are developing a method named GetHash that will return a hash value for a file. The method includes the following code. (Line numbers are included for reference only.) You need to return the cryptographic hash of the bytes contained in the fileBytes variable. Which code segment should you insert at line 05? A. Option A. B. Option B C


crypto/sha256: provide a way to efficiently hash multiple byte slices , crypto/sha256: provide a way to efficiently hash multiple byte slices #21948 the Go 1 compatibility guarantee (while existing calls would still compile, Hash. If it returned a *digest then the compiler would have an easier There was a recent CL that does the first step of devirtualizing this kind of thing. But Hashids is able to encode several integers into one id. This is done by reserving a few characters from the alphabet as separators . These characters are not used in encoding, but instead do the job of purely separating the real encoded values.


Digital Libraries: Technology and Management of Indigenous , all the 256 one-byte characters are considered, the number of possible 5-​grams is 2565 = 240 which So we can use a hash table to represent a document vector and this way saves lots of computer resources. (2) 5) Use a hash function to get the value of this value. the paragraph is not reached, go back to step 3). Find answers to How do I return a %hash from a subroutine from the expert community at Experts Exchange How do I return a %hash from a subroutine Solutions | Experts Exchange Need support for your remote team?


sha256, The size of a SHA224 checksum in bytes. const Size224 = 28. func New ¶. func New() hash.Hash. New returns a  Return how big a hash is. hashStr(String, Hash) Static utility routine for hashing a String in one step. prepare() Prepare the hash bytes for use. reset() Initialize (reset) the hash. toString() Convert a Hash to a String representation. hashSize protected int hashSize How big a hash is. hashBytes protected byte hashBytes[] The hash bytes. Hash