refactor: simplify the logic for returning timeouts.

Remove the global WASM variable `timeout_occurred` which tracked whether a timeout occurred during the execution of `search_for_pattern`. This variable is not really necessary because once `search_for_pattern` returns to WASM code, the wasmtime's timeout mechanism will produce a timeout error.

lib/src/compiler/emit.rs

@@ -938,28 +938,18 @@ fn emit_lazy_pattern_search(
             // do here.
         },
         |_else| {
-            // Call `search_for_patterns`.
-            _else.call(
-                ctx.function_id(
+            _else
+                // Call `search_for_patterns`.
+                .call(ctx.function_id(
                     wasm::export__search_for_patterns.mangled_name,
-                ),
-            );
-            // `search_for_patterns` returns `true` when everything went ok, and
-            // `false` when a timeout occurs.
-            _else.if_else(
-                None,
-                |_then| {
-                    // Everything ok, set pattern_search_done to true.
-                    _then.i32_const(1);
-                    _then.global_set(ctx.wasm_symbols.pattern_search_done);
-                },
-                |_else| {
-                    // A timeout occurred, set the global variable
-                    // `timeout_occurred` to true.
-                    _else.i32_const(1);
-                    _else.global_set(ctx.wasm_symbols.timeout_occurred);
-                },
-            );
+                ))
+                // Remove the result of `search_for_patterns` from the stack.
+                // The result is `true` if everything went fine and `false`
+                // in case of timeout, but we don't use this result.
+                .drop()
+                // Set `pattern_search_done` to true.
+                .i32_const(1)
+                .global_set(ctx.wasm_symbols.pattern_search_done);
         },
     );
 }

lib/src/scanner/mod.rs

@@ -236,15 +236,6 @@ impl<'r> Scanner<'r> {
         )
         .unwrap();
 
-        // Global variable that is set to `true` when a timeout occurs during
-        // the scanning phase.
-        let timeout_occurred = Global::new(
-            wasm_store.as_context_mut(),
-            GlobalType::new(ValType::I32, Mutability::Var),
-            Val::I32(0),
-        )
-        .unwrap();
-
         // Compute the base offset for the bitmap that contains matching
         // information for patterns. This bitmap has 1 bit per pattern, the
         // N-th bit is set if pattern with PatternId = N matched. The bitmap
@@ -286,13 +277,6 @@ impl<'r> Scanner<'r> {
                 pattern_search_done,
             )
             .unwrap()
-            .define(
-                wasm_store.as_context(),
-                "yara_x",
-                "timeout_occurred",
-                timeout_occurred,
-            )
-            .unwrap()
             .define(
                 wasm_store.as_context(),
                 "yara_x",
@@ -741,10 +725,7 @@ impl<'r> Scanner<'r> {
         // scanning) only if necessary.
         //
         // This will return Err(ScanError::Timeout), when the scan timeout is
-        // reached while WASM code is being executed. If the timeout occurs
-        // while ScanContext::search_for_patterns is being executed, the result
-        // will be Ok(1). If the scan completes successfully the result is
-        // Ok(0).`
+        // reached while WASM code is being executed.
         let func_result =
             self.wasm_main_func.call(self.wasm_store.as_context_mut(), ());
 
@@ -800,8 +781,7 @@ impl<'r> Scanner<'r> {
 
         match func_result {
             Ok(0) => Ok(ScanResults::new(self.wasm_store.data(), data)),
-            Ok(1) => Err(ScanError::Timeout),
-            Ok(_) => unreachable!(),
+            Ok(v) => panic!("WASM main returned: {}", v),
             Err(err) if err.is::<ScanError>() => {
                 Err(err.downcast::<ScanError>().unwrap())
             }

lib/src/wasm/builder.rs

@@ -158,7 +158,6 @@ impl WasmModuleBuilder {
         global_const!(module, matching_patterns_bitmap_base, I32);
         global_var!(module, filesize, I64);
         global_var!(module, pattern_search_done, I32);
-        global_var!(module, timeout_occurred, I32);
 
         let (main_memory, _) = module.add_import_memory(
             "yara_x",
@@ -182,7 +181,6 @@ impl WasmModuleBuilder {
             check_for_pattern_match,
             filesize,
             pattern_search_done,
-            timeout_occurred,
             i64_tmp_a: module.locals.add(I64),
             i64_tmp_b: module.locals.add(I64),
             i32_tmp: module.locals.add(I32),
@@ -203,11 +201,9 @@ impl WasmModuleBuilder {
             FunctionBuilder::new(&mut module.types, &[], &[I32]);
 
         // The first instructions in the main function initialize the global
-        // variables `pattern_search_done` and `timeout_occurred` to 0 (false).
+        // variables `pattern_search_done`.
         main_func.func_body().i32_const(0);
         main_func.func_body().global_set(pattern_search_done);
-        main_func.func_body().i32_const(0);
-        main_func.func_body().global_set(timeout_occurred);
 
         let namespace_block = namespace_func.dangling_instr_seq(None).id();
 
@@ -346,12 +342,10 @@ impl WasmModuleBuilder {
         self.finish_namespace_block();
         self.finish_namespace_func();
 
-        // Emit the last few instructions for the main function, which consist
-        // in putting the return value in the stack. The return value is 0 if
-        // everything went ok and 1 if a timeout occurred.
-        self.main_func
-            .func_body()
-            .global_get(self.wasm_symbols.timeout_occurred);
+        // Emit the last instruction for the main function, which consist
+        // in putting the return value in the stack. The return value is
+        // always 0.
+        self.main_func.func_body().i32_const(0);
 
         let main_func =
             self.main_func.finish(Vec::new(), &mut self.module.funcs);

lib/src/wasm/mod.rs

@@ -693,10 +693,6 @@ pub(crate) struct WasmSymbols {
     /// evaluated and some of them needs to know if a pattern matched or not.
     pub pattern_search_done: walrus::GlobalId,
 
-    /// Global variable that is set to true when a timeout during the scanning
-    /// phase.
-    pub timeout_occurred: walrus::GlobalId,
-
     /// Local variables used for temporary storage.
     pub i64_tmp_a: walrus::LocalId,
     pub i64_tmp_b: walrus::LocalId,