rusty-hash-mask.c

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

typedef unsigned char u8;

const u8 OP_MASK = 0x50;
const u8 OP_0 = 0x00;
const u8 OP_1NEG = 0x4f;
const u8 OP_1 = 0x51;
const u8 OP_16 = 0x60;
const u8 OP_PUSHDATA1 = 0x4c;
const u8 OP_PUSHDATA2 = 0x4d;
const u8 OP_PUSHDATA4 = 0x4e;
const u8 OP_ANYPUSH = 0x65;
const u8 OP_CLTV = 0xb1;
const u8 OP_DROP = 0x75;
const u8 OP_CHECKSIG = 0xac;
const u8 OP_INVALID = 0xff;

u8 pull_opcode(const u8 **cursor, size_t *max, void *pptr)
{
    if (*max < 1) {
      *cursor = NULL;
      *max = 0;
      return OP_INVALID;
    }

    u8 opcode = **cursor;
    size_t skip = *max + 1;
    size_t pushdata_skip = 0;

    if (opcode <= 75) {
        skip = opcode; // push opcode bytes
    } else if (opcode == OP_PUSHDATA1) {
        pushdata_skip = 1;
        if (*max > 1) skip = *(*cursor+1);
    } else if (opcode == OP_PUSHDATA2) {
        pushdata_skip = 2;
        if (*max > 2) skip = *(*cursor+1) + *(*cursor+2)*256 + 3;
    } else if (opcode == OP_PUSHDATA4) {
        pushdata_skip = 4;
        if (*max > 4) skip = *(*cursor+1) + *(*cursor+2)*256 + *(*cursor+3)*(256*256) + *(*cursor+4)*(256*256*256) + 5;
    } else {
        (*cursor)++;
        (*max)--;
        return opcode;
    }

    if (1 + skip + pushdata_skip > *max) {
        *cursor = NULL;
        *max = 0;
        return OP_INVALID;
    }

#if 0
    if (pptr) {
        u8 **pptr = pptr;
        size_t oldsize = tal_count(*pptr);
        tal_resize(pptr, oldsize + skip);
        memcpy(*pptr + oldsize, memcheck(*cursor + 1 + pushdata_skip, skip), skip);
    }
#else
    (void)pptr;
#endif
    *cursor += 1 + pushdata_skip + skip;
    *max -= 1 + pushdata_skip + skip;
    return OP_ANYPUSH;
}

void push_masked_script(const u8* script, size_t len, void (*push)(const void *, size_t, void *), void *pushp)
{
    int skippush = 0;
    const u8 *cursor = script;
    size_t left = len;
    const u8 *start = cursor;

    while (left > 0) {
        if (skippush) {
            skippush = 0;
            if (start < cursor) push(start, cursor-start, pushp);
            u8 opcode = pull_opcode(&cursor, &left, NULL);
            start = cursor;

            if ((OP_1 <= opcode && opcode <= OP_16) || opcode == OP_1NEG) {
                opcode = OP_ANYPUSH;
            }
            assert(opcode == OP_ANYPUSH);
            push(&opcode, 1, pushp);
        } else {
            u8 opcode = pull_opcode(&cursor, &left, NULL);
            if (opcode == OP_MASK) {
                skippush = 1;
            }
        }
    }
    assert(cursor != NULL);
    if (start < cursor) push(start, cursor-start, pushp);
}

void push_printer(const void *pv, size_t len, void *d) {
    (void)d;
    const u8 *p = pv;
    while (len > 0) {
        printf("%02x", *p);
        p++; len--;
    }
}

int main(void) {
    u8 s0[] = { OP_MASK, 4, 0x00, 0x65, 0xcd, 0x1d, OP_CLTV, OP_DROP,
              33, 2, 0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,
                     0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,
              OP_CHECKSIG };
    u8 s1[] = { OP_MASK, 4, 0x00, 0x65, 0xcd, 0x1d, OP_CLTV, OP_DROP,
              OP_MASK, 33, 2, 0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,
                     0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,
              OP_CHECKSIG };

    (void)s0;
    (void)s1;

    push_printer(s0, sizeof(s0), NULL); printf("\n");

    push_masked_script(s0, sizeof(s0), push_printer, NULL); printf("\n");

    return 0;
}