Try to download files from RUBY_BUILD_MIRROR_URL first

bin/ruby-build

@@ -179,14 +179,20 @@ retrieve_url() {
 fetch_tarball() {
   local package_name="$1"
   local package_url="$2"
+  local mirror_url
 
   local checksum="${package_url#*\#}"
   if [ -n "$checksum" ]; then
     package_url="${package_url%%#*}"
+
+    if [ -n "$RUBY_BUILD_MIRROR_URL" ]; then
+      mirror_url="${RUBY_BUILD_MIRROR_URL}/$checksum"
+    fi
   fi
 
   local package_filename="${package_name}.tar.gz"
   symlink_tarball_from_cache "$package_filename" "$checksum" ||
+  download_tarball "$mirror_url" "$package_filename" "$checksum" ||
   download_tarball "$package_url" "$package_filename" "$checksum"
 
   { tar xzvf "$package_filename"
@@ -195,34 +201,34 @@ fetch_tarball() {
 }
 
 symlink_tarball_from_cache() {
-  if [ -n "$RUBY_BUILD_CACHE_PATH" ]; then
-    local package_filename="$1"
-    local cached_package_filename="${RUBY_BUILD_CACHE_PATH}/$package_filename"
-    local checksum="$2"
+  [ -n "$RUBY_BUILD_CACHE_PATH" ] || return 1
 
-    if verify_checksum "$cached_package_filename" "$checksum"; then
-      ln -s "$cached_package_filename" "$package_filename" >&4 2>&1
-      return 0
-    fi
-  fi
-  return 1
+  local package_filename="$1"
+  local cached_package_filename="${RUBY_BUILD_CACHE_PATH}/$package_filename"
+  local checksum="$2"
+
+  { verify_checksum "$cached_package_filename" "$checksum"
+    ln -s "$cached_package_filename" "$package_filename"
+  } >&4 2>&1 || return 1
 }
 
 download_tarball() {
   local package_url="$1"
+  [ -n "$package_url" ] || return 1
+
   local package_filename="$2"
   local checksum="$3"
 
   echo "Downloading ${package_url}..." >&2
   { retrieve_url "$package_url" > "$package_filename"
     verify_checksum "$package_filename" "$checksum"
-  } >&4 2>&1
+  } >&4 2>&1 || return 1
 
   if [ -n "$RUBY_BUILD_CACHE_PATH" ]; then
     local cached_package_filename="${RUBY_BUILD_CACHE_PATH}/$package_filename"
     { mv "$package_filename" "$cached_package_filename"
       ln -s "$cached_package_filename" "$package_filename"
-    } >&4 2>&1
+    } >&4 2>&1 || return 1
   fi
 }
 
@@ -546,6 +552,12 @@ else
   unset RUBY_BUILD_CACHE_PATH
 fi
 
+if [ -z "$RUBY_BUILD_MIRROR_URL" ]; then
+  RUBY_BUILD_MIRROR_URL="http://cloud.github.com/downloads/sstephenson/ruby-build-download-mirror"
+else
+  RUBY_BUILD_MIRROR_URL="${RUBY_BUILD_MIRROR_URL%/}"
+fi
+
 SEED="$(date "+%Y%m%d%H%M%S").$$"
 LOG_PATH="${TMP}/ruby-build.${SEED}.log"
 RUBY_BIN="${PREFIX_PATH}/bin/ruby"