#!/usr/bin/env bash

# Test if HTTP compression (RFC 2616 + SDCH) is enabled for a given URL
# https://github.com/mathiasbynens/dotfiles/blob/master/bin/httpcompression

declare -r hUA="Mozilla/5.0 Gecko"
declare -r hAE="Accept-Encoding: gzip, deflate, sdch"
declare -r maxConTime=15
declare -r maxTime=30

declare availDicts="" dict="" dictClientID="" dicts="" headers="" i="" \
        indent="" url="" encoding="" urlHeaders=""

headers="$( curl --connect-timeout $maxConTime \
                 -A "$hUA"    `# Send a fake UA string for sites
                               # that sniff it instead of using
                               # the Accept-Encoding header` \
                 -D -         `# Get response headers` \
                 -H "$hAE"     \
                 -L           `# If the page was moved to a different
                               # location, redo the request` \
                 -m $maxTime   \
                 -s           `# Don\'t show the progress meter` \
                 -S           `# Show error messages` \
                 -o /dev/null `# Ignore content` \
                 "$1" )" \
&& ( \

	url="$1"

	# Iterate over the headers of all redirects
	while [ -n "$headers" ]; do

		# Get headers for the "current" URL
		urlHeaders="$( printf "%s" "$headers" |
		               sed -n '1,/^HTTP/p' )"

		# Remove the headers for the "current" URL
		headers="${headers/"$urlHeaders"/}"

		# ----------------------------------------------------------------------
		# | SDCH                                                               |
		# ----------------------------------------------------------------------

		# SDCH Specification:
		# - www.blogs.zeenor.com/wp-content/uploads/2011/01/Shared_Dictionary_Compression_over_HTTP.pdf

		# Check if the server advertised any dictionaries
		dicts="$( printf "%s" "$urlHeaders" |
		          grep -i 'Get-Dictionary:' |
		          cut -d':' -f2 |
		          sed s/,/\ /g )"

		if [ -n "$dicts" ]; then

			availDicts=""
			dict=""

			for i in $dicts; do

				# Check If the dictionary location is specified as a path,
				# and if so, construct it's URL from the host name of the
				# referrer URL
				[[ "$i" != http* ]] \
				    && dict="$(printf "$url" |
				               sed -En 's/([^/]*\/\/)?([^/]*)\/?.*/\1\2/p')"

				dict="$dict$i"

				# Request the dictionaries from the server and
				# construct the `Avail-Dictionary` header value
				#
				# [ The user agent identifier for a dictionary is defined
				#   as the URL-safe base64 encoding (as described in RFC
				#   3548, section 4 [RFC3548]) of the first 48 bits (bits
				#   0..47) of the dictionary's SHA-256 digest ]
				#
				dictClientID="$( curl --connect-timeout $maxConTime \
				                      -A "$hUA" -LsS -m $maxTime "$dict" |
				                 openssl dgst -sha256 -binary |
				                 openssl base64 |
				                 cut -c 1-8 |
				                 sed -e 's/\+/-/' -e 's/\//_/' )"

				[ -n $availDicts ] && availDicts="$adics,$dictClientID" \
				                   || availDicts="$dictClientID"

			done

			# Redo the request (advertising the available dictionaries)
			# and replace the old resulted headers with the new ones
			urlHeaders="$( curl --connect-timeout $maxConTime \
			                    -A "$hUA" -D - -H "$hAE" \
			                    -H "Avail-Dictionary: $availDicts" \
			                    -m $maxTime -o /dev/null -sS "$1" )"
		fi

		# ----------------------------------------------------------------------

		# Get the content encoding header values
		encoding="$( printf "%s" "$urlHeaders" |
		             grep -i 'Content-Encoding:' |
		             cut -d' ' -f2 |
		             tr "\r" "," |
		             tr -d "\n" |
		             sed 's/,$//' )"

		[ -n "$encoding" ] && encoding="[$encoding]"

		# Print the output for the "current" URL
		if [ "$url" != "$1" ]; then
			printf "%s\n" "$indent$url $encoding"
			indent="  "$indent
		else
			printf "\n%s\n" " $1 $encoding"
			indent=" ↳"
		fi

		# Get the next URL value
		url="$( printf "%s" "$urlHeaders" |
		        grep -i 'Location' |
		        sed -e 's/Location://' |
		        tr -d '\r' )"

	done
	printf "\n"

) || printf ""