zeek/src/Base64.cc

#include "zeek/Base64.h"

#include "zeek/zeek-config.h"

#include <cmath>

#include "zeek/Conn.h"
#include "zeek/Reporter.h"
#include "zeek/ZeekString.h"

namespace zeek::detail
	{

int Base64Converter::default_base64_table[256];
const std::string Base64Converter::default_alphabet =
	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

void Base64Converter::Encode(int len, const unsigned char* data, int* pblen, char** pbuf)
	{
	int blen;
	char* buf;

	if ( ! pbuf )
		reporter->InternalError("nil pointer to encoding result buffer");

	if ( *pbuf && (*pblen % 4 != 0) )
		reporter->InternalError("Base64 encode buffer not a multiple of 4");

	if ( *pbuf )
		{
		buf = *pbuf;
		blen = *pblen;
		}
	else
		{
		blen = (int)(4 * ceil((double)len / 3));
		*pbuf = buf = new char[blen];
		*pblen = blen;
		}

	for ( int i = 0, j = 0; (i < len) && (j < blen); )
		{
		uint32_t bit32 = data[i++] << 16;
		bit32 += (i++ < len ? data[i - 1] : 0) << 8;
		bit32 += i++ < len ? data[i - 1] : 0;

		buf[j++] = alphabet[(bit32 >> 18) & 0x3f];
		buf[j++] = alphabet[(bit32 >> 12) & 0x3f];
		buf[j++] = (i == (len + 2)) ? '=' : alphabet[(bit32 >> 6) & 0x3f];
		buf[j++] = (i >= (len + 1)) ? '=' : alphabet[bit32 & 0x3f];
		}
	}

int* Base64Converter::InitBase64Table(const std::string& alphabet)
	{
	assert(alphabet.size() == 64);

	static bool default_table_initialized = false;

	if ( alphabet == default_alphabet && default_table_initialized )
		return default_base64_table;

	int* base64_table = nullptr;

	if ( alphabet == default_alphabet )
		{
		base64_table = default_base64_table;
		default_table_initialized = true;
		}
	else
		base64_table = new int[256];

	int i;
	for ( i = 0; i < 256; ++i )
		base64_table[i] = -1;

	for ( i = 0; i < 26; ++i )
		{
		base64_table[int(alphabet[0 + i])] = i;
		base64_table[int(alphabet[26 + i])] = i + 26;
		}

	for ( i = 0; i < 10; ++i )
		base64_table[int(alphabet[52 + i])] = i + 52;

	// Casts to avoid compiler warnings.
	base64_table[int(alphabet[62])] = 62;
	base64_table[int(alphabet[63])] = 63;
	base64_table[int('=')] = 0;

	return base64_table;
	}

Base64Converter::Base64Converter(Connection* arg_conn, const std::string& arg_alphabet)
	{
	if ( arg_alphabet.size() > 0 )
		{
		assert(arg_alphabet.size() == 64);
		alphabet = arg_alphabet;
		}
	else
		{
		alphabet = default_alphabet;
		}

	base64_table = nullptr;
	base64_group_next = 0;
	base64_padding = base64_after_padding = 0;
	errored = 0;
	conn = arg_conn;
	}

Base64Converter::~Base64Converter()
	{
	if ( base64_table != default_base64_table )
		delete[] base64_table;
	}

int Base64Converter::Decode(int len, const char* data, int* pblen, char** pbuf)
	{
	int blen;
	char* buf;

	// Initialization of table on first_time call of Decode.
	if ( ! base64_table )
		base64_table = InitBase64Table(alphabet);

	if ( ! pbuf )
		reporter->InternalError("nil pointer to decoding result buffer");

	if ( *pbuf )
		{
		buf = *pbuf;
		blen = *pblen;
		}
	else
		{
		// Estimate the maximal number of 3-byte groups needed,
		// plus 1 byte for the optional ending NUL.
		blen = int((len + base64_group_next + 3) / 4) * 3 + 1;
		*pbuf = buf = new char[blen];
		}

	int dlen = 0;

	while ( true )
		{
		if ( base64_group_next == 4 )
			{
			// For every group of 4 6-bit numbers,
			// write the decoded 3 bytes to the buffer.
			if ( base64_after_padding )
				{
				if ( ++errored == 1 )
					IllegalEncoding("extra base64 groups after '=' padding are ignored");
				base64_group_next = 0;
				continue;
				}

			int num_octets = 3 - base64_padding;

			if ( buf + num_octets > *pbuf + blen )
				break;

			uint32_t bit32 = ((base64_group[0] & 0x3f) << 18) | ((base64_group[1] & 0x3f) << 12) |
			                 ((base64_group[2] & 0x3f) << 6) | ((base64_group[3] & 0x3f));

			if ( --num_octets >= 0 )
				*buf++ = char((bit32 >> 16) & 0xff);

			if ( --num_octets >= 0 )
				*buf++ = char((bit32 >> 8) & 0xff);

			if ( --num_octets >= 0 )
				*buf++ = char((bit32)&0xff);

			if ( base64_padding > 0 )
				base64_after_padding = 1;

			base64_group_next = 0;
			base64_padding = 0;
			}

		if ( dlen >= len )
			break;

		unsigned char c = (unsigned char)data[dlen];
		if ( c == '=' )
			++base64_padding;

		int k = base64_table[c];
		if ( k >= 0 )
			base64_group[base64_group_next++] = k;
		else
			{
			if ( ++errored == 1 )
				IllegalEncoding(util::fmt("character %d ignored by Base64 decoding", (int)c));
			}

		++dlen;
		}

	*pblen = buf - *pbuf;
	return dlen;
	}

int Base64Converter::Done(int* pblen, char** pbuf)
	{
	const char* padding = "===";

	if ( base64_group_next != 0 )
		{
		if ( base64_group_next < 4 )
			IllegalEncoding(util::fmt("incomplete base64 group, padding with %d bits of 0",
			                          (4 - base64_group_next) * 6));
		Decode(4 - base64_group_next, padding, pblen, pbuf);
		return -1;
		}

	if ( pblen )
		*pblen = 0;

	return 0;
	}

void Base64Converter::IllegalEncoding(const char* msg)
	{
	// strncpy(error_msg, msg, sizeof(error_msg));
	if ( conn )
		conn->Weird("base64_illegal_encoding", msg);
	else
		reporter->Error("%s", msg);
	}

String* decode_base64(const String* s, const String* a, Connection* conn)
	{
	if ( a && a->Len() != 0 && a->Len() != 64 )
		{
		reporter->Error("base64 decoding alphabet is not 64 characters: %s", a->CheckString());
		return nullptr;
		}

	int buf_len = int((s->Len() + 3) / 4) * 3 + 1;
	int rlen2, rlen = buf_len;
	char *rbuf2, *rbuf = new char[rlen];

	Base64Converter dec(conn, a ? a->CheckString() : "");
	dec.Decode(s->Len(), (const char*)s->Bytes(), &rlen, &rbuf);

	if ( dec.Errored() )
		goto err;

	rlen2 = buf_len - rlen;
	rbuf2 = rbuf + rlen;
	// Done() returns -1 if there isn't enough padding, but we just ignore
	// it.
	dec.Done(&rlen2, &rbuf2);
	rlen += rlen2;

	rbuf[rlen] = '\0';
	return new String(true, (u_char*)rbuf, rlen);

err:
	delete[] rbuf;
	return nullptr;
	}

String* encode_base64(const String* s, const String* a, Connection* conn)
	{
	if ( a && a->Len() != 0 && a->Len() != 64 )
		{
		reporter->Error("base64 alphabet is not 64 characters: %s", a->CheckString());
		return nullptr;
		}

	char* outbuf = nullptr;
	int outlen = 0;
	Base64Converter enc(conn, a ? a->CheckString() : "");
	enc.Encode(s->Len(), (const unsigned char*)s->Bytes(), &outlen, &outbuf);

	return new String(true, (u_char*)outbuf, outlen);
	}

	} // namespace zeek::detail