README.md

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.

manifestHash := "f9192507e2e8e118bfedac428c3aa1dec4ae156e954128ec5fb27f63ee67bcac"

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

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

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

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

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.

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

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

content, err := ioutil.ReadAll(file)
if err != nil {
  log.Fatal(err)
}

fmt.Println(string(content)) // hello world

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

---

Full code

Commands

geth account new
export BZZKEY=970ef9790b54425bea2c02e25cab01e48cf92573
swarm --bzzaccount $BZZKEY

swarm_download.go

package main

import (
	"fmt"
	"io/ioutil"
	"log"

	bzzclient "github.com/ethereum/go-ethereum/swarm/api/client"
)

func main() {
	client := bzzclient.NewClient("http://127.0.0.1:8500")
	manifestHash := "2e0849490b62e706a5f1cb8e7219db7b01677f2a859bac4b5f522afd2a5f02c0"
	manifest, isEncrypted, err := client.DownloadManifest(manifestHash)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(isEncrypted) // false

	for _, entry := range manifest.Entries {
		fmt.Println(entry.Hash)        // 42179060941352ba7b400b16c40f1e1290423a826de2a70587034dc14bc4ab2f
		fmt.Println(entry.ContentType) // text/plain; charset=utf-8
		fmt.Println(entry.Size)        // 12
		fmt.Println(entry.Path)        // ""
	}

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

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