1 files changed, 13 insertions, 74 deletions

diff --git a/src/pdf.zig b/src/pdf.zig
index de5e6d86..8ddca497 100644
--- a/src/pdf.zig
+++ b/src/pdf.zig
@@ -2,66 +2,30 @@
 //! setjmp/longjmp; pdf_bridge.c catches every such throw before control returns
 //! to Zig. This module is present in native builds unless `-Dmupdf=false`.
 const std = @import("std");
+const c_heap = @import("c_heap");
 
 const c = @cImport({
     @cInclude("pdf_bridge.h");
 });
 
-const allocation_header_size = 16;
+/// What MuPDF allocates from, itself and the libraries it bundles (they all
+/// allocate through its context): `start`'s allocator, through the shared C
+/// heap. MuPDF's allocator functions carry a user pointer the heap does not
+/// need.
 var bridge_allocator: std.mem.Allocator = undefined;
+const bridge_heap = c_heap.Heap(&bridge_allocator);
 var bridge_started = false;
 
-comptime {
-    if (allocation_header_size < @sizeOf(usize))
-        @compileError("PDF allocation header is too small");
-}
-
-fn bridgeAlloc(user: ?*anyopaque, size_arg: usize) callconv(.c) ?*anyopaque {
-    const user_ptr = user orelse return null;
-    const allocator: *std.mem.Allocator = @ptrCast(@alignCast(user_ptr));
-    const size = @max(size_arg, 1);
-    const total = std.math.add(usize, allocation_header_size, size) catch
-        return null;
-    const bytes = allocator.alignedAlloc(u8, .@"16", total) catch return null;
-    const header: *align(16) usize = @ptrCast(bytes.ptr);
-    header.* = total;
-    return @ptrCast(bytes.ptr + allocation_header_size);
+fn bridgeAlloc(_: ?*anyopaque, size: usize) callconv(.c) ?*anyopaque {
+    return bridge_heap.malloc(size);
 }
 
-fn bridgeFree(user: ?*anyopaque, pointer: ?*anyopaque) callconv(.c) void {
-    const data = pointer orelse return;
-    const user_ptr = user orelse @panic("PDF allocator callback has no allocator");
-    const allocator: *std.mem.Allocator = @ptrCast(@alignCast(user_ptr));
-    const data_bytes: [*]u8 = @ptrCast(data);
-    const base: [*]align(16) u8 =
-        @ptrCast(@alignCast(data_bytes - allocation_header_size));
-    const header: *align(16) usize = @ptrCast(base);
-    allocator.free(base[0..header.*]);
+fn bridgeRealloc(_: ?*anyopaque, block: ?*anyopaque, size: usize) callconv(.c) ?*anyopaque {
+    return bridge_heap.realloc(block, size);
 }
 
-fn bridgeRealloc(
-    user: ?*anyopaque,
-    pointer: ?*anyopaque,
-    size_arg: usize,
-) callconv(.c) ?*anyopaque {
-    if (pointer == null) return bridgeAlloc(user, size_arg);
-    if (size_arg == 0) {
-        bridgeFree(user, pointer);
-        return null;
-    }
-
-    const user_ptr = user orelse return null;
-    const allocator: *std.mem.Allocator = @ptrCast(@alignCast(user_ptr));
-    const total = std.math.add(usize, allocation_header_size, size_arg) catch
-        return null;
-    const data_bytes: [*]u8 = @ptrCast(pointer.?);
-    const base: [*]align(16) u8 =
-        @ptrCast(@alignCast(data_bytes - allocation_header_size));
-    const header: *align(16) usize = @ptrCast(base);
-    const resized = allocator.realloc(base[0..header.*], total) catch return null;
-    const resized_header: *align(16) usize = @ptrCast(resized.ptr);
-    resized_header.* = total;
-    return @ptrCast(resized.ptr + allocation_header_size);
+fn bridgeFree(_: ?*anyopaque, block: ?*anyopaque) callconv(.c) void {
+    bridge_heap.free(block);
 }
 
 /// Installs the allocator used by all subsequently opened PDF documents and
@@ -70,7 +34,7 @@ pub fn start(allocator: std.mem.Allocator) void {
     if (bridge_started) @panic("PDF allocator is already started");
     bridge_allocator = allocator;
     const descriptor = c.pardes_pdf_allocator{
-        .user = &bridge_allocator,
+        .user = null,
         .alloc = bridgeAlloc,
         .realloc = bridgeRealloc,
         .free = bridgeFree,
@@ -90,31 +54,6 @@ pub fn stop() void {
     bridge_allocator = undefined;
 }
 
-test "PDF C allocator callbacks preserve and free exact allocations" {
-    var allocator = std.testing.allocator;
-
-    var live: ?*anyopaque = bridgeAlloc(&allocator, 4) orelse
-        return error.OutOfMemory;
-    defer if (live) |pointer| bridgeFree(&allocator, pointer);
-    const original: [*]u8 = @ptrCast(live.?);
-    @memcpy(original[0..4], "data");
-
-    live = bridgeRealloc(&allocator, live, 32) orelse
-        return error.OutOfMemory;
-    const grown: [*]u8 = @ptrCast(live.?);
-    try std.testing.expectEqualSlices(u8, "data", grown[0..4]);
-
-    try std.testing.expect(bridgeAlloc(
-        &allocator,
-        std.math.maxInt(usize),
-    ) == null);
-
-    const zero = bridgeAlloc(&allocator, 0) orelse return error.OutOfMemory;
-    bridgeFree(&allocator, zero);
-    try std.testing.expect(bridgeRealloc(&allocator, live, 0) == null);
-    live = null;
-}
-
 test "custom allocator owns a complete PDF document lifecycle" {
     start(std.testing.allocator);
     defer stop();