[Thinkit] Add a packet generator headers which generates many fields.

tests/lib/BUILD.bazel

@@ -141,3 +141,40 @@ cc_library(
         "@com_google_absl//absl/synchronization",
     ],
 )
+
+cc_library(
+    name = "packet_generator",
+    testonly = True,
+    srcs = ["packet_generator.cc"],
+    hdrs = ["packet_generator.h"],
+    deps = [
+        "//gutil:proto",
+        "//gutil:status",
+        "//p4_pdpi/netaddr:ipv4_address",
+        "//p4_pdpi/netaddr:mac_address",
+        "//p4_pdpi/packetlib",
+        "//p4_pdpi/packetlib:bit_widths",
+        "//p4_pdpi/packetlib:packetlib_cc_proto",
+        "@com_google_absl//absl/container:btree",
+        "@com_google_absl//absl/numeric:int128",
+        "@com_google_absl//absl/random:distributions",
+        "@com_google_absl//absl/status:statusor",
+        "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/strings:str_format",
+    ],
+)
+
+cc_test(
+    name = "packet_generator_test",
+    srcs = ["packet_generator_test.cc"],
+    deps = [
+        ":packet_generator",
+        "//gutil:proto_matchers",
+        "//gutil:status_matchers",
+        "//p4_pdpi/packetlib",
+        "//p4_pdpi/packetlib:packetlib_cc_proto",
+        "@com_google_absl//absl/container:flat_hash_map",
+        "@com_google_absl//absl/strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)

tests/lib/packet_generator.h

@@ -0,0 +1,115 @@
+// Copyright 2024 Google LLC
+//
+// 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
+//
+//     https://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.
+
+#ifndef PINS_TESTS_LIB_PACKET_GENERATOR_H_
+#define PINS_TESTS_LIB_PACKET_GENERATOR_H_
+
+#include <net/ethernet.h>
+#include <netinet/in.h>
+
+#include <optional>
+#include <string>
+
+#include "absl/container/btree_set.h"
+#include "absl/status/statusor.h"
+#include "absl/strings/str_format.h"
+#include "absl/strings/str_join.h"
+#include "gutil/status.h"  // IWYU pragma: keep
+#include "p4_pdpi/packetlib/packetlib.pb.h"
+
+// Helper library to hold a collection of functions to define a test
+// configuration, define a packet, generate a packet etc.
+namespace pins_test {
+namespace packetgen {
+
+// Modifiable fields within a packet.
+enum class Field {
+  kEthernetSrc,
+  kEthernetDst,
+  kIpSrc,
+  kIpDst,
+  kHopLimit,
+  kDscp,
+  kFlowLabelLower16,
+  kFlowLabelUpper4,
+  kInnerIpSrc,
+  kInnerIpDst,
+  kInnerHopLimit,
+  kInnerDscp,
+  kInnerFlowLabelLower16,
+  kInnerFlowLabelUpper4,
+  kL4SrcPort,
+  kL4DstPort,
+  // Any new Field values must be added to AllFields().
+};
+
+// Returns the string name of a field.
+std::string FieldName(Field field);
+
+// Returns a list of all field enums.
+const absl::btree_set<Field>& AllFields();
+const absl::btree_set<Field>& InnerIpFields();
+
+enum class IpType { kIpv4, kIpv6 };
+
+// Options to define the packet generation behavior.
+struct Options {
+  IpType ip_type;  // IP type of the packet or outer IP type if encapped.
+  absl::btree_set<Field> variables;     // Set of fields to vary.
+  std::optional<IpType> inner_ip_type;  // Inner IP type. Required if encapped.
+};
+inline Options Ipv4PacketOptions() { return {.ip_type = IpType::kIpv4}; }
+inline Options Ipv6PacketOptions() { return {.ip_type = IpType::kIpv6}; }
+
+// Returns ok if the Options struct is valid or an error if it is invalid.
+absl::Status IsValid(const Options& options);
+
+// Returns a string describing the Options struct.
+std::string ToString(const Options& options);
+
+// Returns the number of unique values that can be generated for the field.
+int Range(Field field, IpType ip_type);
+
+// This class generates packets from the provided options. Once the packet
+// generator is created, it is expected that any Packet() call will create a
+// valid packet.
+class PacketGenerator {
+ public:
+  // Factory function.
+  static absl::StatusOr<PacketGenerator> Create(Options options) {
+    RETURN_IF_ERROR(IsValid(options));
+    return PacketGenerator(std::move(options));
+  }
+
+  // Returns a description of the generator options.
+  std::string Description() const { return ToString(options_); }
+
+  // Returns a packet at the given index. Subsequent calls for the same index
+  // will return the same packet.
+  packetlib::Packet Packet(int index = 0) const;
+
+  // Returns multiple packets with sequential indices. An offset may be given to
+  // change the starting index.
+  std::vector<packetlib::Packet> Packets(int count, int offset = 0) const;
+
+ private:
+  explicit PacketGenerator(Options options) : options_(std::move(options)) {}
+
+  const Options options_;
+};
+
+}  // namespace packetgen
+}  // namespace pins_test
+
+#endif  // PINS_TESTS_LIB_PACKET_GENERATOR_H_