1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
|
# frozen_string_literal: true
module ActiveStorage
# = Active Storage \Previewer
#
# This is an abstract base class for previewers, which generate images from blobs. See
# ActiveStorage::Previewer::MuPDFPreviewer and ActiveStorage::Previewer::VideoPreviewer for
# examples of concrete subclasses.
class Previewer
attr_reader :blob
# Implement this method in a concrete subclass. Have it return true when given a blob from which
# the previewer can generate an image.
def self.accept?(blob)
false
end
def initialize(blob)
@blob = blob
end
# Override this method in a concrete subclass. Have it yield an attachable preview image (i.e.
# anything accepted by ActiveStorage::Attached::One#attach). Pass the additional options to
# the underlying blob that is created.
def preview(**options)
raise NotImplementedError
end
private
# Downloads the blob to a tempfile on disk. Yields the tempfile.
def download_blob_to_tempfile(&block) # :doc:
blob.open tmpdir: tmpdir, &block
end
# Executes a system command, capturing its binary output in a tempfile. Yields the tempfile.
#
# Use this method to shell out to a system library (e.g. muPDF or FFmpeg) for preview image
# generation. The resulting tempfile can be used as the +:io+ value in an attachable Hash:
#
# def preview
# download_blob_to_tempfile do |input|
# draw "my-drawing-command", input.path, "--format", "png", "-" do |output|
# yield io: output, filename: "#{blob.filename.base}.png", content_type: "image/png"
# end
# end
# end
#
# The output tempfile is opened in the directory returned by #tmpdir.
def draw(*argv) # :doc:
open_tempfile do |file|
instrument :preview, key: blob.key do
capture(*argv, to: file)
end
yield file
end
end
def open_tempfile
tempfile = Tempfile.open("ActiveStorage-", tmpdir)
begin
yield tempfile
ensure
tempfile.close!
end
end
def instrument(operation, payload = {}, &block)
ActiveSupport::Notifications.instrument "#{operation}.active_storage", payload.merge(service: service_name), &block
end
def service_name
# ActiveStorage::Service::DiskService => Disk
blob.service.class.to_s.split("::").third.remove("Service")
end
def capture(*argv, to:)
to.binmode
open_tempfile do |err|
IO.popen(argv, err: err) { |out| IO.copy_stream(out, to) }
err.rewind
unless $?.success?
raise PreviewError, "#{argv.first} failed (status #{$?.exitstatus}): #{err.read.to_s.chomp}"
end
end
to.rewind
end
def logger # :doc:
ActiveStorage.logger
end
def tmpdir # :doc:
Dir.tmpdir
end
end
end
|
