fix a base85 bug on iOS

PiperOrigin-RevId: 731849590

internal/encoding/base85.cc

@@ -67,7 +67,8 @@ std::string Base85Encode(const std::string& input, bool padding) {
   char* result_buffer_end = result.data() + result.size();
 
   size_t bytes = input.size();
-  const char* data = input.data();
+  const unsigned char* data =
+      reinterpret_cast<const unsigned char*>(input.data());
   while (bytes) {
     int count;
     uint32_t value = 0;

internal/platform/implementation/apple/Tests/NSData+GNCBase85Test.m

@@ -43,6 +43,18 @@
   XCTAssertEqualObjects(decodedData, data);
 }
 
+- (void)testEncodingAndDecoding {
+  unsigned char hexBytes[] = {0x20, 0x25, 0xdf, 0x06, 0x24, 0x00, 0x11, 0x88, 0x07,
+                              0xda, 0x54, 0x65, 0x73, 0x74, 0x20, 0x64, 0x65};
+
+  NSUInteger length = sizeof(hexBytes) / sizeof(hexBytes[0]);
+
+  NSData *data = [NSData dataWithBytes:hexBytes length:length];
+  NSString *actual = [data base85EncodedString];
+  XCTAssertEqualObjects(actual, @"+=5nL,QJF4#MN-gF*&O8AH");
+  XCTAssertEqualObjects([[NSData alloc] initWithBase85EncodedString:actual], data);
+}
+
 - (void)testEncodingEmptyData {
   XCTAssertEqualObjects([[@"" dataUsingEncoding:NSUTF8StringEncoding] base85EncodedString], @"");
 }