Compress. Compression trades time for space. It is used often on files and even on web pages. With the compress package in Go we can use gzip on a string.
With NewWriter, we create a new gzip writer. And then we can write compressed bytes to a file with Write. We must close the file when we are done.
First example. Here we have a string. We want to write a compressed version of this string to a file on the disk. We create a file with os.Create.
Then We use NewWriter to create a gzip writer targeting that file we created. We call Write() to write bytes.
Tip We convert the string into a byte value. This can be done with a simple cast expression.
package main
import (
"compress/gzip""fmt""os"
)
func main() {
// Some text we want to compress.
original := "bird and frog"// Open a file for writing.
f, _ := os.Create("C:\\programs\\file.gz")
// Create gzip writer.
w := gzip.NewWriter(f)
// Write bytes in compressed form to the file.
w.Write([]byte(original))
// Close the file.
w.Close()
fmt.Println("DONE")
}DONEbird and frog
Decompress. Here we decompress data from a file on the disk. We first read in the file with os.Open. Then we create a gzip Reader with the gzip.NewReader call.
Start We make a new empty byte slice. The data returned by Read will be stored in this region of memory.
Next We Read the data and it is decompressed. We can then convert the byte slice to a string and display it.
package main
import (
"compress/gzip""fmt""os"
)
func main() {
// Open the gzip file.
f, _ := os.Open("C:\\programs\\file.gz")
// Create new reader to decompress gzip.
reader, _ := gzip.NewReader(f)
// Empty byte slice.
result := make([]byte, 100)
// Read in data.
count, _ := reader.Read(result)
// Print our decompressed data.
fmt.Println(count)
fmt.Println(string(result))
}13
bird and frog
BestCompression. We can adjust the GZIP algorithm to emphasize speed or the output's compressed file size. Here we build up a string that contains enough characters to show a difference.
And We then compress the string with NewWriterLevel and gzip.BestSpeed. Then we use BestCompression.
Result The output file that uses BestCompression is 4 bytes smaller on the disk than the version that uses BestSpeed.
package main
import (
"compress/gzip""fmt""os"
)
func main() {
test := "this is an example string for testing compression levels"
test += " here is some more example text"
test += " cat 123 bird 456 UPPERCASE TEXT"
test += " __ punct __ // punct"// Write with BestSpeed.
fmt.Println("BESTSPEED")
f, _ := os.Create("C:\\programs\\file-bestspeed.gz")
w, _ := gzip.NewWriterLevel(f, gzip.BestSpeed)
w.Write([]byte(test))
w.Close()
// Write with BestCompression.
fmt.Println("BESTCOMPRESSION")
f, _ = os.Create("C:\\programs\\file-bestcompression.gz")
w, _ = gzip.NewWriterLevel(f, gzip.BestCompression)
w.Write([]byte(test))
w.Close()
}BESTSPEED
BESTCOMPRESSION file-bestspeed.gz: 138 bytes
file-bestcompression.gz: 134 bytes
Compress file. This program reads in a file. It uses ioutil.ReadAll to get all the bytes from the file. It then creates a new file by replacing the extension with "gz" and writing it.
Note By decompressing file.gz with a program like 7-Zip, we can be sure that the correct data was compressed.
Note 2 This program could be used to compress files. You can change the paths and the extensions to handle a specific case.
package main
import (
"bufio""compress/gzip""fmt""io/ioutil""os""strings"
)
func main() {
// Open file on disk.
name := "file.txt"
f, _ := os.Open("C:\\programs\\" + name)
// Create a Reader and use ReadAll to get all the bytes from the file.
reader := bufio.NewReader(f)
content, _ := ioutil.ReadAll(reader)
// Replace txt extension with gz extension.
name = strings.Replace(name, ".txt", ".gz", -1)
// Open file for writing.
f, _ = os.Create("C:\\programs\\" + name)
// Write compressed data.
w := gzip.NewWriter(f)
w.Write(content)
w.Close()
// Done.
fmt.Println("DONE")
}DONEhere is some sample texthere is some sample text
A review. The compress package provides built-in gzip support. Other compression technologies are also supported. The level of compression can be chosen.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Mar 24, 2023 (edit).