fix getenv_s for NULL dest

still return the length. GH rurban#109. Thanks @ulatekh
Also check if dmax is 0, and fix the error handling.

src/os/getenv_s.c

@@ -3,6 +3,7 @@
  *
  * September 2017, Reini Urban
  * January 2022, Reini Urban
+ * October 2022, Reini Urban
  *
  * Copyright (c) 2017,2022 by Reini Urban
  * All rights reserved.
@@ -99,16 +100,42 @@ EXPORT errno_t _getenv_s_chk(size_t *restrict len, char *restrict dest,
     const char *buf;
     size_t len1;
 
-    if (destbos == BOS_UNKNOWN) {
-        CHK_DMAX_MAX("getenv_s", RSIZE_MAX_STR)
-        BND_CHK_PTR_BOUNDS(dest, dmax);
-    } else {
-        CHK_DEST_OVR("getenv_s", destbos)
+    if (likely(dest)) {
+        if (destbos == BOS_UNKNOWN) {
+            if (unlikely(dmax > RSIZE_MAX_STR)) {
+                goto err_dmax;
+            }
+            BND_CHK_PTR_BOUNDS(dest, dmax);
+        } else {
+            if (unlikely(dmax > destbos)) {
+            err_dmax:
+                if (len)
+                    *len = 0;
+                invoke_safe_str_constraint_handler("getenv_s: dmax exceeds max",
+                                                   (void *)dest, ESLEMAX);
+                return RCNEGATE(ESLEMAX);
+            }
+        }
+    }
+    else {
+        if (dmax != 0) { // with dest == NULL
+            if (len)
+                *len = 0;
+            invoke_safe_str_constraint_handler("getenv_s: dmax must be 0",
+                                               NULL, ESNULLP);
+            return ESNULLP;
+        }
     }
     if (unlikely(name == NULL)) {
         if (len)
             *len = 0;
-        handle_error(dest, dmax, "getenv_s: name is null", ESNULLP);
+        if (likely(dest)) {
+            handle_error(dest, dmax, "getenv_s: name is null", ESNULLP);
+        }
+        else {
+            invoke_safe_str_constraint_handler("getenv_s: name is null",
+                                               NULL, ESNULLP);
+        }
         return ESNULLP;
     }
 
@@ -120,11 +147,13 @@ EXPORT errno_t _getenv_s_chk(size_t *restrict len, char *restrict dest,
 #endif
 
     if (buf == NULL) {
+        if (likely(dest)) {
 #ifdef SAFECLIB_STR_NULL_SLACK
-        memset(dest, 0, dmax);
+            memset(dest, 0, dmax);
 #else
-        *dest = '\0';
+            *dest = '\0';
 #endif
+        }
         if (len)
             *len = 0;
         return -1;
@@ -136,10 +165,11 @@ EXPORT errno_t _getenv_s_chk(size_t *restrict len, char *restrict dest,
             *len = 0;
         handle_error(dest, dmax, "getenv_s: dmax is too small", ESNOSPC);
         return RCNEGATE(ESNOSPC);
-    } else if (dest) {
+    } else {
         if (len)
             *len = len1;
-        strcpy_s(dest, dmax, buf);
+        if (dest)
+            strcpy_s(dest, dmax, buf);
     }
 
     return EOK;

tests/test_getenv_s.c

@@ -1,7 +1,7 @@
 /*------------------------------------------------------------------
  * test_getenv_s
  * File 'os/getenv_s.c'
- * Lines executed:100.00% of 29
+ * Lines executed:95.24% of 42
  *
  *------------------------------------------------------------------
  */
@@ -31,6 +31,8 @@ int test_getenv_s(void) {
     const char *name = "PATH";
 
     /*--------------------------------------------------*/
+    /* Note that native getenv_s with MSVC looks completely broken for
+       most cases. Maybe we should force our implementation there. */
 
 #ifndef HAVE_CT_BOS_OVR
     EXPECT_BOS("empty name")
@@ -40,22 +42,40 @@ int test_getenv_s(void) {
         use_msvcrt = false;
     }
     ERR_MSVC(ESNULLP, 0);
-#endif
+    ind = len;
+    if (!use_msvcrt) {
+        INDCMP(!= 0);
+    }
 
-    rc = getenv_s(&len, NULL, 0, name);
-    ERR_MSVC(0, EINVAL);
+    rc = getenv_s(&len, NULL, 0, NULL);
+    ERR_MSVC(ESNULLP, EINVAL);
+    ind = len;
+    if (!use_msvcrt) {
+        INDCMP(!= 0);
+    }
+#endif
 
     /*--------------------------------------------------*/
+    /* cases where name exists */
 
-    rc = getenv_s(&len, dest, 0, name);
+    str2 = getenv(name); // for PATH
+    rc = getenv_s(&len, NULL, 0, name);
     ERR_MSVC(0, EINVAL);
+    ind = strlen(str2);
+    if (!use_msvcrt) {
+        INDCMP(!= (int)len);
+    }
 
     /*--------------------------------------------------*/
 
 #ifndef HAVE_CT_BOS_OVR
     EXPECT_BOS("dest overflow")
     rc = getenv_s(&len, dest, RSIZE_MAX_STR + 1, name);
     ERR_MSVC(ESLEMAX, 0);
+    ind = len;
+    if (!use_msvcrt) {
+        INDCMP(!= 0);
+    }
 #endif
 
     /*--------------------------------------------------*/
@@ -72,7 +92,6 @@ int test_getenv_s(void) {
 
     rc = getenv_s(&len, dest, LEN, name);
     ERR(EOK);
-    str2 = getenv(name);
     EXPSTR(dest, str2);
     ind = strlen(str2);
     if (!use_msvcrt) {
@@ -83,7 +102,26 @@ int test_getenv_s(void) {
     ERR_MSVC(EOK, EINVAL);
     EXPSTR(dest, str2);
 
+    rc = getenv_s(&len, dest, LEN, name);
+    ERR(EOK);
+    EXPSTR(dest, str2);
+    ind = strlen(str2);
+    if (!use_msvcrt) {
+        INDCMP(!= (int)len);
+    }
+
+#ifndef HAVE_CT_BOS_OVR
+    EXPECT_BOS("dest overflow or empty")
+    rc = getenv_s(&len, NULL, LEN, name);
+    ERR_MSVC(ESNULLP, EINVAL); // with NULL dmax must be 0
+    ind = len;
+    if (!use_msvcrt) {
+        INDCMP(!= 0);
+    }
+#endif
+
     /*--------------------------------------------------*/
+    /* cases where name does not exist */
 
     rc = getenv_s(NULL, dest, LEN, "c#hewhc&wehc%erwhc$weh");
     ERR_MSVC(-1, EINVAL);