[iOS] iconv+NSString

iconv.mm

#include <iconv.h>

static NSString *decode(const char *encoding, char *src, size_t len, double capacityRatio=2)
{
    if (len == 0) {
        return @"";
    }
    auto size = size_t(len * capacityRatio);
    auto dest = (char*) malloc(size);
    size_t pos = 0;
    auto ic = iconv_open("UTF-16", encoding);
    for (;;) {
        auto rem = size - pos;
        auto tmp = dest + pos;
        auto ret = iconv(ic, &src, &len, &tmp, &rem);
        pos = size - rem;
        if (ret != size_t(-1)) {
            break;
        }
        switch (errno) {
            case EILSEQ:
            case EINVAL:
                NSLog(@"[warn] Invalid byte sequence found.");
                len --;
                src ++;
                break;
            case E2BIG:
                NSLog(@"[info] Output buffer is too small");
                dest = (char*) realloc(dest, size * 2);
                break;
        }
    }
    iconv_close(ic);
    return [NSString.alloc initWithBytesNoCopy:dest
                                        length:pos
                                      encoding:NSUTF16StringEncoding
                                  freeWhenDone:YES];
}

static NSString *sjis(NSData *data)
{
    return decode("SJIS", (char*) data.bytes, data.length);
}