Fold SkJSON into Skia/utils

It's a tiny, core-ish component -- might as well treat as such to
simplify dependencies.

Change-Id: I6f31ce2d151f9a629d88bfc7f15d64891d5150c0
Reviewed-on: https://skia-review.googlesource.com/135780
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>

1 files changed, 803 insertions, 0 deletions

diff --git a/src/utils/SkJSON.cpp b/src/utils/SkJSON.cpp
new file mode 100644
index 0000000000..2548f4ef41
--- /dev/null
+++ b/src/utils/SkJSON.cpp
@@ -0,0 +1,803 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkJSON.h"
+
+#include "SkMalloc.h"
+#include "SkStream.h"
+#include "SkString.h"
+
+#include <cmath>
+#include <tuple>
+#include <vector>
+
+namespace skjson {
+
+// #define SK_JSON_REPORT_ERRORS
+
+static_assert( sizeof(Value) == 8, "");
+static_assert(alignof(Value) == 8, "");
+
+static constexpr size_t kRecAlign = alignof(Value);
+
+void Value::init_tagged(Tag t) {
+    memset(fData8, 0, sizeof(fData8));
+    fData8[Value::kTagOffset] = SkTo<uint8_t>(t);
+    SkASSERT(this->getTag() == t);
+}
+
+// Pointer values store a type (in the upper kTagBits bits) and a pointer.
+void Value::init_tagged_pointer(Tag t, void* p) {
+    *this->cast<uintptr_t>() = reinterpret_cast<uintptr_t>(p);
+
+    if (sizeof(Value) == sizeof(uintptr_t)) {
+        // For 64-bit, we rely on the pointer upper bits being unused/zero.
+        SkASSERT(!(fData8[kTagOffset] & kTagMask));
+        fData8[kTagOffset] |= SkTo<uint8_t>(t);
+    } else {
+        // For 32-bit, we need to zero-initialize the upper 32 bits
+        SkASSERT(sizeof(Value) == sizeof(uintptr_t) * 2);
+        this->cast<uintptr_t>()[kTagOffset >> 2] = 0;
+        fData8[kTagOffset] = SkTo<uint8_t>(t);
+    }
+
+    SkASSERT(this->getTag()    == t);
+    SkASSERT(this->ptr<void>() == p);
+}
+
+NullValue::NullValue() {
+    this->init_tagged(Tag::kNull);
+    SkASSERT(this->getTag() == Tag::kNull);
+}
+
+BoolValue::BoolValue(bool b) {
+    this->init_tagged(Tag::kBool);
+    *this->cast<bool>() = b;
+    SkASSERT(this->getTag() == Tag::kBool);
+}
+
+NumberValue::NumberValue(int32_t i) {
+    this->init_tagged(Tag::kInt);
+    *this->cast<int32_t>() = i;
+    SkASSERT(this->getTag() == Tag::kInt);
+}
+
+NumberValue::NumberValue(float f) {
+    this->init_tagged(Tag::kFloat);
+    *this->cast<float>() = f;
+    SkASSERT(this->getTag() == Tag::kFloat);
+}
+
+// Vector recs point to externally allocated slabs with the following layout:
+//
+//   [size_t n] [REC_0] ... [REC_n-1] [optional extra trailing storage]
+//
+// Long strings use extra_alloc_size == 1 to store the \0 terminator.
+//
+template <typename T, size_t extra_alloc_size = 0>
+static void* MakeVector(const void* src, size_t size, SkArenaAlloc& alloc) {
+    // The Ts are already in memory, so their size should be safe.
+    const auto total_size = sizeof(size_t) + size * sizeof(T) + extra_alloc_size;
+    auto* size_ptr = reinterpret_cast<size_t*>(alloc.makeBytesAlignedTo(total_size, kRecAlign));
+
+    *size_ptr = size;
+    sk_careful_memcpy(size_ptr + 1, src, size * sizeof(T));
+
+    return size_ptr;
+}
+
+ArrayValue::ArrayValue(const Value* src, size_t size, SkArenaAlloc& alloc) {
+    this->init_tagged_pointer(Tag::kArray, MakeVector<Value>(src, size, alloc));
+    SkASSERT(this->getTag() == Tag::kArray);
+}
+
+// Strings have two flavors:
+//
+// -- short strings (len <= 7) -> these are stored inline, in the record
+//    (one byte reserved for null terminator/type):
+//
+//        [str] [\0]|[max_len - actual_len]
+//
+//    Storing [max_len - actual_len] allows the 'len' field to double-up as a
+//    null terminator when size == max_len (this works 'cause kShortString == 0).
+//
+// -- long strings (len > 7) -> these are externally allocated vectors (VectorRec<char>).
+//
+// The string data plus a null-char terminator are copied over.
+//
+namespace {
+
+// An internal string builder with a fast 8 byte short string load path
+// (for the common case where the string is not at the end of the stream).
+class FastString final : public Value {
+public:
+    FastString(const char* src, size_t size, const char* eos, SkArenaAlloc& alloc) {
+        SkASSERT(src <= eos);
+
+        if (size > kMaxInlineStringSize) {
+            this->initLongString(src, size, alloc);
+            SkASSERT(this->getTag() == Tag::kString);
+            return;
+        }
+
+        static_assert(static_cast<uint8_t>(Tag::kShortString) == 0, "please don't break this");
+        static_assert(sizeof(Value) == 8, "");
+
+        // TODO: LIKELY
+        if (src + 7 <= eos) {
+            this->initFastShortString(src, size);
+        } else {
+            this->initShortString(src, size);
+        }
+
+        SkASSERT(this->getTag() == Tag::kShortString);
+    }
+
+private:
+    static constexpr size_t kMaxInlineStringSize = sizeof(Value) - 1;
+
+    void initLongString(const char* src, size_t size, SkArenaAlloc& alloc) {
+        SkASSERT(size > kMaxInlineStringSize);
+
+        this->init_tagged_pointer(Tag::kString, MakeVector<char, 1>(src, size, alloc));
+
+        auto* data = this->cast<VectorValue<char, Value::Type::kString>>()->begin();
+        const_cast<char*>(data)[size] = '\0';
+    }
+
+    void initShortString(const char* src, size_t size) {
+        SkASSERT(size <= kMaxInlineStringSize);
+
+        this->init_tagged(Tag::kShortString);
+        sk_careful_memcpy(this->cast<char>(), src, size);
+        // Null terminator provided by init_tagged() above (fData8 is zero-initialized).
+    }
+
+    void initFastShortString(const char* src, size_t size) {
+        SkASSERT(size <= kMaxInlineStringSize);
+
+        // Load 8 chars and mask out the tag and \0 terminator.
+        uint64_t* s64 = this->cast<uint64_t>();
+        memcpy(s64, src, 8);
+
+#if defined(SK_CPU_LENDIAN)
+        *s64 &= 0x00ffffffffffffffULL >> ((kMaxInlineStringSize - size) * 8);
+#else
+        static_assert(false, "Big-endian builds are not supported at this time.");
+#endif
+    }
+};
+
+} // namespace
+
+StringValue::StringValue(const char* src, size_t size, SkArenaAlloc& alloc) {
+    new (this) FastString(src, size, src, alloc);
+}
+
+ObjectValue::ObjectValue(const Member* src, size_t size, SkArenaAlloc& alloc) {
+    this->init_tagged_pointer(Tag::kObject, MakeVector<Member>(src, size, alloc));
+    SkASSERT(this->getTag() == Tag::kObject);
+}
+
+
+// Boring public Value glue.
+
+const Value& ObjectValue::operator[](const char* key) const {
+    // Reverse search for duplicates resolution (policy: return last).
+    const auto* begin  = this->begin();
+    const auto* member = this->end();
+
+    while (member > begin) {
+        --member;
+        if (0 == strcmp(key, member->fKey.as<StringValue>().begin())) {
+            return member->fValue;
+        }
+    }
+
+    static const Value g_null = NullValue();
+    return g_null;
+}
+
+namespace {
+
+// Lexer/parser inspired by rapidjson [1], sajson [2] and pjson [3].
+//
+// [1] https://github.com/Tencent/rapidjson/
+// [2] https://github.com/chadaustin/sajson
+// [3] https://pastebin.com/hnhSTL3h
+
+
+// bit 0 (0x01) - plain ASCII string character
+// bit 1 (0x02) - whitespace
+// bit 2 (0x04) - string terminator (" \0 [control chars] **AND } ]** <- see matchString notes)
+// bit 3 (0x08) - 0-9
+// bit 4 (0x10) - 0-9 e E .
+// bit 5 (0x20) - scope terminator (} ])
+static constexpr uint8_t g_token_flags[256] = {
+ // 0    1    2    3    4    5    6    7      8    9    A    B    C    D    E    F
+    4,   4,   4,   4,   4,   4,   4,   4,     4,   6,   6,   4,   4,   6,   4,   4, // 0
+    4,   4,   4,   4,   4,   4,   4,   4,     4,   4,   4,   4,   4,   4,   4,   4, // 1
+    3,   1,   4,   1,   1,   1,   1,   1,     1,   1,   1,   1,   1,   1,   0x11,1, // 2
+ 0x19,0x19,0x19,0x19,0x19,0x19,0x19,0x19,  0x19,0x19,   1,   1,   1,   1,   1,   1, // 3
+    1,   1,   1,   1,   1,   0x11,1,   1,     1,   1,   1,   1,   1,   1,   1,   1, // 4
+    1,   1,   1,   1,   1,   1,   1,   1,     1,   1,   1,   1,   0,0x25,   1,   1, // 5
+    1,   1,   1,   1,   1,   0x11,1,   1,     1,   1,   1,   1,   1,   1,   1,   1, // 6
+    1,   1,   1,   1,   1,   1,   1,   1,     1,   1,   1,   1,   1,0x25,   1,   1, // 7
+
+ // 128-255
+    0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0,
+    0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0,
+    0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0,
+    0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,  0,0,0,0,0,0,0,0
+};
+
+static inline bool is_ws(char c)       { return g_token_flags[static_cast<uint8_t>(c)] & 0x02; }
+static inline bool is_eostring(char c) { return g_token_flags[static_cast<uint8_t>(c)] & 0x04; }
+static inline bool is_digit(char c)    { return g_token_flags[static_cast<uint8_t>(c)] & 0x08; }
+static inline bool is_numeric(char c)  { return g_token_flags[static_cast<uint8_t>(c)] & 0x10; }
+static inline bool is_eoscope(char c)  { return g_token_flags[static_cast<uint8_t>(c)] & 0x20; }
+
+static inline const char* skip_ws(const char* p) {
+    while (is_ws(*p)) ++p;
+    return p;
+}
+
+static inline float pow10(int32_t exp) {
+    static constexpr float g_pow10_table[63] =
+    {
+       1.e-031f, 1.e-030f, 1.e-029f, 1.e-028f, 1.e-027f, 1.e-026f, 1.e-025f, 1.e-024f,
+       1.e-023f, 1.e-022f, 1.e-021f, 1.e-020f, 1.e-019f, 1.e-018f, 1.e-017f, 1.e-016f,
+       1.e-015f, 1.e-014f, 1.e-013f, 1.e-012f, 1.e-011f, 1.e-010f, 1.e-009f, 1.e-008f,
+       1.e-007f, 1.e-006f, 1.e-005f, 1.e-004f, 1.e-003f, 1.e-002f, 1.e-001f, 1.e+000f,
+       1.e+001f, 1.e+002f, 1.e+003f, 1.e+004f, 1.e+005f, 1.e+006f, 1.e+007f, 1.e+008f,
+       1.e+009f, 1.e+010f, 1.e+011f, 1.e+012f, 1.e+013f, 1.e+014f, 1.e+015f, 1.e+016f,
+       1.e+017f, 1.e+018f, 1.e+019f, 1.e+020f, 1.e+021f, 1.e+022f, 1.e+023f, 1.e+024f,
+       1.e+025f, 1.e+026f, 1.e+027f, 1.e+028f, 1.e+029f, 1.e+030f, 1.e+031f
+    };
+
+    static constexpr int32_t k_exp_offset = SK_ARRAY_COUNT(g_pow10_table) / 2;
+
+    // We only support negative exponents for now.
+    SkASSERT(exp <= 0);
+
+    return (exp >= -k_exp_offset) ? g_pow10_table[exp + k_exp_offset]
+                                  : std::pow(10.0f, static_cast<float>(exp));
+}
+
+class DOMParser {
+public:
+    explicit DOMParser(SkArenaAlloc& alloc)
+        : fAlloc(alloc) {
+
+        fValueStack.reserve(kValueStackReserve);
+        fScopeStack.reserve(kScopeStackReserve);
+    }
+
+    const Value parse(const char* p, size_t size) {
+        if (!size) {
+            return this->error(NullValue(), p, "invalid empty input");
+        }
+
+        const char* p_stop = p + size - 1;
+
+        // We're only checking for end-of-stream on object/array close('}',']'),
+        // so we must trim any whitespace from the buffer tail.
+        while (p_stop > p && is_ws(*p_stop)) --p_stop;
+
+        SkASSERT(p_stop >= p && p_stop < p + size);
+        if (!is_eoscope(*p_stop)) {
+            return this->error(NullValue(), p_stop, "invalid top-level value");
+        }
+
+        p = skip_ws(p);
+
+        switch (*p) {
+        case '{':
+            goto match_object;
+        case '[':
+            goto match_array;
+        default:
+            return this->error(NullValue(), p, "invalid top-level value");
+        }
+
+    match_object:
+        SkASSERT(*p == '{');
+        p = skip_ws(p + 1);
+
+        this->pushObjectScope();
+
+        if (*p == '}') goto pop_object;
+
+        // goto match_object_key;
+    match_object_key:
+        p = skip_ws(p);
+        if (*p != '"') return this->error(NullValue(), p, "expected object key");
+
+        p = this->matchString(p, p_stop, [this](const char* key, size_t size, const char* eos) {
+            this->pushObjectKey(key, size, eos);
+        });
+        if (!p) return NullValue();
+
+        p = skip_ws(p);
+        if (*p != ':') return this->error(NullValue(), p, "expected ':' separator");
+
+        ++p;
+
+        // goto match_value;
+    match_value:
+        p = skip_ws(p);
+
+        switch (*p) {
+        case '\0':
+            return this->error(NullValue(), p, "unexpected input end");
+        case '"':
+            p = this->matchString(p, p_stop, [this](const char* str, size_t size, const char* eos) {
+                this->pushString(str, size, eos);
+            });
+            break;
+        case '[':
+            goto match_array;
+        case 'f':
+            p = this->matchFalse(p);
+            break;
+        case 'n':
+            p = this->matchNull(p);
+            break;
+        case 't':
+            p = this->matchTrue(p);
+            break;
+        case '{':
+            goto match_object;
+        default:
+            p = this->matchNumber(p);
+            break;
+        }
+
+        if (!p) return NullValue();
+
+        // goto match_post_value;
+    match_post_value:
+        SkASSERT(!fScopeStack.empty());
+
+        p = skip_ws(p);
+        switch (*p) {
+        case ',':
+            ++p;
+            if (fScopeStack.back() >= 0) {
+                goto match_object_key;
+            } else {
+                goto match_value;
+            }
+        case ']':
+            goto pop_array;
+        case '}':
+            goto pop_object;
+        default:
+            return this->error(NullValue(), p - 1, "unexpected value-trailing token");
+        }
+
+        // unreachable
+        SkASSERT(false);
+
+    pop_object:
+        SkASSERT(*p == '}');
+
+        if (fScopeStack.back() < 0) {
+            return this->error(NullValue(), p, "unexpected object terminator");
+        }
+
+        this->popObjectScope();
+
+        // goto pop_common
+    pop_common:
+        SkASSERT(is_eoscope(*p));
+
+        if (fScopeStack.empty()) {
+            SkASSERT(fValueStack.size() == 1);
+
+            // Success condition: parsed the top level element and reached the stop token.
+            return p == p_stop
+                ? fValueStack.front()
+                : this->error(NullValue(), p + 1, "trailing root garbage");
+        }
+
+        if (p == p_stop) {
+            return this->error(NullValue(), p, "unexpected end-of-input");
+        }
+
+        ++p;
+
+        goto match_post_value;
+
+    match_array:
+        SkASSERT(*p == '[');
+        p = skip_ws(p + 1);
+
+        this->pushArrayScope();
+
+        if (*p != ']') goto match_value;
+
+        // goto pop_array;
+    pop_array:
+        SkASSERT(*p == ']');
+
+        if (fScopeStack.back() >= 0) {
+            return this->error(NullValue(), p, "unexpected array terminator");
+        }
+
+        this->popArrayScope();
+
+        goto pop_common;
+
+        SkASSERT(false);
+        return NullValue();
+    }
+
+    std::tuple<const char*, const SkString> getError() const {
+        return std::make_tuple(fErrorToken, fErrorMessage);
+    }
+
+private:
+    SkArenaAlloc&         fAlloc;
+
+    static constexpr size_t kValueStackReserve = 256;
+    static constexpr size_t kScopeStackReserve = 128;
+    std::vector<Value   > fValueStack;
+    std::vector<intptr_t> fScopeStack;
+
+    const char*           fErrorToken = nullptr;
+    SkString              fErrorMessage;
+
+    template <typename VectorT>
+    void popScopeAsVec(size_t scope_start) {
+        SkASSERT(scope_start > 0);
+        SkASSERT(scope_start <= fValueStack.size());
+
+        using T = typename VectorT::ValueT;
+        static_assert( sizeof(T) >=  sizeof(Value), "");
+        static_assert( sizeof(T)  %  sizeof(Value) == 0, "");
+        static_assert(alignof(T) == alignof(Value), "");
+
+        const auto scope_count = fValueStack.size() - scope_start,
+                         count = scope_count / (sizeof(T) / sizeof(Value));
+        SkASSERT(scope_count % (sizeof(T) / sizeof(Value)) == 0);
+
+        const auto* begin = reinterpret_cast<const T*>(fValueStack.data() + scope_start);
+
+        // Instantiate the placeholder value added in onPush{Object/Array}.
+        fValueStack[scope_start - 1] = VectorT(begin, count, fAlloc);
+
+        // Drop the current scope.
+        fScopeStack.pop_back();
+        fValueStack.resize(scope_start);
+    }
+
+    void pushObjectScope() {
+        // Object placeholder.
+        fValueStack.emplace_back();
+
+        // Object scope marker (size).
+        fScopeStack.push_back(SkTo<intptr_t>(fValueStack.size()));
+    }
+
+    void popObjectScope() {
+        const auto scope_start = fScopeStack.back();
+        SkASSERT(scope_start > 0);
+        this->popScopeAsVec<ObjectValue>(SkTo<size_t>(scope_start));
+
+        SkDEBUGCODE(
+            const auto& obj = fValueStack.back().as<ObjectValue>();
+            SkASSERT(obj.is<ObjectValue>());
+            for (const auto& member : obj) {
+                SkASSERT(member.fKey.is<StringValue>());
+            }
+        )
+    }
+
+    void pushArrayScope() {
+        // Array placeholder.
+        fValueStack.emplace_back();
+
+        // Array scope marker (-size).
+        fScopeStack.push_back(-SkTo<intptr_t>(fValueStack.size()));
+    }
+
+    void popArrayScope() {
+        const auto scope_start = -fScopeStack.back();
+        SkASSERT(scope_start > 0);
+        this->popScopeAsVec<ArrayValue>(SkTo<size_t>(scope_start));
+
+        SkDEBUGCODE(
+            const auto& arr = fValueStack.back().as<ArrayValue>();
+            SkASSERT(arr.is<ArrayValue>());
+        )
+    }
+
+    void pushObjectKey(const char* key, size_t size, const char* eos) {
+        SkASSERT(fScopeStack.back() >= 0);
+        SkASSERT(fValueStack.size() >= SkTo<size_t>(fScopeStack.back()));
+        SkASSERT(!((fValueStack.size() - SkTo<size_t>(fScopeStack.back())) & 1));
+        this->pushString(key, size, eos);
+    }
+
+    void pushTrue() {
+        fValueStack.push_back(BoolValue(true));
+    }
+
+    void pushFalse() {
+        fValueStack.push_back(BoolValue(false));
+    }
+
+    void pushNull() {
+        fValueStack.push_back(NullValue());
+    }
+
+    void pushString(const char* s, size_t size, const char* eos) {
+        fValueStack.push_back(FastString(s, size, eos, fAlloc));
+    }
+
+    void pushInt32(int32_t i) {
+        fValueStack.push_back(NumberValue(i));
+    }
+
+    void pushFloat(float f) {
+        fValueStack.push_back(NumberValue(f));
+    }
+
+    template <typename T>
+    T error(T&& ret_val, const char* p, const char* msg) {
+#if defined(SK_JSON_REPORT_ERRORS)
+        fErrorToken = p;
+        fErrorMessage.set(msg);
+#endif
+        return ret_val;
+    }
+
+    const char* matchTrue(const char* p) {
+        SkASSERT(p[0] == 't');
+
+        if (p[1] == 'r' && p[2] == 'u' && p[3] == 'e') {
+            this->pushTrue();
+            return p + 4;
+        }
+
+        return this->error(nullptr, p, "invalid token");
+    }
+
+    const char* matchFalse(const char* p) {
+        SkASSERT(p[0] == 'f');
+
+        if (p[1] == 'a' && p[2] == 'l' && p[3] == 's' && p[4] == 'e') {
+            this->pushFalse();
+            return p + 5;
+        }
+
+        return this->error(nullptr, p, "invalid token");
+    }
+
+    const char* matchNull(const char* p) {
+        SkASSERT(p[0] == 'n');
+
+        if (p[1] == 'u' && p[2] == 'l' && p[3] == 'l') {
+            this->pushNull();
+            return p + 4;
+        }
+
+        return this->error(nullptr, p, "invalid token");
+    }
+
+    template <typename MatchFunc>
+    const char* matchString(const char* p, const char* p_stop, MatchFunc&& func) {
+        SkASSERT(*p == '"');
+        const auto* s_begin = p + 1;
+
+        // TODO: unescape
+
+        do {
+            // Consume string chars.
+            for (p = p + 1; !is_eostring(*p); ++p);
+
+            if (*p == '"') {
+                // Valid string found.
+                func(s_begin, p - s_begin, p_stop);
+                return p + 1;
+            }
+
+            // End-of-scope chars are special: we use them to tag the end of the input.
+            // Thus they cannot be consumed indiscriminately -- we need to check if we hit the
+            // end of the input.  To that effect, we treat them as string terminators above,
+            // then we catch them here.
+        } while (is_eoscope(*p) && (p != p_stop)); // Safe scope terminator char, keep going.
+
+        // Premature end-of-input, or illegal string char.
+        return this->error(nullptr, s_begin - 1, "invalid string");
+    }
+
+    const char* matchFastFloatDecimalPart(const char* p, int sign, float f, int exp) {
+        SkASSERT(exp <= 0);
+
+        for (;;) {
+            if (!is_digit(*p)) break;
+            f = f * 10.f + (*p++ - '0'); --exp;
+            if (!is_digit(*p)) break;
+            f = f * 10.f + (*p++ - '0'); --exp;
+        }
+
+        if (is_numeric(*p)) {
+            SkASSERT(*p == '.' || *p == 'e' || *p == 'E');
+            // We either have malformed input, or an (unsupported) exponent.
+            return nullptr;
+        }
+
+        this->pushFloat(sign * f * pow10(exp));
+
+        return p;
+    }
+
+    const char* matchFastFloatPart(const char* p, int sign, float f) {
+        for (;;) {
+            if (!is_digit(*p)) break;
+            f = f * 10.f + (*p++ - '0');
+            if (!is_digit(*p)) break;
+            f = f * 10.f + (*p++ - '0');
+        }
+
+        if (!is_numeric(*p)) {
+            // Matched (integral) float.
+            this->pushFloat(sign * f);
+            return p;
+        }
+
+        return (*p == '.') ? this->matchFastFloatDecimalPart(p + 1, sign, f, 0)
+                           : nullptr;
+    }
+
+    const char* matchFast32OrFloat(const char* p) {
+        int sign = 1;
+        if (*p == '-') {
+            sign = -1;
+            ++p;
+        }
+
+        const auto* digits_start = p;
+
+        int32_t n32 = 0;
+
+        // This is the largest absolute int32 value we can handle before
+        // risking overflow *on the next digit* (214748363).
+        static constexpr int32_t kMaxInt32 = (std::numeric_limits<int32_t>::max() - 9) / 10;
+
+        if (is_digit(*p)) {
+            n32 = (*p++ - '0');
+            for (;;) {
+                if (!is_digit(*p) || n32 > kMaxInt32) break;
+                n32 = n32 * 10 + (*p++ - '0');
+            }
+        }
+
+        if (!is_numeric(*p)) {
+            // Did we actually match any digits?
+            if (p > digits_start) {
+                this->pushInt32(sign * n32);
+                return p;
+            }
+            return nullptr;
+        }
+
+        if (*p == '.') {
+            const auto* decimals_start = ++p;
+
+            int exp = 0;
+
+            for (;;) {
+                if (!is_digit(*p) || n32 > kMaxInt32) break;
+                n32 = n32 * 10 + (*p++ - '0'); --exp;
+                if (!is_digit(*p) || n32 > kMaxInt32) break;
+                n32 = n32 * 10 + (*p++ - '0'); --exp;
+            }
+
+            if (!is_numeric(*p)) {
+                // Did we actually match any digits?
+                if (p > decimals_start) {
+                    this->pushFloat(sign * n32 * pow10(exp));
+                    return p;
+                }
+                return nullptr;
+            }
+
+            if (n32 > kMaxInt32) {
+                // we ran out on n32 bits
+                return this->matchFastFloatDecimalPart(p, sign, n32, exp);
+            }
+        }
+
+        return this->matchFastFloatPart(p, sign, n32);
+    }
+
+    const char* matchNumber(const char* p) {
+        if (const auto* fast = this->matchFast32OrFloat(p)) return fast;
+
+        // slow fallback
+        char* matched;
+        float f = strtof(p, &matched);
+        if (matched > p) {
+            this->pushFloat(f);
+            return matched;
+        }
+        return this->error(nullptr, p, "invalid numeric token");
+    }
+};
+
+void Write(const Value& v, SkWStream* stream) {
+    switch (v.getType()) {
+    case Value::Type::kNull:
+        stream->writeText("null");
+        break;
+    case Value::Type::kBool:
+        stream->writeText(*v.as<BoolValue>() ? "true" : "false");
+        break;
+    case Value::Type::kNumber:
+        stream->writeScalarAsText(*v.as<NumberValue>());
+        break;
+    case Value::Type::kString:
+        stream->writeText("\"");
+        stream->writeText(v.as<StringValue>().begin());
+        stream->writeText("\"");
+        break;
+    case Value::Type::kArray: {
+        const auto& array = v.as<ArrayValue>();
+        stream->writeText("[");
+        bool first_value = true;
+        for (const auto& v : array) {
+            if (!first_value) stream->writeText(",");
+            Write(v, stream);
+            first_value = false;
+        }
+        stream->writeText("]");
+        break;
+    }
+    case Value::Type::kObject:
+        const auto& object = v.as<ObjectValue>();
+        stream->writeText("{");
+        bool first_member = true;
+        for (const auto& member : object) {
+            SkASSERT(member.fKey.getType() == Value::Type::kString);
+            if (!first_member) stream->writeText(",");
+            Write(member.fKey, stream);
+            stream->writeText(":");
+            Write(member.fValue, stream);
+            first_member = false;
+        }
+        stream->writeText("}");
+        break;
+    }
+}
+
+} // namespace
+
+SkString Value::toString() const {
+    SkDynamicMemoryWStream wstream;
+    Write(*this, &wstream);
+    const auto data = wstream.detachAsData();
+    // TODO: is there a better way to pass data around without copying?
+    return SkString(static_cast<const char*>(data->data()), data->size());
+}
+
+static constexpr size_t kMinChunkSize = 4096;
+
+DOM::DOM(const char* data, size_t size)
+    : fAlloc(kMinChunkSize) {
+    DOMParser parser(fAlloc);
+
+    fRoot = parser.parse(data, size);
+}
+
+void DOM::write(SkWStream* stream) const {
+    Write(fRoot, stream);
+}
+
+} // namespace skjson