From adfc5bf9dc9230b23b458aad3e8b148129ca5a6e Mon Sep 17 00:00:00 2001
From: Matthew Kim <38759997+friendlymatthew@users.noreply.github.com>
Date: Thu, 2 Apr 2026 20:03:56 -0400
Subject: [PATCH 1/2] add some string test cases

---
 test/values/strings.wast | 97 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)

diff --git a/test/values/strings.wast b/test/values/strings.wast
index 0628effc..0bd9105a 100644
--- a/test/values/strings.wast
+++ b/test/values/strings.wast
@@ -24,6 +24,37 @@
 (assert_return (invoke "f1") (str.const "a"))
 (assert_return (invoke "f2") (str.const "☃☺️öツ"))
 
+;; empty string with ptr=0, len=0
+(component
+  (core module $M
+    (memory (export "mem") 1)
+    (func (export "f") (result i32)
+      (i32.store (i32.const 0) (i32.const 0))
+      (i32.store (i32.const 4) (i32.const 0))
+      (i32.const 0)
+    )
+  )
+  (core instance $m (instantiate $M))
+  (func (export "f") (result string) (canon lift (core func $m "f") (memory $m "mem")))
+)
+(assert_return (invoke "f") (str.const ""))
+
+;; empty string with non-zero in-bounds ptr, len=0
+(component
+  (core module $M
+    (memory (export "mem") 1)
+    (func (export "f") (result i32)
+      (i32.store (i32.const 0) (i32.const 100))
+      (i32.store (i32.const 4) (i32.const 0))
+      (i32.const 0)
+    )
+  )
+  (core instance $m (instantiate $M))
+  (func (export "f") (result string) (canon lift (core func $m "f") (memory $m "mem")))
+)
+(assert_return (invoke "f") (str.const ""))
+
+;; out-of-bounds pointer traps even with len=0
 (component
   (core module $M
     (memory (export "mem") 1)
@@ -37,3 +68,69 @@
   (func (export "f") (result string) (canon lift (core func $m "f") (memory $m "mem")))
 )
 (assert_trap (invoke "f") "string pointer/length out of bounds of memory")
+
+;; invalid UTF-8: 0xFF is never valid
+(component
+  (core module $M
+    (memory (export "mem") 1)
+    (func (export "f") (result i32)
+      (i32.store (i32.const 0) (i32.const 8))
+      (i32.store (i32.const 4) (i32.const 1))
+      (i32.store8 (i32.const 8) (i32.const 0xff))
+      (i32.const 0)
+    )
+  )
+  (core instance $m (instantiate $M))
+  (func (export "f") (result string) (canon lift (core func $m "f") (memory $m "mem")))
+)
+(assert_trap (invoke "f") "invalid utf-8")
+
+;; truncated multibyte UTF-8: leading byte 0xC3 expects a continuation byte
+(component
+  (core module $M
+    (memory (export "mem") 1)
+    (func (export "f") (result i32)
+      (i32.store (i32.const 0) (i32.const 8))
+      (i32.store (i32.const 4) (i32.const 1))
+      (i32.store8 (i32.const 8) (i32.const 0xc3))
+      (i32.const 0)
+    )
+  )
+  (core instance $m (instantiate $M))
+  (func (export "f") (result string) (canon lift (core func $m "f") (memory $m "mem")))
+)
+(assert_trap (invoke "f") "invalid utf-8")
+
+;; string at end of memory page boundary
+(component
+  (core module $M
+    (memory (export "mem") 1)
+    (func (export "f") (result i32)
+      ;; place "ok" at the very end of the first page (65536 - 2 = 65534)
+      (i32.store (i32.const 0) (i32.const 65534))
+      (i32.store (i32.const 4) (i32.const 2))
+      (i32.store8 (i32.const 65534) (i32.const 111)) ;; 'o'
+      (i32.store8 (i32.const 65535) (i32.const 107)) ;; 'k'
+      (i32.const 0)
+    )
+  )
+  (core instance $m (instantiate $M))
+  (func (export "f") (result string) (canon lift (core func $m "f") (memory $m "mem")))
+)
+(assert_return (invoke "f") (str.const "ok"))
+
+;; string one byte past end of memory traps
+(component
+  (core module $M
+    (memory (export "mem") 1)
+    (func (export "f") (result i32)
+      (i32.store (i32.const 0) (i32.const 65535))
+      (i32.store (i32.const 4) (i32.const 2))
+      (i32.store8 (i32.const 65535) (i32.const 111))
+      (i32.const 0)
+    )
+  )
+  (core instance $m (instantiate $M))
+  (func (export "f") (result string) (canon lift (core func $m "f") (memory $m "mem")))
+)
+(assert_trap (invoke "f") "string pointer/length out of bounds of memory")

From 094f94c3fc3789c19a4334f421a58be6046365e8 Mon Sep 17 00:00:00 2001
From: Matthew Kim <38759997+friendlymatthew@users.noreply.github.com>
Date: Mon, 6 Apr 2026 10:59:50 -0400
Subject: [PATCH 2/2] refine trap msg

---
 test/values/strings.wast | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/values/strings.wast b/test/values/strings.wast
index 0bd9105a..e838ccdd 100644
--- a/test/values/strings.wast
+++ b/test/values/strings.wast
@@ -99,7 +99,7 @@
   (core instance $m (instantiate $M))
   (func (export "f") (result string) (canon lift (core func $m "f") (memory $m "mem")))
 )
-(assert_trap (invoke "f") "invalid utf-8")
+(assert_trap (invoke "f") "incomplete utf-8 byte sequence")
 
 ;; string at end of memory page boundary
 (component