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std.json: honor max_value_len for sentinel strings #30782

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This PR fix std.json to honor max_value_len for sentinel-terminated strings and add a regression test.

Fixes #30579

reproduction (before this commit)

❯ zig version
0.16.0-dev.2040+c475f1fcd
❯ zig test sandbox/repro-30579.zig
1/1 repro-30579.test.max_value_len greater than default_max_value_len...FAIL (ValueTooLong)

not commited (snippet just for reproduction) sandbox/repro-30579.zig

const std = @import("std");
const testing = std.testing;
test "max_value_len greater than default_max_value_len" {
 const allocator = testing.allocator;
 const json_string =
 "\"" ++ "a" ** (std.json.default_max_value_len + 1) ++ "\"";
 const res = try std.json.parseFromSlice(
 [:0]const u8,
 allocator,
 json_string,
 .{ .max_value_len = std.json.default_max_value_len + 1 },
 );
 defer res.deinit();
 try testing.expectEqual(res.value.len, std.json.default_max_value_len + 1);
}

verification (after this commit)

❯ mkdir build
❯ cd build
❯ cmake ..
❯ make install
❯ cd ..
❯ ./build/stage3/bin/zig test sandbox/repro-30579.zig 
All 1 tests passed.
This PR fix `std.json` to honor `max_value_len` for sentinel-terminated strings and add a regression test. Fixes https://codeberg.org/ziglang/zig/issues/30579 reproduction (before this commit) ``` ❯ zig version 0.16.0-dev.2040+c475f1fcd ❯ zig test sandbox/repro-30579.zig 1/1 repro-30579.test.max_value_len greater than default_max_value_len...FAIL (ValueTooLong) ``` not commited (snippet just for reproduction) `sandbox/repro-30579.zig` ``` const std = @import("std"); const testing = std.testing; test "max_value_len greater than default_max_value_len" { const allocator = testing.allocator; const json_string = "\"" ++ "a" ** (std.json.default_max_value_len + 1) ++ "\""; const res = try std.json.parseFromSlice( [:0]const u8, allocator, json_string, .{ .max_value_len = std.json.default_max_value_len + 1 }, ); defer res.deinit(); try testing.expectEqual(res.value.len, std.json.default_max_value_len + 1); } ``` verification (after this commit) ``` ❯ mkdir build ❯ cd build ❯ cmake .. ❯ make install ❯ cd .. ❯ ./build/stage3/bin/zig test sandbox/repro-30579.zig All 1 tests passed. ```
std.json: add regression test for sentinel max_value_len
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0b02a8e7b1
Merge branch 'master' into fix-30579
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6f2166c134
std.json: honor max_value_len for sentinel strings
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0abaadb6a3
nash1111 changed title from (削除) WIP: std.json: add regression test for sentinel max_value_len (削除ここまで) to std.json: add regression test for sentinel max_value_len 2026年01月11日 03:17:49 +01:00
zig fmt: format static_test.zig
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95f18b6840
nash1111 changed title from (削除) std.json: add regression test for sentinel max_value_len (削除ここまで) to std.json: honor max_value_len for sentinel strings 2026年01月11日 08:19:00 +01:00
@ -491,3 +491,3 @@
//Useourownarraylistsowecanappendthesentinel.
varvalue_list=ArrayList(u8).init(allocator);
_=trysource.allocNextIntoArrayList(&value_list,.alloc_always);
_=trysource.allocNextIntoArrayListMax(&value_list,.alloc_always,options.max_value_len.?);
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Thanks, but as I understand it, this would completely bypass std.json.default_max_value_len. By default, when parseFromSlice is called with empty options, options.max_value_len ends up being equal to the input string length rather than the default limit, allowing arbitrarily long JSON to be parsed. So I’m not sure if this is the correct fix, but it could be.

Thanks, but as I understand it, this would completely bypass std.json.default_max_value_len. By default, when parseFromSlice is called with empty options, options.max_value_len ends up being equal to the input string length rather than the default limit, allowing arbitrarily long JSON to be parsed. So I’m not sure if this is the correct fix, but it could be.
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Thanks for the note. My understanding (I’m still a beginner, so please correct me if I’m wrong) is that this change only affects the case where options.max_value_len is explicitly set. parseFromSlice still defaults max_value_len to the input length for complete input, and default_max_value_len is only used for Reader-based parsing, so the default behavior remains unchanged. Also, the "unbounded when options are empty" behavior is existing design, this PR doesn’t change that.

Thanks for the note. My understanding (I’m still a beginner, so please correct me if I’m wrong) is that this change only affects the case where `options.max_value_len` is explicitly set. `parseFromSlice` still defaults `max_value_len` to the input length for complete input, and `default_max_value_len` is only used for Reader-based parsing, so the default behavior remains unchanged. Also, the "unbounded when options are empty" behavior is existing design, this PR doesn’t change that.
Merge branch 'master' into fix-30579
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