terminal: make utf8 decoder return length

Lets return the parsed length in term_utf8_decode() instead of a buffer
pointer. Store the pointer in the passed argument.

This makes it adhere to the systemd coding-style, were we always avoid
returning pointers, but store them in output arguments. In this case, the
storage is not allocated, so it doesn't fit 100% to this idiom, but still
looks much nicer.

5 files changed, 43 insertions, 40 deletions

diff --git a/src/libsystemd-terminal/subterm.c b/src/libsystemd-terminal/subterm.c
index 3990fb392b..adc4caa42e 100644
--- a/src/libsystemd-terminal/subterm.c
+++ b/src/libsystemd-terminal/subterm.c
@@ -716,10 +716,10 @@ static int terminal_io_fn(sd_event_source *source, int fd, uint32_t revents, voi
 
         for (i = 0; i < len; ++i) {
                 const term_seq *seq;
-                const uint32_t *str;
+                uint32_t *str;
                 size_t n_str, j;
 
-                str = term_utf8_decode(&t->utf8, &n_str, buf[i]);
+                n_str = term_utf8_decode(&t->utf8, &str, buf[i]);
                 for (j = 0; j < n_str; ++j) {
                         type = term_parser_feed(t->parser, &seq, str[j]);
                         if (type < 0) {
diff --git a/src/libsystemd-terminal/term-parser.c b/src/libsystemd-terminal/term-parser.c
index c8c1d13d2e..f9326d563a 100644
--- a/src/libsystemd-terminal/term-parser.c
+++ b/src/libsystemd-terminal/term-parser.c
@@ -81,15 +81,16 @@ size_t term_utf8_encode(char *out_utf8, uint32_t g) {
 /**
  * term_utf8_decode() - Try decoding the next UCS-4 character
  * @p: decoder object to operate on or NULL
- * @out_len: output buffer for length of decoded UCS-4 string or NULL
+ * @out_len: output storage for pointer to decoded UCS-4 string or NULL
  * @c: next char to push into decoder
  *
  * This decodes a UTF-8 stream. It must be called for each input-byte of the
- * UTF-8 stream and returns a UCS-4 stream. The length of the returned UCS-4
- * string (number of parsed characters) is stored in @out_len if non-NULL. A
- * pointer to the string is returned (or NULL if none was parsed). The string
- * is not zero-terminated! Furthermore, the string is only valid until the next
- * invokation of this function. It is also bound to the parser-state @p.
+ * UTF-8 stream and returns a UCS-4 stream. A pointer to the parsed UCS-4
+ * string is stored in @out_buf if non-NULL. The length of this string (number
+ * of parsed UCS4 characters) is returned as result. The string is not
+ * zero-terminated! Furthermore, the string is only valid until the next
+ * invocation of this function. It is also bound to the parser state @p and
+ * must not be freed nor written to by the caller.
  *
  * This function is highly optimized to work with terminal-emulators. Instead
  * of being strict about UTF-8 validity, this tries to perform a fallback to
@@ -100,9 +101,10 @@ size_t term_utf8_encode(char *out_utf8, uint32_t g) {
  * no helpers to do that for you. To initialize it, simply reset it to all
  * zero. You can reset or free the object at any point in time.
  *
- * Returns: Pointer to the UCS-4 string or NULL.
+ * Returns: Number of parsed UCS4 characters
  */
-const uint32_t *term_utf8_decode(term_utf8 *p, size_t *out_len, char c) {
+size_t term_utf8_decode(term_utf8 *p, uint32_t **out_buf, char c) {
+        static uint32_t ucs4_null = 0;
         uint32_t t, *res = NULL;
         uint8_t byte;
         size_t len = 0;
@@ -246,9 +248,9 @@ const uint32_t *term_utf8_decode(term_utf8 *p, size_t *out_len, char c) {
         p->n_bytes = 0;
 
 out:
-        if (out_len)
-                *out_len = len;
-        return len > 0 ? res : NULL;
+        if (out_buf)
+                *out_buf = res ? : &ucs4_null;
+        return len;
 }
 
 /*
diff --git a/src/libsystemd-terminal/term-screen.c b/src/libsystemd-terminal/term-screen.c
index 14c32aceb9..2f3f6f91cb 100644
--- a/src/libsystemd-terminal/term-screen.c
+++ b/src/libsystemd-terminal/term-screen.c
@@ -3756,7 +3756,7 @@ unsigned int term_screen_get_height(term_screen *screen) {
 }
 
 int term_screen_feed_text(term_screen *screen, const uint8_t *in, size_t size) {
-        const uint32_t *ucs4_str;
+        uint32_t *ucs4_str;
         size_t i, j, ucs4_len;
         const term_seq *seq;
         int r;
@@ -3768,7 +3768,7 @@ int term_screen_feed_text(term_screen *screen, const uint8_t *in, size_t size) {
          * 8bit mode if the stream is not valid UTF-8. This should be more than
          * enough to support old 7bit/8bit modes. */
         for (i = 0; i < size; ++i) {
-                ucs4_str = term_utf8_decode(&screen->utf8, &ucs4_len, in[i]);
+                ucs4_len = term_utf8_decode(&screen->utf8, &ucs4_str, in[i]);
                 for (j = 0; j < ucs4_len; ++j) {
                         r = term_parser_feed(screen->parser, &seq, ucs4_str[j]);
                         if (r < 0) {
diff --git a/src/libsystemd-terminal/term.h b/src/libsystemd-terminal/term.h
index 021cf1c42b..d5b934fc59 100644
--- a/src/libsystemd-terminal/term.h
+++ b/src/libsystemd-terminal/term.h
@@ -111,7 +111,7 @@ struct term_utf8 {
 };
 
 size_t term_utf8_encode(char *out_utf8, uint32_t g);
-const uint32_t *term_utf8_decode(term_utf8 *p, size_t *out_len, char c);
+size_t term_utf8_decode(term_utf8 *p, uint32_t **out_buf, char c);
 
 /*
  * Parsers
diff --git a/src/libsystemd-terminal/test-term-parser.c b/src/libsystemd-terminal/test-term-parser.c
index ed16f5f276..e8d5dcfbf2 100644
--- a/src/libsystemd-terminal/test-term-parser.c
+++ b/src/libsystemd-terminal/test-term-parser.c
@@ -33,39 +33,40 @@
 
 static void test_term_utf8_invalid(void) {
         term_utf8 p = { };
-        const uint32_t *res;
+        uint32_t *res;
         size_t len;
 
-        res = term_utf8_decode(NULL, NULL, 0);
-        assert_se(res == NULL);
+        len = term_utf8_decode(NULL, NULL, 0);
+        assert_se(!len);
 
-        res = term_utf8_decode(&p, NULL, 0);
-        assert_se(res != NULL);
-
-        len = 5;
-        res = term_utf8_decode(NULL, &len, 0);
-        assert_se(res == NULL);
-        assert_se(len == 0);
+        len = term_utf8_decode(&p, NULL, 0);
+        assert_se(len == 1);
 
-        len = 5;
-        res = term_utf8_decode(&p, &len, 0);
+        res = NULL;
+        len = term_utf8_decode(NULL, &res, 0);
+        assert_se(!len);
         assert_se(res != NULL);
+        assert_se(!*res);
+
+        len = term_utf8_decode(&p, &res, 0);
         assert_se(len == 1);
+        assert_se(res != NULL);
+        assert_se(!*res);
 
-        len = 5;
-        res = term_utf8_decode(&p, &len, 0xCf);
-        assert_se(res == NULL);
+        len = term_utf8_decode(&p, &res, 0xCf);
         assert_se(len == 0);
-
-        len = 5;
-        res = term_utf8_decode(&p, &len, 0x0);
         assert_se(res != NULL);
+        assert_se(!*res);
+
+        len = term_utf8_decode(&p, &res, 0);
         assert_se(len == 2);
+        assert_se(res != NULL);
+        assert_se(res[0] == 0xCf && res[1] == 0);
 }
 
 static void test_term_utf8_range(void) {
         term_utf8 p = { };
-        const uint32_t *res;
+        uint32_t *res;
         char u8[4];
         uint32_t i, j;
         size_t ulen, len;
@@ -78,8 +79,8 @@ static void test_term_utf8_range(void) {
                         continue;
 
                 for (j = 0; j < ulen; ++j) {
-                        res = term_utf8_decode(&p, &len, u8[j]);
-                        if (!res) {
+                        len = term_utf8_decode(&p, &res, u8[j]);
+                        if (len < 1) {
                                 assert_se(j + 1 != ulen);
                                 continue;
                         }
@@ -117,13 +118,13 @@ static void test_term_utf8_mix(void) {
                 0x00F0, 0x0080, 0x0080, 0x0001,
         };
         term_utf8 p = { };
-        const uint32_t *res;
+        uint32_t *res;
         unsigned int i, j;
         size_t len;
 
         for (i = 0, j = 0; i < sizeof(source); ++i) {
-                res = term_utf8_decode(&p, &len, source[i]);
-                if (!res)
+                len = term_utf8_decode(&p, &res, source[i]);
+                if (len < 1)
                         continue;
 
                 assert_se(j + len <= ELEMENTSOF(result));