Frozen string for entire library

[Lewiscowles1986]

Description

Working on the String.new has helped move things forward with a downstream consumer of this library.

When I enable frozen strings for the entire library, the tests fail.

Types of Changes

• Bug fix (for downstream consumers who do not expect mutation, or attempt to use frozen string literals with more functionality).
• Breaking change.
• Maintenance.

This currently removes Ruby 2.0, 2.1, 2.2, 2.3 and 2.4 (early 2013-late 2016)

[Edit] At the request of @ioquatix this now also removes Ruby 2.5 to keep CI simple. For anyone interested in 2.5 see commit and more specifically orphaned commit from fork of this repo

Testing

Failing test summary

Finished in 0.01378 seconds (files took 0.1659 seconds to load)
51 examples, 32 failures

Failed examples:

rspec ./spec/multipart/post/composite_read_io_spec.rb:131 # Multipart::Post::CompositeReadIO test_empty_parts
rspec './spec/multipart/post/composite_read_io_spec.rb[1:1:5]' # Multipart::Post::CompositeReadIO generic io test_read_into_buffer
rspec './spec/multipart/post/composite_read_io_spec.rb[1:2:1]' # Multipart::Post::CompositeReadIO composite io test_full_read_from_several_ios
rspec './spec/multipart/post/composite_read_io_spec.rb[1:2:2]' # Multipart::Post::CompositeReadIO composite io test_partial_read
rspec './spec/multipart/post/composite_read_io_spec.rb[1:2:3]' # Multipart::Post::CompositeReadIO composite io test_partial_read_to_boundary
rspec './spec/multipart/post/composite_read_io_spec.rb[1:2:4]' # Multipart::Post::CompositeReadIO composite io test_read_with_size_larger_than_available
rspec './spec/multipart/post/composite_read_io_spec.rb[1:2:5]' # Multipart::Post::CompositeReadIO composite io test_read_into_buffer
rspec './spec/multipart/post/composite_read_io_spec.rb[1:2:6]' # Multipart::Post::CompositeReadIO composite io test_multiple_reads
rspec './spec/multipart/post/composite_read_io_spec.rb[1:2:7]' # Multipart::Post::CompositeReadIO composite io test_read_after_end
rspec './spec/multipart/post/composite_read_io_spec.rb[1:2:8]' # Multipart::Post::CompositeReadIO composite io test_read_after_end_with_amount
rspec './spec/multipart/post/composite_read_io_spec.rb[1:2:9]' # Multipart::Post::CompositeReadIO composite io test_second_full_read_after_rewinding
rspec './spec/multipart/post/composite_read_io_spec.rb[1:3:1]' # Multipart::Post::CompositeReadIO nested composite io test_full_read_from_several_ios
rspec './spec/multipart/post/composite_read_io_spec.rb[1:3:2]' # Multipart::Post::CompositeReadIO nested composite io test_partial_read
rspec './spec/multipart/post/composite_read_io_spec.rb[1:3:3]' # Multipart::Post::CompositeReadIO nested composite io test_partial_read_to_boundary
rspec './spec/multipart/post/composite_read_io_spec.rb[1:3:4]' # Multipart::Post::CompositeReadIO nested composite io test_read_with_size_larger_than_available
rspec './spec/multipart/post/composite_read_io_spec.rb[1:3:5]' # Multipart::Post::CompositeReadIO nested composite io test_read_into_buffer
rspec './spec/multipart/post/composite_read_io_spec.rb[1:3:6]' # Multipart::Post::CompositeReadIO nested composite io test_multiple_reads
rspec './spec/multipart/post/composite_read_io_spec.rb[1:3:7]' # Multipart::Post::CompositeReadIO nested composite io test_read_after_end
rspec './spec/multipart/post/composite_read_io_spec.rb[1:3:8]' # Multipart::Post::CompositeReadIO nested composite io test_read_after_end_with_amount
rspec './spec/multipart/post/composite_read_io_spec.rb[1:3:9]' # Multipart::Post::CompositeReadIO nested composite io test_second_full_read_after_rewinding
rspec './spec/multipart/post/composite_read_io_spec.rb[1:3:10]' # Multipart::Post::CompositeReadIO nested composite io test_compatible_with_copy_stream
rspec ./spec/multipart/post/composite_read_io_spec.rb:112 # Multipart::Post::CompositeReadIO unicode composite io test_read_from_multibyte
rspec ./spec/multipart/post/parts_spec.rb:73 # Multipart::Post::Parts::FilePart test_correct_length
rspec ./spec/multipart/post/parts_spec.rb:77 # Multipart::Post::Parts::FilePart test_multibyte_file_length
rspec ./spec/multipart/post/parts_spec.rb:81 # Multipart::Post::Parts::FilePart test_multibyte_filename
rspec ./spec/multipart/post/parts_spec.rb:88 # Multipart::Post::Parts::FilePart test_force_content_type_header
rspec ./spec/net/http/post/multipart_spec.rb:60 # Net::HTTP::Post::Multipart test_form_multipart_body
rspec ./spec/net/http/post/multipart_spec.rb:67 # Net::HTTP::Post::Multipart test_form_multipart_body_with_stringio
rspec ./spec/net/http/post/multipart_spec.rb:73 # Net::HTTP::Post::Multipart test_form_multiparty_body_with_parts_headers
rspec ./spec/net/http/post/multipart_spec.rb:89 # Net::HTTP::Post::Multipart test_form_multipart_body_with_array_value
rspec ./spec/net/http/post/multipart_spec.rb:106 # Net::HTTP::Post::Multipart test_form_multipart_body_with_arrayparam
rspec ./spec/net/http/post/multipart_spec.rb:117 # Net::HTTP::Put::Multipart test_form_multipart_body_put

• I tested my changes locally.
• I tested my changes in staging.

By mutating inputs, there is more load on downstream consumers of the library. This might require documentation on safely using the library, or .dup calls within the library

[ioquatix]

We can drop support for 2.5 if it keeps things simple.

[Lewiscowles1986]

So I am not sure how obvious it is, but the read implementation now requires it's downstream consumer to provide a mutable buf. Do you think this should have an error which is more readable than the failures?

  FrozenError:
   can't modify frozen String: ""
  # ./lib/multipart/post/composite_read_io.rb:34:in `read'

I Was thinking perhaps for this case

The buf (buffer) parameter must not be frozen
# ./lib/multipart/post/composite_read_io.rb:{n}:in `read'