static file serving supporting byte-ranges and If-Modified-Since header

diff --git a/file.sh b/file.sh
new file mode 100755 (executable)
index 0000000..aaa3723
--- /dev/null
+++ b/file.sh
@@ -0,0 +1,116 @@
+#!/bin/zsh
+
+# Copyright 2016 - 2018 Paul Hänsch
+#
+# This file is part of cgilite.
+# 
+# cgilite is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+# 
+# cgilite 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
+# GNU Affero General Public License for more details.
+# 
+# You should have received a copy of the GNU Affero General Public License
+# along with cgilite.  If not, see <http://www.gnu.org/licenses/>. 
+
+file_type(){
+  case ${1##*.} in
+    html|html) printf 'text/html';;
+    css)       printf 'text/css';;
+    js)        printf 'text/javascript';;
+    txt)       printf 'text/plain';;
+    sh)        printf 'text/shellscript';;
+    jpg|jpeg)  printf 'image/jpeg';;
+    png)       printf 'image/png';;
+    svg)       printf 'image/svg+xml';;
+    gif)       printf 'image/gif';;
+    webm)      printf 'video/webm';;
+    mp4)       printf 'video/mp4';;
+    ogg)       printf 'audio/ogg';;
+    xml)       printf 'application/xml';;
+    *)         printf 'application/octet-stream';;
+  esac
+}
+
+FILE(){
+  unset range file_size file_date http_date cachedate
+  file="$1"
+
+  if ! [ -f "$file" ]; then
+    printf 'Status: 404 Not Found\r\n\r\n'
+    exit 0
+  elif ! [ -r "$file" ]; then
+    printf 'Status: 403 Forbidden\r\n\r\n'
+    exit 0
+  fi
+
+  file_size="$(stat -Lc %s "$file")"
+  file_date="$(stat -Lc %Y "$file")"
+  http_date="$(date -uRd @$file_date)"
+  http_date="${http_date%+0000}GMT"
+  cachedate="$(
+    # Parse the allowable date formats from Section 3.3.1 of
+    # https://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html
+    HEADER If-Modified-Since \
+    | sed -r 's;^[^ ]+, ([0-9]{2}) (...) ([0-9]{4}) (..:..:..) GMT$;\3-\2-\1 \4;;
+              s;^[^ ]+, ([0-9]{2})-(...)-([789][0-9]) (..:..:..) GMT$;19\3-\2-\1 \4;;
+              s;^[^ ]+, ([0-9]{2})-(...)-([0-6][0-9]) (..:..:..) GMT$;20\3-\2-\1 \4;;
+              s;^[^ ]+ (...) ([0-9]{2}) (..:..:..) ([0-9]{4})$;\4-\1-\2 \3;;
+              s;^[^ ]+ (...)  ([0-9]) (..:..:..) ([0-9]{4})$;\4-\1-\2 \3;;
+              s;Jan;01;; s;Feb;02;; s;Mar;03;; s;Apr;04;; s;May;05;; s;Jun;06;;
+              s;Jul;07;; s;Aug;08;; s;Sep;09;; s;Oct;10;; s;Nov;11;; s;Dec;12;;' \
+    | xargs -0 date +%s -ud 2>&-
+  )"
+
+  range="$(HEADER Range |sed -nr 's;^bytes=([0-9]+-[0-9]*|-[0-9]+)$;\1;p;q;')"
+  case "$range" in
+    *-) range="${range}$((file_size - 1))";;
+    -*) [ ${range#-} -le $file_size ] \
+        && range="$((file-size - ${rang#-}))-$((file_size - 1))" \
+        || range="0-$((file_size - 1))";;
+    *-*) [ ${range#*-} -ge $file_size ] \
+         && range="${range%-*}-$((file_size - 1))";;
+  esac
+
+  if [ "$file_date" -lt "$cachedate" ] 2>&-; then
+    printf '%s: %s\r\n' \
+      Status '304 Not Modified' \
+      Last-Modified "$http_date"
+    printf '\r\n'
+  
+  elif [ -z "$range" ]; then
+    printf '%s: %s\r\n' \
+      Status "200 OK" \
+      Accept-Ranges bytes \
+      Last-Modified "$http_date" \
+      Content-Type $(file_type "$file") \
+      Content-Length $file_size
+    printf '\r\n'
+  
+    [ "$REQUEST_METHOD" != HEAD ] && cat "$file"
+
+  elif [ "${range%-*}" -le "${range#*-}" ]; then
+    printf '%s: %s\r\n' \
+      Status "206 Partial Content" \
+      Accept-Ranges bytes \
+      Last-Modified "$http_date" \
+      Content-Type $(file_type "$file") \
+      Content-Range "bytes ${range}/${file_size}" \
+      Content-Length "$((${range#*-} - ${range%-*} + 1))"
+    printf '\r\n'
+  
+    [ "$REQUEST_METHOD" != HEAD ] \
+    && tail -c+$((${range%-*} + 1)) "$file" \
+       | head -c "$((${range#*-} - ${range%-*} + 1))"
+
+  elif [ "${range%-*}" -gt "${range#*-}" ]; then
+    printf '%s: %s\r\n' \
+      Status "216 Range Not Satisfiable" \
+      Content-Range \*/${file_size}
+    printf '\r\n'
+  fi
+}