json: Add new module

Only has methods for writing JSON for now.
Will let you create invalid json, but should assert if you do.

1 files changed, 305 insertions, 0 deletions

diff --git a/src/json.cc b/src/json.cc
new file mode 100644
index 0000000..94ff0d4
--- /dev/null
+++ b/src/json.cc
@@ -0,0 +1,305 @@
+#include "json.hh"
+
+#include <cassert>
+#include <charconv>
+#include <cstddef>
+#include <cstdint>
+#include <memory>
+#include <ostream>
+#include <string>
+#include <string_view>
+#include <system_error>
+#include <vector>
+
+namespace json {
+
+namespace {
+
+struct StackEntry {
+  enum class Type : uint8_t {
+    kRoot,
+    kObject,
+    kArray,
+  };
+
+  Type type;
+  bool need_comma{false};
+
+  explicit StackEntry(Type type) : type(type) {}
+};
+
+class BaseWriter : public Writer {
+ public:
+  BaseWriter() : stack_({StackEntry(StackEntry::Type::kRoot)}) {}
+
+  void value(std::string_view value) override {
+    before_value();
+    quote(value);
+  }
+
+  void value(int64_t value) override {
+    before_value();
+    write(value);
+  }
+
+  void value(uint64_t value) override {
+    before_value();
+    write(value);
+  }
+
+  void value(float value) override {
+    before_value();
+    write(value);
+  }
+
+  void value(double value) override {
+    before_value();
+    write(value);
+  }
+
+  void value(bool value) override {
+    before_value();
+    write(value);
+  }
+
+  void start_array() override {
+    before_value();
+    stack_.emplace_back(StackEntry::Type::kArray);
+    write('[');
+  }
+
+  void end_array() override {
+    if (stack_.empty()) {
+      assert(false);
+      return;
+    }
+    assert(stack_.back().type == StackEntry::Type::kArray);
+    stack_.pop_back();
+    write(']');
+    if (!stack_.empty())
+      stack_.back().need_comma = true;
+  }
+
+  void start_object() override {
+    before_value();
+    stack_.emplace_back(StackEntry::Type::kObject);
+    write('{');
+  }
+
+  void key(std::string_view name) override {
+    if (stack_.empty()) {
+      assert(false);
+      return;
+    }
+    assert(stack_.back().type == StackEntry::Type::kObject);
+    if (stack_.back().need_comma) {
+      write(',');
+      stack_.back().need_comma = false;
+    }
+    quote(name);
+    write(':');
+  }
+
+  void end_object() override {
+    if (stack_.empty()) {
+      assert(false);
+      return;
+    }
+    assert(stack_.back().type == StackEntry::Type::kObject);
+    stack_.pop_back();
+    write('}');
+    if (!stack_.empty())
+      stack_.back().need_comma = true;
+  }
+
+  void clear() override {
+    stack_.clear();
+    stack_.emplace_back(StackEntry::Type::kRoot);
+  }
+
+ protected:
+  virtual void write(int64_t value) = 0;
+  virtual void write(uint64_t value) = 0;
+  virtual void write(float value) = 0;
+  virtual void write(double value) = 0;
+  virtual void write(bool value) = 0;
+  virtual void write(char value) = 0;
+  virtual void write(std::string_view value) = 0;
+
+  void write(char const* value) { this->write(std::string_view(value)); }
+
+ private:
+  void before_value() {
+    if (stack_.empty()) {
+      assert(false);
+      return;
+    }
+    if (stack_.back().need_comma) {
+      assert(stack_.back().type != StackEntry::Type::kRoot);
+      write(',');
+    } else {
+      stack_.back().need_comma = true;
+    }
+  }
+
+  void quote(std::string_view str) {
+    write('"');
+    size_t last = 0;
+    while (true) {
+      auto pos = need_quote(str, last);
+      if (pos == std::string_view::npos) {
+        write(str.substr(last));
+        break;
+      }
+      write(str.substr(last, pos - last));
+      switch (str[pos]) {
+        case '"':
+          write("\\\"");
+          break;
+        case '\\':
+          write("\\\\");
+          break;
+        case '\n':
+          write("\\n");
+          break;
+        case '\r':
+          write("\\r");
+          break;
+        case '\t':
+          write("\\t");
+          break;
+        case '\b':
+          write("\\b");
+          break;
+        case '\f':
+          write("\\f");
+          break;
+        default: {
+          char tmp[4];
+          write("\\u");
+          auto [ptr, ec] = std::to_chars(tmp, tmp + sizeof(tmp), str[pos], 16);
+          if (ec == std::errc()) {
+            size_t len = ptr - tmp;
+            assert(len > 0);
+            for (size_t i = 4; i > len; --i)
+              write('0');
+            write(std::string_view(tmp, len));
+          } else {
+            assert(false);
+          }
+          break;
+        };
+      }
+      last = pos + 1;
+    }
+    write('"');
+  }
+
+  static inline size_t need_quote(std::string_view str, size_t offset) {
+    for (; offset < str.size(); ++offset) {
+      if (str[offset] == '\\' || str[offset] == '"' ||
+          (str[offset] >= 0 && str[offset] < ' '))
+        return offset;
+    }
+    return std::string_view::npos;
+  }
+
+  std::vector<StackEntry> stack_;
+};
+
+class IosWriter : public BaseWriter {
+ public:
+  explicit IosWriter(std::ostream& out) : out_(out) {}
+
+  void write(std::string_view value) override { out_ << value; }
+
+  void write(int64_t value) override { out_ << value; }
+
+  void write(uint64_t value) override { out_ << value; }
+
+  void write(float value) override { out_ << value; }
+
+  void write(double value) override { out_ << value; }
+
+  void write(bool value) override { out_ << value; }
+
+  void write(char value) override { out_ << value; }
+
+ private:
+  std::ostream& out_;
+};
+
+class StringWriter : public BaseWriter {
+ public:
+  explicit StringWriter(std::string& out) : out_(out) {}
+
+  void write(std::string_view value) override { out_.append(value); }
+
+  void write(int64_t value) override {
+    auto [ptr, ec] = std::to_chars(tmp_, tmp_ + sizeof(tmp_), value);
+    if (ec == std::errc()) {
+      out_.append(tmp_, ptr - tmp_);
+    } else {
+      assert(false);
+    }
+  }
+
+  void write(uint64_t value) override {
+    auto [ptr, ec] = std::to_chars(tmp_, tmp_ + sizeof(tmp_), value);
+    if (ec == std::errc()) {
+      out_.append(tmp_, ptr - tmp_);
+    } else {
+      assert(false);
+    }
+  }
+
+  void write(float value) override {
+    auto [ptr, ec] = std::to_chars(tmp_, tmp_ + sizeof(tmp_), value);
+    if (ec == std::errc()) {
+      out_.append(tmp_, ptr - tmp_);
+    } else {
+      assert(false);
+    }
+  }
+
+  void write(double value) override {
+    auto [ptr, ec] = std::to_chars(tmp_, tmp_ + sizeof(tmp_), value);
+    if (ec == std::errc()) {
+      out_.append(tmp_, ptr - tmp_);
+    } else {
+      assert(false);
+    }
+  }
+
+  void write(bool value) override { out_.append(value ? "true" : "false"); }
+
+  void write(char value) override { out_.push_back(value); }
+
+  void clear() override {
+    BaseWriter::clear();
+    out_.clear();
+  }
+
+ private:
+  std::string& out_;
+  char tmp_[100];
+};
+
+}  // namespace
+
+void Writer::value(char const* value) { this->value(std::string_view(value)); }
+
+void Writer::value(int value) {
+  static_assert(sizeof(int) <= sizeof(int64_t));
+  this->value(static_cast<int64_t>(value));
+}
+
+std::unique_ptr<Writer> writer(std::string& out) {
+  return std::make_unique<StringWriter>(out);
+}
+
+std::unique_ptr<Writer> writer(std::ostream& out) {
+  return std::make_unique<IosWriter>(out);
+}
+
+}  // namespace json