src/drivers/vpd/lib_vpd.c

/*
 * Copyright (c) 2014 The Chromium OS Authors. All rights reserved.
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 *
 */
#include <assert.h>
#include "lib_vpd.h"

/* Given an encoded string, this functions decodes the length field which varies
 * from 1 byte to many bytes.
 *
 * The in points the actual byte going to be decoded. The *length returns
 * the decoded length field. The number of consumed bytes will be stroed in
 * decoded_len.
 *
 * Returns VPD_FAIL if more bit is 1, but actually reaches the end of string.
 */
int decodeLen(const int32_t max_len,
	      const uint8_t *in,
	      int32_t *length,
	      int32_t *decoded_len)
{
	uint8_t more;
	int i = 0;

	assert(length);
	assert(decoded_len);

	*length = 0;
	do {
		if (i >= max_len)
			return VPD_FAIL;

		more = in[i] & 0x80;
		*length <<= 7;
		*length |= in[i] & 0x7f;
		++i;
	} while (more);

	*decoded_len = i;

	return VPD_OK;
}

/* Given the encoded string, this function invokes callback with extracted
 * (key, value). The *consumed will be plused the number of bytes consumed in
 * this function.
 *
 * The input_buf points to the first byte of the input buffer.
 *
 * The *consumed starts from 0, which is actually the next byte to be decoded.
 * It can be non-zero to be used in multiple calls.
 *
 * If one entry is successfully decoded, sends it to callback and returns the
 * result.
 */
int decodeVpdString(const int32_t max_len,
		    const uint8_t *input_buf,
		    int32_t *consumed,
		    VpdDecodeCallback callback,
		    void *callback_arg)
{
	int type;
	int32_t key_len, value_len;
	int32_t decoded_len;
	const uint8_t *key, *value;

	/* type */
	if (*consumed >= max_len)
		return VPD_FAIL;

	type = input_buf[*consumed];
	switch (type) {
	case VPD_TYPE_INFO:
	case VPD_TYPE_STRING:
		(*consumed)++;
		/* key */
		if (VPD_OK != decodeLen(max_len - *consumed,
					&input_buf[*consumed], &key_len,
					&decoded_len) ||
				*consumed + decoded_len >= max_len) {
				return VPD_FAIL;
		}

		*consumed += decoded_len;
		key = &input_buf[*consumed];
		*consumed += key_len;

		/* value */
		if (VPD_OK != decodeLen(max_len - *consumed,
					&input_buf[*consumed],
					&value_len, &decoded_len) ||
					*consumed + decoded_len > max_len) {
					return VPD_FAIL;
		}
		*consumed += decoded_len;
		value = &input_buf[*consumed];
		*consumed += value_len;

		if (type == VPD_TYPE_STRING)
			return callback(key, key_len, value, value_len,
					callback_arg);

		return VPD_OK;

	default:
		return VPD_FAIL;
	break;
	}

	return VPD_OK;
}