Fix musl misdetection on glibc systems with musl installed (#692)

.github/workflows/test.yml

@@ -65,3 +65,46 @@ jobs:
           ./sbt test
       - name: JAR Integration Test
         run: ./script/test-jar-integration.sh
+  test-musl:
+    strategy:
+      matrix:
+        include:
+          # musl-based JVM: the x86_64-musl native library must be used
+          - name: alpine
+            container: eclipse-temurin:17-jdk-alpine
+            expected_arch: x86_64-musl
+          # glibc-based JVM with musl also installed (#692): the glibc native library must be used
+          - name: glibc with musl installed
+            container: ''
+            expected_arch: x86_64
+    name: test ${{ matrix.name }}
+    needs: changes
+    if: ${{ needs.changes.outputs.code == 'true' }}
+    runs-on: ubuntu-latest
+    container: ${{ matrix.container }}
+    steps:
+      - name: Install packages (alpine)
+        if: ${{ matrix.container != '' }}
+        run: apk add --no-cache bash curl git
+      - uses: actions/checkout@v6
+      - uses: actions/setup-java@v5
+        if: ${{ matrix.container == '' }}
+        with:
+          distribution: 'zulu'
+          java-version: '17'
+      - name: Install musl
+        if: ${{ matrix.container == '' }}
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y musl
+          ls -l /lib/ld-musl-x86_64.so.1
+      - name: Check native library architecture
+        shell: bash
+        run: |
+          ./sbt compile
+          arch=$(java -cp target/classes org.xerial.snappy.OSInfo --arch)
+          echo "detected arch: $arch"
+          test "$arch" = "${{ matrix.expected_arch }}"
+      - name: Test
+        shell: bash
+        run: ./sbt test

src/main/java/org/xerial/snappy/OSInfo.java

@@ -24,8 +24,9 @@
 //--------------------------------------
 package org.xerial.snappy;
 
+import java.io.BufferedReader;
 import java.io.ByteArrayOutputStream;
-import java.io.File;
+import java.io.FileReader;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.HashMap;
@@ -220,7 +221,7 @@ public static String getArchName() {
             return "android-arm";
         }
 
-        if (isX64Musl()) {
+        if (isX64Musl(osArch)) {
             return "x86_64-musl";
         }
 
@@ -235,10 +236,38 @@ public static String getArchName() {
         return translateArchNameToFolderName(osArch);
     }
 
-    private static boolean isX64Musl() {
+    private static boolean isX64Musl(String osArch) {
+        String lc = osArch == null ? "" : osArch.toLowerCase(Locale.US);
+        if (!System.getProperty("os.name", "").contains("Linux") || !"x86_64".equals(archMapping.get(lc))) {
+            return false;
+        }
+        // Check the C library actually loaded into this JVM process. Testing for the presence of
+        // /lib/ld-musl-x86_64.so.1 is not enough, since musl can be installed on glibc-based systems
+        // (e.g., as a dependency of other software), where the musl build of the native library fails to load.
+        return isMuslLoaded("/proc/self/maps");
+    }
+
+    static boolean isMuslLoaded(String mapsFile) {
         try {
-            return new File("/lib/ld-musl-x86_64.so.1").exists();
-        } catch (SecurityException e) {
+            BufferedReader reader = new BufferedReader(new FileReader(mapsFile));
+            try {
+                String line;
+                while ((line = reader.readLine()) != null) {
+                    if (line.contains("/ld-musl-") || line.contains("/libc.musl-")) {
+                        return true;
+                    }
+                }
+                return false;
+            }
+            finally {
+                reader.close();
+            }
+        }
+        catch (IOException e) {
+            // /proc is unavailable: fall back to the glibc build
+            return false;
+        }
+        catch (SecurityException e) {
             return false;
         }
     }

src/test/java/org/xerial/snappy/OSInfoTest.java

@@ -27,6 +27,8 @@
 import static org.junit.Assert.*;
 
 import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.FileWriter;
 import java.io.PrintStream;
 
 import org.junit.Test;
@@ -112,4 +114,35 @@ public void testMainForArchName()
             System.setOut(out);
         }
     }
+
+    private static File writeMaps(String content)
+            throws Exception
+    {
+        File f = File.createTempFile("snappy-maps", ".txt");
+        f.deleteOnExit();
+        FileWriter w = new FileWriter(f);
+        try {
+            w.write(content);
+        }
+        finally {
+            w.close();
+        }
+        return f;
+    }
+
+    // https://github.com/xerial/snappy-java/issues/692
+    @Test
+    public void detectMuslFromProcessMaps()
+            throws Exception
+    {
+        File musl = writeMaps("7f0000000000-7f0000001000 r-xp 00000000 08:01 123 /lib/ld-musl-x86_64.so.1\n");
+        assertTrue(OSInfo.isMuslLoaded(musl.getPath()));
+
+        // glibc process on a system that also has musl installed
+        File glibc = writeMaps("7f0000000000-7f0000001000 r-xp 00000000 08:01 123 /usr/lib/x86_64-linux-gnu/libc.so.6\n"
+                + "7f0000002000-7f0000003000 r-xp 00000000 08:01 456 /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2\n");
+        assertFalse(OSInfo.isMuslLoaded(glibc.getPath()));
+
+        assertFalse(OSInfo.isMuslLoaded("/non-existent/maps"));
+    }
 }