Read contents of tar file without unzipping to disk

I have been able to loop through the files in a tar file, but I am stuck on how to read the contents of those files as string. I would like to know how to print the contents of the files as a string?

This is my code below

package main

import (
    "archive/tar"
    "fmt"
    "io"
    "log"
    "os"
    "bytes"
    "compress/gzip"
)

func main() {
    file, err := os.Open("testtar.tar.gz")

    archive, err := gzip.NewReader(file)

    if err != nil {
        fmt.Println("There is a problem with os.Open")
    }
    tr := tar.NewReader(archive)

    for {
        hdr, err := tr.Next()
        if err == io.EOF {
            break
        }
        if err != nil {
            log.Fatal(err)
        }

        fmt.Printf("Contents of %s:\n", hdr.Name)
    }
}

Just use the tar.Reader as an io.Reader for each file you want to read.

tr := tar.NewReader(r)

// get the next file entry 
h, _ := tr.Next() 

If you need the whole file as a string:

// read the complete content of the file h.Name into the bs []byte
bs, _ := ioutil.ReadAll(tr)

// convert the []byte to a string
s := string(bs)

If you need to read line by line, then this would be better:

// create a Scanner for reading line by line
s := bufio.NewScanner(tr)

// line reading loop
for s.Scan() {

  // read the current last read line of text
  l := s.Text()

  // ...and do something with l

}

// you should check for error at this point
if s.Err() != nil {
  // handle it
}

Sometimes I have seen people use tar.gz as a makeshift database, so I found it
useful to read the archive into a fstest.MapFS:

package main

import (
   "archive/tar"
   "compress/gzip"
   "io"
   "os"
   "testing/fstest"
)

func tarGzMemory(source string) (fstest.MapFS, error) {
   file, err := os.Open(source)
   if err != nil { return nil, err }
   defer file.Close()
   gzRead, err := gzip.NewReader(file)
   if err != nil { return nil, err }
   tarRead := tar.NewReader(gzRead)
   files := make(fstest.MapFS)
   for {
      cur, err := tarRead.Next()
      if err == io.EOF { break } else if err != nil { return nil, err }
      if cur.Typeflag != tar.TypeReg { continue }
      data, err := io.ReadAll(tarRead)
      if err != nil { return nil, err }
      files[cur.Name] = &fstest.MapFile{Data: data}
   }
   return files, nil
}

Example:

package main

func main() {
   m, e := tarGzMemory("mingw64.db.tar.gz")
   if e != nil {
      panic(e)
   }
   data := m["mingw-w64-x86_64-gcc-10.2.0-10/desc"].Data
   print(string(data))
}

https://golang.org/pkg/testing/fstest

With some help from the official site this is what I had intended previously. Special focus should be turned to the bottom where the conversion from bytes to string is made.

package main

import (
    "archive/tar"
    "fmt"
    "io"
    "log"
    "os"
    "bytes"
    "compress/gzip"
)

func main() {

    file, err := os.Open("testtar.tar.gz")

    archive, err := gzip.NewReader(file)

    if err != nil {
        fmt.Println("There is a problem with os.Open")
    }
    tr := tar.NewReader(archive)

    for {
        hdr, err := tr.Next()
        if err == io.EOF {
            break
        }
        if err != nil {
            log.Fatal(err)
        }

        fmt.Printf("Contents of %s:\n", hdr.Name)
        
        //Using a bytes buffer is an important part to print the values as a string

        bud := new(bytes.Buffer)
        bud.ReadFrom(tr)
        s := bud.String()
        fmt.Println(s)
        fmt.Println()
    }

}