WWelna/cidr-rdns-zig
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William Welna
2026-05-26 22:56:09 -05:00
commit bc9e702bc7
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.gitignore
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.zig-cache
zig-out
LICENSE.md
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# The No Vibe Coders Open Source License
```
Copyright (C) 2026 William Welna (wwelna@occultusterra.com)
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following condition.
* The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
In addition, the following restrictions apply:
* The software, either in source or compiled binary form, with or without any
modification, may not be used with or incorporated into any other software
that used an Artificial Intelligence (AI) model and/or Large Language Model
(LLM) to generate any portion of that other software's source code, binaries,
or artwork.
* The usage of this software is not authorized in the state of California nor are
residents of California authorized to be in possession of this software, either
in source or compiled binary form.
* The usage of this software is not authorized in the state of Colorado nor are
residents of Colorado authorized to be in possession of this software, either
in source or compiled binary form.
* The usage and/or possession of this software, in either source or compiled
binary form, is not authorized in any legal jurisdiction where there is a
requirement of any age verification mechanism and/or identity verification
mechanism as a requirement to use this software under threat of criminal
and/or civil penalties.
* If the unauthorized usage of this software results in financial penalties
towards the developer, William Welna, the responsible individual, corporation,
or other legal entity agrees to fully cover said financial penalties.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
```
README.md
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# cidr-rdns
```
CIDR Reverse DNS Lookup (https://occultusterra.com/WWelna/cidr-rdns-zig)
Copyright (C) 2026 William Welna (wwelna@occultusterra.com)
Usage: cidr-rdns <ip/cidr> <optional output file>
Example: cidr-rdns 127.0.0.0/24 localrdns.json
Example: cidr-rdns 127.0.0.0/24
```
build.zig
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const std = @import("std");
pub fn build(b: *std.Build) void {
const target = b.standardTargetOptions(.{});
const optimize = b.standardOptimizeOption(.{});
const exe = b.addExecutable(.{
.name = "cidr-rdns",
.root_module = b.createModule(.{
.root_source_file = b.path("src/main.zig"),
.target = target,
.optimize = optimize,
.imports = &.{},
.link_libc = true,
}),
});
exe.use_llvm = true;
exe.use_lld = true;
exe.root_module.linkSystemLibrary("cares", .{});
b.installArtifact(exe);
const run_step = b.step("run", "Run the app");
const run_cmd = b.addRunArtifact(exe);
run_step.dependOn(&run_cmd.step);
run_cmd.step.dependOn(b.getInstallStep());
if (b.args) |args| {
run_cmd.addArgs(args);
}
const exe_tests = b.addTest(.{
.root_module = exe.root_module,
});
const run_exe_tests = b.addRunArtifact(exe_tests);
const test_step = b.step("test", "Run tests");
test_step.dependOn(&run_exe_tests.step);
}
build.zig.zon
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.{
// This is the default name used by packages depending on this one. For
// example, when a user runs `zig fetch --save <url>`, this field is used
// as the key in the `dependencies` table. Although the user can choose a
// different name, most users will stick with this provided value.
//
// It is redundant to include "zig" in this name because it is already
// within the Zig package namespace.
.name = .cidr_rdns_zig,
// This is a [Semantic Version](https://semver.org/).
// In a future version of Zig it will be used for package deduplication.
.version = "0.0.0",
// Together with name, this represents a globally unique package
// identifier. This field is generated by the Zig toolchain when the
// package is first created, and then *never changes*. This allows
// unambiguous detection of one package being an updated version of
// another.
//
// When forking a Zig project, this id should be regenerated (delete the
// field and run `zig build`) if the upstream project is still maintained.
// Otherwise, the fork is *hostile*, attempting to take control over the
// original project's identity. Thus it is recommended to leave the comment
// on the following line intact, so that it shows up in code reviews that
// modify the field.
.fingerprint = 0x60d447abe05dca5, // Changing this has security and trust implications.
// Tracks the earliest Zig version that the package considers to be a
// supported use case.
.minimum_zig_version = "0.16.0",
// This field is optional.
// Each dependency must either provide a `url` and `hash`, or a `path`.
// `zig build --fetch` can be used to fetch all dependencies of a package, recursively.
// Once all dependencies are fetched, `zig build` no longer requires
// internet connectivity.
.dependencies = .{
// See `zig fetch --save <url>` for a command-line interface for adding dependencies.
//.example = .{
// // When updating this field to a new URL, be sure to delete the corresponding
// // `hash`, otherwise you are communicating that you expect to find the old hash at
// // the new URL. If the contents of a URL change this will result in a hash mismatch
// // which will prevent zig from using it.
// .url = "https://example.com/foo.tar.gz",
//
// // This is computed from the file contents of the directory of files that is
// // obtained after fetching `url` and applying the inclusion rules given by
// // `paths`.
// //
// // This field is the source of truth; packages do not come from a `url`; they
// // come from a `hash`. `url` is just one of many possible mirrors for how to
// // obtain a package matching this `hash`.
// //
// // Uses the [multihash](https://multiformats.io/multihash/) format.
// .hash = "...",
//
// // When this is provided, the package is found in a directory relative to the
// // build root. In this case the package's hash is irrelevant and therefore not
// // computed. This field and `url` are mutually exclusive.
// .path = "foo",
//
// // When this is set to `true`, a package is declared to be lazily
// // fetched. This makes the dependency only get fetched if it is
// // actually used.
// .lazy = false,
//},
},
// Specifies the set of files and directories that are included in this package.
// Only files and directories listed here are included in the `hash` that
// is computed for this package. Only files listed here will remain on disk
// when using the zig package manager. As a rule of thumb, one should list
// files required for compilation plus any license(s).
// Paths are relative to the build root. Use the empty string (`""`) to refer to
// the build root itself.
// A directory listed here means that all files within, recursively, are included.
.paths = .{
"build.zig",
"build.zig.zon",
"src",
// For example...
//"LICENSE",
//"README.md",
},
}
src/main.zig
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// Copyright (C) 2026 William Welna (wwelna@occultusterra.com)
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following condition.
// * The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
// In addition, the following restrictions apply:
// * The software, either in source or compiled binary form, with or without any
// modification, may not be used with or incorporated into any other software
// that used an Artificial Intelligence (AI) model and/or Large Language Model
// (LLM) to generate any portion of that other software's source code, binaries,
// or artwork.
// * The usage of this software is not authorized in the state of California nor are
// residents of California authorized to be in possession of this software, either
// in source or compiled binary form.
// * The usage of this software is not authorized in the state of Colorado nor are
// residents of Colorado authorized to be in possession of this software, either
// in source or compiled binary form.
// * The usage and/or possession of this software, in either source or compiled
// binary form, is not authorized in any legal jurisdiction where there is a
// requirement of any age verification mechanism and/or identity verification
// mechanism as a requirement to use this software under threat of criminal
// and/or civil penalties.
// * If the unauthorized usage of this software results in financial penalties
// towards the developer, William Welna, the responsible individual, corporation,
// or other legal entity agrees to fully cover said financial penalties.
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
const std = @import("std");
const builtin = @import("builtin");
const c = @cImport({
@cInclude("ares.h");
@cInclude("netdb.h");
@cInclude("string.h");
@cInclude("sys/select.h");
@cInclude("sys/time.h");
});
const Entry = struct {
ip: u32,
ip_str: []u8,
hostname: []u8,
};
var global_entries: std.ArrayList(Entry) = undefined;
var global_counter: usize = undefined;
var global_ares_chan: c.ares_channel = undefined;
var allocator: std.mem.Allocator = undefined;
inline fn ip2String(ip_num: u32, buf: *[16]u8) ![]u8 {
const w = (ip_num >> 24) & 0xFF;
const x = (ip_num >> 16) & 0xFF;
const y = (ip_num >> 8) & 0xFF;
const z = ip_num & 0xFF;
const ret = try std.fmt.bufPrint(buf[0..15], "{d}.{d}.{d}.{d}", .{ w, x, y, z });
return try allocator.dupe(u8, ret);
}
inline fn String2ip(ip_str: []const u8) !u32 {
var ret: u32 = 0;
var parts = std.mem.splitScalar(u8, ip_str, '.');
var bytes: [4]u8 = undefined;
bytes[3] = try std.fmt.parseInt(u8, parts.next().?, 10);
bytes[2] = try std.fmt.parseInt(u8, parts.next().?, 10);
bytes[1] = try std.fmt.parseInt(u8, parts.next().?, 10);
bytes[0] = try std.fmt.parseInt(u8, parts.next().?, 10);
ret = @as(u32, @bitCast(bytes));
return ret;
}
fn calculateSubnet(cidr: []const u8) !struct {
start: u32,
end: u32,
total: u32,
prefix: u8,
ip_s: []u8,
ip_e: []u8,
} {
var buf: [16]u8 = undefined;
const slash = std.mem.findScalar(u8, cidr, '/') orelse 0;
const ip_str = if (slash > 0) cidr[0..slash] else cidr;
const prefix_str = if (slash > 0) cidr[slash + 1 ..] else "";
const prefix = if (slash > 0) try std.fmt.parseInt(u8, prefix_str, 10) else 0;
if (prefix > 32) return error.InvalidPrefix;
const mask: u32 = if (prefix == 0) 0 else (~@as(u32, 0)) << @as(u5, @intCast(32 - prefix));
const ip = try String2ip(ip_str);
var start: u32 = undefined;
var end: u32 = undefined;
var ip_s: []u8 = undefined;
var ip_e: []u8 = undefined;
if (prefix > 0) {
start = ip & mask;
end = start | (~mask & (~@as(u32, 0)));
ip_s = try ip2String(start, &buf);
ip_e = try ip2String(end, &buf);
} else {
start = ip;
end = ip;
ip_s = try allocator.dupe(u8, ip_str);
ip_e = ip_s;
}
const total = if (end > start) end - start + 1 else 1;
return .{
.start = start,
.end = end,
.total = total,
.prefix = prefix,
.ip_s = ip_s,
.ip_e = ip_e,
};
}
fn rdns_Callback(arg: ?*anyopaque, status: c_int, timeouts: c_int, host: ?*c.hostent) callconv(.c) void {
const entry = @as(*Entry, @ptrCast(@alignCast(arg orelse return)));
_ = timeouts;
if (status == c.ARES_SUCCESS and host != null) {
const h_name = host.?.h_name;
entry.hostname = allocator.dupe(u8, std.mem.span(h_name)) catch &[_]u8{};
}
global_counter += 1;
if (global_counter < global_entries.items.len) {
c.ares_gethostbyaddr(global_ares_chan, &global_entries.items[global_counter].ip, 4, c.AF_INET, rdns_Callback, &global_entries.items[global_counter]);
}
}
fn toFile(io: std.Io, fileName: []const u8) !void {
var file = try std.Io.Dir.cwd().createFile(io, fileName, .{});
defer file.close(io);
var buffer: [4096]u8 = undefined;
var file_writer: std.Io.File.Writer = file.writer(io, &buffer);
const writer = &file_writer.interface;
std.log.info("Opened {s} for writing.", .{fileName});
var stringify: std.json.Stringify = .{
.writer = writer,
};
for (global_entries.items) |entry| {
try stringify.write(.{ .ip_str = entry.ip_str, .hostname = entry.hostname });
try writer.writeByte('\n');
}
try writer.flush();
std.log.info("Finished writting to file.", .{});
}
pub fn main(init: std.process.Init) !void {
allocator = init.arena.allocator();
std.debug.print("CIDR Reverse DNS Lookup (https://occultusterra.com/WWelna/cidr-rdns-zig)\n", .{});
std.debug.print("Copyright (C) 2026 William Welna (wwelna@occultusterra.com)\n\n", .{});
const args = try init.minimal.args.toSlice(allocator);
const exe_name = std.fs.path.basename(args[0]);
if (args.len > 3 or args.len == 1) {
std.debug.print("Usage: {s} <ip/cidr> <optional output file>\n", .{exe_name});
std.debug.print("\tExample: {s} 127.0.0.0/24 localrdns.json\n", .{exe_name});
std.debug.print("\tExample: {s} 127.0.0.0/24\n\n", .{exe_name});
return;
}
const cidr = args[1];
if (c.ares_library_init(c.ARES_LIB_INIT_ALL) != c.ARES_SUCCESS) {
std.log.err("Error: ares_library_init() failed\n", .{});
return;
}
defer c.ares_library_cleanup();
if (c.ares_init(&global_ares_chan) != c.ARES_SUCCESS) {
std.log.err("Error: ares_init() failed\n", .{});
return;
}
defer c.ares_destroy(global_ares_chan);
const subnet = try calculateSubnet(cidr);
std.log.info("Resolving {s} → {s} ({d} IPs)", .{ subnet.ip_s, subnet.ip_e, subnet.total });
global_entries = try std.ArrayList(Entry).initCapacity(allocator, subnet.total);
var buf: [16]u8 = undefined;
for (subnet.start..subnet.end + 1) |x| {
try global_entries.append(allocator, .{ .ip = @intCast(x), .ip_str = try ip2String(@intCast(x), &buf), .hostname = "" });
}
global_counter = @min(global_entries.items.len, 60);
for (0..@min(global_entries.items.len, 60)) |x| {
c.ares_gethostbyaddr(global_ares_chan, @ptrCast(&global_entries.items[x].ip), 4, c.AF_INET, rdns_Callback, @ptrCast(&global_entries.items[x]));
}
// Resolve loop
var readfds: c.fd_set = undefined;
var writefds: c.fd_set = undefined;
var tv: c.timeval = .{
.tv_sec = 0,
.tv_usec = 100_000,
};
while (true) {
@memset(std.mem.asBytes(&readfds), 0);
@memset(std.mem.asBytes(&writefds), 0);
const nfds = c.ares_fds(global_ares_chan, &readfds, &writefds);
if (nfds == 0) break;
const tvp: ?*c.timeval = c.ares_timeout(global_ares_chan, null, &tv);
_ = c.select(nfds, &readfds, &writefds, null, tvp);
_ = c.ares_process(global_ares_chan, &readfds, &writefds);
}
std.log.info("Finished Resolving {d} IPs.", .{subnet.total});
if (args.len == 2) {
std.debug.print("\n", .{});
var stdout_buffer: [1024]u8 = undefined;
var stdout_file_writer: std.Io.File.Writer = .init(.stdout(), init.io, &stdout_buffer);
const stdout_writer = &stdout_file_writer.interface;
for (global_entries.items) |entry| {
try stdout_writer.print("{s} -> {s}\n", .{ entry.ip_str, entry.hostname });
}
try stdout_writer.flush();
} else if (args.len == 3) {
try toFile(init.io, args[2]);
} else {}
}