14 files changed, 971 insertions, 0 deletions
diff --git a/sax/inc/sax_decoder.hh b/sax/inc/sax_decoder.hh
new file mode 100644
index 0000000..40a56c9
--- /dev/null
+++ b/sax/inc/sax_decoder.hh
@@ -0,0 +1,57 @@
+#ifndef SAX_DECODER_HH
+#define SAX_DECODER_HH
+
+#include <memory>
+#include <string>
+#include <string_view>
+
+namespace modxml {
+namespace sax {
+
+/**
+ * Decoder returned by DecoderFactory. Used by Processor to turn bytes into
+ * unicode characters.
+ */
+class Decoder {
+ public:
+  virtual ~Decoder() = default;
+
+  enum class State {
+    GOOD = 0,
+    // too little data was given to advance
+    NEED_MORE,
+    // invalid data was given to advance
+    INVALID,
+  };
+
+  /**
+   * Decode as many code points as possible from in (start at in_offset) and
+   * write them to out (start at out_offset) as UTF-8.
+   * All written code points must be valid per Unicode, so inside the
+   * range U+0 to U+10FFFF and not a surrogate pair (U+D800-U+DFFF).
+   * No partial output, only write to out if the whole UTF-8 sequence is
+   * going to fit.
+   * The is always at least 4 bytes available (out.size() - out_offset) when
+   * called.
+   * Advance in_offset for data consumed.
+   * Advance out_offset for code points written. Do NOT write past out.size().
+   * Do NOT resize out.
+   * If at least one code point is decoded and written to out, return GOOD.
+   * If it is not possible to decode a single code point, in_offset and
+   * out_offset should not be advanced and something other than GOOD returned.
+   * Do not keep any references to any of the parameters after returning, next
+   * advance() call will point to the following bytes, but all parameters
+   * may have changed as they are subject to the buffer implementations of the
+   * Processor.
+   */
+  virtual State decode(std::string_view in, std::size_t& in_offset,
+                       std::string& out, std::size_t& out_offset) = 0;
+
+ protected:
+  Decoder() = default;
+};
+
+}  // namespace sax
+}  // namespace modxml
+
+#endif  // SAX_DECODER_HH
diff --git a/sax/inc/sax_decoder_factory.hh b/sax/inc/sax_decoder_factory.hh
new file mode 100644
index 0000000..80f1af3
--- /dev/null
+++ b/sax/inc/sax_decoder_factory.hh
@@ -0,0 +1,35 @@
+#ifndef SAX_DECODER_FACTORY_HH
+#define SAX_DECODER_FACTORY_HH
+
+#include <memory>
+#include <string>
+
+namespace modxml {
+namespace sax {
+
+class Decoder;
+
+/**
+ * Factory for decoders. You can give one to ProcessBuilder.
+ */
+class DecoderFactory {
+ public:
+  virtual ~DecoderFactory() = default;
+
+  /**
+   * If encoding is supported, return a decoder for that encoding.
+   * Return nullptr if not supported and Processor will return
+   * UNKNOWN_ENCODING error.
+   * Note that encoding value isn't cleaned up or validated in any way, it is
+   * reported EXACTLY as found (even if not valid per XML spec).
+   */
+  virtual std::unique_ptr<Decoder> create(std::string const& encoding) = 0;
+
+ protected:
+  DecoderFactory() = default;
+};
+
+}  // namespace sax
+}  // namespace modxml
+
+#endif  // SAX_DECODER_FACTORY_HH
diff --git a/sax/inc/sax_delegate.hh b/sax/inc/sax_delegate.hh
new file mode 100644
index 0000000..ba63e72
--- /dev/null
+++ b/sax/inc/sax_delegate.hh
@@ -0,0 +1,22 @@
+#ifndef MODXML_SAX_DELEGATE_HH
+#define MODXML_SAX_DELEGATE_HH
+
+namespace modxml {
+namespace sax {
+
+/**
+ * Delegate for processor.
+ * Implement to handle events.
+ */
+class Delegate {
+ public:
+  virtual ~Delegate() = default;
+
+ protected:
+  Delegate() = default;
+};
+
+}  // namespace sax
+}  // namespace modxml
+
+#endif  // MODXML_SAX_DELEGATE_HH
diff --git a/sax/inc/sax_error.hh b/sax/inc/sax_error.hh
new file mode 100644
index 0000000..748f995
--- /dev/null
+++ b/sax/inc/sax_error.hh
@@ -0,0 +1,36 @@
+#ifndef MODXML_SAX_ERROR_HH
+#define MODXML_SAX_ERROR_HH
+
+namespace modxml {
+namespace sax {
+
+enum class Error {
+  /**
+   * The XML spec has a list of characters that are never allowed in a document.
+   */
+  INVALID_CHAR,
+  /**
+   * If the document encoding is unsupported or unkown.
+   */
+  UNKNOWN_ENCODING,
+  /**
+   * If the document is incomplete. The is one of the few recoverable errors,
+   * if you call the processor with more data it will continue.
+   */
+  INCOMPLETE,
+  /**
+   * A entity in the document exeeded max buffer size (either set by
+   * ProcessBuilder or the default 10 MiB).
+   */
+  MAX_MEMORY_EXCEEDED,
+  /**
+   * A memory allocation failed. Note that this doesn't protect against
+   * usage of overallocated memory.
+   */
+  OUT_OF_MEMORY,
+};
+
+}  // namespace sax
+}  // namespace modxml
+
+#endif  // MODXML_SAX_ERROR_HH
diff --git a/sax/inc/sax_processor.hh b/sax/inc/sax_processor.hh
new file mode 100644
index 0000000..7ca32f7
--- /dev/null
+++ b/sax/inc/sax_processor.hh
@@ -0,0 +1,37 @@
+#ifndef MODXML_SAX_PROCESSOR_HH
+#define MODXML_SAX_PROCESSOR_HH
+
+#include <memory>
+
+namespace modxml {
+namespace sax {
+
+class Delegate;
+
+/**
+ * The XML processor, or parser if you like that term better.
+ * Feed it data and the processor will give the delegate calls with events or
+ * possibly errors.
+ */
+class Processor {
+ public:
+  virtual ~Processor() = default;
+
+  /**
+   * Construct a Processor. Same as creating a ProcessorBuilder
+   * and not changing any options and just calling build.
+   */
+  static std::unique_ptr<Processor> create(std::shared_ptr<Delegate> delegate);
+
+ protected:
+  Processor() = default;
+
+ private:
+  Processor(Processor const&) = delete;
+  Processor& operator=(Processor const&) = delete;
+};
+
+}  // namespace sax
+}  // namespace modxml
+
+#endif  // MODXML_SAX_PROCESSOR_HH
diff --git a/sax/inc/sax_processor_builder.hh b/sax/inc/sax_processor_builder.hh
new file mode 100644
index 0000000..070fbbf
--- /dev/null
+++ b/sax/inc/sax_processor_builder.hh
@@ -0,0 +1,82 @@
+#ifndef MODXML_SAX_PROCESSOR_BUILDER_HH
+#define MODXML_SAX_PROCESSOR_BUILDER_HH
+
+#include <memory>
+#include <string>
+
+namespace modxml {
+namespace sax {
+
+class DecoderFactory;
+class Delegate;
+class Processor;
+
+/**
+ * Used to construct Processor's with options set if needed.
+ */
+class ProcessorBuilder {
+ public:
+  virtual ~ProcessorBuilder() = default;
+
+  /**
+   * Construct a ProcessorBuilder. All options are set to default.
+   */
+  static std::unique_ptr<ProcessorBuilder> create();
+
+  /**
+   * If you know the encoding of the data sent to the processor set it here,
+   * this will stop the processor from trying to autodetect and will ignore
+   * encoding in any xml declaration if found.
+   * If the encoding is unsupported/unknown the processor will fail with
+   * an error indicating this, same as if it read a xml declaration with
+   * an unsupported or unknown encoding.
+   */
+  virtual ProcessorBuilder* force_encoding(std::string const& str) = 0;
+
+  /**
+   * Set a decoder factory for encodings not supported by library.
+   * Library only calls this for encodings it doesn't support itself.
+   * Library supports UTF-8, UTF-16, UTF-32 and US-ASCII.
+   * If you want to force the decoder factory to be used, force a custom
+   * encoding with force_encoding above.
+   */
+  virtual ProcessorBuilder* custom_decoder_factory(
+      std::shared_ptr<DecoderFactory> custom_decoder_factory) = 0;
+
+  /**
+   * Set the default buffer size the processor should use.
+   * If you give a too small buffer size (such as zero) it will be ignored
+   * and a implementation specific minimum will be used instead.
+   * This is meant as a possible optimization and can be completely ignored.
+   * Note that the processor will allocate more data if it needed.
+   */
+  virtual ProcessorBuilder* set_default_buffer_size(std::size_t size) = 0;
+
+  /**
+   * Set the max buffer size the processor should use.
+   * If you have memory constraints this will block the processing of CDATA,
+   * or other entities from allocating more than the given size.
+   * Default is 10MiB.
+   */
+  virtual ProcessorBuilder* set_max_buffer_size(std::size_t size) = 0;
+
+  /**
+   * Call to construct a Processor with the options setup in this builder,
+   * using the delegate given as parameter.
+   * May be called multiple times, will create an unique Processor each time.
+   */
+  virtual std::unique_ptr<Processor> build(
+      std::shared_ptr<Delegate> delegate) const = 0;
+
+ protected:
+  ProcessorBuilder() = default;
+
+ private:
+  ProcessorBuilder(ProcessorBuilder const&) = delete;
+  ProcessorBuilder& operator=(ProcessorBuilder const&) = delete;
+};
+
+}  // namespace sax
+}  // namespace modxml
+
+#endif  // MODXML_SAX_PROCESSOR_BUILDER_HH
diff --git a/sax/meson.build b/sax/meson.build
new file mode 100644
index 0000000..ccbdef4
--- /dev/null
+++ b/sax/meson.build
@@ -0,0 +1,22 @@
+deps = [
+  base_dep,
+  utf_dep,
+]
+
+inc = include_directories('inc')
+lib = shared_library(
+  'modxmlsax',
+  'src/decoder.cc',
+  'src/sax_processor.cc',
+  'src/sax_processor_builder.cc',
+  'src/utils.cc',
+  dependencies: deps,
+  include_directories: inc,
+  install: true,
+)
+
+sax_dep = declare_dependency(
+  dependencies: deps,
+  include_directories: inc,
+  link_with: lib,
+)
diff --git a/sax/src/decoder.cc b/sax/src/decoder.cc
new file mode 100644
index 0000000..30b1735
--- /dev/null
+++ b/sax/src/decoder.cc
@@ -0,0 +1,321 @@
+#include "decoder.hh"
+
+#include "macros.hh"
+#include "sax_decoder.hh"
+#include "utf16.hh"
+#include "utf32.hh"
+#include "utf8.hh"
+#include "utf_error.hh"
+
+namespace modxml {
+namespace sax {
+
+namespace {
+
+class UtfDecoder : public Decoder {
+ public:
+  State decode(std::string_view in, std::size_t& in_offset,
+               uint32_t* out, std::size_t out_size,
+               std::size_t& out_offset) override {
+    std::size_t const out_start = out_offset;
+    if (bom_ == -1) UNLIKELY {
+      std::size_t tmp = in_offset;
+      uint32_t ret = read(in, tmp);
+      if (ret == utf::NEED_MORE) {
+        return State::NEED_MORE;
+      }
+      if (ret == utf::INVALID) {
+        return State::INVALID;
+      }
+      if (ret == 0xfeff) {
+        // To allow offset to advance and to return, we need to
+        // read at least one more character completely.
+        ret = read(in, tmp);
+        if (ret == utf::NEED_MORE) {
+          return State::NEED_MORE;
+        }
+        if (ret == utf::INVALID) {
+          return State::INVALID;
+        }
+        bom_ = 1;
+      } else {
+        bom_ = 0;
+      }
+      in_offset = tmp;
+      out[out_offset++] = ret;
+      if (out_offset == out_size)
+        return State::GOOD;
+    }
+
+    do {
+      uint32_t ret = read(in, in_offset);
+      if (ret == utf::NEED_MORE) {
+        return out_offset > out_start ? State::GOOD : State::NEED_MORE;
+      }
+      if (ret == utf::INVALID) {
+        return out_offset > out_start ? State::GOOD : State::INVALID;
+      }
+      out[out_offset++] = ret;
+    } while (out_offset < out_size);
+    return State::GOOD;
+  }
+
+ protected:
+  UtfDecoder() = default;
+
+  virtual uint32_t read(std::string_view data, std::size_t& offset) const = 0;
+
+ private:
+  int8_t bom_{-1};
+};
+
+class Utf8Decoder : public UtfDecoder {
+ public:
+  Utf8Decoder() = default;
+
+  uint32_t read(std::string_view data, std::size_t& offset) const override {
+    return utf::read8(data, offset);
+  }
+};
+
+class Utf16BeDecoder : public UtfDecoder {
+ public:
+  Utf16BeDecoder() = default;
+
+  uint32_t read(std::string_view data, std::size_t& offset) const override {
+    return utf::read16be(data, offset);
+  }
+};
+
+class Utf16LeDecoder : public UtfDecoder {
+ public:
+  Utf16LeDecoder() = default;
+
+  uint32_t read(std::string_view data, std::size_t& offset) const override {
+    return utf::read16le(data, offset);
+  }
+};
+
+class Utf32BeDecoder : public UtfDecoder {
+ public:
+  Utf32BeDecoder() = default;
+
+  uint32_t read(std::string_view data, std::size_t& offset) const override {
+    return utf::read32be(data, offset);
+  }
+};
+
+class Utf32LeDecoder : public UtfDecoder {
+ public:
+  Utf32LeDecoder() = default;
+
+  uint32_t read(std::string_view data, std::size_t& offset) const override {
+    return utf::read32le(data, offset);
+  }
+};
+
+class Utf16Decoder : public Decoder {
+ public:
+  Utf16Decoder() = default;
+
+  State decode(std::string_view in, std::size_t& in_offset,
+               uint32_t* out, std::size_t out_size,
+               std::size_t& out_offset) override {
+    std::size_t const out_start = out_offset;
+    if (endian_ == -1) UNLIKELY {
+      std::size_t tmp = in_offset;
+      uint32_t ret = utf::read16be(in, tmp);
+      int8_t endian;
+      if (ret == utf::NEED_MORE) {
+        return State::NEED_MORE;
+      }
+      if (ret == utf::INVALID) {
+        return State::INVALID;
+      }
+      if (ret == 0xfeff) {
+        endian = 1;  // Big endian
+      } else if (ret == 0xfffe) {
+        endian = 0;  // Little endian
+      } else {
+        return State::INVALID;
+      }
+
+      // To allow offset to advance and to return, we need to
+      // read at least one more character completely.
+      ret = endian == 1 ? utf::read16be(in, tmp) : utf::read16le(in, tmp);
+      if (ret == utf::NEED_MORE) {
+        return State::NEED_MORE;
+      }
+      if (ret == utf::INVALID) {
+        return State::INVALID;
+      }
+
+      endian_ = endian;
+      in_offset = tmp;
+      out[out_offset++] = ret;
+      if (out_offset == out_size)
+        return State::GOOD;
+    }
+
+    if (endian_ == 1) {
+      do {
+        uint32_t ret = utf::read16be(in, in_offset);
+        if (ret == utf::NEED_MORE) {
+          return out_offset > out_start ? State::GOOD : State::NEED_MORE;
+        }
+        if (ret == utf::INVALID) {
+          return out_offset > out_start ? State::GOOD : State::INVALID;
+        }
+        out[out_offset++] = ret;
+      } while (out_offset < out_size);
+    } else {
+      do {
+        uint32_t ret = utf::read16le(in, in_offset);
+        if (ret == utf::NEED_MORE) {
+          return out_offset > out_start ? State::GOOD : State::NEED_MORE;
+        }
+        if (ret == utf::INVALID) {
+          return out_offset > out_start ? State::GOOD : State::INVALID;
+        }
+        out[out_offset++] = ret;
+      } while (out_offset < out_size);
+    }
+    return State::GOOD;
+  }
+
+ private:
+  int8_t endian_{-1};
+};
+
+class Utf32Decoder : public Decoder {
+ public:
+  Utf32Decoder() = default;
+
+  State decode(std::string_view in, std::size_t& in_offset,
+               uint32_t* out, std::size_t out_size,
+               std::size_t& out_offset) override {
+    std::size_t const out_start = out_offset;
+    if (endian_ == -1) UNLIKELY {
+      std::size_t tmp = in_offset;
+      uint32_t ret = utf::read32be(in, tmp);
+      int8_t endian;
+      if (ret == utf::NEED_MORE) {
+        return State::NEED_MORE;
+      }
+      if (ret == utf::INVALID) {
+        tmp = in_offset;
+        ret = utf::read32le(in, tmp);
+        if (ret == 0xfeff) {
+          endian = 0;  // Little endian
+        } else {
+          return State::INVALID;
+        }
+      } else if (ret == 0xfeff) {
+        endian = 1;  // Big endian
+      } else {
+        return State::INVALID;
+      }
+
+      // To allow offset to advance and to return, we need to
+      // read the next character completely.
+      ret = endian == 1 ? utf::read32be(in, tmp) : utf::read32le(in, tmp);
+      if (ret == utf::NEED_MORE) {
+        return State::NEED_MORE;
+      }
+      if (ret == utf::INVALID) {
+        return State::INVALID;
+      }
+
+      endian_ = endian;
+      in_offset = tmp;
+      out[out_offset++] = ret;
+      if (out_offset == out_size)
+        return State::GOOD;
+    }
+
+    if (endian_ == 1) {
+      do {
+        uint32_t ret = utf::read32be(in, in_offset);
+        if (ret == utf::NEED_MORE) {
+          return out_offset > out_start ? State::GOOD : State::NEED_MORE;
+        }
+        if (ret == utf::INVALID) {
+          return out_offset > out_start ? State::GOOD : State::INVALID;
+        }
+        out[out_offset++] = ret;
+      } while (out_offset < out_size);
+    } else {
+      do {
+        uint32_t ret = utf::read32le(in, in_offset);
+        if (ret == utf::NEED_MORE) {
+          return out_offset > out_start ? State::GOOD : State::NEED_MORE;
+        }
+        if (ret == utf::INVALID) {
+          return out_offset > out_start ? State::GOOD : State::INVALID;
+        }
+        out[out_offset++] = ret;
+      } while (out_offset < out_size);
+    }
+    return State::GOOD;
+  }
+
+ private:
+  int8_t endian_{-1};
+};
+
+class AsciiDecoder : public Decoder {
+ public:
+  AsciiDecoder() = default;
+
+  State decode(std::string_view in, std::size_t& in_offset,
+               uint32_t* out, std::size_t out_size,
+               std::size_t& out_offset) override {
+    std::size_t const out_start = out_offset;
+    do {
+      if (in_offset == in.size())
+        return out_offset > out_start ? State::GOOD : State::NEED_MORE;
+      if (in[in_offset] & 0x80)
+        return out_offset > out_start ? State::GOOD : State::INVALID;
+      out[out_offset++] = in[in_offset++];
+    } while (out_offset < out_size);
+    return State::GOOD;
+  }
+};
+
+}  // namespace
+
+std::unique_ptr<Decoder> create_utf8_decoder() {
+  return std::make_unique<Utf8Decoder>();
+}
+
+std::unique_ptr<Decoder> create_utf16be_decoder() {
+  return std::make_unique<Utf16BeDecoder>();
+}
+
+std::unique_ptr<Decoder> create_utf16le_decoder() {
+  return std::make_unique<Utf16LeDecoder>();
+}
+
+std::unique_ptr<Decoder> create_utf32be_decoder() {
+  return std::make_unique<Utf32BeDecoder>();
+}
+
+std::unique_ptr<Decoder> create_utf32le_decoder() {
+  return std::make_unique<Utf32LeDecoder>();
+}
+
+std::unique_ptr<Decoder> create_utf16_decoder() {
+  return std::make_unique<Utf16Decoder>();
+}
+
+std::unique_ptr<Decoder> create_utf32_decoder() {
+  return std::make_unique<Utf32Decoder>();
+}
+
+std::unique_ptr<Decoder> create_ascii_decoder() {
+  return std::make_unique<AsciiDecoder>();
+}
+
+}  // namespace sax
+}  // namespace modxml
+
diff --git a/sax/src/decoder.hh b/sax/src/decoder.hh
new file mode 100644
index 0000000..bd2a99a
--- /dev/null
+++ b/sax/src/decoder.hh
@@ -0,0 +1,33 @@
+#ifndef DECODER_HH
+#define DECODER_HH
+
+#include "macros.hh"
+
+#include <memory>
+
+namespace modxml {
+namespace sax {
+
+class Decoder;
+
+// UTF-8 with optional BOM
+std::unique_ptr<Decoder> HIDDEN create_utf8_decoder();
+// UTF-16 with BOM
+std::unique_ptr<Decoder> HIDDEN create_utf16_decoder();
+// UTF-16BE with optional BOM
+std::unique_ptr<Decoder> HIDDEN create_utf16be_decoder();
+// UTF-16LE with optional BOM
+std::unique_ptr<Decoder> HIDDEN create_utf16le_decoder();
+// UTF-32 with BOM
+std::unique_ptr<Decoder> HIDDEN create_utf32_decoder();
+// UTF-32BE with optional BOM
+std::unique_ptr<Decoder> HIDDEN create_utf32be_decoder();
+// UTF-32LE with optional BOM
+std::unique_ptr<Decoder> HIDDEN create_utf32le_decoder();
+// US-ASCII
+std::unique_ptr<Decoder> HIDDEN create_ascii_decoder();
+
+}  // namespace sax
+}  // namespace modxml
+
+#endif  // DECODER_HH
diff --git a/sax/src/processor.hh b/sax/src/processor.hh
new file mode 100644
index 0000000..4a2de29
--- /dev/null
+++ b/sax/src/processor.hh
@@ -0,0 +1,27 @@
+#ifndef PROCESSOR_HH
+#define PROCESSOR_HH
+
+#include "macros.hh"
+
+#include <memory>
+#include <optional>
+#include <string>
+
+namespace modxml {
+namespace sax {
+
+class DecoderFactory;
+class Delegate;
+class Processor;
+
+std::unique_ptr<Processor> HIDDEN create_processor(
+    std::shared_ptr<Delegate> delegate,
+    std::shared_ptr<DecoderFactory> decoder_factory,
+    std::optional<std::string> force_encoding,
+    std::optional<std::size_t> default_buffer_size,
+    std::optional<std::size_t> max_buffer_size);
+
+}  // namespace sax
+}  // namespace modxml
+
+#endif  // PROCESSOR_HH
diff --git a/sax/src/sax_processor.cc b/sax/src/sax_processor.cc
new file mode 100644
index 0000000..ea9f753
--- /dev/null
+++ b/sax/src/sax_processor.cc
@@ -0,0 +1,145 @@
+#include "sax_processor.hh"
+
+#include "sax_decoder.hh"
+#include "processor.hh"
+#include "utils.hh"
+
+#include <algorithm>
+#include <optional>
+#include <utility>
+
+namespace modxml {
+namespace sax {
+
+namespace {
+
+// 2.2 Characters
+// [2] Char ::= #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]
+
+inline bool valid_char(uint32_t c) {
+  // Assume valid unicode (U+0 - U+10ffff except surrogate blocks)
+  if (c >= 0x20 && c <= 0xfffd)
+    return true;
+  if (c == 0x9 || c == 0xa || c == 0xd)
+    return true;
+  return c >= 0x10000;
+}
+
+// 2.3 Common Syntactic Constructs
+// [3] S ::= (#x20 | #x9 | #xD | #xA)+
+
+inline bool is_ws(uint32_t c) {
+  // Assume we already checked for valid_char.
+  return c <= 0x20;
+}
+
+// [4] NameStartChar ::= ":" | [A-Z] | "_" | [a-z] | [#xC0-#xD6] | [#xD8-#xF6] | [#xF8-#x2FF] | [#x370-#x37D] | [#x37F-#x1FFF] | [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF] | [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD] | [#x10000-#xEFFFF]
+// [4a]	NameChar ::= NameStartChar | "-" | "." | [0-9] | #xB7 | [#x0300-#x036F] | [#x203F-#x2040]
+
+inline bool is_namestartchar(uint32_t c) {
+  if (c < 0x41 /* A */)
+    return c == 0x3a /* : */;
+  if (c <= 0x5a /* Z */)
+    return true;
+  if (c < 0x61 /* a */)
+    return c == 0x5f /* _ */;
+  if (c <= 0x7a /* z */)
+    return true;
+  if (c < 0xc0)
+    return false;
+  if (c < 0x300)
+    return c != 0xd7 && c != 0xf7;
+  if (c > 0x37d && c < 0x37f)
+    return false;
+  if (c > 0x1fff && c < 0x200c)
+    return false;
+  if (c > 0x200d && c < 0x2070)
+    return false;
+  if (c > 0x218f && c < 0x2c00)
+    return false;
+  if (c > 0x2fef && c < 0x3001)
+    return false;
+  // Already valid_char so don't check for surrogate pair here.
+  if (c > 0xdfff && c < 0xf900)
+    return false;
+  if (c > 0xfdcf && c < 0xfdf0)
+    return false;
+  if (c > 0xfffd && c < 0x10000)
+    return false;
+  return true;
+}
+
+inline bool is_namechar(uint32_t c) {
+  return is_namestartchar(c) || (c >= 0x2d /* - */ && c <= 0x2e /* . */) ||
+      (c >= 0x30 /* 0 */ && c <= 0x39 /* 9 */) || (c == 0xb7) ||
+      (c >= 0x300 && c <= 0x36f) || (c >= 0x203f && c <= 0x2040);
+}
+
+/* [5]   	Name	   ::=   	NameStartChar (NameChar)*
+[6]   	Names	   ::=   	Name (#x20 Name)*
+[7]   	Nmtoken	   ::=   	(NameChar)+
+[8]   	Nmtokens	   ::=   	Nmtoken (#x20 Nmtoken)*
+*/
+
+class ProcessorImpl : public Processor {
+ public:
+  ProcessorImpl(std::shared_ptr<Delegate> delegate,
+                std::shared_ptr<DecoderFactory> decoder_factory,
+                std::unique_ptr<Decoder> decoder,
+                std::size_t default_buffer_size,
+                std::size_t max_buffer_size)
+      : delegate_(std::move(delegate)),
+        decoder_factory_(std::move(decoder_factory)),
+        decoder_(std::move(decoder)),
+        default_buffer_size_(default_buffer_size),
+        max_buffer_size_(max_buffer_size) {}
+
+ private:
+  std::shared_ptr<Delegate> delegate_;
+  std::shared_ptr<DecoderFactory> decoder_factory_;
+  std::unique_ptr<Decoder> decoder_;
+  std::size_t default_buffer_size_;
+  std::size_t max_buffer_size_;
+};
+
+}  // namespace
+
+std::unique_ptr<Processor> create_processor(
+    std::shared_ptr<Delegate> delegate,
+    std::shared_ptr<DecoderFactory> decoder_factory,
+    std::optional<std::string> force_encoding,
+    std::optional<std::size_t> opt_default_buffer_size,
+    std::optional<std::size_t> opt_max_buffer_size) {
+
+  std::unique_ptr<Decoder> decoder;
+  if (force_encoding.has_value()) {
+    decoder = pick_decoder_for_encoding(force_encoding.value(),
+                                        decoder_factory.get());
+  }
+
+  std::size_t default_buffer_size = 8192;
+  if (opt_default_buffer_size.has_value())
+    default_buffer_size = std::max(static_cast<std::size_t>(128),
+                                   opt_default_buffer_size.value());
+  // This value is documented in public headers. Do NOT change.
+  std::size_t max_buffer_size = 10 * 1024 * 1024;
+  // No validation for user set value. If it is too small MAX_MEMORY_EXCEEDED
+  // error will be thrown. If it is too large we will get OUT_OF_MEMORY or
+  // crash depending on platform.
+  if (opt_max_buffer_size.has_value())
+    max_buffer_size = opt_max_buffer_size.value();
+
+  return std::make_unique<ProcessorImpl>(std::move(delegate),
+                                         std::move(decoder_factory),
+                                         std::move(decoder),
+                                         default_buffer_size,
+                                         max_buffer_size);
+}
+
+std::unique_ptr<Processor> create(std::shared_ptr<Delegate> delegate) {
+  return create_processor(std::move(delegate), nullptr,
+                          std::nullopt, std::nullopt, std::nullopt);
+}
+
+}  // namespace sax
+}  // namespace modxml
diff --git a/sax/src/sax_processor_builder.cc b/sax/src/sax_processor_builder.cc
new file mode 100644
index 0000000..8817099
--- /dev/null
+++ b/sax/src/sax_processor_builder.cc
@@ -0,0 +1,62 @@
+#include "sax_processor_builder.hh"
+
+#include "processor.hh"
+#include "sax_processor.hh"
+
+#include <optional>
+#include <utility>
+
+namespace modxml {
+namespace sax {
+
+namespace {
+
+class ProcessorBuilderImpl : public ProcessorBuilder {
+ public:
+  ProcessorBuilder* force_encoding(std::string const& str) override {
+    force_encoding_ = str;
+    return this;
+  }
+
+  ProcessorBuilder* custom_decoder_factory(
+      std::shared_ptr<DecoderFactory> custom_decoder_factory) override {
+    decoder_factory_ = std::move(custom_decoder_factory);
+    return this;
+  }
+
+  ProcessorBuilder* set_default_buffer_size(std::size_t size) override {
+    default_buffer_size_ = size;
+    return this;
+  }
+
+  ProcessorBuilder* set_max_buffer_size(std::size_t size) override {
+    max_buffer_size_ = size;
+    return this;
+  }
+
+  std::unique_ptr<Processor> build(
+      std::shared_ptr<Delegate> delegate) const override {
+    return create_processor(std::move(delegate),
+                            decoder_factory_,
+                            force_encoding_,
+                            default_buffer_size_,
+                            max_buffer_size_);
+  }
+
+  ProcessorBuilderImpl() = default;
+
+ private:
+  std::shared_ptr<DecoderFactory> decoder_factory_;
+  std::optional<std::string> force_encoding_;
+  std::optional<std::size_t> default_buffer_size_;
+  std::optional<std::size_t> max_buffer_size_;
+};
+
+}  // namespace
+
+std::unique_ptr<ProcessorBuilder> ProcessorBuilder::create() {
+  return std::make_unique<ProcessorBuilderImpl>();
+}
+
+}  // namespace sax
+}  // namespace modxml
diff --git a/sax/src/utils.cc b/sax/src/utils.cc
new file mode 100644
index 0000000..f0366d5
--- /dev/null
+++ b/sax/src/utils.cc
@@ -0,0 +1,70 @@
+#include "utils.hh"
+
+#include "decoder.hh"
+#include "sax_decoder.hh"
+#include "sax_decoder_factory.hh"
+
+namespace modxml {
+namespace sax {
+
+namespace {
+
+std::string cleanup_encoding(std::string const& str) {
+  std::string ret;
+  ret.reserve(str.size());
+  for (auto c : str) {
+    if (c >= 'A' && c <= 'Z') {
+      ret.push_back(c | 0x20);
+    } else if ((c >= 'a' && c <= 'z') || (c >= '0' && c <= '9')) {
+      ret.push_back(c);
+    } else if (c == '.' || c == '_' || c == '-') {
+      ret.push_back('-');
+    }
+  }
+  return ret;
+}
+
+}  // namespace
+
+// Names inspired by:
+// https://www.iana.org/assignments/character-sets/character-sets.xhtml
+std::unique_ptr<Decoder> pick_decoder_for_encoding(
+    std::string const& encoding, DecoderFactory* factory) {
+  auto clean_enc = cleanup_encoding(encoding);
+  if (clean_enc == "utf-8" || clean_enc == "utf8") {
+    return create_utf8_decoder();
+  }
+  if (clean_enc == "utf-16" || clean_enc == "utf16") {
+    return create_utf16_decoder();
+  }
+  if (clean_enc == "utf-16be" || clean_enc == "utf16be") {
+    return create_utf16be_decoder();
+  }
+  if (clean_enc == "utf-16le" || clean_enc == "utf16le") {
+    return create_utf16le_decoder();
+  }
+  if (clean_enc == "utf-32" || clean_enc == "utf32") {
+    return create_utf32_decoder();
+  }
+  if (clean_enc == "utf-32be" || clean_enc == "utf32be") {
+    return create_utf32be_decoder();
+  }
+  if (clean_enc == "utf-32le" || clean_enc == "utf32le") {
+    return create_utf32le_decoder();
+  }
+  if (clean_enc == "ascii" || clean_enc == "us-ascii" ||
+      clean_enc == "usascii" || clean_enc == "iso-ir-6" ||
+      clean_enc == "ansi-x3-4-1968" || clean_enc == "ansi-x3-4-1986" ||
+      clean_enc == "iso-646-irv1991" || clean_enc == "iso646-us" ||
+      clean_enc == "us" || clean_enc == "ibm367" || clean_enc == "cp367") {
+    return create_ascii_decoder();
+  }
+  if (factory) {
+    return factory->create(encoding);
+  }
+  return nullptr;
+}
+
+}  // namespace sax
+
+}  // namespace modxml
diff --git a/sax/src/utils.hh b/sax/src/utils.hh
new file mode 100644
index 0000000..206d003
--- /dev/null
+++ b/sax/src/utils.hh
@@ -0,0 +1,22 @@
+#ifndef UTILS_HH
+#define UTILS_HH
+
+#include "macros.hh"
+
+#include <memory>
+#include <string>
+
+namespace modxml {
+namespace sax {
+
+class Decoder;
+class DecoderFactory;
+
+std::unique_ptr<Decoder> HIDDEN pick_decoder_for_encoding(
+    std::string const& encoding,
+    DecoderFactory* factory);
+
+}  // namespace sax
+}  // namespace modxml
+
+#endif  // UTILS_HH