amahi/platform

# Amahi Home Server
# Copyright (C) 2007-2011 Amahi
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License v3
# (29 June 2007), as published in the COPYING file.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# file COPYING for more details.
#
# You should have received a copy of the GNU General Public
# License along with this program; if not, write to the Amahi
# team at http://www.amahi.org/ under "Contact Us."

require 'net/http'
require 'digest/sha1'

class Downloader

    HDA_DOWNLOAD_CACHE = File.join(HDA_TMP_DIR, "amahi-download-cache")
    AMAHI_DOWNLOAD_CACHE_SITE = 'http://mirror.amahi.org'

    class SHA1VerificationFailed < Exception; end
    class TooManyRedirects < Exception; end

    # download a file, but check in the cache first, also
    # check the sha1
    def self.download_and_check_sha1(url, sha1)

        raise SHA1VerificationFailed, "#{url}, sha1sum provided is empty!" unless sha1
        TempCache.expire_unused_files
        FileUtils.mkdir_p(HDA_DOWNLOAD_CACHE)
        cached_filename = File.join(HDA_DOWNLOAD_CACHE, sha1)
        if File.exists?(cached_filename)
            file = IO.binread(cached_filename)
            new_sha1 = Digest::SHA1.hexdigest(file)
            if new_sha1 == sha1
                puts "file #{cached_filename} picked up from cache."
                FileUtils.touch cached_filename
                # return the file name, not the data
                return cached_filename
            else
                puts "WARNING: file #{cached_filename} in cache was found to be corrupted! Discarding it."
            end
        end

        # download if the above fails, i.e. no cached file OR the sha1sum failed!
        download(url, cached_filename, sha1)

        # return the file name, not the data
        cached_filename
    end

    private

    def self.download_direct(url)

        redirect_limit = 5

        while redirect_limit > 0
            u = URI.parse(url)
            http = Net::HTTP.new(u.host, u.port)
            http.use_ssl = (u.scheme == 'https')
            request = Net::HTTP::Get.new(u.path, { 'accept-encoding' => '' })
            response = http.start { |http| http.request(request) }
            return response.body unless response.kind_of?(Net::HTTPRedirection)
            # it's a redirection
            location = response['location']
            old_url = url
            url = location.nil? ? (response.body.match(/<a href=\"([^>]+)\">/i)[1]) : location
            puts "NOTICE: redirected '#{old_url}' --> '#{url}' ..."
            redirect_limit -= 1
        end
        # reached end of redirect limit]!
        raise TooManyRedirects, "#{url}"
    end

    # try to download from the original download site. if that fails,
    # then try to download from amahi's mirror
    def self.download(url, filename, sha1)
        new_sha1 = "badbadsha1"

        begin

            file = download_direct(url)
            open(filename, "wb") {|f| f.write file }
            puts "file #{filename} written in cache"

            new_sha1 = Digest::SHA1.hexdigest(file)
        rescue => e
            puts "WARNING: primary downloaded of #{url} barfed with exception \"#{e.inspect}\""
        end

        if new_sha1 != sha1
            puts "WARNING: primary downloaded file #{filename} did not pass signature check - got #{new_sha1}, expected #{sha1}"
            new_url = File.join(AMAHI_DOWNLOAD_CACHE_SITE, sha1)
            file = download_direct(new_url)
            open(filename, "wb") { |f| f.write file }
            puts "new file #{filename} from Amahi's cache written in the cache"

            new_sha1 = Digest::SHA1.hexdigest(file)
            raise SHA1VerificationFailed, "#{new_url} (from original #{url}), '#{new_sha1}' vs. '#{sha1}' " if new_sha1 != sha1
        end
    end
end