src/msgbuf.h

/* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later */
#ifndef PLDM_MSGBUF_H
#define PLDM_MSGBUF_H

#include "compiler.h"

/*
 * Historically, many of the structs exposed in libpldm's public headers are
 * defined with __attribute__((packed)). This is unfortunate: it gives the
 * impression that a wire-format buffer can be cast to the message type to make
 * the message's fields easily accessible. As it turns out, that's not
 * that's valid for several reasons:
 *
 * 1. Casting the wire-format buffer to a struct of the message type doesn't
 *    abstract the endianness of message field values
 *
 * 2. Some messages contain packed tagged union fields which cannot be properly
 *    described in a C struct.
 *
 * The msgbuf APIs exist to assist with (un)packing the wire-format in a way
 * that is type-safe, spatially memory-safe, endian-safe, performant, and
 * free of undefined-behaviour. Message structs that are added to the public
 * library API should no-longer be marked __attribute__((packed)), and the
 * implementation of their encode and decode functions must exploit the msgbuf
 * API.
 *
 * However, we would like to allow implementation of codec functions in terms of
 * msgbuf APIs even if they're decoding a message into a (historically) packed
 * struct. Some of the complexity that follows is a consequence of the packed/
 * unpacked conflict.
 */

#ifdef __cplusplus
/*
 * Fix up C11's _Static_assert() vs C++'s static_assert().
 *
 * Can we please have nice things for once.
 */
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
#define _Static_assert(...) static_assert(__VA_ARGS__)
extern "C" {
#endif

#include <libpldm/base.h>
#include <libpldm/pldm_types.h>

#include "compiler.h"

#include <assert.h>
#include <endian.h>
#include <errno.h>
#include <limits.h>
#include <stdbool.h>
#include <stdint.h>
#include <string.h>
#include <sys/types.h>
#include <uchar.h>

/*
 * We can't use static_assert() outside of some other C construct. Deal
 * with high-level global assertions by burying them in an unused struct
 * declaration, that has a sole member for compliance with the requirement that
 * types must have a size.
*/
static struct {
	static_assert(
		INTMAX_MAX != SIZE_MAX,
		"Extraction and insertion value comparisons may be broken");
	static_assert(INTMAX_MIN + INTMAX_MAX <= 0,
		      "Extraction and insertion arithmetic may be broken");
	int compliance;
} build_assertions LIBPLDM_CC_UNUSED;

struct pldm_msgbuf {
	uint8_t *cursor;
	intmax_t remaining;
};

/**
 * @brief Initialize pldm buf struct for buf extractor
 *
 * @param[out] ctx - pldm_msgbuf context for extractor
 * @param[in] minsize - The minimum required length of buffer `buf`
 * @param[in] buf - buffer to be extracted
 * @param[in] len - size of buffer
 *
 * @return 0 on success, otherwise an error code appropriate for the current
 *         personality.
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE
LIBPLDM_CC_WARN_UNUSED_RESULT
int
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
pldm_msgbuf_init_errno(struct pldm_msgbuf *ctx, size_t minsize, const void *buf,
		       size_t len)
{
	if ((minsize > len)) {
		return -EOVERFLOW;
	}

#if INTMAX_MAX < SIZE_MAX
	if (len > INTMAX_MAX) {
		return -EOVERFLOW;
	}
#endif

	if (UINTPTR_MAX - (uintptr_t)buf < len) {
		return -EOVERFLOW;
	}

	ctx->cursor = (uint8_t *)buf;
	ctx->remaining = (intmax_t)len;

	return 0;
}

/**
 * @brief Validate buffer overflow state
 *
 * @param[in] ctx - pldm_msgbuf context for extractor
 *
 * @return PLDM_SUCCESS if there are zero or more bytes of data that remain
 * unread from the buffer. Otherwise, PLDM_ERROR_INVALID_LENGTH indicates that a
 * prior accesses would have occurred beyond the bounds of the buffer, and
 * PLDM_ERROR_INVALID_DATA indicates that the provided context was not a valid
 * pointer.
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE
LIBPLDM_CC_WARN_UNUSED_RESULT
int pldm_msgbuf_validate(struct pldm_msgbuf *ctx)
{
	if (ctx->remaining < 0) {
		return -EOVERFLOW;
	}

	return 0;
}

/**
 * @brief Test whether a message buffer has been exactly consumed
 *
 * @param[in] ctx - pldm_msgbuf context for extractor
 *
 * @return 0 iff there are zero bytes of data that remain unread from the buffer
 * and no overflow has occurred. Otherwise, -EBADMSG if the buffer has not been
 * completely consumed, or -EOVERFLOW if accesses were attempted beyond the
 * bounds of the buffer.
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE
LIBPLDM_CC_WARN_UNUSED_RESULT
int pldm_msgbuf_consumed(struct pldm_msgbuf *ctx)
{
	if (ctx->remaining > 0) {
		return -EBADMSG;
	}

	if (ctx->remaining < 0) {
		return -EOVERFLOW;
	}

	return 0;
}

/**
 * @brief Complete the pldm_msgbuf instance
 *
 * @param[in] ctx - pldm_msgbuf context for extractor
 *
 * @return 0 if all buffer accesses were in-bounds, -EOVERFLOW otherwise.
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE
LIBPLDM_CC_WARN_UNUSED_RESULT
int pldm_msgbuf_complete(struct pldm_msgbuf *ctx)
{
	int valid;

	valid = pldm_msgbuf_validate(ctx);

	ctx->cursor = NULL;
	ctx->remaining = 0;

	return valid;
}

/**
 * @brief Complete the pldm_msgbuf instance, and check that the underlying buffer
 * has been entirely consumed without overflow
 *
 * @param[in] ctx - pldm_msgbuf context
 *
 * @return 0 if all buffer access were in-bounds and completely consume the
 * underlying buffer. Otherwise, -EBADMSG if the buffer has not been completely
 * consumed, or -EOVERFLOW if accesses were attempted beyond the bounds of the
 * buffer.
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE
LIBPLDM_CC_WARN_UNUSED_RESULT
int pldm_msgbuf_complete_consumed(struct pldm_msgbuf *ctx)
{
	int consumed;

	consumed = pldm_msgbuf_consumed(ctx);

	ctx->cursor = NULL;
	ctx->remaining = 0;

	return consumed;
}

/*
 * Exploit the pre-processor to perform type checking by macro substitution.
 *
 * A C type is defined by its alignment as well as its object
 * size, and compilers have a hammer to enforce it in the form of
 * `-Waddress-of-packed-member`. Due to the unpacked/packed struct conflict in
 * the libpldm public API this presents a problem: Naively attempting to use the
 * msgbuf APIs on a member of a packed struct would yield an error.
 *
 * The msgbuf APIs are implemented such that data is moved through unaligned
 * pointers in a safe way, but to mitigate `-Waddress-of-packed-member` we must
 * make the object pointers take a trip through `void *` at its API boundary.
 * That presents a bit too much of an opportunity to non-surgically remove your
 * own foot, so here we set about doing something to mitigate that as well.
 *
 * pldm_msgbuf_extract_typecheck() exists to enforce pointer type correctness
 * only for the purpose of object sizes, disregarding alignment. We have a few
 * constraints that cause some headaches:
 *
 * 1. We have to perform the type-check before a call through a C function,
 *    as the function must take the object pointer argument as `void *`.
 *    Essentially, this constrains us to doing something with macros.
 *
 * 2. While libpldm is a C library, its test suite is written in C++ to take
 *    advantage of gtest.
 *
 * 3. Ideally we'd do something with C's `static_assert()`, however
 *    `static_assert()` is defined as void, and as we're constrained to macros,
 *    using `static_assert()` would require a statement-expression
 *
 * 4. Currently the project is built with `-std=c17`. CPP statement-expressions
 *    are a GNU extension. We prefer to avoid switching to `-std=gnu17` just for
 *    the purpose of enabling statement-expressions in this one instance.
 *
 * 5. We can achieve a conditional build error using `pldm_require_obj_type()`,
 *    however it's implemented in terms of `_Generic()`, which is not available
 *    in C++.
 *
 * Combined this means we need separate solutions for C and C++.
 *
 * For C, as we don't have statement-expressions, we need to exploit some other
 * language feature to inject a `pldm_require_obj_type()` prior to the msgbuf
 * API function call. We also have to take care of the fact that the call-sites
 * may be in the context of a variable assignment for error-handling purposes.
 * The key observation is that we can use the comma operator as a sequence point
 * to order the type check before the API call, discarding the "result" value of
 * the type check and yielding the return value of the API call.
 *
 * C++ could be less of a headache than the C as we can leverage template
 * functions. An advantage of template functions is that while their definition
 * is driven by instantion, the definition does not appear at the source
 * location of the instantiation, which gives it a great leg-up over the problems
 * we have in the C path. However, the use of the msgbuf APIs in the test suite
 * still makes things somewhat tricky, as the call-sites in the test suite are
 * wrapped up in EXPECT_*() gtest macros. Ideally we'd implement functions that
 * takes both the object type and the required type as template arguments, and
 * then define the object pointer parameter as `void *` for a call through to
 * the appropriate msgbuf API. However, because the msgbuf API call-sites are
 * encapsulated in gtest macros, use of commas in the template specification
 * causes pre-processor confusion. In this way we're constrained to only one
 * template argument per function.
 *
 * Implement the C++ path using template functions that take the destination
 * object type as a template argument, while the name of the function symbols
 * are derived from the required type. The manual implementations of these
 * appear at the end of the header. The type safety is actually enforced
 * by `static_assert()` this time, as we can use statements as we're not
 * constrained to an expression in the templated function body.
 *
 * The invocations of pldm_msgbuf_extract_typecheck() typically result in
 * double-evaluation of some arguments. We're not yet bothered by this for two
 * reasons:
 *
 * 1. The nature of the current call-sites are such that there are no
 *    argument expressions that result in undesirable side-effects
 *
 * 2. It's an API internal to the libpldm implementation, and we can fix things
 *    whenever something crops up the violates the observation in 1.
 */
#ifdef __cplusplus
#define pldm_msgbuf_extract_typecheck(ty, fn, dst, ...)                        \
	pldm_msgbuf_typecheck_##ty<decltype(dst)>(__VA_ARGS__)
#else
#define pldm_msgbuf_extract_typecheck(ty, fn, dst, ...)                        \
	(pldm_require_obj_type(dst, ty), fn(__VA_ARGS__))
#endif

/**
 * @brief pldm_msgbuf extractor for a uint8_t
 *
 * @param[in,out] ctx - pldm_msgbuf context for extractor
 * @param[out] dst - destination of extracted value
 *
 * @return PLDM_SUCCESS if buffer accesses were in-bounds,
 * PLDM_ERROR_INVALID_LENGTH otherwise.
 * PLDM_ERROR_INVALID_DATA if input a invalid ctx
 */
#define pldm_msgbuf_extract_uint8(ctx, dst)                                    \
	pldm_msgbuf_extract_typecheck(uint8_t, pldm__msgbuf_extract_uint8,     \
				      dst, ctx, (void *)&(dst))
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
pldm__msgbuf_extract_uint8(struct pldm_msgbuf *ctx, void *dst)
{
	if (!ctx->cursor) {
		return -EINVAL;
	}

	if (ctx->remaining >= (intmax_t)sizeof(uint8_t)) {
		memcpy(dst, ctx->cursor, sizeof(uint8_t));
		ctx->cursor++;
		ctx->remaining -= sizeof(uint8_t);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(uint8_t)) {
		ctx->remaining -= sizeof(uint8_t);
	}

	return -EOVERFLOW;
}

#define pldm_msgbuf_extract_int8(ctx, dst)                                     \
	pldm_msgbuf_extract_typecheck(int8_t, pldm__msgbuf_extract_int8, dst,  \
				      ctx, (void *)&(dst))
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
pldm__msgbuf_extract_int8(struct pldm_msgbuf *ctx, void *dst)
{
	if (!ctx->cursor) {
		return -EINVAL;
	}

	if (ctx->remaining >= (intmax_t)sizeof(int8_t)) {
		memcpy(dst, ctx->cursor, sizeof(int8_t));
		ctx->cursor++;
		ctx->remaining -= sizeof(int8_t);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(int8_t)) {
		ctx->remaining -= sizeof(int8_t);
	}

	return -EOVERFLOW;
}

#define pldm_msgbuf_extract_uint16(ctx, dst)                                   \
	pldm_msgbuf_extract_typecheck(uint16_t, pldm__msgbuf_extract_uint16,   \
				      dst, ctx, (void *)&(dst))
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
pldm__msgbuf_extract_uint16(struct pldm_msgbuf *ctx, void *dst)
{
	uint16_t ldst;

	if (!ctx->cursor) {
		return -EINVAL;
	}

	// Check for underflow while tracking the magnitude of the buffer overflow
	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(ldst) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(ldst)) {
		// Use memcpy() to have the compiler deal with any alignment
		// issues on the target architecture
		memcpy(&ldst, ctx->cursor, sizeof(ldst));

		// Only assign the target value once it's correctly decoded
		ldst = le16toh(ldst);

		// Allow storing to unaligned
		memcpy(dst, &ldst, sizeof(ldst));

		ctx->cursor += sizeof(ldst);
		ctx->remaining -= sizeof(ldst);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(ldst)) {
		ctx->remaining -= sizeof(ldst);
	}

	return -EOVERFLOW;
}

#define pldm_msgbuf_extract_int16(ctx, dst)                                    \
	pldm_msgbuf_extract_typecheck(int16_t, pldm__msgbuf_extract_int16,     \
				      dst, ctx, (void *)&(dst))
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
pldm__msgbuf_extract_int16(struct pldm_msgbuf *ctx, void *dst)
{
	int16_t ldst;

	if (!ctx->cursor) {
		return -EINVAL;
	}

	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(ldst) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(ldst)) {
		memcpy(&ldst, ctx->cursor, sizeof(ldst));
		ldst = le16toh(ldst);
		memcpy(dst, &ldst, sizeof(ldst));
		ctx->cursor += sizeof(ldst);
		ctx->remaining -= sizeof(ldst);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(ldst)) {
		ctx->remaining -= sizeof(ldst);
	}

	return -EOVERFLOW;
}

#define pldm_msgbuf_extract_uint32(ctx, dst)                                   \
	pldm_msgbuf_extract_typecheck(uint32_t, pldm__msgbuf_extract_uint32,   \
				      dst, ctx, (void *)&(dst))
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
pldm__msgbuf_extract_uint32(struct pldm_msgbuf *ctx, void *dst)
{
	uint32_t ldst;

	if (!ctx->cursor) {
		return -EINVAL;
	}

	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(ldst) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(ldst)) {
		memcpy(&ldst, ctx->cursor, sizeof(ldst));
		ldst = le32toh(ldst);
		memcpy(dst, &ldst, sizeof(ldst));
		ctx->cursor += sizeof(ldst);
		ctx->remaining -= sizeof(ldst);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(ldst)) {
		ctx->remaining -= sizeof(ldst);
	}

	return -EOVERFLOW;
}

#define pldm_msgbuf_extract_int32(ctx, dst)                                    \
	pldm_msgbuf_extract_typecheck(int32_t, pldm__msgbuf_extract_int32,     \
				      dst, ctx, (void *)&(dst))
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
pldm__msgbuf_extract_int32(struct pldm_msgbuf *ctx, void *dst)
{
	int32_t ldst;

	if (!ctx->cursor) {
		return -EINVAL;
	}

	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(ldst) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(ldst)) {
		memcpy(&ldst, ctx->cursor, sizeof(ldst));
		ldst = le32toh(ldst);
		memcpy(dst, &ldst, sizeof(ldst));
		ctx->cursor += sizeof(ldst);
		ctx->remaining -= sizeof(ldst);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(ldst)) {
		ctx->remaining -= sizeof(ldst);
	}

	return -EOVERFLOW;
}

#define pldm_msgbuf_extract_real32(ctx, dst)                                   \
	pldm_msgbuf_extract_typecheck(real32_t, pldm__msgbuf_extract_real32,   \
				      dst, ctx, (void *)&(dst))
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
pldm__msgbuf_extract_real32(struct pldm_msgbuf *ctx, void *dst)
{
	uint32_t ldst;

	static_assert(sizeof(real32_t) == sizeof(ldst),
		      "Mismatched type sizes for dst and ldst");

	if (!ctx->cursor) {
		return -EINVAL;
	}

	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(ldst) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(ldst)) {
		memcpy(&ldst, ctx->cursor, sizeof(ldst));
		ldst = le32toh(ldst);
		memcpy(dst, &ldst, sizeof(ldst));
		ctx->cursor += sizeof(ldst);
		ctx->remaining -= sizeof(ldst);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(ldst)) {
		ctx->remaining -= sizeof(ldst);
	}

	return -EOVERFLOW;
}

/**
 * Extract the field at the msgbuf cursor into the lvalue named by dst.
 *
 * @param ctx The msgbuf context object
 * @param dst The lvalue into which the field at the msgbuf cursor should be
 *            extracted
 *
 * @return PLDM_SUCCESS on success, otherwise another value on error
 */
#define pldm_msgbuf_extract(ctx, dst)                                          \
	_Generic((dst),                                                        \
		uint8_t: pldm__msgbuf_extract_uint8,                           \
		int8_t: pldm__msgbuf_extract_int8,                             \
		uint16_t: pldm__msgbuf_extract_uint16,                         \
		int16_t: pldm__msgbuf_extract_int16,                           \
		uint32_t: pldm__msgbuf_extract_uint32,                         \
		int32_t: pldm__msgbuf_extract_int32,                           \
		real32_t: pldm__msgbuf_extract_real32)(ctx, (void *)&(dst))

/**
 * Extract the field at the msgbuf cursor into the object pointed-to by dst.
 *
 * @param ctx The msgbuf context object
 * @param dst The pointer to the object into which the field at the msgbuf
 *            cursor should be extracted
 *
 * @return PLDM_SUCCESS on success, otherwise another value on error
 */
#define pldm_msgbuf_extract_p(ctx, dst)                                        \
	_Generic((dst),                                                        \
		uint8_t *: pldm__msgbuf_extract_uint8,                         \
		int8_t *: pldm__msgbuf_extract_int8,                           \
		uint16_t *: pldm__msgbuf_extract_uint16,                       \
		int16_t *: pldm__msgbuf_extract_int16,                         \
		uint32_t *: pldm__msgbuf_extract_uint32,                       \
		int32_t *: pldm__msgbuf_extract_int32,                         \
		real32_t *: pldm__msgbuf_extract_real32)(ctx, dst)

/**
 * @ref pldm_msgbuf_extract_array
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_WARN_UNUSED_RESULT
LIBPLDM_CC_ALWAYS_INLINE int
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
pldm__msgbuf_extract_array_void(struct pldm_msgbuf *ctx, size_t count,
				void *dst, size_t dst_count)
{
	if (!ctx->cursor || count > dst_count) {
		return -EINVAL;
	}

	if (!count) {
		return 0;
	}

#if INTMAX_MAX < SIZE_MAX
	if (count > INTMAX_MAX) {
		return -EOVERFLOW;
	}
#endif

	if (ctx->remaining >= (intmax_t)count) {
		memcpy(dst, ctx->cursor, count);
		ctx->cursor += count;
		ctx->remaining -= (intmax_t)count;
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)count) {
		ctx->remaining -= (intmax_t)count;
	}

	return -EOVERFLOW;
}

/**
 * @ref pldm_msgbuf_extract_array
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_WARN_UNUSED_RESULT
LIBPLDM_CC_ALWAYS_INLINE int
pldm_msgbuf_extract_array_char(struct pldm_msgbuf *ctx, size_t count, char *dst,
			       size_t dst_count)
{
	return pldm__msgbuf_extract_array_void(ctx, count, dst, dst_count);
}

/**
 * @ref pldm_msgbuf_extract_array
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_WARN_UNUSED_RESULT
LIBPLDM_CC_ALWAYS_INLINE int
pldm_msgbuf_extract_array_uint8(struct pldm_msgbuf *ctx, size_t count,
				uint8_t *dst, size_t dst_count)
{
	return pldm__msgbuf_extract_array_void(ctx, count, dst, dst_count);
}

/**
 * Extract an array of data from the msgbuf instance
 *
 * @param ctx - The msgbuf instance from which to extract an array of data
 * @param count - The number of array elements to extract
 * @param dst - The array object into which elements from @p ctx should be
                extracted
 * @param dst_count - The maximum number of elements to place into @p dst
 *
 * Note that both @p count and @p dst_count can only be counted by `sizeof` for
 * arrays where `sizeof(*dst) == 1` holds. Specifically, they count the number
 * of array elements and _not_ the object size of the array.
 */
#define pldm_msgbuf_extract_array(ctx, count, dst, dst_count)                  \
	_Generic((*(dst)),                                                     \
		uint8_t: pldm_msgbuf_extract_array_uint8,                      \
		char: pldm_msgbuf_extract_array_char)(ctx, count, dst,         \
						      dst_count)

LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int pldm_msgbuf_insert_uint64(struct pldm_msgbuf *ctx,
						       const uint64_t src)
{
	uint64_t val = htole64(src);

	if (!ctx->cursor) {
		return -EINVAL;
	}

	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(src) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(src)) {
		memcpy(ctx->cursor, &val, sizeof(val));
		ctx->cursor += sizeof(src);
		ctx->remaining -= sizeof(src);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(src)) {
		ctx->remaining -= sizeof(src);
	}

	return -EOVERFLOW;
}

LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int pldm_msgbuf_insert_uint32(struct pldm_msgbuf *ctx,
						       const uint32_t src)
{
	uint32_t val = htole32(src);

	if (!ctx->cursor) {
		return -EINVAL;
	}

	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(src) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(src)) {
		memcpy(ctx->cursor, &val, sizeof(val));
		ctx->cursor += sizeof(src);
		ctx->remaining -= sizeof(src);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(src)) {
		ctx->remaining -= sizeof(src);
	}

	return -EOVERFLOW;
}

LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int pldm_msgbuf_insert_uint16(struct pldm_msgbuf *ctx,
						       const uint16_t src)
{
	uint16_t val = htole16(src);

	if (!ctx->cursor) {
		return -EINVAL;
	}

	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(src) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(src)) {
		memcpy(ctx->cursor, &val, sizeof(val));
		ctx->cursor += sizeof(src);
		ctx->remaining -= sizeof(src);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(src)) {
		ctx->remaining -= sizeof(src);
	}

	return -EOVERFLOW;
}

LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int pldm_msgbuf_insert_uint8(struct pldm_msgbuf *ctx,
						      const uint8_t src)
{
	if (!ctx->cursor) {
		return -EINVAL;
	}

	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(src) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(src)) {
		memcpy(ctx->cursor, &src, sizeof(src));
		ctx->cursor += sizeof(src);
		ctx->remaining -= sizeof(src);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(src)) {
		ctx->remaining -= sizeof(src);
	}

	return -EOVERFLOW;
}

LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int pldm_msgbuf_insert_int32(struct pldm_msgbuf *ctx,
						      const int32_t src)
{
	int32_t val = htole32(src);

	if (!ctx->cursor) {
		return -EINVAL;
	}

	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(src) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(src)) {
		memcpy(ctx->cursor, &val, sizeof(val));
		ctx->cursor += sizeof(src);
		ctx->remaining -= sizeof(src);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(src)) {
		ctx->remaining -= sizeof(src);
	}

	return -EOVERFLOW;
}

LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int pldm_msgbuf_insert_int16(struct pldm_msgbuf *ctx,
						      const int16_t src)
{
	int16_t val = htole16(src);

	if (!ctx->cursor) {
		return -EINVAL;
	}

	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(src) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(src)) {
		memcpy(ctx->cursor, &val, sizeof(val));
		ctx->cursor += sizeof(src);
		ctx->remaining -= sizeof(src);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(src)) {
		ctx->remaining -= sizeof(src);
	}

	return -EOVERFLOW;
}

LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int pldm_msgbuf_insert_int8(struct pldm_msgbuf *ctx,
						     const int8_t src)
{
	if (!ctx->cursor) {
		return -EINVAL;
	}

	static_assert(
		// NOLINTNEXTLINE(bugprone-sizeof-expression)
		sizeof(src) < INTMAX_MAX,
		"The following addition may not uphold the runtime assertion");

	if (ctx->remaining >= (intmax_t)sizeof(src)) {
		memcpy(ctx->cursor, &src, sizeof(src));
		ctx->cursor += sizeof(src);
		ctx->remaining -= sizeof(src);
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)sizeof(src)) {
		ctx->remaining -= sizeof(src);
	}

	return -EOVERFLOW;
}

#define pldm_msgbuf_insert(dst, src)                                           \
	_Generic((src),                                                        \
		uint8_t: pldm_msgbuf_insert_uint8,                             \
		int8_t: pldm_msgbuf_insert_int8,                               \
		uint16_t: pldm_msgbuf_insert_uint16,                           \
		int16_t: pldm_msgbuf_insert_int16,                             \
		uint32_t: pldm_msgbuf_insert_uint32,                           \
		int32_t: pldm_msgbuf_insert_int32,                             \
		uint64_t: pldm_msgbuf_insert_uint64)(dst, src)

/**
 * @ref pldm_msgbuf_insert_array
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_WARN_UNUSED_RESULT
LIBPLDM_CC_ALWAYS_INLINE int
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
pldm__msgbuf_insert_array_void(struct pldm_msgbuf *ctx, size_t count,
			       const void *src, size_t src_count)
{
	if (!ctx->cursor || count > src_count) {
		return -EINVAL;
	}

	if (!count) {
		return 0;
	}

#if INTMAX_MAX < SIZE_MAX
	if (count > INTMAX_MAX) {
		return -EOVERFLOW;
	}
#endif

	if (ctx->remaining >= (intmax_t)count) {
		memcpy(ctx->cursor, src, count);
		ctx->cursor += count;
		ctx->remaining -= (intmax_t)count;
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)count) {
		ctx->remaining -= (intmax_t)count;
	}

	return -EOVERFLOW;
}

/**
 * @ref pldm_msgbuf_insert_array
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_WARN_UNUSED_RESULT
LIBPLDM_CC_ALWAYS_INLINE int
pldm_msgbuf_insert_array_char(struct pldm_msgbuf *ctx, size_t count,
			      const char *src, size_t src_count)
{
	return pldm__msgbuf_insert_array_void(ctx, count, src, src_count);
}

/**
 * @ref pldm_msgbuf_insert_array
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_WARN_UNUSED_RESULT
LIBPLDM_CC_ALWAYS_INLINE int
pldm_msgbuf_insert_array_uint8(struct pldm_msgbuf *ctx, size_t count,
			       const uint8_t *src, size_t src_count)
{
	return pldm__msgbuf_insert_array_void(ctx, count, src, src_count);
}

/**
 * Insert an array of data into the msgbuf instance
 *
 * @param ctx - The msgbuf instance into which the array of data should be
 *              inserted
 * @param count - The number of array elements to insert
 * @param src - The array object from which elements should be inserted into
                @p ctx
 * @param src_count - The maximum number of elements to insert from @p src
 *
 * Note that both @p count and @p src_count can only be counted by `sizeof` for
 * arrays where `sizeof(*dst) == 1` holds. Specifically, they count the number
 * of array elements and _not_ the object size of the array.
 */
#define pldm_msgbuf_insert_array(dst, count, src, src_count)                   \
	_Generic((*(src)),                                                     \
		uint8_t: pldm_msgbuf_insert_array_uint8,                       \
		char: pldm_msgbuf_insert_array_char)(dst, count, src,          \
						     src_count)

LIBPLDM_CC_NONNULL_ARGS(1)
LIBPLDM_CC_ALWAYS_INLINE int pldm_msgbuf_span_required(struct pldm_msgbuf *ctx,
						       size_t required,
						       void **cursor)
{
	if (!ctx->cursor) {
		return -EINVAL;
	}

#if INTMAX_MAX < SIZE_MAX
	if (required > INTMAX_MAX) {
		return -EOVERFLOW;
	}
#endif

	if (ctx->remaining >= (intmax_t)required) {
		if (cursor) {
			*cursor = ctx->cursor;
		}
		ctx->cursor += required;
		ctx->remaining -= (intmax_t)required;
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)required) {
		ctx->remaining -= (intmax_t)required;
	}

	return -EOVERFLOW;
}

LIBPLDM_CC_NONNULL_ARGS(1)
LIBPLDM_CC_ALWAYS_INLINE int
pldm_msgbuf_span_string_ascii(struct pldm_msgbuf *ctx, void **cursor,
			      size_t *length)
{
	intmax_t measured;

	if (!ctx->cursor) {
		return -EINVAL;
	}

	if (ctx->remaining < 0) {
		/* Tracking the amount of overflow gets disturbed here */
		return -EOVERFLOW;
	}

	measured = (intmax_t)strnlen((const char *)ctx->cursor, ctx->remaining);
	if (measured == ctx->remaining) {
		/*
		 * We have hit the end of the buffer prior to the NUL terminator.
		 * Optimistically, the NUL terminator was one-beyond-the-end. Setting
		 * ctx->remaining negative ensures the `pldm_msgbuf_complete*()` APIs also
		 * return an error.
		 */
		ctx->remaining = -1;
		return -EOVERFLOW;
	}

	/* Include the NUL terminator in the span length, as spans are opaque */
	measured++;

	if (ctx->remaining >= measured) {
		if (cursor) {
			*cursor = ctx->cursor;
		}

		ctx->cursor += measured;

		if (length) {
			*length = measured;
		}

		ctx->remaining -= measured;
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + measured) {
		ctx->remaining -= measured;
	}

	return -EOVERFLOW;
}

LIBPLDM_CC_NONNULL_ARGS(1)
LIBPLDM_CC_ALWAYS_INLINE int
pldm_msgbuf_span_string_utf16(struct pldm_msgbuf *ctx, void **cursor,
			      size_t *length)
{
	static const char16_t term = 0;
	ptrdiff_t measured;
	void *end;

	if (!ctx->cursor) {
		return -EINVAL;
	}

	if (ctx->remaining < 0) {
		/* Tracking the amount of overflow gets disturbed here */
		return -EOVERFLOW;
	}

	/*
	 * Avoid tripping up on UTF16-LE: We may have consecutive NUL _bytes_ that do
	 * not form a UTF16 NUL _code-point_ due to alignment with respect to the
	 * start of the string
	 */
	end = ctx->cursor;
	do {
		if (end != ctx->cursor) {
			/*
			 * If we've looped we've found a relatively-unaligned NUL code-point.
			 * Scan again from a relatively-aligned start point.
			 */
			end = (char *)end + 1;
		}
		measured = (char *)end - (char *)ctx->cursor;
		end = memmem(end, ctx->remaining - measured, &term,
			     sizeof(term));
	} while (end && ((uintptr_t)end & 1) != ((uintptr_t)ctx->cursor & 1));

	if (!end) {
		/*
		 * Optimistically, the last required pattern byte was one beyond the end of
		 * the buffer. Setting ctx->remaining negative ensures the
		 * `pldm_msgbuf_complete*()` APIs also return an error.
		 */
		ctx->remaining = -1;
		return -EOVERFLOW;
	}

	end = (char *)end + sizeof(char16_t);
	measured = (char *)end - (char *)ctx->cursor;

#if INTMAX_MAX < PTRDIFF_MAX
	if (measured >= INTMAX_MAX) {
		return pldm_msgbuf_status(ctx, EOVERFLOW);
	}
#endif

	if (ctx->remaining >= (intmax_t)measured) {
		if (cursor) {
			*cursor = ctx->cursor;
		}

		ctx->cursor += measured;

		if (length) {
			*length = (size_t)measured;
		}

		ctx->remaining -= (intmax_t)measured;
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)measured) {
		ctx->remaining -= (intmax_t)measured;
	}

	return -EOVERFLOW;
}

LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int
pldm_msgbuf_span_remaining(struct pldm_msgbuf *ctx, void **cursor, size_t *len)
{
	if (!ctx->cursor) {
		return -EINVAL;
	}

	if (ctx->remaining < 0) {
		return -EOVERFLOW;
	}

	*cursor = ctx->cursor;
	ctx->cursor += ctx->remaining;
	*len = ctx->remaining;
	ctx->remaining = 0;

	return 0;
}

LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int
pldm_msgbuf_peek_remaining(struct pldm_msgbuf *ctx, void **cursor, size_t *len)
{
	if (!ctx->cursor) {
		return -EINVAL;
	}

	if (ctx->remaining < 0) {
		return -EOVERFLOW;
	}

	*cursor = ctx->cursor;
	*len = ctx->remaining;

	return 0;
}

LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int pldm_msgbuf_skip(struct pldm_msgbuf *ctx,
					      size_t count)
{
	if (!ctx->cursor) {
		return -EINVAL;
	}

#if INTMAX_MAX < SIZE_MAX
	if (count > INTMAX_MAX) {
		return -EOVERFLOW;
	}
#endif

	if (ctx->remaining >= (intmax_t)count) {
		ctx->cursor += count;
		ctx->remaining -= (intmax_t)count;
		return 0;
	}

	if (ctx->remaining >= INTMAX_MIN + (intmax_t)count) {
		ctx->remaining -= (intmax_t)count;
	}

	return -EOVERFLOW;
}

/**
 * @brief Complete the pldm_msgbuf instance and return the number of bytes
 * consumed.
 *
 * @param ctx - The msgbuf.
 * @param orig_len - The original size of the msgbuf, the `len` argument passed to
 * 		pldm_msgbuf_init_errno().
 * @param ret_used_len - The number of bytes that have been used from the msgbuf instance.
 *
 * This can be called after a number of pldm_msgbuf_insert...() calls to
 * determine the total size that was written.
 *
 * @return 0 on success, -EOVERFLOW if an implausible orig_len was provided or
 * an out-of-bounds access occurred.
 */
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE
LIBPLDM_CC_WARN_UNUSED_RESULT
int pldm_msgbuf_complete_used(struct pldm_msgbuf *ctx, size_t orig_len,
			      size_t *ret_used_len)
{
	int rc;

	rc = pldm_msgbuf_validate(ctx);
	if (rc) {
		return rc;
	}

	if ((size_t)ctx->remaining > orig_len) {
		/* Caller passed incorrect orig_len */
		return -EOVERFLOW;
	}

	*ret_used_len = orig_len - ctx->remaining;
	return 0;
}

/**
 * @brief pldm_msgbuf copy data between two msg buffers
 *
 * @param[in,out] src - pldm_msgbuf for source from where value should be copied
 * @param[in,out] dst - destination of copy from source
 * @param[in] size - size of data to be copied
 * @param[in] description - description of data copied
 *
 * @return PLDM_SUCCESS if buffer accesses were in-bounds,
 * PLDM_ERROR_INVALID_LENGTH otherwise.
 * PLDM_ERROR_INVALID_DATA if input is invalid
 */
#define pldm_msgbuf_copy(dst, src, type, name)                                 \
	pldm__msgbuf_copy(dst, src, sizeof(type), #name)
LIBPLDM_CC_NONNULL
LIBPLDM_CC_ALWAYS_INLINE int
// NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
pldm__msgbuf_copy(struct pldm_msgbuf *dst, struct pldm_msgbuf *src, size_t size,
		  const char *description LIBPLDM_CC_UNUSED)
{
	if (!src->cursor || !dst->cursor) {
		return -EINVAL;
	}

#if INTMAX_MAX < SIZE_MAX
	if (size > INTMAX_MAX) {
		return -EOVERFLOW;
	}
#endif

	if (src->remaining >= (intmax_t)size &&
	    dst->remaining >= (intmax_t)size) {
		memcpy(dst->cursor, src->cursor, size);
		src->cursor += size;
		src->remaining -= (intmax_t)size;
		dst->cursor += size;
		dst->remaining -= (intmax_t)size;
		return 0;
	}

	if (src->remaining >= INTMAX_MIN + (intmax_t)size) {
		src->remaining -= (intmax_t)size;
	}

	if (dst->remaining >= INTMAX_MIN + (intmax_t)size) {
		dst->remaining -= (intmax_t)size;
	}

	return -EOVERFLOW;
}

LIBPLDM_CC_NONNULL
LIBPLDM_CC_WARN_UNUSED_RESULT
LIBPLDM_CC_ALWAYS_INLINE int
pldm_msgbuf_copy_string_ascii(struct pldm_msgbuf *dst, struct pldm_msgbuf *src)
{
	void *ascii = NULL;
	size_t len = 0;
	int rc;

	rc = pldm_msgbuf_span_string_ascii(src, &ascii, &len);
	if (rc < 0) {
		return rc;
	}

	return pldm__msgbuf_insert_array_void(dst, len, ascii, len);
}

LIBPLDM_CC_NONNULL
LIBPLDM_CC_WARN_UNUSED_RESULT
LIBPLDM_CC_ALWAYS_INLINE int
pldm_msgbuf_copy_string_utf16(struct pldm_msgbuf *dst, struct pldm_msgbuf *src)
{
	void *utf16 = NULL;
	size_t len = 0;
	int rc;

	rc = pldm_msgbuf_span_string_utf16(src, &utf16, &len);
	if (rc < 0) {
		return rc;
	}

	return pldm__msgbuf_insert_array_void(dst, len, utf16, len);
}

#ifdef __cplusplus
}
#endif

#ifdef __cplusplus
#include <type_traits>

template <typename T>
static inline int pldm_msgbuf_typecheck_uint8_t(struct pldm_msgbuf *ctx,
						void *buf)
{
	static_assert(std::is_same<uint8_t, T>::value);
	return pldm__msgbuf_extract_uint8(ctx, buf);
}

template <typename T>
static inline int pldm_msgbuf_typecheck_int8_t(struct pldm_msgbuf *ctx,
					       void *buf)
{
	static_assert(std::is_same<int8_t, T>::value);
	return pldm__msgbuf_extract_int8(ctx, buf);
}

template <typename T>
static inline int pldm_msgbuf_typecheck_uint16_t(struct pldm_msgbuf *ctx,
						 void *buf)
{
	static_assert(std::is_same<uint16_t, T>::value);
	return pldm__msgbuf_extract_uint16(ctx, buf);
}

template <typename T>
static inline int pldm_msgbuf_typecheck_int16_t(struct pldm_msgbuf *ctx,
						void *buf)
{
	static_assert(std::is_same<int16_t, T>::value);
	return pldm__msgbuf_extract_int16(ctx, buf);
}

template <typename T>
static inline int pldm_msgbuf_typecheck_uint32_t(struct pldm_msgbuf *ctx,
						 void *buf)
{
	static_assert(std::is_same<uint32_t, T>::value);
	return pldm__msgbuf_extract_uint32(ctx, buf);
}

template <typename T>
static inline int pldm_msgbuf_typecheck_int32_t(struct pldm_msgbuf *ctx,
						void *buf)
{
	static_assert(std::is_same<int32_t, T>::value);
	return pldm__msgbuf_extract_int32(ctx, buf);
}

template <typename T>
static inline int pldm_msgbuf_typecheck_real32_t(struct pldm_msgbuf *ctx,
						 void *buf)
{
	static_assert(std::is_same<real32_t, T>::value);
	return pldm__msgbuf_extract_real32(ctx, buf);
}
#endif

#endif /* BUF_H */