Merge pull request #1954 from ghostty-org/base64

SIMD base64 decode for Kitty graphics data

build.zig

@@ -1054,6 +1054,7 @@ fn addDeps(
 
         step.addCSourceFiles(.{
             .files = &.{
+                "src/simd/base64.cpp",
                 "src/simd/codepoint_width.cpp",
                 "src/simd/index_of.cpp",
                 "src/simd/vt.cpp",

src/simd/base64.cpp

@@ -0,0 +1,20 @@
+#include <simdutf.h>
+
+extern "C" {
+
+size_t ghostty_simd_base64_max_length(const char* input, size_t length) {
+  return simdutf::maximal_binary_length_from_base64(input, length);
+}
+
+size_t ghostty_simd_base64_decode(const char* input,
+                                  size_t length,
+                                  char* output) {
+  simdutf::result r = simdutf::base64_to_binary(input, length, output);
+  if (r.error) {
+    return -1;
+  }
+
+  return r.count;
+}
+
+}  // extern "C"

src/simd/base64.zig

@@ -0,0 +1,39 @@
+const std = @import("std");
+
+// base64.cpp
+extern "c" fn ghostty_simd_base64_max_length(
+    input: [*]const u8,
+    len: usize,
+) usize;
+extern "c" fn ghostty_simd_base64_decode(
+    input: [*]const u8,
+    len: usize,
+    output: [*]u8,
+) isize;
+
+pub fn maxLen(input: []const u8) usize {
+    return ghostty_simd_base64_max_length(input.ptr, input.len);
+}
+
+pub fn decode(input: []const u8, output: []u8) error{Base64Invalid}![]const u8 {
+    const res = ghostty_simd_base64_decode(input.ptr, input.len, output.ptr);
+    if (res < 0) return error.Base64Invalid;
+    return output[0..@intCast(res)];
+}
+
+test "base64 maxLen" {
+    const testing = std.testing;
+    const len = maxLen("aGVsbG8gd29ybGQ=");
+    try testing.expectEqual(11, len);
+}
+
+test "base64 decode" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+    const input = "aGVsbG8gd29ybGQ=";
+    const len = maxLen(input);
+    const output = try alloc.alloc(u8, len);
+    defer alloc.free(output);
+    const str = try decode(input, output);
+    try testing.expectEqualStrings("hello world", str);
+}

src/simd/main.zig

@@ -1,6 +1,7 @@
 const std = @import("std");
 
 pub usingnamespace @import("codepoint_width.zig");
+pub const base64 = @import("base64.zig");
 pub const index_of = @import("index_of.zig");
 pub const vt = @import("vt.zig");
 

src/terminal/kitty/graphics_command.zig

@@ -2,6 +2,7 @@ const std = @import("std");
 const assert = std.debug.assert;
 const Allocator = std.mem.Allocator;
 const ArenaAllocator = std.heap.ArenaAllocator;
+const simd = @import("../../simd/main.zig");
 
 const log = std.log.scoped(.kitty_gfx);
 
@@ -179,29 +180,24 @@ pub const CommandParser = struct {
             return "";
         }
 
-        const Base64Decoder = std.base64.standard_no_pad.Decoder;
-
-        // We remove any padding, since it's optional, and decode without it.
-        while (self.data.items[self.data.items.len - 1] == '=') {
-            self.data.items.len -= 1;
-        }
-
-        const size = Base64Decoder.calcSizeForSlice(self.data.items) catch |err| {
-            log.warn("failed to calculate base64 size for payload: {}", .{err});
-            return error.InvalidData;
-        };
+        const max_len = simd.base64.maxLen(self.data.items);
+        assert(max_len <= self.data.items.len);
 
         // This is kinda cursed, but we can decode the base64 on top of
         // itself, since it's guaranteed that the encoded size is larger,
         // and any bytes in areas that are written to will have already
         // been used (assuming scalar decoding).
-        Base64Decoder.decode(self.data.items[0..size], self.data.items) catch |err| {
+        const decoded = simd.base64.decode(
+            self.data.items,
+            self.data.items[0..max_len],
+        ) catch |err| {
             log.warn("failed to decode base64 payload data: {}", .{err});
             return error.InvalidData;
         };
+        assert(decoded.len <= max_len);
 
         // Remove the extra bytes.
-        self.data.items.len = size;
+        self.data.items.len = decoded.len;
 
         return try self.data.toOwnedSlice();
     }