forked from Mirrorlandia_minetest/minetest
Optimize JSON string (de)serialization routines
stringstreams were shown to be slow when reading/writing single characters and there is lots of potential by having functions perform on existing buffers whenever possible.
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sfan5
parent
70dc23f996
commit
9ee3dc71f1
@ -18,15 +18,14 @@ with this program; if not, write to the Free Software Foundation, Inc.,
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*/
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#include "serialize.h"
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#include "pointer.h"
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#include "porting.h"
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#include "util/string.h"
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#include "util/hex.h"
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#include "exceptions.h"
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#include "irrlichttypes.h"
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#include <sstream>
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#include <iomanip>
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#include <vector>
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#include <iostream>
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#include <cassert>
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FloatType g_serialize_f32_type = FLOATTYPE_UNKNOWN;
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@ -120,118 +119,148 @@ std::string deSerializeString32(std::istream &is)
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}
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////
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//// JSON
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//// JSON-like strings
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////
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std::string serializeJsonString(const std::string &plain)
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{
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std::ostringstream os(std::ios::binary);
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os << "\"";
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std::string tmp;
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tmp.reserve(plain.size() + 2);
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tmp.push_back('"');
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for (char c : plain) {
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switch (c) {
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case '"':
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os << "\\\"";
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tmp.append("\\\"");
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break;
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case '\\':
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os << "\\\\";
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tmp.append("\\\\");
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break;
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case '\b':
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os << "\\b";
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tmp.append("\\b");
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break;
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case '\f':
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os << "\\f";
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tmp.append("\\f");
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break;
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case '\n':
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os << "\\n";
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tmp.append("\\n");
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break;
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case '\r':
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os << "\\r";
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tmp.append("\\r");
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break;
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case '\t':
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os << "\\t";
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tmp.append("\\t");
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break;
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default: {
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if (c >= 32 && c <= 126) {
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os << c;
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tmp.push_back(c);
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} else {
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u32 cnum = (u8)c;
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os << "\\u" << std::hex << std::setw(4)
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<< std::setfill('0') << cnum;
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// We pretend that Unicode codepoints map to bytes (they don't)
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u8 cnum = static_cast<u8>(c);
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tmp.append("\\u00");
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tmp.push_back(hex_chars[cnum >> 4]);
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tmp.push_back(hex_chars[cnum & 0xf]);
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}
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break;
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}
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}
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}
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os << "\"";
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return os.str();
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tmp.push_back('"');
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return tmp;
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}
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static void deSerializeJsonString(std::string &s)
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{
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assert(s.size() >= 2);
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assert(s.front() == '"' && s.back() == '"');
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size_t w = 0; // write index
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size_t i = 1; // read index
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const size_t len = s.size() - 1; // string length with trailing quote removed
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while (i < len) {
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char c = s[i++];
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assert(c != '"');
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if (c != '\\') {
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s[w++] = c;
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continue;
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}
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if (i >= len)
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throw SerializationError("JSON string ended prematurely");
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char c2 = s[i++];
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switch (c2) {
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case 'b':
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s[w++] = '\b';
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break;
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case 'f':
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s[w++] = '\f';
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break;
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case 'n':
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s[w++] = '\n';
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break;
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case 'r':
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s[w++] = '\r';
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break;
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case 't':
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s[w++] = '\t';
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break;
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case 'u': {
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if (i + 3 >= len)
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throw SerializationError("JSON string ended prematurely");
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unsigned char v[4] = {};
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for (int j = 0; j < 4; j++)
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hex_digit_decode(s[i+j], v[j]);
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i += 4;
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u32 hexnumber = (v[0] << 12) | (v[1] << 8) | (v[2] << 4) | v[3];
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// Note that this does not work for anything other than ASCII
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// but these functions do not actually interact with real JSON input.
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s[w++] = (int) hexnumber;
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break;
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}
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default:
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s[w++] = c2;
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break;
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}
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}
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assert(w <= i && i <= len);
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// Truncate string to current write index
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s.resize(w);
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}
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std::string deSerializeJsonString(std::istream &is)
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{
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std::ostringstream os(std::ios::binary);
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char c, c2;
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std::string tmp;
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char c;
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bool was_backslash = false;
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// Parse initial doublequote
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is >> c;
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c = is.get();
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if (c != '"')
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throw SerializationError("JSON string must start with doublequote");
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tmp.push_back(c);
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// Parse characters
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// Grab the entire json string
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for (;;) {
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c = is.get();
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if (is.eof())
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throw SerializationError("JSON string ended prematurely");
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if (c == '"') {
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return os.str();
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tmp.push_back(c);
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if (was_backslash)
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was_backslash = false;
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else if (c == '\\')
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was_backslash = true;
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else if (c == '"')
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break; // found end of string
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}
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if (c == '\\') {
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c2 = is.get();
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if (is.eof())
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throw SerializationError("JSON string ended prematurely");
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switch (c2) {
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case 'b':
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os << '\b';
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break;
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case 'f':
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os << '\f';
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break;
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case 'n':
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os << '\n';
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break;
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case 'r':
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os << '\r';
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break;
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case 't':
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os << '\t';
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break;
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case 'u': {
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int hexnumber;
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char hexdigits[4 + 1];
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is.read(hexdigits, 4);
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if (is.eof())
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throw SerializationError("JSON string ended prematurely");
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hexdigits[4] = 0;
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std::istringstream tmp_is(hexdigits, std::ios::binary);
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tmp_is >> std::hex >> hexnumber;
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os << (char)hexnumber;
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break;
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}
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default:
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os << c2;
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break;
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}
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} else {
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os << c;
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}
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}
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return os.str();
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deSerializeJsonString(tmp);
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return tmp;
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}
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std::string serializeJsonStringIfNeeded(const std::string &s)
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@ -245,41 +274,21 @@ std::string serializeJsonStringIfNeeded(const std::string &s)
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std::string deSerializeJsonStringIfNeeded(std::istream &is)
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{
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std::stringstream tmp_os(std::ios_base::binary | std::ios_base::in | std::ios_base::out);
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bool expect_initial_quote = true;
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bool is_json = false;
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bool was_backslash = false;
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for (;;) {
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char c = is.get();
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// Check for initial quote
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char c = is.peek();
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if (is.eof())
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break;
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return "";
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if (expect_initial_quote && c == '"') {
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tmp_os << c;
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is_json = true;
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} else if(is_json) {
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tmp_os << c;
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if (was_backslash)
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was_backslash = false;
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else if (c == '\\')
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was_backslash = true;
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else if (c == '"')
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break; // Found end of string
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} else {
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if (c == ' ') {
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// Found end of word
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is.unget();
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break;
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if (c == '"') {
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// json string: defer to the right implementation
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return deSerializeJsonString(is);
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}
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tmp_os << c;
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}
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expect_initial_quote = false;
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}
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if (is_json) {
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return deSerializeJsonString(tmp_os);
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}
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return tmp_os.str();
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// not a json string:
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std::string tmp;
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std::getline(is, tmp, ' ');
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if (!is.eof())
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is.unget(); // we hit a space, put it back
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return tmp;
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}
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