Do not hardcode temporary directory

src/fmail.c

@@ -27,6 +27,8 @@
 #include <string.h>
 #include <ctype.h>
 #include <time.h>
+#include <unistd.h>
+#include <sys/stat.h>
 
 #include <gpgme.h>
 #include <magic.h>
@@ -424,30 +426,55 @@ get_editor(void)
     return editor;
 }
 
+static int
+is_usable_as_tmp_dir(const char *dirname)
+{
+    struct stat st_buf;
+
+    if ( stat(dirname, &st_buf) != -1 )
+        if ( S_ISDIR(st_buf.st_mode) )
+            if ( access(dirname, R_OK | W_OK) != -1 )
+                return 0;
+
+    return -1;
+}
+
+static const char *
+get_tmp_dir(void)
+{
+    const char *tmp;
+
+    if ( ! ((tmp = getenv("TMPDIR")) && is_usable_as_tmp_dir(tmp)) )
+        if ( ! ((tmp = getenv("TMP")) && is_usable_as_tmp_dir(tmp)) )
+            tmp = is_usable_as_tmp_dir("/tmp") ? "/tmp" : ".";
+
+    return tmp;
+}
+
 static FILE *
 read_input_from_editor(void)
 {
-    char tmp_filename[] = "/tmp/fmailXXXXXX";
-    const char *editor;
-    char *command;
-    int tmp_fd;
+    char *command, *filename;
+    int fd;
     FILE *f;
 
-    editor = get_editor();
+    if ( asprintf(&filename, "%s/fmailXXXXXX", get_tmp_dir()) == -1 )
+        err(EXIT_FAILURE, "cannot create temporary file");
 
-    if ( (tmp_fd = mkstemp(tmp_filename)) == -1 )
+    if ( (fd = mkstemp(filename)) == -1 )
         err(EXIT_FAILURE, "cannot create temporary file");
 
-    command = xmalloc(strlen(editor) + sizeof(tmp_filename) + 1);
-    sprintf(command, "%s %s", editor, tmp_filename);
+    if ( asprintf(&command, "%s %s", get_editor(), filename) == -1 )
+        err(EXIT_FAILURE, "cannot execute editor");
 
     if ( system(command) == -1 )
-        err(EXIT_FAILURE, "cannot execute editor '%s'", editor);
+        err(EXIT_FAILURE, "cannot execute editor");
 
-    if ( (f = fdopen(tmp_fd, "r")) == NULL )
+    if ( (f = fdopen(fd, "r")) == NULL )
         err(EXIT_FAILURE, "cannot open temporary file");
 
-    unlink(tmp_filename);
+    unlink(filename);
+    free(filename);
     free(command);
 
     return f;