avutil/avstring: add av_strreplace API into avstring

refer to: http://creativeandcritical.net/str-replace-c
add av_strreplace API for replace string operations.
Signed-off-by: Steven Liu <lq@chinaffmpeg.org>

libavutil/avstring.c

@@ -231,6 +231,83 @@ int av_strncasecmp(const char *a, const char *b, size_t n)
     return c1 - c2;
 }
 
+char *av_strreplace(const char *str, const char *from, const char *to)
+{
+    /* Adjust each of the below values to suit your needs. */
+    /* Increment positions cache size initially by this number. */
+    size_t cache_sz_inc = 16;
+    /* Thereafter, each time capacity needs to be increased,
+     * multiply the increment by this factor. */
+    const size_t cache_sz_inc_factor = 3;
+    /* But never increment capacity by more than this number. */
+    const size_t cache_sz_inc_max = 1048576;
+
+    char *pret, *ret = NULL;
+    const char *pstr2, *pstr = str;
+    size_t i, count = 0;
+    uintptr_t *pos_cache_tmp, *pos_cache = NULL;
+    size_t cache_sz = 0;
+    size_t cpylen, orglen, retlen, tolen, fromlen = strlen(from);
+
+    /* Find all matches and cache their positions. */
+    while ((pstr2 = av_stristr(pstr, from))) {
+        count++;
+        /* Increase the cache size when necessary. */
+        if (cache_sz < count) {
+            cache_sz += cache_sz_inc;
+            pos_cache_tmp = av_realloc(pos_cache, sizeof(*pos_cache) * cache_sz);
+            if (!pos_cache_tmp) {
+                goto end_strreplace;
+            } else pos_cache = pos_cache_tmp;
+            cache_sz_inc *= cache_sz_inc_factor;
+            if (cache_sz_inc > cache_sz_inc_max) {
+                cache_sz_inc = cache_sz_inc_max;
+            }
+        }
+
+        pos_cache[count-1] = pstr2 - str;
+        pstr = pstr2 + fromlen;
+    }
+    orglen = pstr - str + strlen(pstr);
+    /* Allocate memory for the post-replacement string. */
+    if (count > 0) {
+        tolen = strlen(to);
+        retlen = orglen + (tolen - fromlen) * count;
+    } else {
+        retlen = orglen;
+    }
+    ret = av_malloc(retlen + 1);
+    if (!ret) {
+        goto end_strreplace;
+    }
+
+    if (!count) {
+        /* If no matches, then just duplicate the string. */
+        av_strlcpy(ret, str, retlen + 1);
+    } else {
+        /* Otherwise, duplicate the string whilst performing
+         * the replacements using the position cache. */
+        pret = ret;
+        memcpy(pret, str, pos_cache[0]);
+        pret += pos_cache[0];
+        for (i = 0; i < count; i++) {
+            memcpy(pret, to, tolen);
+            pret += tolen;
+            pstr = str + pos_cache[i] + fromlen;
+            cpylen = (i == count-1 ? orglen : pos_cache[i+1]) - pos_cache[i] - fromlen;
+            memcpy(pret, pstr, cpylen);
+            pret += cpylen;
+        }
+        ret[retlen] = '\0';
+    }
+
+end_strreplace:
+    /* Free the cache and return the post-replacement string,
+     * which will be NULL in the event of an error. */
+    av_free(pos_cache);
+    return ret;
+}
+
 const char *av_basename(const char *path)
 {
     char *p = strrchr(path, '/');

libavutil/avstring.h

@@ -266,6 +266,11 @@ int av_strcasecmp(const char *a, const char *b);
  */
 int av_strncasecmp(const char *a, const char *b, size_t n);
 
+/**
+ * Locale-independent strings replace.
+ * @note This means only ASCII-range characters are replace
+ */
+char *av_strreplace(const char *str, const char *from, const char *to);
 
 /**
  * Thread safe basename.