Down is a utility tool for streaming, flexible and safe downloading of remote
files. It can use open-uri + Net::HTTP
, http.rb or wget
as the backend
HTTP library.
gem "down", "~> 5.0"
The primary method is Down.download
, which downloads the remote file into a
Tempfile
:
require "down"
tempfile = Down.download("http://example.com/nature.jpg")
tempfile #=> #<Tempfile:/var/folders/k7/6zx6dx6x7ys3rv3srh0nyfj00000gn/T/20150925-55456-z7vxqz.jpg>
The returned Tempfile
has some additional attributes extracted from the
response data:
tempfile.content_type #=> "text/plain"
tempfile.original_filename #=> "document.txt"
tempfile.charset #=> "utf-8"
When you're accepting URLs from an outside source, it's a good idea to limit
the filesize (because attackers want to give a lot of work to your servers).
Down allows you to pass a :max_size
option:
Down.download("http://example.com/image.jpg", max_size: 5 * 1024 * 1024) # 5 MB
# Down::TooLarge: file is too large (max is 5MB)
What is the advantage over simply checking size after downloading? Well, Down
terminates the download very early, as soon as it gets the Content-Length
header. And if the Content-Length
header is missing, Down will terminate the
download as soon as the downloaded content surpasses the maximum size.
By default the remote file will be downloaded into a temporary location and
returned as a Tempfile
. If you would like the file to be downloaded to a
specific location on disk, you can specify the :destination
option:
Down.download("http://example.com/image.jpg", destination: "/path/to/destination")
#=> nil
In this case Down.download
won't have any return value, so if you need a File
object you'll have to create it manually.
You can also keep the tempfile, but override the extension:
tempfile = Down.download("http://example.com/some/file", extension: "txt")
File.extname(tempfile.path) #=> ".txt"
Down.download
and Down.open
will automatically detect and apply HTTP basic
authentication from the URL:
Down.download("http://user:password@example.org")
Down.open("http://user:password@example.org")
Down.download
supports :content_length_proc
, which gets called with the
value of the Content-Length
header as soon as it's received, and
:progress_proc
, which gets called with current filesize whenever a new chunk
is downloaded.
Down.download "http://example.com/movie.mp4",
content_length_proc: -> (content_length) { ... },
progress_proc: -> (progress) { ... }
Down has the ability to retrieve content of the remote file as it is being
downloaded. The Down.open
method returns a Down::ChunkedIO
object which
represents the remote file on the given URL. When you read from it, Down
internally downloads chunks of the remote file, but only how much is needed.
remote_file = Down.open("http://example.com/image.jpg")
remote_file.size # read from the "Content-Length" header
remote_file.read(1024) # downloads and returns first 1 KB
remote_file.read(1024) # downloads and returns next 1 KB
remote_file.eof? #=> false
remote_file.read # downloads and returns the rest of the file content
remote_file.eof? #=> true
remote_file.close # closes the HTTP connection and deletes the internal Tempfile
The following IO methods are implemented:
#read
&#readpartial
#gets
#seek
#pos
&#tell
#eof?
#rewind
#close
By default the downloaded content is internally cached into a Tempfile
, so
that when you rewind the Down::ChunkedIO
, it continues reading the cached
content that it had already retrieved.
remote_file = Down.open("http://example.com/image.jpg")
remote_file.read(1*1024*1024) # downloads, caches, and returns first 1MB
remote_file.rewind
remote_file.read(1*1024*1024) # reads the cached content
remote_file.read(1*1024*1024) # downloads the next 1MB
If you want to save on IO calls and on disk usage, and don't need to be able to
rewind the Down::ChunkedIO
, you can disable caching downloaded content:
Down.open("http://example.com/image.jpg", rewindable: false)
You can also yield chunks directly as they're downloaded via #each_chunk
, in
which case the downloaded content is not cached into a file regardless of the
:rewindable
option.
remote_file = Down.open("http://example.com/image.jpg")
remote_file.each_chunk { |chunk| ... }
remote_file.close
You can access the response status and headers of the HTTP request that was made:
remote_file = Down.open("http://example.com/image.jpg")
remote_file.data[:status] #=> 200
remote_file.data[:headers] #=> { "Content-Type" => "image/jpeg", ... } (header names are normalized)
remote_file.data[:response] # returns the response object
Note that a Down::ResponseError
exception will automatically be raised if
response status was 4xx or 5xx.
The Down.open
performs HTTP logic and returns an instance of
Down::ChunkedIO
. However, Down::ChunkedIO
is a generic class that can wrap
any kind of streaming. It accepts an Enumerator
that yields chunks of
content, and provides IO-like interface over that enumerator, calling it
whenever more content is needed.
require "down/chunked_io"
Down::ChunkedIO.new(...)
:chunks
–Enumerator
that yields chunks of content:size
– size of the file if it's known (returned by#size
):on_close
– called when streaming finishes or IO is closed:data
- custom data that you want to store (returned by#data
):rewindable
- whether to cache retrieved data into a file (defaults totrue
):encoding
- force content to be returned in specified encoding (defaults toEncoding::BINARY
)
Here is an example of creating a streaming IO of a MongoDB GridFS file:
require "down/chunked_io"
mongo = Mongo::Client.new(...)
bucket = mongo.database.fs
content_length = bucket.find(_id: id).first[:length]
stream = bucket.open_download_stream(id)
io = Down::ChunkedIO.new(
size: content_length,
chunks: stream.enum_for(:each),
on_close: -> { stream.close },
)
Down tries to recognize various types of exceptions and re-raise them as one of
the Down::Error
subclasses. This is Down's exception hierarchy:
Down::Error
Down::TooLarge
Down::InvalidUrl
Down::TooManyRedirects
Down::NotModified
Down::ResponseError
Down::ClientError
Down::NotFound
Down::ServerError
Down::ConnectionError
Down::TimeoutError
Down::SSLError
The following backends are available:
- Down::NetHttp (default)
- Down::Http
- Down::Wget
You can use the backend directly:
require "down/net_http"
Down::NetHttp.download("...")
Down::NetHttp.open("...")
Or you can set the backend globally (default is :net_http
):
require "down"
Down.backend :http # use the Down::Http backend
Down.download("...")
Down.open("...")
The Down::NetHttp
backend implements downloads using open-uri and
Net::HTTP standard libraries.
gem "down", "~> 5.0"
require "down/net_http"
tempfile = Down::NetHttp.download("http://nature.com/forest.jpg")
tempfile #=> #<Tempfile:/var/folders/k7/6zx6dx6x7ys3rv3srh0nyfj00000gn/T/20150925-55456-z7vxqz.jpg>
io = Down::NetHttp.open("http://nature.com/forest.jpg")
io #=> #<Down::ChunkedIO ...>
Down::NetHttp.download
is implemented as a wrapper around open-uri, and fixes
some of open-uri's undesired behaviours:
- uses
URI::HTTP#open
orURI::HTTPS#open
directly for security - always returns a
Tempfile
object, whereas open-uri returnsStringIO
when file is smaller than 10KB - gives the extension to the
Tempfile
object from the URL - allows you to limit maximum number of redirects
On the other hand Down::NetHttp.open
is implemented using Net::HTTP directly,
as open-uri doesn't support downloading on-demand.
Down::NetHttp#download
turns off open-uri's following redirects, as open-uri
doesn't have a way to limit the maximum number of hops, and implements its own.
By default maximum of 2 redirects will be followed, but you can change it via
the :max_redirects
option:
Down::NetHttp.download("http://example.com/image.jpg") # 2 redirects allowed
Down::NetHttp.download("http://example.com/image.jpg", max_redirects: 5) # 5 redirects allowed
Down::NetHttp.download("http://example.com/image.jpg", max_redirects: 0) # 0 redirects allowed
Down::NetHttp.open("http://example.com/image.jpg") # 2 redirects allowed
Down::NetHttp.open("http://example.com/image.jpg", max_redirects: 5) # 5 redirects allowed
Down::NetHttp.open("http://example.com/image.jpg", max_redirects: 0) # 0 redirects allowed
An HTTP proxy can be specified via the :proxy
option:
Down::NetHttp.download("http://example.com/image.jpg", proxy: "http://proxy.org")
Down::NetHttp.open("http://example.com/image.jpg", proxy: "http://user:password@proxy.org")
Timeouts can be configured via the :open_timeout
and :read_timeout
options:
Down::NetHttp.download("http://example.com/image.jpg", open_timeout: 5)
Down::NetHttp.open("http://example.com/image.jpg", read_timeout: 10)
Request headers can be added via the :headers
option:
Down::NetHttp.download("http://example.com/image.jpg", headers: { "Header" => "Value" })
Down::NetHttp.open("http://example.com/image.jpg", headers: { "Header" => "Value" })
The :ssl_ca_cert
and :ssl_verify_mode
options are supported, and they have
the same semantics as in open-uri
:
Down::NetHttp.open("http://example.com/image.jpg",
ssl_ca_cert: "/path/to/cert",
ssl_verify_mode: OpenSSL::SSL::VERIFY_PEER)
If the URL isn't parseable by URI.parse
, Down::NetHttp
will
attempt to normalize the URL using Addressable::URI, URI-escaping
any potentially unescaped characters. You can change the normalizer
via the :uri_normalizer
option:
# this skips URL normalization
Down::NetHttp.download("http://example.com/image.jpg", uri_normalizer: -> (url) { url })
Any additional options passed to Down.download
will be forwarded to
open-uri, so you can for example add basic authentication or a timeout:
Down::NetHttp.download "http://example.com/image.jpg",
http_basic_authentication: ['john', 'secret'],
read_timeout: 5
You can also initialize the backend with default options:
net_http = Down::NetHttp.new(open_timeout: 3)
net_http.download("http://example.com/image.jpg")
net_http.open("http://example.com/image.jpg")
The Down::Http
backend implements downloads using the http.rb gem.
gem "down", "~> 5.0"
gem "http", "~> 5.0"
require "down/http"
tempfile = Down::Http.download("http://nature.com/forest.jpg")
tempfile #=> #<Tempfile:/var/folders/k7/6zx6dx6x7ys3rv3srh0nyfj00000gn/T/20150925-55456-z7vxqz.jpg>
io = Down::Http.open("http://nature.com/forest.jpg")
io #=> #<Down::ChunkedIO ...>
Some features that give the http.rb backend an advantage over open-uri
and
Net::HTTP
include:
- Low memory usage (10x less than
open-uri
/Net::HTTP
) - Proper SSL support
- Support for persistent connections
- Global timeouts (limiting how long the whole request can take)
- Chainable builder API for setting default options
All additional options will be forwarded to HTTP::Client#request
:
Down::Http.download("http://example.org/image.jpg", headers: { "Foo" => "Bar" })
Down::Http.open("http://example.org/image.jpg", follow: { max_hops: 0 })
However, it's recommended to configure request options using http.rb's chainable API, as it's more convenient than passing raw options.
Down::Http.open("http://example.org/image.jpg") do |client|
client.timeout(connect: 3, read: 3)
end
You can also initialize the backend with default options:
http = Down::Http.new(headers: { "Foo" => "Bar" })
# or
http = Down::Http.new { |client| client.timeout(connect: 3) }
http.download("http://example.com/image.jpg")
http.open("http://example.com/image.jpg")
By default Down::Http
makes a GET
request to the specified endpoint, but you
can specify a different request method using the :method
option:
Down::Http.download("http://example.org/image.jpg", method: :post)
Down::Http.open("http://example.org/image.jpg", method: :post)
down = Down::Http.new(method: :post)
down.download("http://example.org/image.jpg")
The Down::Wget
backend implements downloads using the wget
command line
utility.
gem "down", "~> 5.0"
gem "posix-spawn" # omit if on JRuby
gem "http_parser.rb"
require "down/wget"
tempfile = Down::Wget.download("http://nature.com/forest.jpg")
tempfile #=> #<Tempfile:/var/folders/k7/6zx6dx6x7ys3rv3srh0nyfj00000gn/T/20150925-55456-z7vxqz.jpg>
io = Down::Wget.open("http://nature.com/forest.jpg")
io #=> #<Down::ChunkedIO ...>
One major advantage of wget
is that it automatically resumes downloads that
were interrupted due to network failures, which is very useful when you're
downloading large files.
However, the Wget backend should still be considered experimental, as it wasn't easy to implement a CLI wrapper that streams output, so it's possible that I've made mistakes. Let me know how it's working out for you 😉.
You can pass additional arguments to the underlying wget
commmand via symbols:
Down::Wget.download("http://nature.com/forest.jpg", :no_proxy, connect_timeout: 3)
Down::Wget.open("http://nature.com/forest.jpg", user: "janko", password: "secret")
You can also initialize the backend with default arguments:
wget = Down::Wget.new(:no_proxy, connect_timeout: 3)
wget.download("http://nature.com/forest.jpg")
wget.open("http://nature.com/forest.jpg")
- MRI 2.3
- MRI 2.4
- MRI 2.5
- MRI 2.6
- MRI 2.7
- JRuby 9.2
You can run tests with
$ bundle exec rake test
The test suite pulls and runs kennethreitz/httpbin as a Docker container, so you'll need to have Docker installed and running.