Add library path override system properties

Author: lopcode

README.md

@@ -172,6 +172,12 @@ yet (which could manifest as crashes/segfaults):
 * `vipsffm.abinumber.glib.override`, default: `0`
 * `vipsffm.abinumber.gobject.override`, default: `0`
 
+If you want to manually override the library lookup path for any of the above (for example, if you're using a platform
+like Android where it's hard to set the system library path), you can do so using these system properties:
+* libvips: `vipsffm.libpath.vips.override` (eg `/opt/homebrew/lib/libvips.dylib`)
+* glib: `vipsffm.libpath.glib.override`
+* gobject: `vipsffm.libpath.gobject.override`
+
 ## Project goals
 
 Ideas and suggestions are welcome, but please make sure they fit in to these goals, or you have a good argument about

core/src/main/java/app/photofox/vipsffm/VipsLibLookup.java

@@ -2,6 +2,7 @@
 
 import java.lang.foreign.Arena;
 import java.lang.foreign.SymbolLookup;
+import java.nio.file.Path;
 import java.util.List;
 import java.util.Optional;
 
@@ -25,6 +26,10 @@ public static SymbolLookup buildSymbolLoader(Arena arena) {
     }
 
     private static SymbolLookup findVipsLoader(Arena arena) {
+        var overrideLookup = makeOptionalLibraryLookup("vips", arena);
+        if (overrideLookup.isPresent()) {
+            return overrideLookup.get();
+        }
         var abiNumber = Optional.ofNullable(System.getProperty("vipsffm.abinumber.vips.override"))
             .orElse("42");
         var names = List.of(
@@ -36,6 +41,10 @@ private static SymbolLookup findVipsLoader(Arena arena) {
     }
 
     private static SymbolLookup findGlibLoader(Arena arena) {
+        var overrideLookup = makeOptionalLibraryLookup("glib", arena);
+        if (overrideLookup.isPresent()) {
+            return overrideLookup.get();
+        }
         var abiNumber = Optional.ofNullable(System.getProperty("vipsffm.abinumber.glib.override"))
             .orElse("0");
         var names = List.of(
@@ -47,6 +56,10 @@ private static SymbolLookup findGlibLoader(Arena arena) {
     }
 
     private static SymbolLookup findGObjectLoader(Arena arena) {
+        var overrideLookup = makeOptionalLibraryLookup("gobject", arena);
+        if (overrideLookup.isPresent()) {
+            return overrideLookup.get();
+        }
         var abiNumber = Optional.ofNullable(System.getProperty("vipsffm.abinumber.gobject.override"))
             .orElse("0");
         var names = List.of(
@@ -79,4 +92,26 @@ static Optional<SymbolLookup> attemptLibraryLookup(String name, Arena arena) {
             return Optional.empty();
         }
     }
+
+    private static Optional<SymbolLookup> makeOptionalLibraryLookup(String libraryName, Arena arena) {
+        var propertyPath = "vipsffm.libpath.%s.override".formatted(libraryName);
+        var overridePath = Optional.ofNullable(System.getProperty(propertyPath));
+        return overridePath.map(path -> {
+            SymbolLookup symbolLookup;
+            try {
+                symbolLookup = SymbolLookup.libraryLookup(Path.of(path), arena);
+            } catch (IllegalArgumentException exception) {
+                throw makeOverriddenPathMissingException(libraryName, path);
+            }
+            return symbolLookup;
+        });
+    }
+
+    private static IllegalArgumentException makeOverriddenPathMissingException(
+        String libraryName,
+        String overridePath
+    ) {
+        var message = "path override requested for %s, but library not found at path: %s".formatted(libraryName, overridePath);
+        return new IllegalArgumentException(message);
+    }
 }

run_samples.sh

@@ -4,12 +4,15 @@ set -eou pipefail
 echo "building samples..."
 ./gradlew sample:clean sample:shadowJar
 
+export JAVA_PATH_OPTS=""
 if [[ "$OSTYPE" == "darwin"* ]]; then
   export DYLD_LIBRARY_PATH=/opt/homebrew/lib
+  # this tests the library path override feature
+  export JAVA_PATH_OPTS="-Dvipsffm.libpath.vips.override=/opt/homebrew/lib/libvips.dylib"
 fi
 
 echo "running samples..."
-java -jar sample/build/libs/sample-all.jar 2>&1 | tee sample_output.log
+java $JAVA_PATH_OPTS -jar sample/build/libs/sample-all.jar 2>&1 | tee sample_output.log
 
 echo "checking for leaks..."
 if grep --quiet "objects alive:" sample_output.log; then