Fix fd_seek for boundary parameters

src/wasi_snapshot_preview1.rs

@@ -488,11 +488,11 @@ pub(crate) unsafe fn fd_seek<S: Storage>(
 ) -> Result<Filesize, Error> {
     let fd = fs.get_backing_fd(fd)?;
     fn compute_new_offset(base: usize, offset: Filedelta) -> Result<usize, Error> {
-        let new_offset = if offset > 0 {
+        let new_offset = if offset >= 0 {
             base + (offset as usize)
         } else {
             let neg_offset = (-offset) as usize;
-            if neg_offset < base {
+            if neg_offset <= base {
                 base - neg_offset
             } else {
                 return Err(wasi::ERRNO_INVAL.into());

tests/run-make/seek/Makefile

@@ -0,0 +1,12 @@
+-include ../tools.mk
+
+objs = $(TMPDIR)/main.c.o
+
+check: $(objs)
+	$(CC) $(LDFLAGS) $(objs) $(LIB_WASI_VFS) -o $(TMPDIR)/main.wasm
+	wasmtime --mapdir /fixtures::./fixtures $(TMPDIR)/main.wasm
+	$(WASI_VFS_CLI) pack $(TMPDIR)/main.wasm --mapdir /fixtures::./fixtures -o $(TMPDIR)/main.packed.wasm
+	$(WASI_RUN) $(TMPDIR)/main.packed.wasm
+
+clean:
+	rm -rf $(PROG) $(objs)

tests/run-make/seek/fixtures/file1.txt

@@ -0,0 +1,2 @@
+file1.1
+file1.2

tests/run-make/seek/main.c

@@ -0,0 +1,59 @@
+#include "../check.h"
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <wasi/api.h>
+#include <errno.h>
+#include <assert.h>
+
+int main(int argc, char *argv[]) {
+  int err;
+  int file1 = open("/fixtures/file1.txt", O_RDONLY);
+  assert(file1 != -1);
+
+  struct stat st;
+  err = fstat(file1, &st);
+  assert(err == 0);
+
+  char buffer[st.st_size];
+
+  __wasi_filesize_t off;
+
+  // reset the cursor
+  assert(__wasi_fd_seek(file1, 0, SEEK_SET, &off) == 0);
+  assert(off == 0);
+
+  // keep the initial cursor position
+  assert(__wasi_fd_seek(file1, 0, SEEK_CUR, &off) == 0);
+  assert(off == 0);
+  assert(read(file1, buffer, st.st_size) == st.st_size);
+
+  assert(__wasi_fd_seek(file1, 2, SEEK_SET, &off) == 0);
+  assert(off == 2);
+  assert(read(file1, buffer, st.st_size) == st.st_size - 2);
+
+  assert(__wasi_fd_seek(file1, st.st_size, SEEK_SET, &off) == 0);
+  assert(off == st.st_size);
+  assert(read(file1, buffer, 1) == 0);
+
+  assert(__wasi_fd_seek(file1, st.st_size + 1, SEEK_SET, &off) == 0);
+  assert(err == 0);
+  assert(read(file1, buffer, 1) == 0);
+
+  // reset the cursor
+  assert(__wasi_fd_seek(file1, 0, SEEK_SET, &off) == 0);
+
+  assert(__wasi_fd_seek(file1, 0, SEEK_END, &off) == 0);
+  assert(err == 0);
+  assert(read(file1, buffer, 1) == 0);
+
+  assert(__wasi_fd_seek(file1, -1, SEEK_END, &off) == 0);
+  assert(err == 0);
+  assert(read(file1, buffer, 1) == 1);
+
+  assert(__wasi_fd_seek(file1, -st.st_size, SEEK_END, &off) == 0);
+  assert(err == 0);
+  assert(off == 0);
+  assert(read(file1, buffer, st.st_size) == st.st_size);
+
+  return 0;
+}