Decodes "varint-delimited" protocol buffer messages and wraps them into a normal protocol buffer repeated message container with tag 1

varint-decode.c

#include <stdio.h>

static int convertHeaderAndGetLength(FILE *in, FILE *out, int typedTag) {
  int value = 0;
  int bitshift = 0;
  int first = 1;
  while (1) {
    int byte = fgetc(in);
    if (byte == EOF) {
      if (!first) fprintf(stderr, "unexpected EOF on length read\n");
      return -1;
    }
    if (first) {
      if (byte > 0) {
        fputc(typedTag, out);
        first = 0;
      } else {
        fprintf(stderr, "empty chunk!\n");
        return 0;
      }
    }
    fputc(byte, out);
    value = value | ((byte & 0x7f) << bitshift);
    bitshift += 7;
    if ((byte & 0x80) == 0) return value;
  }
}

int main() {
  const int TAG = 0xa; // wire type = buffer/string, tag = 1
  int length, i;
  while ((length = convertHeaderAndGetLength(stdin, stdout, TAG)) != -1) {
    fprintf(stderr, "length %d\n", length);
    for (i = 0; i < length; ++i) {
      int b = fgetc(stdin);
      if (b == EOF) {
        fprintf(stderr, "unexpected EOF!\n");
        break;
      }
      fputc(b, stdout);
    }
  }
  return 0;
}