core.p4

/*
Copyright 2013-present Barefoot Networks, Inc.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
    http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

/* This is the P4-16 core library, which declares some built-in P4 constructs using P4 */

#ifndef _CORE_P4_
#define _CORE_P4_

/// Standard error codes.  New error codes can be declared by users.
error {
    NoError,           /// No error.
    PacketTooShort,    /// Not enough bits in packet for 'extract'.
    NoMatch,           /// 'select' expression has no matches.
    StackOutOfBounds,  /// Reference to invalid element of a header stack.
    HeaderTooShort,    /// Extracting too many bits into a varbit field.
    ParserTimeout,     /// Parser execution time limit exceeded.
    ParserInvalidArgument  /// Parser operation was called with a value
                           /// not supported by the implementation.
}

extern packet_in {
    /// Read a header from the packet into a fixed-sized header @hdr and advance the cursor.
    /// May trigger error PacketTooShort or StackOutOfBounds.
    /// @T must be a fixed-size header type
    void extract<T>(out T hdr);
    /// Read bits from the packet into a variable-sized header @variableSizeHeader
    /// and advance the cursor.
    /// @T must be a header containing exactly 1 varbit field.
    /// May trigger errors PacketTooShort, StackOutOfBounds, or HeaderTooShort.
    void extract<T>(out T variableSizeHeader,
                    in bit<32> variableFieldSizeInBits);
    /// Read bits from the packet without advancing the cursor.
    /// @returns: the bits read from the packet.
    /// T may be an arbitrary fixed-size type.
    T lookahead<T>();
    /// Advance the packet cursor by the specified number of bits.
    void advance(in bit<32> sizeInBits);
    /// @return packet length in bytes.  This method may be unavailable on
    /// some target architectures.
    bit<32> length();
}

extern packet_out {
    /// Write @hdr into the output packet, advancing cursor.
    /// @T can be a header type, a header stack, a header_union, or a struct
    /// containing fields with such types.
    void emit<T>(in T hdr);
}

// TODO: remove from this file, convert to built-in
/// Check a predicate @check in the parser; if the predicate is true do nothing,
/// otherwise set the parser error to @toSignal, and transition to the `reject` state.
extern void verify(in bool check, in error toSignal);

/// Built-in action that does nothing.
@noWarn("unused")
action NoAction() {}

/// Standard match kinds for table key fields.
/// Some architectures may not support all these match kinds.
/// Architectures can declare additional match kinds.
match_kind {
    /// Match bits exactly.
    exact,
    /// Ternary match, using a mask.
    ternary,
    /// Longest-prefix match.
    lpm
}

/// Static assert evaluates a boolean expression
/// at compilation time.  If the expression evaluates to
/// false, compilation is stopped and the corresponding message is printed.
/// The function returns a boolean, so that it can be used
/// as a global constant value in a program, e.g.:
/// const bool _check = static_assert(V1MODEL_VERSION > 20180000, "Expected a v1 model version >= 20180000");
extern bool static_assert(bool check, string message);

/// Like the above but using a default message.
extern bool static_assert(bool check);

#endif  /* _CORE_P4_ */