description: Tutorial on downloadig files from swarm in Go.

Downloading Files from Swarm

In the previous section we uploaded a hello.txt file to swarm and in return we got a manifest hash.

  1. manifestHash := "f9192507e2e8e118bfedac428c3aa1dec4ae156e954128ec5fb27f63ee67bcac"

Let’s inspect the manifest by downloading it first by calling DownloadManfest.

  1. manifest, isEncrypted, err := client.DownloadManifest(manifestHash)
  2. if err != nil {
  3.   log.Fatal(err)
  4. }

We can iterate over the manifest entries and see what the content-type, size, and content hash are.

  1. for _, entry := range manifest.Entries {
  2.   fmt.Println(entry.Hash)        // 42179060941352ba7b400b16c40f1e1290423a826de2a70587034dc14bc4ab2f
  3.   fmt.Println(entry.ContentType) // text/plain; charset=utf-8
  4.   fmt.Println(entry.Path)        // ""
  5. }

If you’re familiar with swarm urls, they’re in the format bzz:/<hash>/<path>, so in order to download the file we specify the manifest hash and path. The path in this case is an empty string. We pass this data to the Download function and get back a file object.

  1. file, err := client.Download(manifestHash, "")
  2. if err != nil {
  3.   log.Fatal(err)
  4. }

We may now read and print the contents of the returned file reader.

  1. content, err := ioutil.ReadAll(file)
  2. if err != nil {
  3.   log.Fatal(err)
  4. }
  6. fmt.Println(string(content)) // hello world

As expected, it logs hello world which what our original file contained.

Full code

Commands

  1. geth account new
  2. export BZZKEY=970ef9790b54425bea2c02e25cab01e48cf92573
  3. swarm --bzzaccount $BZZKEY

swarm_download.go

  1. package main
  3. import (
  4.     "fmt"
  5.     "io/ioutil"
  6.     "log"
  8.     bzzclient "github.com/ethersphere/swarm/api/client"
  9. )
  11. func main() {
  12.     client := bzzclient.NewClient("http://127.0.0.1:8500")
  13.     manifestHash := "2e0849490b62e706a5f1cb8e7219db7b01677f2a859bac4b5f522afd2a5f02c0"
  14.     manifest, isEncrypted, err := client.DownloadManifest(manifestHash)
  15.     if err != nil {
  16.         log.Fatal(err)
  17.     }
  18.     fmt.Println(isEncrypted) // false
  20.     for _, entry := range manifest.Entries {
  21.         fmt.Println(entry.Hash)        // 42179060941352ba7b400b16c40f1e1290423a826de2a70587034dc14bc4ab2f
  22.         fmt.Println(entry.ContentType) // text/plain; charset=utf-8
  23.         fmt.Println(entry.Size)        // 12
  24.         fmt.Println(entry.Path)        // ""
  25.     }
  27.     file, err := client.Download(manifestHash, "")
  28.     if err != nil {
  29.         log.Fatal(err)
  30.     }
  32.     content, err := ioutil.ReadAll(file)
  33.     if err != nil {
  34.         log.Fatal(err)
  35.     }
  36.     fmt.Println(string(content)) // hello world
  37. }