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/data_row.zig | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

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

diff --git a/src/proto/data_row.zig b/src/proto/data_row.zig
index c20b794..43c4526 100644
--- a/src/proto/data_row.zig
+++ b/src/proto/data_row.zig
@@ -12,25 +12,23 @@ const DataRow = @This();
 buf: ?[]const u8 = null, // owned
 columns: [][]const u8, // also owned
 
-pub fn read(a: std.mem.Allocator, b: []const u8) !DataRow {
-    if (b.len < 2) return ProtocolError.InvalidMessageLength;
-    var buf = try a.dupe(u8, b);
-    var res: DataRow = undefined;
-    res.buf  = buf;
-    errdefer res.deinit(a);
-
+pub fn read(a: std.mem.Allocator, buf: []const u8) !DataRow {
+    if (buf.len < 2) return ProtocolError.InvalidMessageLength;
+    errdefer a.free(buf);
     const n_columns = std.mem.readIntBig(u16, buf[0..2]);
     const columns = try a.alloc([]const u8, n_columns);
     errdefer a.free(columns);
     var pos: usize = 2;
     for (0..n_columns) |col| {
-        const len = std.mem.readIntBig(u32, buf[pos..(pos+4)][0..4]); // second slice forces the slice size to be known at comptime and satisfy the type check on readIntBig!
-        const data = if (len > 0) buf[(pos+4)..(pos+4+len)] else &[_]u8{};
+        const len = std.mem.readIntBig(u32, buf[pos..(pos + 4)][0..4]); // second slice forces the slice size to be known at comptime and satisfy the type check on readIntBig!
+        const data = if (len > 0) buf[(pos + 4)..(pos + 4 + len)] else &[_]u8{};
         columns[col] = data;
-        pos += (4+len);
+        pos += (4 + len);
     }
-    res.columns = columns;
-    return res;
+    return .{
+        .buf = buf,
+        .columns = columns,
+    };
 }
 
 pub fn write(self: DataRow, a: std.mem.Allocator, stream_writer: anytype) !void {
@@ -77,7 +75,6 @@ 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 DataRow.read(allocator, buf);
     defer sm2.deinit(allocator);
-- 
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