An SMTP client and server library for Zig implementing RFC 5321.
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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 const mod = b.addModule("zsmtp", .{
35 // The root source file is the "entry point" of this module. Users of
36 // this module will only be able to access public declarations contained
37 // in this file, which means that if you have declarations that you
38 // intend to expose to consumers that were defined in other files part
39 // of this module, you will have to make sure to re-export them from
40 // the root file.
41 .root_source_file = b.path("src/root.zig"),
42 // Later on we'll use this module as the root module of a test executable
43 // which requires us to specify a target.
44 .target = target,
45 });
46
47 // Here we define an executable. An executable needs to have a root module
48 // which needs to expose a `main` function. While we could add a main function
49 // to the module defined above, it's sometimes preferable to split business
50 // logic and the CLI into two separate modules.
51 //
52 // If your goal is to create a Zig library for others to use, consider if
53 // it might benefit from also exposing a CLI tool. A parser library for a
54 // data serialization format could also bundle a CLI syntax checker, for example.
55 //
56 // If instead your goal is to create an executable, consider if users might
57 // be interested in also being able to embed the core functionality of your
58 // program in their own executable in order to avoid the overhead involved in
59 // subprocessing your CLI tool.
60 //
61 // If neither case applies to you, feel free to delete the declaration you
62 // don't need and to put everything under a single module.
63 const exe = b.addExecutable(.{
64 .name = "zsmtp",
65 .root_module = b.createModule(.{
66 // b.createModule defines a new module just like b.addModule but,
67 // unlike b.addModule, it does not expose the module to consumers of
68 // this package, which is why in this case we don't have to give it a name.
69 .root_source_file = b.path("src/main.zig"),
70 // Target and optimization levels must be explicitly wired in when
71 // defining an executable or library (in the root module), and you
72 // can also hardcode a specific target for an executable or library
73 // definition if desireable (e.g. firmware for embedded devices).
74 .target = target,
75 .optimize = optimize,
76 // List of modules available for import in source files part of the
77 // root module.
78 .imports = &.{
79 // Here "zsmtp" is the name you will use in your source code to
80 // import this module (e.g. `@import("zsmtp")`). The name is
81 // repeated because you are allowed to rename your imports, which
82 // can be extremely useful in case of collisions (which can happen
83 // importing modules from different packages).
84 .{ .name = "zsmtp", .module = mod },
85 },
86 }),
87 });
88
89 // This declares intent for the executable to be installed into the
90 // install prefix when running `zig build` (i.e. when executing the default
91 // step). By default the install prefix is `zig-out/` but can be overridden
92 // by passing `--prefix` or `-p`.
93 b.installArtifact(exe);
94
95 // This creates a top level step. Top level steps have a name and can be
96 // invoked by name when running `zig build` (e.g. `zig build run`).
97 // This will evaluate the `run` step rather than the default step.
98 // For a top level step to actually do something, it must depend on other
99 // steps (e.g. a Run step, as we will see in a moment).
100 const run_step = b.step("run", "Run the app");
101
102 // This creates a RunArtifact step in the build graph. A RunArtifact step
103 // invokes an executable compiled by Zig. Steps will only be executed by the
104 // runner if invoked directly by the user (in the case of top level steps)
105 // or if another step depends on it, so it's up to you to define when and
106 // how this Run step will be executed. In our case we want to run it when
107 // the user runs `zig build run`, so we create a dependency link.
108 const run_cmd = b.addRunArtifact(exe);
109 run_step.dependOn(&run_cmd.step);
110
111 // By making the run step depend on the default step, it will be run from the
112 // installation directory rather than directly from within the cache directory.
113 run_cmd.step.dependOn(b.getInstallStep());
114
115 // This allows the user to pass arguments to the application in the build
116 // command itself, like this: `zig build run -- arg1 arg2 etc`
117 if (b.args) |args| {
118 run_cmd.addArgs(args);
119 }
120
121 // Creates an executable that will run `test` blocks from the provided module.
122 // Here `mod` needs to define a target, which is why earlier we made sure to
123 // set the releative field.
124 const mod_tests = b.addTest(.{
125 .root_module = mod,
126 });
127
128 // A run step that will run the test executable.
129 const run_mod_tests = b.addRunArtifact(mod_tests);
130
131 // Creates an executable that will run `test` blocks from the executable's
132 // root module. Note that test executables only test one module at a time,
133 // hence why we have to create two separate ones.
134 const exe_tests = b.addTest(.{
135 .root_module = exe.root_module,
136 });
137
138 // A run step that will run the second test executable.
139 const run_exe_tests = b.addRunArtifact(exe_tests);
140
141 // A top level step for running all tests. dependOn can be called multiple
142 // times and since the two run steps do not depend on one another, this will
143 // make the two of them run in parallel.
144 const test_step = b.step("test", "Run tests");
145 test_step.dependOn(&run_mod_tests.step);
146 test_step.dependOn(&run_exe_tests.step);
147
148 // Just like flags, top level steps are also listed in the `--help` menu.
149 //
150 // The Zig build system is entirely implemented in userland, which means
151 // that it cannot hook into private compiler APIs. All compilation work
152 // orchestrated by the build system will result in other Zig compiler
153 // subcommands being invoked with the right flags defined. You can observe
154 // these invocations when one fails (or you pass a flag to increase
155 // verbosity) to validate assumptions and diagnose problems.
156 //
157 // Lastly, the Zig build system is relatively simple and self-contained,
158 // and reading its source code will allow you to master it.
159}