win32: rework adding of extensions to filenames

Previously there was one function to handle adding extensions to
executable filenames, add_win32_extension().  Refactor this into
three functions:

add_win32_extension() appends the suffix to the argument string
in-place.  The argument must be long enough to cope with this,
as is the case in ash where path_advance() adds 4 bytes to each
filename for just this reason.

alloc_win32_extension() is equivalent to the old add_win32_extension().
It allocates a string to hold the new filename then calls the new
add_win32_extension() function.  The caller is responsible for
managing the returned string.

auto_win32_extension() calls alloc_win32_extension() and saves the
resulting string using auto_string().  It's used where the new
filename is consumed immediately or the actual value isn't needed.

Rewrite code to use the most appropriate function.  Also reorder
some code in find_executable() and find_command().

1 files changed, 11 insertions, 21 deletions

diff --git a/libbb/executable.c b/libbb/executable.c
index aec829945..835341ed9 100644
--- a/libbb/executable.c
+++ b/libbb/executable.c
@@ -28,10 +28,6 @@ int FAST_FUNC file_is_executable(const char *name)
  * in all cases (*PATHp) contents are temporarily modified
  * but are restored on return (s/:/NUL/ and back).
  */
-#if !ENABLE_PLATFORM_MINGW32
-#define next_path_sep(s) strchr(s, ':')
-#endif
-
 char* FAST_FUNC find_executable(const char *filename, char **PATHp)
 {
         /* About empty components in $PATH:
@@ -44,38 +40,32 @@ char* FAST_FUNC find_executable(const char *filename, char **PATHp)
          */
         char *p, *n;
 #if ENABLE_PLATFORM_MINGW32
-        char *w;
+        char sep, *w;
 #endif
 
         p = *PATHp;
         while (p) {
                 int ex;
-#if ENABLE_PLATFORM_MINGW32
-                char sep;
 
-                n = (char*)next_path_sep(p);
-                if (n) {
-                        sep = *n;
-                        *n = '\0';
-                }
-#else
+#if !ENABLE_PLATFORM_MINGW32
                 n = strchr(p, ':');
                 if (n) *n = '\0';
+#else
+                n = (char*)next_path_sep(p);
+                if (n) { sep = *n; *n = '\0'; }
 #endif
                 p = concat_path_file(
                         p[0] ? p : ".", /* handle "::" case */
                         filename
                 );
-#if ENABLE_PLATFORM_MINGW32
-                if (n) *n++ = sep;
-#else
+#if !ENABLE_PLATFORM_MINGW32
                 if (n) *n++ = ':';
-#endif
-#if ENABLE_PLATFORM_MINGW32
-                if ((w=add_win32_extension(p))) {
-                        *PATHp = n;
+#else
+                if (n) *n++ = sep;
+                if ((w=alloc_win32_extension(p))) {
                         free(p);
-                        return w;
+                        p = w;
+                        /* following test will succeed */
                 }
 #endif
                 ex = file_is_executable(p);