Expose errors to the host

Signed-off-by: Edoardo Vacchi <[email protected]>

src/main/java/org/extism/chicory/sdk/ExtismException.java

@@ -1,6 +1,6 @@
 package org.extism.chicory.sdk;
 
-public class ExtismException extends RuntimeException{
+public class ExtismException extends RuntimeException {
 
     public ExtismException(String message) {
         super(message);

src/main/java/org/extism/chicory/sdk/ExtismFunctionException.java

@@ -0,0 +1,19 @@
+package org.extism.chicory.sdk;
+
+public class ExtismFunctionException extends ExtismException {
+
+    private final String error;
+
+    public ExtismFunctionException(String function, String message) {
+        super(String.format("function %s returned an error: %s", function, message));
+        this.error = message;
+    }
+
+    /**
+     * Underlying error returned by the plugin call
+     */
+    public String getError() {
+        return error;
+    }
+
+}

src/main/java/org/extism/chicory/sdk/HostEnv.java

@@ -64,10 +64,15 @@ public byte[] getOutput() {
         return kernel.getOutput();
     }
 
+    public String getError() {
+        return kernel.getError();
+    }
+
     public Memory memory() {
         return this.memory;
     }
 
+
     public class Memory {
 
         public long length(long offset) {

src/main/java/org/extism/chicory/sdk/Kernel.java

@@ -4,13 +4,10 @@
 import com.dylibso.chicory.runtime.HostFunction;
 import com.dylibso.chicory.runtime.Instance;
 import com.dylibso.chicory.wasm.Parser;
-import com.dylibso.chicory.wasm.types.Value;
 import com.dylibso.chicory.wasm.types.ValueType;
 
 import java.util.List;
 
-import static com.dylibso.chicory.wasm.types.Value.i64;
-
 public class Kernel {
     static final String IMPORT_MODULE_NAME = "extism:host/env";
     final com.dylibso.chicory.runtime.Memory instanceMemory;
@@ -77,6 +74,11 @@ byte[] getOutput() {
         return instanceMemory.readBytes((int) ptr, (int) len);
     }
 
+    public String getError() {
+        long ptr = errorGet.apply()[0];
+        long len = length.apply(ptr)[0];
+        return instanceMemory.readString((int) ptr, (int) len);
+    }
 
     HostFunction[] toHostFunctions() {
         var hostFunctions = new HostFunction[20];
@@ -241,7 +243,7 @@ HostFunction[] toHostFunctions() {
                         "error_set",
                         List.of(ValueType.I64),
                         List.of(),
-                        (Instance instance, long... args) -> reset.apply(args)
+                        (Instance instance, long... args) -> errorSet.apply(args)
                 );
 
         hostFunctions[count++] =

src/main/java/org/extism/chicory/sdk/Plugin.java

@@ -70,7 +70,8 @@ public byte[] call(String funcName, byte[] input) {
         if (result == 0) {
             return hostEnv.getOutput();
         } else {
-            throw new ExtismException("Failed");
+            String error = hostEnv.getError();
+            throw new ExtismFunctionException(funcName, error);
         }
     }
 }

src/test/java/org/extism/chicory/sdk/ExtismHostFunctionTest.java

@@ -6,6 +6,8 @@
 import com.dylibso.chicory.wasm.types.Value;
 import junit.framework.TestCase;
 
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
 import java.util.List;
 
 public class ExtismHostFunctionTest extends TestCase {