lavu/opt: add API for retrieving array-type option values

Previously one could only convert the entire array to a string, not
access individual elements.

doc/APIchanges

@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2024-03-07
 
 API changes, most recent first:
 
+2024-08-xx - xxxxxxxxx - lavu 59.35.100 - opt.h
+  Add av_opt_get_array_size() and av_opt_get_array().
+
 2024-08-xx - xxxxxxxxx - lavc 61.11.100- avcodec.h
   Clarify the documentation for get_buffer*() functions, making it
   clear that the memory returned by them should not contain sensitive

libavutil/opt.c

@@ -121,9 +121,9 @@ static unsigned *opt_array_pcount(const void *parray)
     return (unsigned *)((const void * const *)parray + 1);
 }
 
-static void opt_free_elem(const AVOption *o, void *ptr)
+static void opt_free_elem(enum AVOptionType type, void *ptr)
 {
-    switch (TYPE_BASE(o->type)) {
+    switch (TYPE_BASE(type)) {
     case AV_OPT_TYPE_STRING:
     case AV_OPT_TYPE_BINARY:
         av_freep(ptr);
@@ -145,7 +145,7 @@ static void opt_free_elem(const AVOption *o, void *ptr)
 static void opt_free_array(const AVOption *o, void *parray, unsigned *count)
 {
     for (unsigned i = 0; i < *count; i++)
-        opt_free_elem(o, opt_array_pelem(o, *(void **)parray, i));
+        opt_free_elem(o->type, opt_array_pelem(o, *(void **)parray, i));
 
     av_freep(parray);
     *count = 0;
@@ -153,7 +153,7 @@ static void opt_free_array(const AVOption *o, void *parray, unsigned *count)
 
 static int read_number(const AVOption *o, const void *dst, double *num, int *den, int64_t *intnum)
 {
-    switch (o->type) {
+    switch (TYPE_BASE(o->type)) {
     case AV_OPT_TYPE_FLAGS:
         *intnum = *(unsigned int*)dst;
         return 0;
@@ -992,7 +992,7 @@ static void format_duration(char *buf, size_t size, int64_t d)
 }
 
 static int opt_get_elem(const AVOption *o, uint8_t **pbuf, size_t buf_len,
-                        void *dst, int search_flags)
+                        const void *dst, int search_flags)
 {
     int ret;
 
@@ -1920,7 +1920,7 @@ void av_opt_free(void *obj)
         if (o->type & AV_OPT_TYPE_FLAG_ARRAY)
             opt_free_array(o, pitem, opt_array_pcount(pitem));
         else
-            opt_free_elem(o, pitem);
+            opt_free_elem(o->type, pitem);
     }
 }
 
@@ -2137,6 +2137,113 @@ int av_opt_copy(void *dst, const void *src)
     return ret;
 }
 
+int av_opt_get_array_size(void *obj, const char *name, int search_flags,
+                          unsigned int *out_val)
+{
+    void *target_obj, *parray;
+    const AVOption *o;
+
+    o = av_opt_find2(obj, name, NULL, 0, search_flags, &target_obj);
+    if (!o || !target_obj)
+        return AVERROR_OPTION_NOT_FOUND;
+    if (!(o->type & AV_OPT_TYPE_FLAG_ARRAY))
+        return AVERROR(EINVAL);
+
+    parray = (uint8_t *)target_obj + o->offset;
+    *out_val = *opt_array_pcount(parray);
+
+    return 0;
+}
+
+int av_opt_get_array(void *obj, const char *name, int search_flags,
+                     unsigned int start_elem, unsigned int nb_elems,
+                     enum AVOptionType out_type, void *out_val)
+{
+    const size_t elem_size_out = opt_elem_size[TYPE_BASE(out_type)];
+
+    const AVOption *o;
+    void *target_obj;
+
+    const void *parray;
+    unsigned array_size;
+
+    int ret;
+
+    o = av_opt_find2(obj, name, NULL, 0, search_flags, &target_obj);
+    if (!o || !target_obj)
+        return AVERROR_OPTION_NOT_FOUND;
+    if (!(o->type & AV_OPT_TYPE_FLAG_ARRAY) ||
+        (out_type & AV_OPT_TYPE_FLAG_ARRAY))
+        return AVERROR(EINVAL);
+
+    parray     = (uint8_t *)target_obj + o->offset;
+    array_size = *opt_array_pcount(parray);
+
+    if (start_elem >= array_size ||
+        array_size - start_elem < nb_elems)
+        return AVERROR(EINVAL);
+
+    for (unsigned i = 0; i < nb_elems; i++) {
+        const void *src = opt_array_pelem(o, *(void**)parray, start_elem + i);
+        void       *dst = (uint8_t*)out_val + i * elem_size_out;
+
+        if (out_type == TYPE_BASE(o->type)) {
+            ret = opt_copy_elem(obj, out_type, dst, src);
+            if (ret < 0)
+                goto fail;
+        } else if (out_type == AV_OPT_TYPE_STRING) {
+            uint8_t buf[128], *out = buf;
+
+            ret = opt_get_elem(o, &out, sizeof(buf), src, search_flags);
+            if (ret < 0)
+                goto fail;
+
+            if (out == buf) {
+                out = av_strdup(buf);
+                if (!out) {
+                    ret = AVERROR(ENOMEM);
+                    goto fail;
+                }
+            }
+
+            *(uint8_t**)dst = out;
+        } else if (out_type == AV_OPT_TYPE_INT64    ||
+                   out_type == AV_OPT_TYPE_DOUBLE   ||
+                   out_type == AV_OPT_TYPE_RATIONAL) {
+            double     num = 1.0;
+            int        den = 1;
+            int64_t intnum = 1;
+            int ret;
+
+            ret = read_number(o, src, &num, &den, &intnum);
+            if (ret < 0)
+                goto fail;
+
+            switch (out_type) {
+            case AV_OPT_TYPE_INT64:
+                *(int64_t*)dst = (num == den) ?  intnum : num * intnum / den;
+                break;
+            case AV_OPT_TYPE_DOUBLE:
+                *(double*)dst = num * intnum / den;
+                break;
+            case AV_OPT_TYPE_RATIONAL:
+                *(AVRational*)dst = (num == 1.0 && (int)intnum == intnum) ?
+                                    (AVRational){ intnum, den }           :
+                                    av_d2q(num * intnum / den, 1<<24);
+                break;
+            default: av_assert0(0);
+            }
+        } else
+            return AVERROR(ENOSYS);
+    }
+
+    return 0;
+fail:
+    for (unsigned i = 0; i < nb_elems; i++)
+        opt_free_elem(out_type, (uint8_t*)out_val + i * elem_size_out);
+    return ret;
+}
+
 int av_opt_query_ranges(AVOptionRanges **ranges_arg, void *obj, const char *key, int flags)
 {
     int ret;

libavutil/opt.h

@@ -944,6 +944,46 @@ int av_opt_get_chlayout(void *obj, const char *name, int search_flags, AVChannel
  * be freed with av_dict_free() by the caller
  */
 int av_opt_get_dict_val(void *obj, const char *name, int search_flags, AVDictionary **out_val);
+
+/**
+ * For an array-type option, get the number of elements in the array.
+ */
+int av_opt_get_array_size(void *obj, const char *name, int search_flags,
+                          unsigned int *out_val);
+
+/**
+ * For an array-type option, retrieve the values of one or more array elements.
+ *
+ * @param start_elem index of the first array element to retrieve
+ * @param nb_elems number of array elements to retrieve; start_elem+nb_elems
+ *                 must not be larger than array size as returned by
+ *                 av_opt_get_array_size()
+ *
+ * @param out_type Option type corresponding to the desired output.
+ *
+ *                 The array elements produced by this function will
+ *                 will be as if av_opt_getX() was called for each element,
+ *                 where X is specified by out_type. E.g. AV_OPT_TYPE_STRING
+ *                 corresponds to av_opt_get().
+ *
+ *                 Typically this should be the same as the scalarized type of
+ *                 the AVOption being retrieved, but certain conversions are
+ *                 also possible - the same as those done by the corresponding
+ *                 av_opt_get*() function. E.g. any option type can be retrieved
+ *                 as a string, numeric types can be retrieved as int64, double,
+ *                 or rational, etc.
+ *
+ * @param out_val  Array with nb_elems members into which the output will be
+ *                 written. The array type must match the underlying C type as
+ *                 documented for out_type, and be zeroed on entry to this
+ *                 function.
+ *
+ *                 For dynamically allocated types (strings, binary, dicts,
+ *                 etc.), the result is owned and freed by the caller.
+ */
+int av_opt_get_array(void *obj, const char *name, int search_flags,
+                     unsigned int start_elem, unsigned int nb_elems,
+                     enum AVOptionType out_type, void *out_val);
 /**
  * @}
  */

libavutil/tests/opt.c

@@ -300,6 +300,69 @@ int main(void)
         av_opt_free(&test2_ctx);
     }
 
+    printf("\nTesting av_opt_get_array()\n");
+    {
+        static const int int_array[] = { 5, 0, 42, 137, INT_MAX };
+
+        TestContext test_ctx = { 0 };
+
+        int     out_int   [FF_ARRAY_ELEMS(int_array)] = { 0 };
+        double  out_double[FF_ARRAY_ELEMS(int_array)] = { 0. };
+        char   *out_str   [FF_ARRAY_ELEMS(int_array)] = { NULL };
+        AVDictionary *out_dict[2] = { NULL };
+
+        int ret;
+
+        test_ctx.class = &test_class;
+
+        av_log_set_level(AV_LOG_QUIET);
+
+        av_opt_set_defaults(&test_ctx);
+
+        test_ctx.array_int    = av_memdup(int_array, sizeof(int_array));
+        test_ctx.nb_array_int = FF_ARRAY_ELEMS(int_array);
+
+        // retrieve as int
+        ret = av_opt_get_array(&test_ctx, "array_int", 0,
+                               1, 3, AV_OPT_TYPE_INT, out_int);
+        printf("av_opt_get_array(\"array_int\", 1, 3, INT)=%d -> [ %d, %d, %d ]\n",
+               ret, out_int[0], out_int[1], out_int[2]);
+
+        // retrieve as double
+        ret = av_opt_get_array(&test_ctx, "array_int", 0,
+                               3, 2, AV_OPT_TYPE_DOUBLE, out_double);
+        printf("av_opt_get_array(\"array_int\", 3, 2, DOUBLE)=%d -> [ %.2f, %.2f ]\n",
+               ret, out_double[0], out_double[1]);
+
+        // retrieve as str
+        ret = av_opt_get_array(&test_ctx, "array_int", 0,
+                               0, 5, AV_OPT_TYPE_STRING, out_str);
+        printf("av_opt_get_array(\"array_int\", 0, 5, STRING)=%d -> "
+               "[ %s, %s, %s, %s, %s ]\n", ret,
+               out_str[0], out_str[1], out_str[2], out_str[3], out_str[4]);
+
+        for (int i = 0; i < FF_ARRAY_ELEMS(out_str); i++)
+            av_freep(&out_str[i]);
+
+        ret = av_opt_get_array(&test_ctx, "array_dict", 0, 0, 2,
+                               AV_OPT_TYPE_DICT, out_dict);
+        printf("av_opt_get_array(\"array_dict\", 0, 2, DICT)=%d\n", ret);
+
+        for (int i = 0; i < test_ctx.nb_array_dict; i++) {
+            const AVDictionaryEntry *e = NULL;
+            while ((e = av_dict_iterate(test_ctx.array_dict[i], e))) {
+                const AVDictionaryEntry *e1 = av_dict_get(out_dict[i], e->key, NULL, 0);
+                if (!e1 || strcmp(e->value, e1->value)) {
+                    printf("mismatching dict entry %s: %s/%s\n",
+                           e->key, e->value, e1 ? e1->value : "<missing>");
+                }
+            }
+            av_dict_free(&out_dict[i]);
+        }
+
+        av_opt_free(&test_ctx);
+    }
+
     printf("\nTest av_opt_serialize()\n");
     {
         TestContext test_ctx = { 0 };

libavutil/version.h

@@ -79,7 +79,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  59
-#define LIBAVUTIL_VERSION_MINOR  34
+#define LIBAVUTIL_VERSION_MINOR  35
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \

tests/ref/fate/opt

@@ -154,6 +154,12 @@ av_opt_set("array_dict", NULL) -> 0
 array_dict=NULL; nb_array_dict=0
 av_opt_get("array_dict") -> NULL
 
+Testing av_opt_get_array()
+av_opt_get_array("array_int", 1, 3, INT)=0 -> [ 0, 42, 137 ]
+av_opt_get_array("array_int", 3, 2, DOUBLE)=0 -> [ 137.00, 2147483647.00 ]
+av_opt_get_array("array_int", 0, 5, STRING)=0 -> [ 5, 0, 42, 137, 2147483647 ]
+av_opt_get_array("array_dict", 0, 2, DICT)=0
+
 Test av_opt_serialize()
 num=0,unum=2147483648,toggle=1,rational=1/1,string=default,escape=\\\=\,,flags=0x00000001,size=200x300,pix_fmt=0bgr,sample_fmt=s16,video_rate=25/1,duration=0.001,color=0xffc0cbff,cl=hexagonal,bin=62696E00,bin1=,bin2=,num64=4294967296,flt=0.333333,dbl=0.333333,bool1=auto,bool2=true,bool3=false,dict1=,dict2=happy\=\\:-),array_int=,array_str=str0|str\\|1|str\\\\2,array_dict=k00\=v\\\\\\\\00:k01\=v\\\,01\,k10\=v\\\\\=1\\\\:0
 Setting entry with key 'num' to value '0'