From 35494bc81b59165ee9264cd1004bb05a120279a3 Mon Sep 17 00:00:00 2001
From: Martin Ashby <martin@ashbysoft.com>
Date: Thu, 28 Sep 2023 10:54:58 +0100
Subject: Reduce allocations, the message takes ownership of the bytes read
 from the stream and is responsible for deallocating, rather than copying them
 to their own storage.

---
 src/proto/row_description.zig | 35 ++++++++++++++++++-----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

(limited to 'src/proto/row_description.zig')

diff --git a/src/proto/row_description.zig b/src/proto/row_description.zig
index b8105e2..ff17716 100644
--- a/src/proto/row_description.zig
+++ b/src/proto/row_description.zig
@@ -11,7 +11,7 @@ pub const Tag: u8 = 'T';
 const RowDescription = @This();
 
 buf: ?[]const u8 = null, // owned
-fields: ?[]Field = null, // owned
+fields: []Field, // owned
 
 pub const Field = struct {
     name: []const u8,
@@ -23,19 +23,18 @@ pub const Field = struct {
     format_code: FormatCode,
 };
 
-pub fn read(a: std.mem.Allocator, b: []const u8) !RowDescription {
-    var res: RowDescription = undefined;
-    res.buf = try a.dupe(u8, b);
-    errdefer res.deinit(a);
-    var fbs = std.io.fixedBufferStream(res.buf.?);
+pub fn read(a: std.mem.Allocator, buf: []const u8) !RowDescription {
+    errdefer a.free(buf);
+    var fbs = std.io.fixedBufferStream(buf);
     var reader = fbs.reader();
     const n_fields = try reader.readIntBig(u16);
-    res.fields = try a.alloc(Field, n_fields);
+    var fields = try a.alloc(Field, n_fields);
+    errdefer a.free(fields);
     for (0..n_fields) |i| {
         const name_start = fbs.pos;
         try reader.skipUntilDelimiterOrEof(0);
         const name_end = fbs.pos - 1;
-        const name = res.buf.?[name_start..name_end];
+        const name = buf[name_start..name_end];
         const field = Field{
             .name = name,
             .table_oid = try reader.readIntBig(u32),
@@ -45,9 +44,12 @@ pub fn read(a: std.mem.Allocator, b: []const u8) !RowDescription {
             .data_type_modifier = try reader.readIntBig(u32),
             .format_code = enum_from_int(FormatCode, try reader.readIntBig(u16)) orelse return ProtocolError.InvalidFormatCode,
         };
-        res.fields.?[i] = field;
+        fields[i] = field;
     }
-    return res;
+    return .{
+        .buf = buf,
+        .fields = fields,
+    };
 }
 
 pub fn write(self: RowDescription, a: std.mem.Allocator, stream_writer: anytype) !void {
@@ -57,8 +59,8 @@ pub fn write(self: RowDescription, a: std.mem.Allocator, stream_writer: anytype)
     var cw = std.io.countingWriter(al.writer());
     var writer = cw.writer();
     try writer.writeIntBig(u32, 0); // length placeholder
-    try writer.writeIntBig(u16, @as(u16, @intCast(self.fields.?.len)));
-    for (self.fields.?) |field| {
+    try writer.writeIntBig(u16, @as(u16, @intCast(self.fields.len)));
+    for (self.fields) |field| {
         try writer.writeAll(field.name);
         try writer.writeByte(0);
         try writer.writeIntBig(u32, field.table_oid);
@@ -73,7 +75,7 @@ pub fn write(self: RowDescription, a: std.mem.Allocator, stream_writer: anytype)
 }
 
 pub fn deinit(self: *RowDescription, a: std.mem.Allocator) void {
-    if (self.fields != null) a.free(self.fields.?);
+    a.free(self.fields);
     if (self.buf != null) a.free(self.buf.?);
 }
 
@@ -125,12 +127,11 @@ test "round trip" {
     try std.testing.expectEqual(Tag, tag);
     const len = try reader.readIntBig(u32);
     const buf = try allocator.alloc(u8, len - 4);
-    defer allocator.free(buf);
     try reader.readNoEof(buf);
     var sm2 = try RowDescription.read(allocator, buf);
     defer sm2.deinit(allocator);
 
-    try std.testing.expectEqualDeep(f0, sm2.fields.?[0]);
-    try std.testing.expectEqualDeep(f1, sm2.fields.?[1]);
-    try std.testing.expectEqualDeep(f2, sm2.fields.?[2]);
+    try std.testing.expectEqualDeep(f0, sm2.fields[0]);
+    try std.testing.expectEqualDeep(f1, sm2.fields[1]);
+    try std.testing.expectEqualDeep(f2, sm2.fields[2]);
 }
-- 
cgit v1.2.3-ZIG