Feature: more flexible mirror URL by a command

README.md

@@ -74,7 +74,8 @@ The build process may be configured through the following environment variables:
 | `RUBY_BUILD_CURL_OPTS`          | Additional options to pass to `curl` for downloading.                                            |
 | `RUBY_BUILD_WGET_OPTS`          | Additional options to pass to `wget` for downloading.                                            |
 | `RUBY_BUILD_MIRROR_URL`         | Custom mirror URL root.                                                                          |
-| `RUBY_BUILD_MIRROR_PACKAGE_URL` | Custom complete mirror URL (e.g. http://mirror.example.com/package-1.0.0.tar.gz).                  |
+| `RUBY_BUILD_MIRROR_PACKAGE_URL` | Custom complete mirror URL (e.g. http://mirror.example.com/package-1.0.0.tar.gz).                |
+| `RUBY_BUILD_MIRROR_CMD`         | Custom mirror command (see [below](#more-flexible-mirror-url) for the usage).                    |
 | `RUBY_BUILD_SKIP_MIRROR`        | Bypass the download mirror and fetch all package files from their original URLs.                 |
 | `RUBY_BUILD_ROOT`               | Custom build definition directory. (Default: `share/ruby-build`)                                 |
 | `RUBY_BUILD_DEFINITIONS`        | Additional paths to search for build definitions. (Colon-separated list)                         |
@@ -142,6 +143,25 @@ complete URL by setting `RUBY_BUILD_MIRROR_PACKAGE_URL`. It behaves the same as
 The default ruby-build download mirror is sponsored by
 [Basecamp](https://basecamp.com/).
 
+#### More flexible mirror URL
+
+For more flexible mirror URL, you can provide a custom command to output the
+desired mirror URL, as shown below:
+
+```sh
+# There are two arguments:
+#   1st arg: the original URL without checksum
+#   2nd arg: the checksum
+$ cat <<'EOF' >./get_mirror_url && chmod +x ./get_mirror_url
+#!/bin/sh
+echo "$1" | sed "s/cache.ruby-lang.org/mirror.example.com/"
+EOF
+
+$ export RUBY_BUILD_MIRROR_CMD="$(pwd)/get_mirror_url"
+```
+
+After executing the above script in your shell, install a version as usual.
+
 #### Keeping the build directory after installation
 
 Both `ruby-build` and `rbenv install` accept the `-k` or `--keep` flag, which

bin/ruby-build

@@ -367,6 +367,8 @@ fetch_tarball() {
       fi
     elif [ -n "$RUBY_BUILD_MIRROR_PACKAGE_URL" ]; then
       mirror_url="$RUBY_BUILD_MIRROR_PACKAGE_URL"
+    elif [ -n "$RUBY_BUILD_MIRROR_CMD" ]; then
+      mirror_url="$(command "$RUBY_BUILD_MIRROR_CMD" "$package_url" "$checksum")"
     fi
   fi
 
@@ -1421,7 +1423,7 @@ else
   unset RUBY_BUILD_CACHE_PATH
 fi
 
-if [ -z "$RUBY_BUILD_MIRROR_URL" -a -z "$RUBY_BUILD_MIRROR_PACKAGE_URL" ]; then
+if [ -z "$RUBY_BUILD_MIRROR_URL" -a -z "$RUBY_BUILD_MIRROR_PACKAGE_URL" -a -z "$RUBY_BUILD_MIRROR_CMD" ]; then
   RUBY_BUILD_MIRROR_URL="https://dqw8nmjcqpjn7.cloudfront.net"
   RUBY_BUILD_DEFAULT_MIRROR=1
 else
@@ -1430,7 +1432,7 @@ else
 fi
 
 if [ -n "$RUBY_BUILD_SKIP_MIRROR" ] || ! has_checksum_support compute_sha2; then
-  unset RUBY_BUILD_MIRROR_URL RUBY_BUILD_MIRROR_PACKAGE_URL
+  unset RUBY_BUILD_MIRROR_URL RUBY_BUILD_MIRROR_PACKAGE_URL RUBY_BUILD_MIRROR_CMD
 fi
 
 ARIA2_OPTS="${RUBY_BUILD_ARIA2_OPTS} ${IPV4+--disable-ipv6=true} ${IPV6+--disable-ipv6=false}"

test/mirror.bats

@@ -185,3 +185,27 @@ DEF
   unstub curl
   unstub shasum
 }
+
+
+@test "package is fetched from the URL returned by a commond" {
+  export RUBY_BUILD_MIRROR_URL=
+  export RUBY_BUILD_MIRROR_CMD=get_mirror_url
+
+  local checksum="ba988b1bb4250dee0b9dd3d4d722f9c64b2bacfc805d1b6eba7426bda72dd3c5"
+
+  stub get_mirror_url 'echo "${1/cache.ruby-lang.org/mirror.example.com}#$2"'
+  stub shasum true "echo $checksum"
+  stub curl "-*I* https://mirror.example.com/packages/package-1.0.0.tar.gz#$checksum : true" \
+    "-q -o * -*S* https://mirror.example.com/packages/package-1.0.0.tar.gz#$checksum : cp $FIXTURE_ROOT/package-1.0.0.tar.gz \$3"
+
+  run_inline_definition <<DEF
+install_package "package-1.0.0" "https://cache.ruby-lang.org/packages/package-1.0.0.tar.gz#$checksum" copy
+DEF
+
+  assert_success
+  assert [ -x "${INSTALL_ROOT}/bin/package" ]
+
+  unstub curl
+  unstub shasum
+  unstub get_mirror_url
+}