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Niels Lohmann
2231c4af41
An image is a document stored so that loading it needs no
parsing: save() writes the node index, the text and the decoded
strings; the static load() reads an image written by save().
load() takes a pointer and size, a borrowed vector, or an owned
rvalue vector; the nodes are copied so they are aligned and can
be edited, while the text and decoded strings stay in the image.
image_check controls how much load() trusts the input: full
checks structure, bounds, strings and numbers, the parser's own
guarantees; bounds checks structure and bounds only; none skips
all checks, for images from a trusted source.
Layout is little-endian only ("NJVI" header, nodes, text, decoded
strings), following the idea of zero-copy formats such as
FlatBuffers and YaFF; the check follows FlatBuffers' Verifier.
New errors: parse_error.116 for a malformed image or a failed
check, type_error.320 for a discarded document or a big-endian
target.
A dedicated fuzzer and 6,000 seeded corruptions, checked under
ASan/UBSan, found and fixed two gaps: unchecked reserved header
fields, and unbounded null/boolean offsets that could make
dump() throw std::length_error.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
31 lines
1.1 KiB
C++
31 lines
1.1 KiB
C++
#include <cstdint>
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#include <iostream>
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#include <string>
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#include <vector>
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#include <nlohmann/json_view.hpp>
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using json_document = nlohmann::json_document;
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int main()
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{
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std::cout << std::boolalpha;
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// a configuration a service parses once and then caches as an image, so
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// that later requests can load() it instead of parsing the text again
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const std::string text = R"({"name": "cache", "host": "db1", "port": 6379, "replicas": ["db2", "db3"]})";
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const json_document config = json_document::parse(text);
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// save() turns the parsed document into a byte buffer: a 64-byte header,
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// the node index, the source text, and the decoded strings
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const std::vector<std::uint8_t> image = config.save();
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std::cout << image.size() << '\n';
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// the same document always saves to the same bytes
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std::cout << (image == json_document::parse(text).save()) << '\n';
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// loading the image back needs no parsing, yet dumps exactly what
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// parsing the text produced
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const json_document reloaded = json_document::load(image);
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std::cout << (reloaded.root().dump() == config.root().dump()) << '\n';
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}
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