From dd9ab5fc0b6c0b706288f8f5e20989b6e24921e9 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Tue, 17 May 2022 20:52:44 -0700
Subject: ffi: bugfix: null terminated string as flexible member.

* ffi.c (ffi_char_array_get, ffi_zchar_array_get, ffi_wchar_array_get,
ffi_bchar_array_get): Rearrange so that we test for tft->null_term
first, and not nelem == 0. If nelem happens to be zero, but we are
supposed to decode a null-terminated string, we will do the wrong
thing and return the null string.
(ffi_varray_in): The body can't be conditional on vec being non-nil,
because then we do nothing if we don't have a Lisp object, which means
we skip the cases when we should decode a null-terminated array.
Now if vec is nil, we must guard against calling ffi_varray_dynsize.
---
 ffi.c                 | 66 ++++++++++++++++++++++-----------------------------
 tests/017/ffi-misc.tl |  6 +++++
 2 files changed, 34 insertions(+), 38 deletions(-)

diff --git a/ffi.c b/ffi.c
index a12ef4a3..c8c8ca82 100644
--- a/ffi.c
+++ b/ffi.c
@@ -2460,16 +2460,14 @@ static void ffi_struct_release(struct txr_ffi_type *tft, val strct,
 static val ffi_char_array_get(struct txr_ffi_type *tft, mem_t *src,
                               cnum nelem)
 {
-  if (nelem == 0) {
+  const char *chptr = coerce(const char *, src);
+  if (tft->null_term) {
+    return string_utf8(chptr);
+  } else if (nelem == 0) {
     return null_string;
   } else {
-    const char *chptr = coerce(const char *, src);
-    if (tft->null_term) {
-      return string_utf8(chptr);
-    } else {
-      wchar_t *wch = utf8_dup_from_buf(chptr, nelem);
-      return string_own(wch);
-    }
+    wchar_t *wch = utf8_dup_from_buf(chptr, nelem);
+    return string_own(wch);
   }
 }
 
@@ -2496,36 +2494,30 @@ static void ffi_char_array_put(struct txr_ffi_type *tft, val str, mem_t *dst,
 static val ffi_zchar_array_get(struct txr_ffi_type *tft, mem_t *src,
                                cnum nelem)
 {
-  if (nelem == 0) {
+  const char *chptr = coerce(const char *, src);
+  if (tft->null_term) {
+    return string_utf8(chptr);
+  } else if (nelem == 0) {
     return null_string;
+  } else if (memchr(chptr, 0, nelem)) {
+    return string_utf8(chptr);
   } else {
-    const char *chptr = coerce(const char *, src);
-    if (tft->null_term) {
-      return string_utf8(chptr);
-    } else if (memchr(chptr, 0, nelem)) {
-      return string_utf8(chptr);
-    } else {
-      wchar_t *wch = utf8_dup_from_buf(chptr, nelem);
-      return string_own(wch);
-    }
+    wchar_t *wch = utf8_dup_from_buf(chptr, nelem);
+    return string_own(wch);
   }
 }
 
-
 static val ffi_wchar_array_get(struct txr_ffi_type *tft, mem_t *src,
                                cnum nelem, val self)
 {
-  if (nelem == 0) {
+  const wchar_t *wchptr = coerce(const wchar_t *, src);
+  if (tft->null_term) {
+    return string(wchptr);
+  } else if (nelem == 0) {
     return null_string;
   } else {
-    const wchar_t *wchptr = coerce(const wchar_t *, src);
-
-    if (tft->null_term) {
-      return string(wchptr);
-    } else {
-      val ustr = mkustring(num_fast(nelem));
-      return init_str(ustr, wchptr, self);
-    }
+    val ustr = mkustring(num_fast(nelem));
+    return init_str(ustr, wchptr, self);
   }
 }
 
@@ -2541,15 +2533,13 @@ static void ffi_wchar_array_put(struct txr_ffi_type *tft, val str, mem_t *dst,
 static val ffi_bchar_array_get(struct txr_ffi_type *tft, mem_t *src,
                                cnum nelem)
 {
-  if (nelem == 0) {
+  const unsigned char *chptr = coerce(const unsigned char *, src);
+  if (tft->null_term)
+    return string_8bit(chptr);
+  else if (nelem == 0)
     return null_string;
-  } else {
-    const unsigned char *chptr = coerce(const unsigned char *, src);
-    if (tft->null_term)
-      return string_8bit(chptr);
-    else
-      return string_8bit_size(chptr, nelem);
-  }
+  else
+    return string_8bit_size(chptr, nelem);
 }
 
 static void ffi_bchar_array_put(struct txr_ffi_type *tft, val str, mem_t *dst,
@@ -2858,9 +2848,9 @@ static void ffi_varray_put(struct txr_ffi_type *tft, val vec, mem_t *dst,
 static val ffi_varray_in(struct txr_ffi_type *tft, int copy, mem_t *src,
                          val vec, val self)
 {
-  if (copy && vec) {
+  if (copy) {
     struct txr_ffi_type *etft = ffi_type_struct(tft->eltype);
-    cnum nelem = ffi_varray_dynsize(tft, vec, self) / etft->size;
+    cnum nelem = if3(vec, ffi_varray_dynsize(tft, vec, self) / etft->size, 0);
 
     switch (tft->ch_conv) {
     case conv_char:
diff --git a/tests/017/ffi-misc.tl b/tests/017/ffi-misc.tl
index 7053f78e..d0785513 100644
--- a/tests/017/ffi-misc.tl
+++ b/tests/017/ffi-misc.tl
@@ -88,3 +88,9 @@
   (copy-cptr (cptr-int 3)) "#<cptr: 3>"
   (copy (cptr-int 3)) "#<cptr: 3>"
   (copy-cptr 3) :error)
+
+(ffi (struct flex (x char) (y (zarray char))))
+
+(mtest
+  (ffi-put (new flex x #\a y "bcd") (ffi (struct flex))) #b'6100000062636400'
+  (ffi-get #b'6100000062636400' (ffi (struct flex))) #S(flex x #\a y "bcd"))
-- 
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