feat: extend mime with Prism and Mime

lib/prism/multipart.rb

@@ -0,0 +1,117 @@
+require 'tempfile'
+
+module Prism
+  # A single uploaded file extracted from a multipart/form-data request.
+  # Backed by a Tempfile so large uploads do not sit fully in memory as
+  # part of the request/params hash (Rails' UploadedFile does the same).
+  class UploadedFile
+    attr_reader :original_filename, :content_type, :tempfile
+
+    def initialize(original_filename:, content_type:, tempfile:)
+      @original_filename = original_filename
+      @content_type = content_type
+      @tempfile = tempfile
+    end
+
+    def path
+      tempfile.path
+    end
+
+    def size
+      tempfile.size
+    end
+
+    def read(*args)
+      tempfile.read(*args)
+    end
+
+    def rewind
+      tempfile.rewind
+    end
+
+    def to_s
+      original_filename.to_s
+    end
+  end
+
+  # Parses `multipart/form-data` request bodies (RFC 2046/7578) into a flat
+  # hash of field name => value, where file parts become UploadedFile
+  # instances and everything else stays a String, mirroring how the rest of
+  # Request#parse_body treats JSON/urlencoded bodies.
+  module Multipart
+    MalformedError = Class.new(StandardError)
+
+    CONTENT_TYPE_RE = %r{\Amultipart/form-data}i.freeze
+
+    module_function
+
+    def multipart?(content_type)
+      !content_type.nil? && CONTENT_TYPE_RE.match?(content_type)
+    end
+
+    def boundary_from(content_type)
+      return nil unless content_type
+      match = content_type.match(/boundary=(?:"([^"]*)"|([^;\s]+))/i)
+      return nil unless match
+      match[1] || match[2]
+    end
+
+    def parse(body, boundary)
+      return Prism::Params.new if boundary.nil? || boundary.empty? || body.nil?
+
+      body = body.dup.force_encoding(Encoding::BINARY)
+      delimiter = "--#{boundary}"
+      pieces = body.split(delimiter)
+      # pieces[0] is the preamble before the first delimiter, pieces[-1] is
+      # the "--\r\n" closing marker (or trailing epilogue) after the last one.
+      pairs = pieces[1..-2].to_a.filter_map do |piece|
+        part = piece.sub(/\A\r\n/, '').sub(/\r\n\z/, '')
+        part.empty? ? nil : part_pair(part)
+      end.compact
+      Prism::Params.nested_from(pairs)
+    end
+
+    def part_pair(part)
+      header_block, separator, content = part.partition("\r\n\r\n")
+      return nil if separator.empty?
+
+      headers = parse_headers(header_block)
+      disposition = headers['content-disposition']
+      return nil unless disposition
+
+      name = extract_token(disposition, 'name')
+      return nil unless name
+
+      filename = extract_token(disposition, 'filename')
+      value =
+        if filename
+          build_uploaded_file(filename, headers['content-type'], content)
+        else
+          content.dup.force_encoding(Encoding::UTF_8)
+        end
+
+      [name, value]
+    end
+
+    def build_uploaded_file(filename, content_type, content)
+      tempfile = Tempfile.new('prism-upload')
+      tempfile.binmode
+      tempfile.write(content)
+      tempfile.rewind
+      UploadedFile.new(original_filename: filename, content_type: content_type, tempfile: tempfile)
+    end
+
+    def parse_headers(block)
+      block.split("\r\n").each_with_object({}) do |line, acc|
+        key, value = line.split(':', 2)
+        next unless key && value
+        acc[key.strip.downcase] = value.strip
+      end
+    end
+
+    def extract_token(header_value, key)
+      match = header_value.match(/#{key}="([^"]*)"/) || header_value.match(/#{key}=([^;\s]+)/)
+      match && match[1]
+    end
+  end
+end