add homedir utility

src/homedir.zig

@@ -0,0 +1,91 @@
+const std = @import("std");
+const builtin = @import("builtin");
+const assert = std.debug.assert;
+const passwd = @import("passwd.zig");
+
+const Error = error{
+    /// The buffer used for output is not large enough to store the value.
+    BufferTooSmall,
+};
+
+/// Determine the home directory for the currently executing user. This
+/// is generally an expensive process so the value should be cached.
+pub inline fn home(buf: []u8) !?[]u8 {
+    return switch (builtin.os.tag) {
+        inline .linux, .macos => try homeUnix(buf),
+        else => @compileError("unimplemented"),
+    };
+}
+
+fn homeUnix(buf: []u8) !?[]u8 {
+    // First: if we have a HOME env var, then we use that.
+    if (std.os.getenv("HOME")) |result| {
+        if (buf.len < result.len) return Error.BufferTooSmall;
+        std.mem.copy(u8, buf, result);
+        return buf[0..result.len];
+    }
+
+    // Everything below here will require some allocation
+    var tempBuf: [1024]u8 = undefined;
+    var fba = std.heap.FixedBufferAllocator.init(&tempBuf);
+
+    // If we're on darwin, we try the directory service. I'm not sure if there
+    // is a Mac API to do this but if so we can link to that...
+    if (builtin.os.tag == .macos) {
+        const exec = try std.ChildProcess.exec(.{
+            .allocator = fba.allocator(),
+            .argv = &[_][]const u8{
+                "/bin/sh",
+                "-c",
+                "dscl -q . -read /Users/\"$(whoami)\" NFSHomeDirectory | sed 's/^[^ ]*: //'",
+            },
+            .max_output_bytes = fba.buffer.len / 2,
+        });
+
+        if (exec.term == .Exited and exec.term.Exited == 0) {
+            const result = trimSpace(exec.stdout);
+            if (buf.len < result.len) return Error.BufferTooSmall;
+            std.mem.copy(u8, buf, result);
+            return buf[0..result.len];
+        }
+    }
+
+    // We try passwd. This doesn't work on multi-user mac but we try it anyways.
+    fba.reset();
+    const pw = try passwd.get(fba.allocator());
+    if (pw.home) |result| {
+        if (buf.len < result.len) return Error.BufferTooSmall;
+        std.mem.copy(u8, buf, result);
+        return buf[0..result.len];
+    }
+
+    // If all else fails, have the shell tell us...
+    fba.reset();
+    const exec = try std.ChildProcess.exec(.{
+        .allocator = fba.allocator(),
+        .argv = &[_][]const u8{ "/bin/sh", "-c", "cd && pwd" },
+        .max_output_bytes = fba.buffer.len / 2,
+    });
+
+    if (exec.term == .Exited and exec.term.Exited == 0) {
+        const result = trimSpace(exec.stdout);
+        if (buf.len < result.len) return Error.BufferTooSmall;
+        std.mem.copy(u8, buf, result);
+        return buf[0..result.len];
+    }
+
+    return null;
+}
+
+fn trimSpace(input: []const u8) []const u8 {
+    return std.mem.trim(u8, input, " \n\t");
+}
+
+test {
+    const testing = std.testing;
+
+    var buf: [1024]u8 = undefined;
+    const result = try home(&buf);
+    try testing.expect(result != null);
+    try testing.expect(result.?.len > 0);
+}

src/main.zig

@@ -177,6 +177,7 @@ test {
 
     // TODO
     _ = @import("config.zig");
+    _ = @import("homedir.zig");
     _ = @import("passwd.zig");
     _ = @import("cli_args.zig");
     _ = @import("lru.zig");