Add Wireshark Lua dissector generator backend for Emboss

build_defs.bzl

@@ -22,9 +22,12 @@ cc_emboss_library, which creates a header file and can be used as a dep in a
 
 There is also a convenience macro, `emboss_cc_library()`, which creates an
 `emboss_library` and a `cc_emboss_library` based on it.
+
+For Wireshark Lua dissector generation, use `emboss_lua_library()`.
 """
 
 load("@bazel_tools//tools/cpp:toolchain_utils.bzl", "find_cpp_toolchain")
+load("//compiler/back_end/lua:build_defs.bzl", _lua_emboss_library = "lua_emboss_library")
 
 def emboss_cc_library(name, srcs, deps = [], import_dirs = [], enable_enum_traits = True, **kwargs):
     """Constructs a C++ library from an .emb file."""
@@ -257,3 +260,33 @@ cc_emboss_library = rule(
     },
     provides = [CcInfo, EmbossInfo],
 )
+
+def emboss_lua_library(name, srcs, deps = [], import_dirs = [], **kwargs):
+    """Constructs a Wireshark Lua dissector from an .emb file.
+
+    Args:
+        name: The name of the library.
+        srcs: List of .emb source files (must be exactly one).
+        deps: List of emboss_library dependencies.
+        import_dirs: List of import directories.
+        **kwargs: Additional arguments.
+    """
+    if len(srcs) != 1:
+        fail(
+            "Must specify exactly one Emboss source file for emboss_lua_library.",
+            "srcs",
+        )
+
+    emboss_library(
+        name = name + "_ir",
+        srcs = srcs,
+        deps = [dep + "_ir" for dep in deps],
+        import_dirs = import_dirs,
+        **kwargs
+    )
+
+    _lua_emboss_library(
+        name = name,
+        deps = [":" + name + "_ir"],
+        **kwargs
+    )

compiler/back_end/lua/BUILD

@@ -0,0 +1,54 @@
+# Copyright 2019 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.
+
+# Emboss Wireshark Lua dissector code generator.
+
+load("@rules_python//python:py_binary.bzl", "py_binary")
+load("@rules_python//python:py_library.bzl", "py_library")
+load("@rules_python//python:py_test.bzl", "py_test")
+
+package(
+    default_visibility = [
+        "//visibility:private",
+    ],
+)
+
+py_binary(
+    name = "emboss_codegen_lua",
+    srcs = ["emboss_codegen_lua.py"],
+    python_version = "PY3",
+    visibility = ["//visibility:public"],
+    deps = [
+        ":dissector_generator",
+        "//compiler/util:ir_data",
+    ],
+)
+
+py_library(
+    name = "dissector_generator",
+    srcs = ["dissector_generator.py"],
+    deps = [
+        "//compiler/util:ir_data",
+        "//compiler/util:ir_util",
+    ],
+)
+
+py_test(
+    name = "dissector_generator_test",
+    srcs = ["dissector_generator_test.py"],
+    deps = [
+        ":dissector_generator",
+        "//compiler/util:ir_data",
+    ],
+)

compiler/back_end/lua/QUICKSTART.md

@@ -0,0 +1,146 @@
+# Quick Start Guide: Wireshark Lua Dissector Generator
+
+This guide will help you quickly generate and use Wireshark dissectors from your Emboss protocol definitions.
+
+## Step 1: Define Your Protocol in Emboss
+
+Create a `.emb` file with your protocol definition:
+
+```emboss
+# myprotocol.emb
+
+-- My custom network protocol
+[(wireshark_filter): "myproto"]
+
+[$default byte_order: "LittleEndian"]
+
+-- Packet types
+enum PacketType:
+  -- Data packet
+  DATA = 0x01
+  -- Acknowledgment
+  ACK  = 0x02
+
+-- Protocol header
+struct Header:
+  -- Packet type identifier
+  0 [+1]  PacketType  type
+  -- Packet sequence number
+  1 [+4]  UInt        seq_num
+  -- Payload length
+  5 [+2]  UInt        length
+```
+
+## Step 2: Add to Your BUILD File
+
+```python
+load("//:build_defs.bzl", "emboss_lua_library")
+
+emboss_lua_library(
+    name = "myprotocol_dissector",
+    srcs = ["myprotocol.emb"],
+)
+```
+
+## Step 3: Build the Dissector
+
+```bash
+bazel build :myprotocol_dissector
+```
+
+The generated `.lua` file will be in `bazel-bin/myprotocol.emb.lua`
+
+## Step 4: Install in Wireshark
+
+Copy the generated `.lua` file to your Wireshark plugins directory:
+
+**Linux:**
+```bash
+cp bazel-bin/myprotocol.emb.lua ~/.local/lib/wireshark/plugins/
+```
+
+**macOS:**
+```bash
+cp bazel-bin/myprotocol.emb.lua ~/.wireshark/plugins/
+```
+
+**Windows:**
+```powershell
+copy bazel-bin\myprotocol.emb.lua %APPDATA%\Wireshark\plugins\
+```
+
+## Step 5: Configure Port Registration
+
+Edit the generated `.lua` file and uncomment the registration code at the bottom:
+
+```lua
+-- Register the dissector
+local udp_table = DissectorTable.get("udp.port")
+udp_table:add(12345, myproto_proto)  -- Replace 12345 with your port
+```
+
+For TCP:
+```lua
+local tcp_table = DissectorTable.get("tcp.port")
+tcp_table:add(12345, myproto_proto)
+```
+
+## Step 6: Load in Wireshark
+
+1. Open Wireshark
+2. Reload Lua plugins: Analyze → Reload Lua Plugins (or Ctrl+Shift+L)
+3. Your dissector is now active!
+
+## Testing Your Dissector
+
+1. Capture some traffic on your configured port
+2. Wireshark should automatically use your dissector
+3. You should see your fields displayed with their names and descriptions
+4. Enum values will show as text (e.g., "DATA" instead of "0x01")
+
+## Troubleshooting
+
+**Dissector not loading?**
+- Check Wireshark's Lua console (Tools → Lua → Console) for errors
+- Verify the .lua file is in the correct plugins directory
+- Make sure you reloaded Lua plugins
+
+**Fields not displaying?**
+- Verify your port registration matches your traffic
+- Check that byte order matches your data
+- Ensure field sizes are correct in your .emb file
+
+**Want to see all available filters?**
+- In Wireshark, go to Edit → Preferences → Protocols
+- Find your protocol in the list
+- Or use the filter expression builder (Analyze → Display Filter Expression)
+
+## Advanced Features
+
+### Custom Filter Names
+
+```emboss
+struct MyStruct:
+  [(wireshark_filter): "myproto.custom"]
+  0 [+1]  UInt  field1
+    [(wireshark_filter): "myproto.special_field"]
+```
+
+### Nested Structures
+
+```emboss
+struct Inner:
+  0 [+2]  UInt  value
+
+struct Outer:
+  0 [+2]  Inner  inner_data
+  2 [+4]  UInt   other_field
+```
+
+The dissector will maintain the hierarchy.
+
+## Next Steps
+
+- See the full README.md for all features
+- Check out example_protocol.emb for a comprehensive example
+- Read about Emboss language features in the main Emboss documentation