Golang Compress GZIP Examples

Use the compress package to write a string to a gzip file. Compact an existing file.

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.File

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.

Golang program that uses compress package 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") } Output DONE Compressed contents of file.gz: bird 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.

Make: We make a new empty byte slice. The data returned by Read will be stored in this region of memory.

Slice

Read: We Read the data and it is decompressed. We can then convert the byte slice to a string and display it.

Convert

Golang program that uses gzip, NewReader 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)) } Output 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.

Results: The output file that uses BestCompression is 4 bytes smaller on the disk than the version that uses BestSpeed.

Golang program that uses gzip.BestSpeed, BestCompression 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() } Output BESTSPEED BESTCOMPRESSION Output 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.

Golang program that compresses file on disk 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") } Output DONE Contents of file.txt: here is some sample text Compressed contents of file.gz: here is some sample text

Notes, research. The gzip package is part of the "compress" package. We are not limited to gzip: we can apply bzip2, flate, lzw and zlib compression.

Quote: Package gzip implements reading and writing of gzip format compressed files.

Gzip: golang.org

A review. The compress package provides built-in gzip support. Other compression technologies are also supported. The level of compression can be chosen.

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Golang Compress GZIP Examples

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