wip refactoring PackedUser

src/user.zig

@@ -4,50 +4,11 @@ const pad = @import("padding.zig");
 const assert = std.debug.assert;
 const Allocator = std.mem.Allocator;
 const ArrayList = std.ArrayList;
-const cast = std.math.cast;
+const math = std.math;
+const mem = std.mem;
 
-const PackedUserSize = @divExact(@bitSizeOf(PackedUser), 8);
-pub const PackedUser = packed struct {
-    uid: u32,
-    gid: u32,
-    additional_gids_offset: u29,
-    shell_here: bool,
-    shell_len_or_idx: u6,
-    home_len: u6,
-    name_is_a_suffix: bool,
-    name_len: u5,
-    gecos_len: u8,
-
-    // blobLength returns the length of the blob storing string values.
-    pub fn blobLength(self: *const PackedUser) usize {
-        var result: usize = self.realHomeLen();
-        if (!self.name_is_a_suffix) {
-            result += self.realNameLen();
-        }
-        result += self.realGecosLen();
-        if (self.shell_here) {
-            result += self.realShellLen();
-        }
-
-        return result;
-    }
-
-    pub fn realHomeLen(self: *const PackedUser) usize {
-        return @as(u32, self.home_len) + 1;
-    }
-
-    pub fn realNameLen(self: *const PackedUser) usize {
-        return @as(u32, self.name_len) + 1;
-    }
-
-    pub fn realShellLen(self: *const PackedUser) usize {
-        return @as(u32, self.shell_len_or_idx) + 1;
-    }
-
-    pub fn realGecosLen(self: *const PackedUser) usize {
-        return self.gecos_len;
-    }
-};
+// TODO(motiejus) move to the struct where it's used.
+const shellIndexProto = fn (u6) []const u8;
 const PackedUserAlignmentBits = 3;
 
 pub const User = struct {
@@ -59,28 +20,94 @@ pub const User = struct {
     shell: []const u8,
 };
 
-// UserWriter accepts a naive User struct and returns a PackedUser
-pub const UserWriter = struct {
-    // shellIndexFnType is a signature for a function that accepts a shell
-    // string and returns it's index in the global shell section. Passing a
-    // function makes tests easier, and removes the Shell dependency of this
-    // module.
+pub const PackedUser = struct {
+    // TODO: use @bitSizeOf(Inner)/8:
+    //const InnerSize = @divExact(@bitSizeOf(Inner), 8);
     const shellIndexFnType = fn ([]const u8) ?u6;
 
-    appendTo: *ArrayList(u8),
-    shellIndexFn: shellIndexFnType,
+    const InnerSize = @sizeOf(Inner);
+    const Inner = packed struct {
+        uid: u32,
+        gid: u32,
+        additional_gids_offset: u29,
+        shell_here: bool,
+        shell_len_or_idx: u6,
+        home_len: u6,
+        name_is_a_suffix: bool,
+        name_len: u5,
+        gecos_len: u8,
 
-    pub fn init(
-        appendTo: *ArrayList(u8),
-        shellIndexFn: shellIndexFnType,
-    ) UserWriter {
-        return UserWriter{
-            .appendTo = appendTo,
-            .shellIndexFn = shellIndexFn,
+        pub fn homeLen(self: *const PackedUser) usize {
+            return @as(u32, self.home_len) + 1;
+        }
+
+        pub fn nameLen(self: *const PackedUser) usize {
+            return @as(u32, self.name_len) + 1;
+        }
+
+        pub fn gecosLen(self: *const PackedUser) usize {
+            return self.gecos_len;
+        }
+
+        pub fn shellLen(self: *const PackedUser) usize {
+            return @as(u32, self.shell_len_or_idx) + 1;
+        }
+
+        // blobLength returns the length of the blob storing string values.
+        pub fn blobLength(self: *const Inner) usize {
+            var result: usize = self.homeLen();
+            if (!self.name_is_a_suffix) {
+                result += self.nameLen();
+            }
+            result += self.gecosLen();
+            if (self.shell_here) {
+                result += self.shellLen();
+            }
+
+            return result;
+        }
+
+        pub fn namePos(self: *const Inner) usize {
+            const name_len = self.nameLen();
+            if (self.name_is_a_suffix) {
+                return self.inner.homeLen() - name_len;
+            } else {
+                return self.homeLen();
+            }
+        }
+
+        pub fn gecosPos(self: *const Inner) usize {
+            if (self.name_is_a_suffix) {
+                return self.homeLen();
+            } else {
+                return self.homeLen() + self.nameLen();
+            }
+        }
+
+        pub fn maybeShellPos(self: *const Inner) usize {
+            assert(self.shell_here);
+            return self.gecosPos() + self.gecosLen();
+        }
+    };
+
+    inner: Inner,
+    userdata: []const u8,
+
+    pub fn fromBytes(bytes: []const u8) PackedUser {
+        const inner = std.mem.bytesAsValue(
+            PackedUser,
+            bytes[0..@sizeOf(Inner)][0..@sizeOf(Inner)],
+        );
+
+        const startBlob = InnerSize;
+        const endBlob = startBlob + inner.blobLength();
+        return PackedUser{
+            .inner = inner,
+            .userdata = bytes[startBlob..endBlob],
         };
     }
 
-    pub fn downCast(comptime T: type, n: u64) error{InvalidRecord}!T {
+    fn downCast(comptime T: type, n: u64) error{InvalidRecord}!T {
         return std.math.cast(T, n) catch |err| switch (err) {
             error.Overflow => {
                 return error.InvalidRecord;
@@ -88,23 +115,19 @@ pub const UserWriter = struct {
         };
     }
 
-    pub fn validateUtf8(s: []const u8) error{InvalidRecord}!void {
+    fn validateUtf8(s: []const u8) error{InvalidRecord}!void {
         if (!std.unicode.utf8ValidateSlice(s)) {
             return error.InvalidRecord;
         }
     }
 
-    // FIXME(motiejus) record valiation should return a separate type. For User
-    // case, it should be length-bound slices and utf8-codepoints instead of
-    // strings.
-    //
-    // zig does not have error contexts
-    // (https://github.com/ziglang/zig/issues/2647) and length-limited slices.
-    // (It does have bounded_array, but that preallocates the maximum length,
-    // which is not great for User records). So I am using those excuses to
-    // do the validation here. I may move it once I learn the language better.
-    const appendUserErr = error{InvalidRecord} || Allocator.Error;
-    pub fn appendUser(self: *UserWriter, user: User) appendUserErr!void {
+    // packTo packs the User record and copies it to the given byte slice. The
+    // slice must have at least maxRecordSize() bytes available.
+    pub fn packTo(buf1: *[]u8, user: User, shellIndexFn: shellIndexFnType) error{InvalidRecord}!void {
+        std.debug.print("\nbuf1.len: {d}\n", .{buf1.*.len});
+        var buf = buf1.*;
+        const bufStart = @ptrToInt(&buf[0]);
+
         const home_len = try downCast(u6, user.home.len - 1);
         const name_len = try downCast(u5, user.name.len - 1);
         const shell_len = try downCast(u6, user.shell.len - 1);
@@ -115,39 +138,79 @@ pub const UserWriter = struct {
         try validateUtf8(user.shell);
         try validateUtf8(user.gecos);
 
-        var puser = PackedUser{
+        const inner = Inner{
             .uid = user.uid,
             .gid = user.gid,
-            .additional_gids_offset = 1 << 29 - 1,
-            .shell_here = self.shellIndexFn(user.shell) == null,
-            .shell_len_or_idx = self.shellIndexFn(user.shell) orelse shell_len,
+            .additional_gids_offset = std.math.maxInt(u29),
+            .shell_here = shellIndexFn(user.shell) == null,
+            .shell_len_or_idx = shellIndexFn(user.shell) orelse shell_len,
             .home_len = home_len,
             .name_is_a_suffix = std.mem.endsWith(u8, user.home, user.name),
             .name_len = name_len,
             .gecos_len = gecos_len,
         };
+        const innerBytes = mem.asBytes(&inner);
 
-        try self.appendTo.appendSlice(std.mem.asBytes(&puser));
-        try self.appendTo.appendSlice(user.home);
-        if (!puser.name_is_a_suffix) {
-            try self.appendTo.appendSlice(user.name);
+        mem.copy(u8, buf, innerBytes);
+        buf = buf[innerBytes.len..];
+        mem.copy(u8, buf, user.home);
+        buf = buf[user.home.len..];
+
+        if (!inner.name_is_a_suffix) {
+            mem.copy(u8, buf, user.name);
+            buf = buf[user.name.len..];
         }
-        try self.appendTo.appendSlice(user.gecos);
-        if (puser.shell_here) {
-            try self.appendTo.appendSlice(user.shell);
+        mem.copy(u8, buf, user.gecos);
+        buf = buf[user.gecos.len..];
+        if (inner.shell_here) {
+            mem.copy(u8, buf, user.shell);
+            buf = buf[user.shell.len..];
         }
 
-        try self.appendTo.appendNTimes(0, pad.roundUpPadding(
-            u64,
-            PackedUserAlignmentBits,
-            self.appendTo.items.len,
-        ));
+        _ = bufStart;
+        //const bufLen = @ptrToInt(&buf[0]) - bufStart;
+        //const padding = pad.roundUpPadding(u64, PackedUserAlignmentBits, bufLen);
+        //mem.set(u8, buf[0..padding], 0);
+    }
+
+    // maxSize is the maximum number of records a PackedUser can take
+    // (struct + userdata).
+    pub fn maxSize() usize {
+        const unpadded = InnerSize +
+            std.math.maxInt(u6) + // home
+            std.math.maxInt(u5) + // name
+            std.math.maxInt(u6) + // shell
+            std.math.maxInt(u8); // gecos
+        return pad.roundUp(u64, PackedUserAlignmentBits, unpadded);
+    }
+
+    pub fn home(self: *const PackedUser) []const u8 {
+        return self.userdata[0..self.inner.homeLen()];
+    }
+
+    pub fn name(self: *const PackedUser) []const u8 {
+        const name_pos = self.inner.namePos();
+        const name_len = self.inner.nameLen();
+        return self.userdata[name_pos .. name_pos + name_len];
+    }
+
+    pub fn gecos(self: *const PackedUser) []const u8 {
+        const gecos_pos = self.inner.gecosPos();
+        const gecos_len = self.inner.gecosLen();
+        return self.userdata[gecos_pos .. gecos_pos + gecos_len];
+    }
+
+    pub fn shell(self: *const PackedUser, shellIndex: shellIndexProto) []const u8 {
+        if (self.inner.shell_here) {
+            const shell_pos = self.inner.maybeShellPos();
+            const shell_len = self.inner.shellLen();
+            return self.userdata[shell_pos .. shell_pos + shell_len];
+        }
+        return shellIndex(self.inner.shell_len_or_idx);
     }
 };
 
 pub const UserReader = struct {
-    const shellIndexProto = fn (u6) []const u8;
-
     section: []const u8,
     shellIndex: shellIndexProto,
 
@@ -182,25 +245,25 @@ pub const UserReader = struct {
         const endBlob = startBlob + u.blobLength();
         const section = self.section[startBlob..endBlob];
 
-        const home = section[0..u.realHomeLen()];
+        const home = section[0..u.homeLen()];
         var name: []const u8 = undefined;
         var pos: usize = undefined;
 
         if (u.name_is_a_suffix) {
-            const name_start = u.realHomeLen() - u.realNameLen();
-            name = section[name_start..u.realHomeLen()];
-            pos = u.realHomeLen();
+            const name_start = u.homeLen() - u.nameLen();
+            name = section[name_start..u.homeLen()];
+            pos = u.homeLen();
         } else {
-            const name_start = u.realHomeLen();
-            name = section[name_start .. name_start + u.realNameLen()];
-            pos = name_start + u.realNameLen();
+            const name_start = u.homeLen();
+            name = section[name_start .. name_start + u.nameLen()];
+            pos = name_start + u.nameLen();
         }
-        const gecos = section[pos .. pos + u.realGecosLen()];
-        pos += u.realGecosLen();
+        const gecos = section[pos .. pos + u.gecosLen()];
+        pos += u.gecosLen();
 
         var shell: []const u8 = undefined;
         if (u.shell_here) {
-            shell = section[pos .. pos + u.realShellLen()];
+            shell = section[pos .. pos + u.shellLen()];
         } else {
             shell = self.shellIndex(u.shell_len_or_idx);
         }
@@ -272,7 +335,6 @@ test "construct PackedUser section" {
     var buf = ArrayList(u8).init(testing.allocator);
     defer buf.deinit();
 
-    var writer = UserWriter.init(&buf, testShellIndex);
     const users = [_]User{ User{
         .uid = 1000,
         .gid = 1000,
@@ -296,19 +358,23 @@ test "construct PackedUser section" {
         .shell = "s" ** 64,
     } };
     for (users) |user| {
-        try writer.appendUser(user);
+        std.debug.print("\nmaxSize: {d}\n", .{PackedUser.maxSize()});
+        try buf.ensureUnusedCapacity(PackedUser.maxSize());
+        buf.items[0] = 1;
+        std.debug.print("\nbuf.items.len: {d}\n", .{buf.items.len});
+        try PackedUser.packTo(&buf.items, user, testShellIndex);
     }
 
-    var rd = UserReader.init(buf.items, testShell);
+    //var rd = UserReader.init(buf.items, testShell);
 
-    var it = rd.iterator();
-    var i: u32 = 0;
-    while (it.next()) |user| : (i += 1) {
-        try testing.expectEqual(users[i].uid, user.uid);
-        try testing.expectEqual(users[i].gid, user.gid);
-        try testing.expectEqualStrings(users[i].name, user.name);
-        try testing.expectEqualStrings(users[i].gecos, user.gecos);
-        try testing.expectEqualStrings(users[i].home, user.home);
-        try testing.expectEqualStrings(users[i].shell, user.shell);
-    }
+    //var it = rd.iterator();
+    //var i: u32 = 0;
+    //while (it.next()) |user| : (i += 1) {
+    //    try testing.expectEqual(users[i].uid, user.uid);
+    //    try testing.expectEqual(users[i].gid, user.gid);
+    //    try testing.expectEqualStrings(users[i].name, user.name);
+    //    try testing.expectEqualStrings(users[i].gecos, user.gecos);
+    //    try testing.expectEqualStrings(users[i].home, user.home);
+    //    try testing.expectEqualStrings(users[i].shell, user.shell);
+    //}
 }