avio: add avio_get_str()

Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>
(cherry picked from commit 41d8555f72)

libavformat/avio.h

@@ -525,6 +525,20 @@ unsigned int avio_rl24(AVIOContext *s);
 unsigned int avio_rl32(AVIOContext *s);
 uint64_t     avio_rl64(AVIOContext *s);
 
+/**
+ * Read a string from pb into buf. The reading will terminate when either
+ * a NULL character was encountered, maxlen bytes have been read, or nothing
+ * more can be read from pb. The result is guaranteed to be NULL-terminated, it
+ * will be truncated if buf is too small.
+ * Note that the string is not interpreted or validated in any way, it
+ * might get truncated in the middle of a sequence for multi-byte encodings.
+ *
+ * @return number of bytes read (is always <= maxlen).
+ * If reading ends on EOF or error, the return value will be one more than
+ * bytes actually read.
+ */
+int avio_get_str(AVIOContext *pb, int maxlen, char *buf, int buflen);
+
 /**
  * Read a UTF-16 string from pb and convert it to UTF-8.
  * The reading will terminate when either a null or invalid character was

libavformat/aviobuf.c

@@ -705,6 +705,23 @@ int ff_get_line(AVIOContext *s, char *buf, int maxlen)
     return i;
 }
 
+int avio_get_str(AVIOContext *s, int maxlen, char *buf, int buflen)
+{
+    int i;
+
+    // reserve 1 byte for terminating 0
+    buflen = FFMIN(buflen - 1, maxlen);
+    for (i = 0; i < buflen; i++)
+        if (!(buf[i] = avio_r8(s)))
+            return i + 1;
+    if (buflen)
+        buf[i] = 0;
+    for (; i < maxlen; i++)
+        if (!avio_r8(s))
+            return i + 1;
+    return maxlen;
+}
+
 #define GET_STR16(type, read) \
     int avio_get_str16 ##type(AVIOContext *pb, int maxlen, char *buf, int buflen)\
 {\