Basic support for reading and writing JSON objects.

runtime/vm/json.cc

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "vm/json.h"
+
+#include "platform/assert.h"
+#include "platform/utils.h"
+#include "vm/os.h"
+
+namespace dart {
+
+
+JSONScanner::JSONScanner(const char* json_text) {
+  SetText(json_text);
+}
+
+
+void JSONScanner::SetText(const char* json_text) {
+  current_pos_ = json_text;
+  token_start_ = json_text;
+  token_length_ = 0;
+  token_ = TokenIllegal;
+}
+
+
+void JSONScanner::Recognize(Token t) {
+  ++current_pos_;
+  token_ = t;
+}
+
+
+bool JSONScanner::IsLetter(char ch) const {
+  return (('A' <= ch) && (ch <= 'Z')) || (('a' <= ch) && (ch <= 'z'));
+}
+
+
+bool JSONScanner::IsDigit(char ch) const {
+  return ('0' <= ch) && (ch <= '9');
+}
+
+
+bool JSONScanner::IsLiteral(const char* literal) {
+  int i = 0;
+  while ((literal[i] != '\0') && (current_pos_[i] == literal[i])) {

[turnidge, 2012/04/11 17:06:45]

What if current_pos_[i] == '\0'?  Might access beyond the end of the string. 
Please add a test for this case.

+    i++;
+  }
+  if ((literal[i] == '\0') && !IsLetter(current_pos_[i])) {
+    current_pos_ += i;
+    return true;
+  }
+  return false;
+}
+
+
+bool JSONScanner::IsStringLiteral(const char* literal) const {
+  if (token_ != TokenString) {
+    return false;
+  }
+  int i = 0;
+  while ((i < token_length_) && (token_start_[i] == literal[i])) {

[turnidge, 2012/04/11 17:06:45]

What if literal is shorter than the current token?  You might access beyond the
end of the string.  Please add a test for this case.

+    i++;
+  }
+  return (i == token_length_) && (literal[i] == '\0');
+}
+
+
+void JSONScanner::Skip(Token matching_token) {
+  while (!EOM() && (token_ != TokenIllegal)) {
+    Scan();
+    if (token_ == TokenLBrace) {
+      Skip(TokenRBrace);
+    } else if (token_ == TokenLBrack) {
+      Skip(TokenRBrack);
+    } else if (token_ == matching_token) {
+      return;
+    } else if ((token_ == TokenRBrace) || (token_ == TokenRBrack)) {
+      // Mismatched brace or bracket.
+      token_ = TokenIllegal;
+    }
+  }
+}
+
+
+void JSONScanner::ScanString() {
+  ASSERT(*current_pos_ == '"');
+  ++current_pos_;
+  token_start_ = current_pos_;
+  while (*current_pos_ != '"') {
+    if (*current_pos_ == '\0') {
+      token_length_ = 0;
+      token_ = TokenIllegal;
+      return;
+    } else if (*current_pos_ == '\\') {
+      // TODO(hausner): Implement escape sequence.
+      UNIMPLEMENTED();
+    } else if (*current_pos_ < 0) {
+      // UTF-8 not supported.
+      token_length_ = 0;
+      token_ = TokenIllegal;
+      return;
+    } else {
+      ++current_pos_;
+    }
+  }
+  token_ = TokenString;
+  token_length_ = current_pos_ - token_start_;
+  ++current_pos_;
+}
+
+
+void JSONScanner::ScanNumber() {
+  if (*current_pos_ == '-') {
+    ++current_pos_;
+  }
+  if (!IsDigit(*current_pos_)) {
+    token_ = TokenIllegal;
+    token_length_ = 0;
+    return;
+  }
+  while (IsDigit(*current_pos_)) {
+    ++current_pos_;
+  }
+  if ((*current_pos_ == '.') ||
+      (*current_pos_ == 'e') ||
+      (*current_pos_ == 'E')) {
+    // Floating point numbers not supported.
+    token_ = TokenIllegal;
+    token_length_ = 0;
+    return;
+  }
+  token_ = TokenInteger;
+  token_length_ = current_pos_ - token_start_;
+}
+
+
+void JSONScanner::Scan() {
+  while ((*current_pos_ == ' ') ||
+         (*current_pos_ == '\t') ||
+         (*current_pos_ == '\n')) {
+    ++current_pos_;
+  }
+  token_start_ = current_pos_;
+  if (*current_pos_ == '\0') {
+    token_length_ = 0;
+    token_ = TokenEOM;
+    return;
+  }
+  switch (*current_pos_) {
+    case '{':
+      Recognize(TokenLBrace);
+      break;
+    case '}':
+      Recognize(TokenRBrace);
+      break;
+    case '[':
+      Recognize(TokenLBrack);
+      break;
+    case ']':
+      Recognize(TokenRBrack);
+      break;
+    case ':':
+      Recognize(TokenColon);
+      break;
+    case ',':
+      Recognize(TokenComma);
+      break;
+    case '"':
+      ScanString();
+      break;
+    case '0':
+    case '1':
+    case '2':
+    case '3':
+    case '4':
+    case '5':
+    case '6':
+    case '7':
+    case '8':
+    case '9':
+    case '-':
+      ScanNumber();
+      break;
+    default:
+      if (IsLiteral("true")) {
+        token_ = TokenTrue;
+      } else if (IsLiteral("false")) {
+        token_ = TokenFalse;
+      } else if (IsLiteral("null")) {
+        token_ = TokenNull;
+      } else {
+        token_length_ = 0;
+        token_ = TokenIllegal;
+      }
+  }
+}
+
+
+JSONReader::JSONReader(const char* json_object)
+: scanner_(json_object) {
+  Set(json_object);
+}
+
+void JSONReader::Set(const char* json_object) {
+  scanner_.SetText(json_object);
+  json_object_ = json_object;
+  error_ = false;
+}
+
+
+bool JSONReader::Seek(const char* name) {
+  scanner_.SetText(json_object_);
+  scanner_.Scan();
+  if (scanner_.CurrentToken() != JSONScanner::TokenLBrace) {
+    error_ = true;
+    return false;
+  }
+  scanner_.Scan();
+  while (scanner_.CurrentToken() == JSONScanner::TokenString) {
+    bool found = scanner_.IsStringLiteral(name);
+    scanner_.Scan();
+    if (scanner_.CurrentToken() != JSONScanner::TokenColon) {
+      error_ = true;
+      return false;
+    }
+    scanner_.Scan();
+    switch (scanner_.CurrentToken()) {
+      case JSONScanner::TokenString:
+      case JSONScanner::TokenInteger:
+      case JSONScanner::TokenLBrace:
+      case JSONScanner::TokenLBrack:
+      case JSONScanner::TokenTrue:
+      case JSONScanner::TokenFalse:
+      case JSONScanner::TokenNull:
+        // Found a legal value.
+        if (found) {
+          return true;
+        }
+        break;
+      default:
+        error_ = true;
+        return false;
+    }
+    // Skip the value.
+    if (scanner_.CurrentToken() == JSONScanner::TokenLBrace) {
+      scanner_.Skip(JSONScanner::TokenRBrace);
+      if (scanner_.CurrentToken() != JSONScanner::TokenRBrace) {
+        error_ = true;
+        return false;
+      }
+    } else if (scanner_.CurrentToken() == JSONScanner::TokenLBrack) {
+      scanner_.Skip(JSONScanner::TokenRBrack);
+      if (scanner_.CurrentToken() != JSONScanner::TokenRBrack) {
+        error_ = true;
+        return false;
+      }
+    }
+    scanner_.Scan();  // Value or closing brace or bracket.
+    if (scanner_.CurrentToken() == JSONScanner::TokenComma) {
+      scanner_.Scan();
+    } else {
+      // End of json object or malformed object. Value not found.
+      error_ = true;
+      break;
+    }
+  }
+  return false;
+}
+
+
+JSONReader::JSONType JSONReader::Type() const {
+  if (error_) {
+    return kNone;
+  }
+  switch (scanner_.CurrentToken()) {
+    case JSONScanner::TokenString:
+      return kString;
+    case JSONScanner::TokenInteger:
+      return kInteger;
+    case JSONScanner::TokenLBrace:
+      return kObject;
+    case JSONScanner::TokenLBrack:
+      return kArray;
+    case JSONScanner::TokenTrue:
+    case JSONScanner::TokenFalse:
+    case JSONScanner::TokenNull:
+      return kLiteral;
+    default:
+      return kNone;
+  }
+}
+
+
+TextBuffer::TextBuffer(intptr_t buf_size) {
+  ASSERT(buf_size > 0);
+  buf_ = reinterpret_cast<char*>(malloc(buf_size));
+  buf_size_ = buf_size;
+  Clear();
+}
+
+
+TextBuffer::~TextBuffer() {
+  free(buf_);
+  buf_ = NULL;
+}
+
+
+void TextBuffer::Clear() {
+  msg_len_ = 0;
+  buf_[0] = '\0';
+}
+
+
+intptr_t TextBuffer::Printf(const char* format, ...) {
+  va_list args;
+  va_start(args, format);
+  intptr_t remaining = buf_size_ - msg_len_;
+  ASSERT(remaining >= 0);
+  intptr_t len = OS::VSNPrint(buf_ + msg_len_, remaining, format, args);
+  va_end(args);
+  if (len >= remaining) {
+    const int kBufferSpareCapacity = 64;  // Somewhat arbitrary.
+    GrowBuffer(len + kBufferSpareCapacity);
+    remaining = buf_size_ - msg_len_;
+    ASSERT(remaining > len);
+    va_list args2;
+    va_start(args2, format);
+    intptr_t len2 = OS::VSNPrint(buf_ + msg_len_, remaining, format, args2);
+    va_end(args2);
+    ASSERT(len == len2);
+  }
+  msg_len_ += len;
+  buf_[msg_len_] = '\0';
+  return len;
+}
+
+
+void TextBuffer::GrowBuffer(intptr_t len) {
+  intptr_t new_size = buf_size_ + len;
+  char* new_buf = reinterpret_cast<char*>(realloc(buf_, new_size));
+  ASSERT(new_buf != NULL);
+  buf_ = new_buf;
+  buf_size_ = new_size;
+}
+
+}  // namespace dart