strv: convert strv_split_quotes into a generic strv_split_extract

strv_split_extract is to strv_split_quotes as extract_first_word was to
unquote_first_word.

Now there's extract_first_word for extracting a single argument,
extract_many_words for extracting a bounded number of arguments,
and strv_split_extract for extracting an arbitrary number of arguments.

src/basic/env-util.c

@@ -550,7 +550,7 @@ char **replace_env_argv(char **argv, char **env) {
                         if (e) {
                                 int r;
 
-                                r = strv_split_quoted(&m, e, EXTRACT_RELAX);
+                                r = strv_split_extract(&m, e, WHITESPACE, EXTRACT_RELAX|EXTRACT_QUOTES);
                                 if (r < 0) {
                                         ret[k] = NULL;
                                         strv_free(ret);

src/basic/strv.c

@@ -278,7 +278,7 @@ char **strv_split_newlines(const char *s) {
         return l;
 }
 
-int strv_split_quoted(char ***t, const char *s, ExtractFlags flags) {
+int strv_split_extract(char ***t, const char *s, const char *separators, ExtractFlags flags) {
         size_t n = 0, allocated = 0;
         _cleanup_strv_free_ char **l = NULL;
         int r;
@@ -289,11 +289,12 @@ int strv_split_quoted(char ***t, const char *s, ExtractFlags flags) {
         for (;;) {
                 _cleanup_free_ char *word = NULL;
 
-                r = extract_first_word(&s, &word, NULL, flags|EXTRACT_QUOTES);
+                r = extract_first_word(&s, &word, separators, flags);
                 if (r < 0)
                         return r;
-                if (r == 0)
+                if (r == 0) {
                         break;
+                }
 
                 if (!GREEDY_REALLOC(l, allocated, n + 2))
                         return -ENOMEM;

src/basic/strv.h

@@ -73,7 +73,7 @@ static inline bool strv_isempty(char * const *l) {
 char **strv_split(const char *s, const char *separator);
 char **strv_split_newlines(const char *s);
 
-int strv_split_quoted(char ***t, const char *s, ExtractFlags flags);
+int strv_split_extract(char ***t, const char *s, const char *separators, ExtractFlags flags);
 
 char *strv_join(char **l, const char *separator);
 char *strv_join_quoted(char **l);