Improve bin/ext printer for unprintable characters.

msgpack_object_print used fwrite to write binary data to a stream. The intention
of the function is to produce a human-readable representation of the object for
debugging purposes. Having arbitrary data dumped as is can cause issues with
terminals that interpret it as control sequences.

This change prints printable characters as is and unprintable characters as
hex-escapes ("\xNN"). Note that UTF-8 encoded characters will now be printed as
escaped sequence of UTF-8 bytes. This is an acceptable compromise, as doing
otherwise would require a light form of UTF-8 decoding and BIN-typed objects
should not be used to transport UTF-8 strings anyway (STR should be used
instead).

src/objectc.c

@@ -9,6 +9,7 @@
  */
 #include "msgpack/object.h"
 #include "msgpack/pack.h"
+#include <ctype.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -112,6 +113,21 @@ int msgpack_pack_object(msgpack_packer* pk, msgpack_object d)
 }
 
 
+static void msgpack_object_bin_print(FILE* out, const char *ptr, size_t size)
+{
+    size_t i;
+    for (i = 0; i < size; i++) {
+        if (ptr[i] == '"') {
+            fputs("\\\"", out);
+        } else if (isprint(ptr[i])) {
+            fputc(ptr[i], out);
+        } else {
+            fprintf(out, "\\x%02x", (unsigned char)ptr[i]);
+        }
+    }
+}
+
+
 void msgpack_object_print(FILE* out, msgpack_object o)
 {
     switch(o.type) {
@@ -159,7 +175,7 @@ void msgpack_object_print(FILE* out, msgpack_object o)
 
     case MSGPACK_OBJECT_BIN:
         fprintf(out, "\"");
-        fwrite(o.via.bin.ptr, o.via.bin.size, 1, out);
+        msgpack_object_bin_print(out, o.via.bin.ptr, o.via.bin.size);
         fprintf(out, "\"");
         break;
 
@@ -170,7 +186,7 @@ void msgpack_object_print(FILE* out, msgpack_object o)
         fprintf(out, "(ext: %d)", (int)o.via.ext.type);
 #endif
         fprintf(out, "\"");
-        fwrite(o.via.ext.ptr, o.via.ext.size, 1, out);
+        msgpack_object_bin_print(out, o.via.ext.ptr, o.via.ext.size);
         fprintf(out, "\"");
         break;