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+# xdelta3 — open-source VCDIFF (RFC 3284) delta compression by Joshua MacDonald.
+#
+# The most widely used VCDIFF implementation outside Google's own
+# open-vcdiff (which is archived as of 2023-08). xdelta is what
+# Chromium auto-update uses for some delta channels, what many
+# embedded firmware update pipelines run, and the canonical
+# alternative reference for the format.
+#
+# Upstream is dormant since 2020 but the project is not archived;
+# the algorithm and CLI surface are RFC-stable. C autotools build,
+# GPL-2.0+.
+#
+# This packages the modern v3 line (`xdelta3/`). The older `xdelta1/`
+# subdir is left out — that's the 1998 prototype, of historical
+# interest only.
+
+distributable:
+  url: https://github.com/jmacd/xdelta/archive/refs/tags/{{version.tag}}.tar.gz
+  strip-components: 1
+
+versions:
+  # Upstream publishes git tags but ZERO GitHub Releases. Use /tags.
+  github: jmacd/xdelta/tags
+
+build:
+  working-directory: xdelta3
+  dependencies:
+    gnu.org/autoconf: "*"
+    gnu.org/automake: "*"
+    gnu.org/libtool: "*"
+    linux:
+      gnu.org/gcc: "*"
+  script:
+    - autoreconf -fi
+    - ./configure --prefix={{prefix}}
+    - make --jobs {{ hw.concurrency }}
+    - make install
+
+provides:
+  - bin/xdelta3
+
+test:
+  # Round-trip: source → delta → reconstructed-target; verify identity.
+  - printf 'the quick brown fox jumps over the lazy dog\n' > source.txt
+  - printf 'the quick brown FOX jumps over the lazy DOG\n' > target.txt
+  - xdelta3 -e -s source.txt target.txt delta.vcdiff
+  - xdelta3 -d -s source.txt delta.vcdiff out.txt
+  - diff target.txt out.txt