An SMTP client and server library for Zig implementing RFC 5321.
12 kB
233 lines
1// SPDX-FileCopyrightText: © 2026 Jeffrey C. Ollie <jeff@ocjtech.us>
2// SPDX-License-Identifier: MIT
3
4const std = @import("std");
5
6// Although this function looks imperative, it does not perform the build
7// directly and instead it mutates the build graph (`b`) that will be then
8// executed by an external runner. The functions in `std.Build` implement a DSL
9// for defining build steps and express dependencies between them, allowing the
10// build runner to parallelize the build automatically (and the cache system to
11// know when a step doesn't need to be re-run).
12pub fn build(b: *std.Build) void {
13 // Standard target options allow the person running `zig build` to choose
14 // what target to build for. Here we do not override the defaults, which
15 // means any target is allowed, and the default is native. Other options
16 // for restricting supported target set are available.
17 const target = b.standardTargetOptions(.{});
18 // Standard optimization options allow the person running `zig build` to select
19 // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
20 // set a preferred release mode, allowing the user to decide how to optimize.
21 const optimize = b.standardOptimizeOption(.{});
22 // It's also possible to define more custom flags to toggle optional features
23 // of this build script using `b.option()`. All defined flags (including
24 // target and optimize options) will be listed when running `zig build --help`
25 // in this directory.
26
27 // This creates a module, which represents a collection of source files alongside
28 // some compilation options, such as optimization mode and linked system libraries.
29 // Zig modules are the preferred way of making Zig code available to consumers.
30 // addModule defines a module that we intend to make available for importing
31 // to our consumers. We must give it a name because a Zig package can expose
32 // multiple modules and consumers will need to be able to specify which
33 // module they want to access.
34 // SASL mechanisms (PLAIN, LOGIN, CRAM-MD5, XOAUTH2, ...) live outside
35 // this library, so that SMTP, POP3 and IMAP clients share one
36 // implementation of each instead of keeping three.
37 const sasl_dep = b.dependency("sasl", .{
38 .target = target,
39 .optimize = optimize,
40 });
41
42 const tls_dep = b.dependency("tls", .{
43 .target = target,
44 .optimize = optimize,
45 });
46
47 const mod = b.addModule("smtp", .{
48 // The root source file is the "entry point" of this module. Users of
49 // this module will only be able to access public declarations contained
50 // in this file, which means that if you have declarations that you
51 // intend to expose to consumers that were defined in other files part
52 // of this module, you will have to make sure to re-export them from
53 // the root file.
54 .root_source_file = b.path("src/root.zig"),
55 // Later on we'll use this module as the root module of a test executable
56 // which requires us to specify a target.
57 .target = target,
58 .imports = &.{
59 .{ .name = "tls", .module = tls_dep.module("tls") },
60 .{ .name = "sasl", .module = sasl_dep.module("sasl") },
61 },
62 });
63
64 // Here we define an executable. An executable needs to have a root module
65 // which needs to expose a `main` function. While we could add a main function
66 // to the module defined above, it's sometimes preferable to split business
67 // logic and the CLI into two separate modules.
68 //
69 // If your goal is to create a Zig library for others to use, consider if
70 // it might benefit from also exposing a CLI tool. A parser library for a
71 // data serialization format could also bundle a CLI syntax checker, for example.
72 //
73 // If instead your goal is to create an executable, consider if users might
74 // be interested in also being able to embed the core functionality of your
75 // program in their own executable in order to avoid the overhead involved in
76 // subprocessing your CLI tool.
77 //
78 // If neither case applies to you, feel free to delete the declaration you
79 // don't need and to put everything under a single module.
80 const exe = b.addExecutable(.{
81 .name = "zig-smtp",
82 .root_module = b.createModule(.{
83 // b.createModule defines a new module just like b.addModule but,
84 // unlike b.addModule, it does not expose the module to consumers of
85 // this package, which is why in this case we don't have to give it a name.
86 .root_source_file = b.path("src/main.zig"),
87 // Target and optimization levels must be explicitly wired in when
88 // defining an executable or library (in the root module), and you
89 // can also hardcode a specific target for an executable or library
90 // definition if desireable (e.g. firmware for embedded devices).
91 .target = target,
92 .optimize = optimize,
93 // List of modules available for import in source files part of the
94 // root module.
95 .imports = &.{
96 // Here "smtp" is the name you will use in your source code to
97 // import this module (e.g. `@import("smtp")`). The name is
98 // repeated because you are allowed to rename your imports, which
99 // can be extremely useful in case of collisions (which can happen
100 // importing modules from different packages).
101 .{ .name = "smtp", .module = mod },
102 },
103 }),
104 });
105
106 // This declares intent for the executable to be installed into the
107 // install prefix when running `zig build` (i.e. when executing the default
108 // step). By default the install prefix is `zig-out/` but can be overridden
109 // by passing `--prefix` or `-p`.
110 b.installArtifact(exe);
111
112 // This creates a top level step. Top level steps have a name and can be
113 // invoked by name when running `zig build` (e.g. `zig build run`).
114 // This will evaluate the `run` step rather than the default step.
115 // For a top level step to actually do something, it must depend on other
116 // steps (e.g. a Run step, as we will see in a moment).
117 const run_step = b.step("run", "Run the app");
118
119 // This creates a RunArtifact step in the build graph. A RunArtifact step
120 // invokes an executable compiled by Zig. Steps will only be executed by the
121 // runner if invoked directly by the user (in the case of top level steps)
122 // or if another step depends on it, so it's up to you to define when and
123 // how this Run step will be executed. In our case we want to run it when
124 // the user runs `zig build run`, so we create a dependency link.
125 const run_cmd = b.addRunArtifact(exe);
126 run_step.dependOn(&run_cmd.step);
127
128 // By making the run step depend on the default step, it will be run from the
129 // installation directory rather than directly from within the cache directory.
130 run_cmd.step.dependOn(b.getInstallStep());
131
132 // This allows the user to pass arguments to the application in the build
133 // command itself, like this: `zig build run -- arg1 arg2 etc`
134 if (b.args) |args| {
135 run_cmd.addArgs(args);
136 }
137
138 const lib = b.addLibrary(.{
139 .name = "zig-smtp",
140 .root_module = mod,
141 });
142
143 const install_docs = b.addInstallDirectory(.{
144 .source_dir = lib.getEmittedDocs(),
145 .install_dir = .prefix,
146 .install_subdir = "docs",
147 });
148
149 const docs_step = b.step("docs", "Build the API docs");
150 docs_step.dependOn(&install_docs.step);
151
152 // The is_email address corpus test embeds its XML test files from the
153 // lazy isemail dependency, fetched only on demand:
154 // zig build test -Disemail-corpus
155 const isemail_corpus = b.option(bool, "isemail-corpus", "Fetch Dominic Sayers' is_email suite and run the address corpus test") orelse false;
156 var isemail_available = false;
157 if (isemail_corpus) {
158 if (b.lazyDependency("isemail", .{})) |isemail_dep| {
159 mod.addAnonymousImport("isemail_tests_xml", .{
160 .root_source_file = isemail_dep.path("test/tests.xml"),
161 });
162 mod.addAnonymousImport("isemail_tests_original_xml", .{
163 .root_source_file = isemail_dep.path("test/tests-original.xml"),
164 });
165 isemail_available = true;
166 }
167 }
168 const test_options = b.addOptions();
169 test_options.addOption(bool, "isemail_corpus", isemail_available);
170 mod.addOptions("build_options", test_options);
171
172 // Exim's scriptable SMTP test client, handy for driving the zig-smtp
173 // server through raw protocol dialogues with reply expectations (see
174 // test/protocol-torture.script). Guarded by an option so the lazy exim
175 // dependency is only fetched on demand:
176 // zig build -Dexim-client && ./zig-out/bin/exim-client <host> <port>
177 if (b.option(bool, "exim-client", "Build exim's scriptable SMTP test client (fetches the exim source)") orelse false) {
178 if (b.lazyDependency("exim", .{})) |exim_dep| {
179 const exim_client = b.addExecutable(.{
180 .name = "exim-client",
181 .root_module = b.createModule(.{
182 .target = target,
183 .optimize = optimize,
184 .link_libc = true,
185 }),
186 });
187 exim_client.root_module.addCSourceFile(.{
188 .file = exim_dep.path("test/src/client.c"),
189 .flags = &.{"-w"},
190 });
191 b.installArtifact(exim_client);
192 }
193 }
194
195 // Creates an executable that will run `test` blocks from the provided module.
196 // Here `mod` needs to define a target, which is why earlier we made sure to
197 // set the releative field.
198 const mod_tests = b.addTest(.{
199 .root_module = mod,
200 });
201
202 // A run step that will run the test executable.
203 const run_mod_tests = b.addRunArtifact(mod_tests);
204
205 // Creates an executable that will run `test` blocks from the executable's
206 // root module. Note that test executables only test one module at a time,
207 // hence why we have to create two separate ones.
208 const exe_tests = b.addTest(.{
209 .root_module = exe.root_module,
210 });
211
212 // A run step that will run the second test executable.
213 const run_exe_tests = b.addRunArtifact(exe_tests);
214
215 // A top level step for running all tests. dependOn can be called multiple
216 // times and since the two run steps do not depend on one another, this will
217 // make the two of them run in parallel.
218 const test_step = b.step("test", "Run tests");
219 test_step.dependOn(&run_mod_tests.step);
220 test_step.dependOn(&run_exe_tests.step);
221
222 // Just like flags, top level steps are also listed in the `--help` menu.
223 //
224 // The Zig build system is entirely implemented in userland, which means
225 // that it cannot hook into private compiler APIs. All compilation work
226 // orchestrated by the build system will result in other Zig compiler
227 // subcommands being invoked with the right flags defined. You can observe
228 // these invocations when one fails (or you pass a flag to increase
229 // verbosity) to validate assumptions and diagnose problems.
230 //
231 // Lastly, the Zig build system is relatively simple and self-contained,
232 // and reading its source code will allow you to master it.
233}