From 0b42e57bb6fa4e039585f1ebac8584b8d45b7a2a Mon Sep 17 00:00:00 2001
From: Mikel Olasagasti Uranga <mikel@olasagasti.info>
Date: Wed, 16 Apr 2025 23:50:52 +0200
Subject: [PATCH] filter/config: restore "system‑first, bundled‑fallback" Brotli detection

63ca02a made the bundled sub‑module mandatory by hard‑coding
deps/brotli and linking the objects produced in ../out. This broke
distribution builds that are required to link against the shared
libbrotli already shipped by the system.

This change brings back the original behaviour while integrating
`pkg-config`:

* Detect a system installation with `pkg-config libbrotlienc`;
  if found, use the reported cflags/libs and compile only the NGINX
  wrapper source.
* If no suitable system copy exists, fall back to the bundled
  git sub‑module exactly as before.
* Abort early with a clear error message when neither flavour is
  available, including instructions to initialise the sub‑module.

No command‑line flags are needed for the common case; packagers simply
omit the sub‑module and let `pkg-config` do the work, while end users
who prefer the bundled copy keep the sub‑module checked out.

Fixes: 63ca02a (“filter: require bundled Brotli out/ artifacts”)

Signed-off-by: Mikel Olasagasti Uranga <mikel@olasagasti.info>
---
 filter/config | 50 +++++++++++++++++++++++++++++++++++---------------
 1 file changed, 35 insertions(+), 15 deletions(-)

diff --git a/filter/config b/filter/config
index 167e1d2..98b2504 100644
--- a/filter/config
+++ b/filter/config
@@ -42,31 +42,51 @@ fi
 ngx_module_type=HTTP_FILTER
 ngx_module_name=ngx_http_brotli_filter_module
 
-brotli="$ngx_addon_dir/deps/brotli/c"
-if [ ! -f "$brotli/include/brotli/encode.h" ]; then
-cat << END
+use_system_brotli=no
+brotli_prefix=""
+
+if pkg-config --exists libbrotlienc 2>/dev/null ; then
+    brotli_prefix=$(pkg-config --variable=prefix libbrotlienc)
+    if [ -f "$brotli_prefix/include/brotli/encode.h" ]; then
+        use_system_brotli=yes
+    fi
+fi
+
+if [ "$use_system_brotli" = no ]; then
+    brotli="$ngx_addon_dir/deps/brotli/c"
+    if [ ! -f "$brotli/include/brotli/encode.h" ]; then
+cat <<END
 
-$0: error: \
-Brotli library is missing from the $brotli directory.
+$0: error:
+Brotli library not found – neither a system installation detected
+(tried \`pkg-config libbrotlienc\`) nor the bundled sub‑module present.
 
-Please make sure that the git submodule has been checked out:
+If you want to use the bundled copy, run:
 
     cd $ngx_addon_dir && git submodule update --init && cd $PWD
 
 END
-    exit 1
+        exit 1
+    fi
 fi
 
-BROTLI_OUTPUT_DIRECTORY="$brotli/../out"
-BROTLI_ENC_H="$brotli/include/brotli/encode.h \
-              $brotli/include/brotli/port.h \
-              $brotli/include/brotli/types.h"
+ngx_module_srcs="$BROTLI_MODULE_SRC_DIR/ngx_http_brotli_filter_module.c"
 
+if [ "$use_system_brotli" = yes ]; then
+    ngx_module_incs="$(pkg-config --cflags-only-I libbrotlienc)"
+    ngx_module_libs="$(pkg-config --libs libbrotlienc) -lm"
+    ngx_module_deps=""
+else
+    BROTLI_OUTPUT_DIRECTORY="$brotli/../out"
+    BROTLI_ENC_H="$brotli/include/brotli/encode.h \
+                  $brotli/include/brotli/port.h \
+                  $brotli/include/brotli/types.h"
+
+    ngx_module_incs="$brotli/include"
+    ngx_module_deps="$BROTLI_ENC_H"
+    ngx_module_libs="-L$BROTLI_OUTPUT_DIRECTORY -lbrotlienc -lbrotlicommon -lm"
+fi
 
-ngx_module_incs="$brotli/include"
-ngx_module_deps="$BROTLI_ENC_H"
-ngx_module_srcs="$BROTLI_MODULE_SRC_DIR/ngx_http_brotli_filter_module.c"
-ngx_module_libs="-L$BROTLI_OUTPUT_DIRECTORY -lbrotlienc -lbrotlicommon -lm"
 ngx_module_order="$ngx_module_name \
                   ngx_pagespeed \
                   ngx_http_postpone_filter_module \