1018 lines
36 KiB
C++
1018 lines
36 KiB
C++
// vim: set sw=2 ts=2 sts=2 et tw=100:
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//
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// pdf-simple-sign: simple PDF signer
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//
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// Copyright (c) 2017 - 2020, Přemysl Eric Janouch <p@janouch.name>
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted.
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//
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// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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//
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#include <cmath>
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#include <cstdio>
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#undef NDEBUG
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#include <cassert>
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#include <map>
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#include <memory>
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#include <regex>
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#include <set>
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#include <vector>
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#if defined __GLIBCXX__ && __GLIBCXX__ < 20140422
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#error Need libstdc++ >= 4.9 for <regex>
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#endif
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#include <getopt.h>
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#include <openssl/err.h>
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#include <openssl/pkcs12.h>
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#include <openssl/x509v3.h>
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#include <unistd.h>
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#include "config.h"
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// -------------------------------------------------------------------------------------------------
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using uint = unsigned int;
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using ushort = unsigned short;
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static std::string concatenate(const std::vector<std::string>& v, const std::string& delim) {
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std::string res;
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if (v.empty())
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return res;
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for (const auto& s : v)
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res += s + delim;
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return res.substr(0, res.length() - delim.length());
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}
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template<typename... Args>
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std::string ssprintf(const std::string& format, Args... args) {
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size_t size = std::snprintf(nullptr, 0, format.c_str(), args...) + 1;
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std::unique_ptr<char[]> buf(new char[size]);
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std::snprintf(buf.get(), size, format.c_str(), args...);
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return std::string(buf.get(), buf.get() + size - 1);
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}
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// -------------------------------------------------------------------------------------------------
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/// PDF token/object thingy. Objects may be composed either from one or a sequence of tokens.
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/// The PDF Reference doesn't actually speak of tokens, though ISO 32000-1:2008 does.
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struct pdf_object {
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enum type {
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END, NL, COMMENT, NIL, BOOL, NUMERIC, KEYWORD, NAME, STRING,
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// Simple tokens
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B_ARRAY, E_ARRAY, B_DICT, E_DICT,
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// Higher-level objects
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ARRAY, DICT, OBJECT, REFERENCE,
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} type = END;
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std::string string; ///< END (error message), COMMENT/KEYWORD/NAME/STRING
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double number = 0.; ///< BOOL, NUMERIC
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std::vector<pdf_object> array; ///< ARRAY, OBJECT
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std::map<std::string, pdf_object> dict; ///< DICT, in the future also STREAM
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uint n = 0, generation = 0; ///< OBJECT, REFERENCE
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pdf_object(enum type type = END) : type(type) {}
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pdf_object(enum type type, double v) : type(type), number(v) {}
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pdf_object(enum type type, const std::string& v) : type(type), string(v) {}
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pdf_object(enum type type, uint n, uint g) : type(type), n(n), generation(g) {}
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pdf_object(const std::vector<pdf_object>& array) : type(ARRAY), array(array) {}
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pdf_object(const std::map<std::string, pdf_object>& dict) : type(DICT), dict(dict) {}
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pdf_object(const pdf_object&) = default;
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pdf_object(pdf_object&&) = default;
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pdf_object& operator=(const pdf_object&) = default;
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pdf_object& operator=(pdf_object&&) = default;
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/// Return whether this is a number without a fractional part
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bool is_integer() const {
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double tmp;
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return type == NUMERIC && std::modf(number, &tmp) == 0.;
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}
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};
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/// Basic lexical analyser for the Portable Document Format, giving limited error information
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struct pdf_lexer {
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const unsigned char* p;
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pdf_lexer(const char* s) : p(reinterpret_cast<const unsigned char*>(s)) {}
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static constexpr const char* oct_alphabet = "01234567";
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static constexpr const char* dec_alphabet = "0123456789";
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static constexpr const char* hex_alphabet = "0123456789abcdefABCDEF";
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static constexpr const char* whitespace = "\t\n\f\r ";
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static constexpr const char* delimiters = "()<>[]{}/%";
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bool eat_newline(int ch) {
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if (ch == '\r') {
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if (*p == '\n') p++;
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return true;
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}
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return ch == '\n';
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}
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pdf_object string() {
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std::string value;
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int parens = 1;
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while (1) {
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if (!*p) return {pdf_object::END, "unexpected end of string"};
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auto ch = *p++;
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if (eat_newline(ch)) ch = '\n';
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else if (ch == '(') { parens++; }
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else if (ch == ')') { if (!--parens) break; }
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else if (ch == '\\') {
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if (!*p) return {pdf_object::END, "unexpected end of string"};
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switch ((ch = *p++)) {
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case 'n': ch = '\n'; break;
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case 'r': ch = '\r'; break;
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case 't': ch = '\t'; break;
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case 'b': ch = '\b'; break;
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case 'f': ch = '\f'; break;
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default:
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if (eat_newline(ch))
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continue;
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std::string octal;
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if (ch && strchr(oct_alphabet, ch)) {
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octal += ch;
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if (*p && strchr(oct_alphabet, *p)) octal += *p++;
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if (*p && strchr(oct_alphabet, *p)) octal += *p++;
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ch = std::stoi(octal, nullptr, 8);
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}
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}
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}
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value += ch;
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}
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return {pdf_object::STRING, value};
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}
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pdf_object string_hex() {
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std::string value, buf;
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while (*p != '>') {
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if (!*p) return {pdf_object::END, "unexpected end of hex string"};
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if (!strchr(hex_alphabet, *p))
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return {pdf_object::END, "invalid hex string"};
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buf += *p++;
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if (buf.size() == 2) {
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value += char(std::stoi(buf, nullptr, 16));
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buf.clear();
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}
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}
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p++;
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if (!buf.empty()) value += char(std::stoi(buf + '0', nullptr, 16));
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return {pdf_object::STRING, value};
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}
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pdf_object name() {
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std::string value;
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while (!strchr(whitespace, *p) && !strchr(delimiters, *p)) {
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auto ch = *p++;
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if (ch == '#') {
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std::string hexa;
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if (*p && strchr(hex_alphabet, *p)) hexa += *p++;
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if (*p && strchr(hex_alphabet, *p)) hexa += *p++;
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if (hexa.size() != 2)
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return {pdf_object::END, "invalid name hexa escape"};
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ch = char(std::stoi(hexa, nullptr, 16));
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}
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value += ch;
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}
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if (value.empty()) return {pdf_object::END, "unexpected end of name"};
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return {pdf_object::NAME, value};
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}
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pdf_object comment() {
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std::string value;
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while (*p && *p != '\r' && *p != '\n')
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value += *p++;
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return {pdf_object::COMMENT, value};
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}
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// XXX maybe invalid numbers should rather be interpreted as keywords
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pdf_object number() {
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std::string value;
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if (*p == '-')
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value += *p++;
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bool real = false, digits = false;
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while (*p) {
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if (strchr(dec_alphabet, *p))
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digits = true;
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else if (*p == '.' && !real)
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real = true;
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else
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break;
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value += *p++;
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}
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if (!digits) return {pdf_object::END, "invalid number"};
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return {pdf_object::NUMERIC, std::stod(value, nullptr)};
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}
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pdf_object next() {
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if (!*p)
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return {pdf_object::END};
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if (strchr("-0123456789.", *p))
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return number();
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// {} end up being keywords, we might want to error out on those
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std::string value;
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while (!strchr(whitespace, *p) && !strchr(delimiters, *p))
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value += *p++;
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if (!value.empty()) {
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if (value == "null") return {pdf_object::NIL};
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if (value == "true") return {pdf_object::BOOL, 1};
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if (value == "false") return {pdf_object::BOOL, 0};
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return {pdf_object::KEYWORD, value};
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}
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switch (char ch = *p++) {
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case '/': return name();
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case '%': return comment();
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case '(': return string();
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case '[': return {pdf_object::B_ARRAY};
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case ']': return {pdf_object::E_ARRAY};
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case '<':
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if (*p++ == '<')
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return {pdf_object::B_DICT};
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p--;
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return string_hex();
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case '>':
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if (*p++ == '>')
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return {pdf_object::E_DICT};
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p--;
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return {pdf_object::END, "unexpected '>'"};
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default:
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if (eat_newline(ch))
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return {pdf_object::NL};
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if (strchr(whitespace, ch))
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return next();
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return {pdf_object::END, "unexpected input"};
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}
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}
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};
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// FIXME lines /should not/ be longer than 255 characters, some wrapping is in order
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static std::string pdf_serialize(const pdf_object& o) {
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switch (o.type) {
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case pdf_object::NL: return "\n";
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case pdf_object::NIL: return "null";
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case pdf_object::BOOL: return o.number ? "true" : "false";
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case pdf_object::NUMERIC: {
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if (o.is_integer()) return std::to_string((long long) o.number);
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return std::to_string(o.number);
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}
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case pdf_object::KEYWORD: return o.string;
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case pdf_object::NAME: {
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std::string escaped = "/";
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for (char c : o.string) {
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if (c == '#' || strchr(pdf_lexer::delimiters, c) || strchr(pdf_lexer::whitespace, c))
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escaped += ssprintf("#%02x", c);
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else
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escaped += c;
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}
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return escaped;
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}
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case pdf_object::STRING: {
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std::string escaped;
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for (char c : o.string) {
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if (c == '\\' || c == '(' || c == ')')
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escaped += '\\';
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escaped += c;
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}
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return "(" + escaped + ")";
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}
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case pdf_object::B_ARRAY: return "[";
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case pdf_object::E_ARRAY: return "]";
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case pdf_object::B_DICT: return "<<";
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case pdf_object::E_DICT: return ">>";
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case pdf_object::ARRAY: {
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std::vector<std::string> v;
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for (const auto& i : o.array)
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v.push_back(pdf_serialize(i));
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return "[ " + concatenate(v, " ") + " ]";
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}
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case pdf_object::DICT: {
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std::string s;
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for (const auto i : o.dict)
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// FIXME the key is also supposed to be escaped by pdf_serialize()
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s += " /" + i.first + " " + pdf_serialize(i.second);
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return "<<" + s + " >>";
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}
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case pdf_object::OBJECT:
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return ssprintf("%u %u obj\n", o.n, o.generation) + pdf_serialize(o.array.at(0)) + "\nendobj";
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case pdf_object::REFERENCE:
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return ssprintf("%u %u R", o.n, o.generation);
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default:
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assert(!"unsupported token for serialization");
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}
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}
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// -------------------------------------------------------------------------------------------------
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/// Utility class to help read and possibly incrementally update PDF files
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class pdf_updater {
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struct ref {
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size_t offset = 0; ///< File offset or N of the next free entry
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uint generation = 0; ///< Object generation
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bool free = true; ///< Whether this N has been deleted
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};
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std::vector<ref> xref; ///< Cross-reference table
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size_t xref_size = 0; ///< Current cross-reference table size, correlated to xref.size()
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std::set<uint> updated; ///< List of updated objects
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pdf_object parse_obj(pdf_lexer& lex, std::vector<pdf_object>& stack) const;
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pdf_object parse_R(std::vector<pdf_object>& stack) const;
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pdf_object parse(pdf_lexer& lex, std::vector<pdf_object>& stack) const;
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std::string load_xref(pdf_lexer& lex, std::set<uint>& loaded_entries);
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public:
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/// The new trailer dictionary to be written, initialized with the old one
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std::map<std::string, pdf_object> trailer;
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std::string& document;
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pdf_updater(std::string& document) : document(document) {}
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/// Build the cross-reference table and prepare a new trailer dictionary
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std::string initialize();
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/// Try to extract the claimed PDF version as a positive decimal number, e.g. 17 for PDF 1.7.
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/// Returns zero on failure.
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int version(const pdf_object& root) const;
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/// Retrieve an object by its number and generation -- may return NIL or END with an error
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pdf_object get(uint n, uint generation) const;
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/// Allocate a new object number
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uint allocate();
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/// Append an updated object to the end of the document
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void update(uint n, std::function<void()> fill);
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/// Write an updated cross-reference table and trailer
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void flush_updates();
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};
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// -------------------------------------------------------------------------------------------------
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/// If the object is an error, forward its message, otherwise return err.
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static std::string pdf_error(const pdf_object& o, const char* err) {
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if (o.type != pdf_object::END || o.string.empty()) return err;
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return o.string;
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}
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pdf_object pdf_updater::parse_obj(pdf_lexer& lex, std::vector<pdf_object>& stack) const {
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if (stack.size() < 2)
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return {pdf_object::END, "missing object ID pair"};
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auto g = stack.back(); stack.pop_back();
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auto n = stack.back(); stack.pop_back();
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if (!g.is_integer() || g.number < 0 || g.number > UINT_MAX ||
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!n.is_integer() || n.number < 0 || n.number > UINT_MAX)
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return {pdf_object::END, "invalid object ID pair"};
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pdf_object obj{pdf_object::OBJECT};
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obj.n = n.number;
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obj.generation = g.number;
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while (1) {
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auto object = parse(lex, obj.array);
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if (object.type == pdf_object::END)
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return {pdf_object::END, pdf_error(object, "object doesn't end")};
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if (object.type == pdf_object::KEYWORD && object.string == "endobj")
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break;
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obj.array.push_back(std::move(object));
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}
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return obj;
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}
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pdf_object pdf_updater::parse_R(std::vector<pdf_object>& stack) const {
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if (stack.size() < 2)
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return {pdf_object::END, "missing reference ID pair"};
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auto g = stack.back(); stack.pop_back();
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auto n = stack.back(); stack.pop_back();
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if (!g.is_integer() || g.number < 0 || g.number > UINT_MAX ||
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!n.is_integer() || n.number < 0 || n.number > UINT_MAX)
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return {pdf_object::END, "invalid reference ID pair"};
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pdf_object ref{pdf_object::REFERENCE};
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ref.n = n.number;
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ref.generation = g.number;
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return ref;
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}
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/// Read an object at the lexer's position. Not a strict parser.
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pdf_object pdf_updater::parse(pdf_lexer& lex, std::vector<pdf_object>& stack) const {
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auto token = lex.next();
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switch (token.type) {
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case pdf_object::NL:
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case pdf_object::COMMENT:
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// These are not important to parsing, not even for this procedure's needs
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return parse(lex, stack);
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case pdf_object::B_ARRAY: {
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std::vector<pdf_object> array;
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while (1) {
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auto object = parse(lex, array);
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if (object.type == pdf_object::END)
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return {pdf_object::END, pdf_error(object, "array doesn't end")};
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if (object.type == pdf_object::E_ARRAY)
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break;
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array.push_back(std::move(object));
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}
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return array;
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}
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case pdf_object::B_DICT: {
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std::vector<pdf_object> array;
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while (1) {
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auto object = parse(lex, array);
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if (object.type == pdf_object::END)
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return {pdf_object::END, pdf_error(object, "dictionary doesn't end")};
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if (object.type == pdf_object::E_DICT)
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break;
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array.push_back(std::move(object));
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}
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if (array.size() % 2)
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return {pdf_object::END, "unbalanced dictionary"};
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std::map<std::string, pdf_object> dict;
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for (size_t i = 0; i < array.size(); i += 2) {
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if (array[i].type != pdf_object::NAME)
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return {pdf_object::END, "invalid dictionary key type"};
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dict.insert({array[i].string, std::move(array[i + 1])});
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}
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return dict;
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}
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case pdf_object::KEYWORD:
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// Appears in the document body, typically needs to access the cross-reference table
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// TODO use the xref to read /Length etc. once we actually need to read such objects;
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// presumably streams can use the pdf_object::string member
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if (token.string == "stream") return {pdf_object::END, "streams are not supported yet"};
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if (token.string == "obj") return parse_obj(lex, stack);
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if (token.string == "R") return parse_R(stack);
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return token;
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default:
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return token;
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}
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}
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std::string pdf_updater::load_xref(pdf_lexer& lex, std::set<uint>& loaded_entries) {
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std::vector<pdf_object> throwaway_stack;
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{
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auto keyword = parse(lex, throwaway_stack);
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if (keyword.type != pdf_object::KEYWORD || keyword.string != "xref")
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return "invalid xref table";
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}
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while (1) {
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auto object = parse(lex, throwaway_stack);
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if (object.type == pdf_object::END)
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return pdf_error(object, "unexpected EOF while looking for the trailer");
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if (object.type == pdf_object::KEYWORD && object.string == "trailer")
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break;
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auto second = parse(lex, throwaway_stack);
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if (!object.is_integer() || object.number < 0 || object.number > UINT_MAX ||
|
|
!second.is_integer() || second.number < 0 || second.number > UINT_MAX)
|
|
return "invalid xref section header";
|
|
|
|
const size_t start = object.number;
|
|
const size_t count = second.number;
|
|
for (size_t i = 0; i < count; i++) {
|
|
auto off = parse(lex, throwaway_stack);
|
|
auto gen = parse(lex, throwaway_stack);
|
|
auto key = parse(lex, throwaway_stack);
|
|
if (!off.is_integer() || off.number < 0 || off.number > document.length() ||
|
|
!gen.is_integer() || gen.number < 0 || gen.number > 65535 ||
|
|
key.type != pdf_object::KEYWORD)
|
|
return "invalid xref entry";
|
|
|
|
bool free = true;
|
|
if (key.string == "n")
|
|
free = false;
|
|
else if (key.string != "f")
|
|
return "invalid xref entry";
|
|
|
|
auto n = start + i;
|
|
if (loaded_entries.count(n))
|
|
continue;
|
|
if (n >= xref.size())
|
|
xref.resize(n + 1);
|
|
loaded_entries.insert(n);
|
|
|
|
auto& ref = xref[n];
|
|
ref.generation = gen.number;
|
|
ref.offset = off.number;
|
|
ref.free = free;
|
|
}
|
|
}
|
|
return "";
|
|
}
|
|
|
|
// -------------------------------------------------------------------------------------------------
|
|
|
|
std::string pdf_updater::initialize() {
|
|
// We only need to look for startxref roughly within the last kibibyte of the document
|
|
static std::regex haystack_re(R"([\s\S]*\sstartxref\s+(\d+)\s+%%EOF)");
|
|
std::string haystack = document.substr(document.length() < 1024 ? 0 : document.length() - 1024);
|
|
|
|
std::smatch m;
|
|
if (!std::regex_search(haystack, m, haystack_re, std::regex_constants::match_continuous))
|
|
return "cannot find startxref";
|
|
|
|
size_t xref_offset = std::stoul(m.str(1)), last_xref_offset = xref_offset;
|
|
std::set<size_t> loaded_xrefs;
|
|
std::set<uint> loaded_entries;
|
|
|
|
std::vector<pdf_object> throwaway_stack;
|
|
while (1) {
|
|
if (loaded_xrefs.count(xref_offset))
|
|
return "circular xref offsets";
|
|
if (xref_offset >= document.length())
|
|
return "invalid xref offset";
|
|
|
|
pdf_lexer lex(document.c_str() + xref_offset);
|
|
auto err = load_xref(lex, loaded_entries);
|
|
if (!err.empty()) return err;
|
|
|
|
auto trailer = parse(lex, throwaway_stack);
|
|
if (trailer.type != pdf_object::DICT)
|
|
return pdf_error(trailer, "invalid trailer dictionary");
|
|
if (loaded_xrefs.empty())
|
|
this->trailer = trailer.dict;
|
|
loaded_xrefs.insert(xref_offset);
|
|
|
|
const auto prev_offset = trailer.dict.find("Prev");
|
|
if (prev_offset == trailer.dict.end())
|
|
break;
|
|
// FIXME do not read offsets and sizes as floating point numbers
|
|
if (!prev_offset->second.is_integer() || prev_offset->second.number < 0)
|
|
return "invalid Prev offset";
|
|
xref_offset = prev_offset->second.number;
|
|
}
|
|
|
|
trailer["Prev"] = {pdf_object::NUMERIC, double(last_xref_offset)};
|
|
const auto last_size = trailer.find("Size");
|
|
if (last_size == trailer.end() || !last_size->second.is_integer() ||
|
|
last_size->second.number <= 0)
|
|
return "invalid or missing cross-reference table Size";
|
|
|
|
xref_size = last_size->second.number;
|
|
return "";
|
|
}
|
|
|
|
int pdf_updater::version(const pdf_object& root) const {
|
|
auto version = root.dict.find("Version");
|
|
if (version != root.dict.end() && version->second.type == pdf_object::NAME) {
|
|
const auto& v = version->second.string;
|
|
if (isdigit(v[0]) && v[1] == '.' && isdigit(v[2]) && !v[3])
|
|
return (v[0] - '0') * 10 + (v[2] - '0');
|
|
}
|
|
|
|
// We only need to look for the comment roughly within the first kibibyte of the document
|
|
static std::regex version_re(R"((?:^|[\r\n])%(?:!PS-Adobe-\d\.\d )?PDF-(\d)\.(\d)[\r\n])");
|
|
std::string haystack = document.substr(0, 1024);
|
|
|
|
std::smatch m;
|
|
if (std::regex_search(haystack, m, version_re, std::regex_constants::match_default))
|
|
return std::stoul(m.str(1)) * 10 + std::stoul(m.str(2));
|
|
|
|
return 0;
|
|
}
|
|
|
|
pdf_object pdf_updater::get(uint n, uint generation) const {
|
|
if (n >= xref_size)
|
|
return {pdf_object::NIL};
|
|
|
|
const auto& ref = xref[n];
|
|
if (ref.free || ref.generation != generation || ref.offset >= document.length())
|
|
return {pdf_object::NIL};
|
|
|
|
pdf_lexer lex(document.c_str() + ref.offset);
|
|
std::vector<pdf_object> stack;
|
|
while (1) {
|
|
auto object = parse(lex, stack);
|
|
if (object.type == pdf_object::END)
|
|
return object;
|
|
if (object.type != pdf_object::OBJECT)
|
|
stack.push_back(std::move(object));
|
|
else if (object.n != n || object.generation != generation)
|
|
return {pdf_object::END, "object mismatch"};
|
|
else
|
|
return std::move(object.array.at(0));
|
|
}
|
|
}
|
|
|
|
uint pdf_updater::allocate() {
|
|
assert(xref_size < UINT_MAX);
|
|
|
|
auto n = xref_size++;
|
|
if (xref.size() < xref_size)
|
|
xref.resize(xref_size);
|
|
|
|
// We don't make sure it gets a subsection in the update yet because we
|
|
// make no attempts at fixing the linked list of free items either
|
|
return n;
|
|
}
|
|
|
|
void pdf_updater::update(uint n, std::function<void()> fill) {
|
|
auto& ref = xref.at(n);
|
|
ref.offset = document.length() + 1;
|
|
ref.free = false;
|
|
updated.insert(n);
|
|
|
|
document += ssprintf("\n%u %u obj\n", n, ref.generation);
|
|
// Separately so that the callback can use document.length() to get the current offset
|
|
fill();
|
|
document += "\nendobj";
|
|
}
|
|
|
|
void pdf_updater::flush_updates() {
|
|
std::map<uint, size_t> groups;
|
|
for (auto i = updated.cbegin(); i != updated.cend(); ) {
|
|
size_t start = *i, count = 1;
|
|
while (++i != updated.cend() && *i == start + count)
|
|
count++;
|
|
groups[start] = count;
|
|
}
|
|
|
|
// Taking literally "Each cross-reference section begins with a line containing the keyword xref.
|
|
// Following this line are one or more cross-reference subsections." from 3.4.3 in PDF Reference
|
|
if (groups.empty())
|
|
groups[0] = 0;
|
|
|
|
auto startxref = document.length() + 1;
|
|
document += "\nxref\n";
|
|
for (const auto& g : groups) {
|
|
document += ssprintf("%u %zu\n", g.first, g.second);
|
|
for (size_t i = 0; i < g.second; i++) {
|
|
auto& ref = xref[g.first + i];
|
|
document += ssprintf("%010zu %05u %c \n", ref.offset, ref.generation, "nf"[!!ref.free]);
|
|
}
|
|
}
|
|
|
|
trailer["Size"] = {pdf_object::NUMERIC, double(xref_size)};
|
|
document +=
|
|
"trailer\n" + pdf_serialize(trailer) + ssprintf("\nstartxref\n%zu\n%%%%EOF\n", startxref);
|
|
}
|
|
|
|
// -------------------------------------------------------------------------------------------------
|
|
|
|
/// Make a PDF object representing the given point in time
|
|
static pdf_object pdf_date(time_t timestamp) {
|
|
struct tm parts;
|
|
assert(localtime_r(×tamp, &parts));
|
|
|
|
char buf[64];
|
|
assert(strftime(buf, sizeof buf, "D:%Y%m%d%H%M%S", &parts));
|
|
|
|
std::string offset = "Z";
|
|
auto offset_min = parts.tm_gmtoff / 60;
|
|
if (parts.tm_gmtoff < 0)
|
|
offset = ssprintf("-%02ld'%02ld'", -offset_min / 60, -offset_min % 60);
|
|
if (parts.tm_gmtoff > 0)
|
|
offset = ssprintf("+%02ld'%02ld'", +offset_min / 60, +offset_min % 60);
|
|
return {pdf_object::STRING, buf + offset};
|
|
}
|
|
|
|
static pdf_object pdf_get_first_page(pdf_updater& pdf, uint node_n, uint node_generation) {
|
|
auto obj = pdf.get(node_n, node_generation);
|
|
if (obj.type != pdf_object::DICT)
|
|
return {pdf_object::NIL};
|
|
|
|
// Out of convenience; these aren't filled normally
|
|
obj.n = node_n;
|
|
obj.generation = node_generation;
|
|
|
|
auto type = obj.dict.find("Type");
|
|
if (type == obj.dict.end() || type->second.type != pdf_object::NAME)
|
|
return {pdf_object::NIL};
|
|
if (type->second.string == "Page")
|
|
return obj;
|
|
if (type->second.string != "Pages")
|
|
return {pdf_object::NIL};
|
|
|
|
// XXX technically speaking, this may be an indirect reference. The correct way to solve this
|
|
// seems to be having "pdf_updater" include a wrapper around "obj.dict.find"
|
|
auto kids = obj.dict.find("Kids");
|
|
if (kids == obj.dict.end() || kids->second.type != pdf_object::ARRAY ||
|
|
kids->second.array.empty() ||
|
|
kids->second.array.at(0).type != pdf_object::REFERENCE)
|
|
return {pdf_object::NIL};
|
|
|
|
// XXX nothing prevents us from recursing in an evil circular graph
|
|
return pdf_get_first_page(pdf, kids->second.array.at(0).n, kids->second.array.at(0).generation);
|
|
}
|
|
|
|
// -------------------------------------------------------------------------------------------------
|
|
|
|
static std::string pkcs12_path, pkcs12_pass;
|
|
|
|
// /All/ bytes are checked, except for the signature hexstring itself
|
|
static std::string pdf_fill_in_signature(std::string& document, size_t sign_off, size_t sign_len) {
|
|
size_t tail_off = sign_off + sign_len, tail_len = document.size() - tail_off;
|
|
if (pkcs12_path.empty())
|
|
return "undefined path to the signing key";
|
|
|
|
auto pkcs12_fp = fopen(pkcs12_path.c_str(), "r");
|
|
if (!pkcs12_fp)
|
|
return pkcs12_path + ": " + strerror(errno);
|
|
|
|
// Abandon hope, all ye who enter OpenSSL! Half of it is undocumented.
|
|
OpenSSL_add_all_algorithms();
|
|
ERR_load_crypto_strings();
|
|
ERR_clear_error();
|
|
|
|
PKCS12* p12 = nullptr;
|
|
EVP_PKEY* private_key = nullptr;
|
|
X509* certificate = nullptr;
|
|
STACK_OF(X509)* chain = nullptr;
|
|
PKCS7* p7 = nullptr;
|
|
int len = 0, sign_flags = PKCS7_DETACHED | PKCS7_BINARY | PKCS7_NOSMIMECAP | PKCS7_PARTIAL;
|
|
BIO* p7bio = nullptr;
|
|
unsigned char* buf = nullptr;
|
|
|
|
// OpenSSL error reasons will usually be of more value than any distinction I can come up with
|
|
std::string err = "OpenSSL failure";
|
|
|
|
if (!(p12 = d2i_PKCS12_fp(pkcs12_fp, nullptr)) ||
|
|
!PKCS12_parse(p12, pkcs12_pass.c_str(), &private_key, &certificate, &chain)) {
|
|
err = pkcs12_path + ": parse failure";
|
|
goto error;
|
|
}
|
|
if (!private_key || !certificate) {
|
|
err = pkcs12_path + ": must contain a private key and a valid certificate chain";
|
|
goto error;
|
|
}
|
|
// Prevent useless signatures -- makes pdfsig from poppler happy at least (and NSS by extension)
|
|
if (!(X509_get_key_usage(certificate) & (KU_DIGITAL_SIGNATURE | KU_NON_REPUDIATION))) {
|
|
err = "the certificate's key usage must include digital signatures or non-repudiation";
|
|
goto error;
|
|
}
|
|
if (!(X509_get_extended_key_usage(certificate) & (XKU_SMIME | XKU_ANYEKU))) {
|
|
err = "the certificate's extended key usage must include S/MIME";
|
|
goto error;
|
|
}
|
|
#if 0 // This happily ignores XKU_ANYEKU and I want my tiny world to make a tiny bit more sense
|
|
if (X509_check_purpose(certificate, X509_PURPOSE_SMIME_SIGN, false /* not a CA certificate */)) {
|
|
err = "the certificate can't be used for S/MIME digital signatures";
|
|
goto error;
|
|
}
|
|
#endif
|
|
|
|
// The default digest is SHA1, which is mildly insecure now -- hence using PKCS7_sign_add_signer
|
|
if (!(p7 = PKCS7_sign(nullptr, nullptr, nullptr, nullptr, sign_flags)) ||
|
|
!PKCS7_sign_add_signer(p7, certificate, private_key, EVP_sha256(), sign_flags))
|
|
goto error;
|
|
// For RFC 3161, this is roughly how a timestamp token would be attached (see Appendix A):
|
|
// PKCS7_add_attribute(signer_info, NID_id_smime_aa_timeStampToken, V_ASN1_SEQUENCE, value)
|
|
for (int i = 0; i < sk_X509_num(chain); i++)
|
|
if (!PKCS7_add_certificate(p7, sk_X509_value(chain, i)))
|
|
goto error;
|
|
|
|
// Adaptation of the innards of the undocumented PKCS7_final() -- I didn't feel like making
|
|
// a copy of the whole document. Hopefully this writes directly into a digest BIO.
|
|
if (!(p7bio = PKCS7_dataInit(p7, nullptr)) ||
|
|
(ssize_t) sign_off != BIO_write(p7bio, document.data(), sign_off) ||
|
|
(ssize_t) tail_len != BIO_write(p7bio, document.data() + tail_off, tail_len) ||
|
|
BIO_flush(p7bio) != 1 || !PKCS7_dataFinal(p7, p7bio))
|
|
goto error;
|
|
|
|
#if 0
|
|
{
|
|
// Debugging: openssl cms -inform PEM -in pdf_signature.pem -noout -cmsout -print
|
|
// Context: https://stackoverflow.com/a/29253469
|
|
auto fp = fopen("pdf_signature.pem", "wb");
|
|
assert(PEM_write_PKCS7(fp, p7) && !fclose(fp));
|
|
}
|
|
#endif
|
|
|
|
if ((len = i2d_PKCS7(p7, &buf)) < 0)
|
|
goto error;
|
|
if (size_t(len) * 2 > sign_len - 2 /* hexstring quotes */) {
|
|
// The obvious solution is to increase the allocation... or spend a week reading specifications
|
|
// while losing all faith in humanity as a species, and skip the PKCS7 API entirely
|
|
err = ssprintf("not enough space reserved for the signature (%zu nibbles vs %zu nibbles)",
|
|
sign_len - 2, size_t(len) * 2);
|
|
goto error;
|
|
}
|
|
for (int i = 0; i < len; i++) {
|
|
document[sign_off + 2 * i + 1] = "0123456789abcdef"[buf[i] / 16];
|
|
document[sign_off + 2 * i + 2] = "0123456789abcdef"[buf[i] % 16];
|
|
}
|
|
err.clear();
|
|
|
|
error:
|
|
OPENSSL_free(buf);
|
|
BIO_free_all(p7bio);
|
|
PKCS7_free(p7);
|
|
sk_X509_pop_free(chain, X509_free);
|
|
X509_free(certificate);
|
|
EVP_PKEY_free(private_key);
|
|
PKCS12_free(p12);
|
|
|
|
// In any case, clear the error stack (it's a queue, really) to avoid confusion elsewhere
|
|
while (auto code = ERR_get_error())
|
|
if (auto reason = ERR_reason_error_string(code))
|
|
err = err + "; " + reason;
|
|
|
|
fclose(pkcs12_fp);
|
|
return err;
|
|
}
|
|
|
|
// -------------------------------------------------------------------------------------------------
|
|
|
|
/// The presumption here is that the document is valid and that it doesn't employ cross-reference
|
|
/// streams from PDF 1.5, or at least constitutes a hybrid-reference file. The results with
|
|
/// PDF 2.0 (2017) are currently unknown as the standard costs money.
|
|
///
|
|
/// https://www.adobe.com/devnet-docs/acrobatetk/tools/DigSig/Acrobat_DigitalSignatures_in_PDF.pdf
|
|
/// https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/pdf_reference_1-7.pdf
|
|
/// https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/PPKAppearances.pdf
|
|
static std::string pdf_sign(std::string& document, ushort reservation) {
|
|
pdf_updater pdf(document);
|
|
auto err = pdf.initialize();
|
|
if (!err.empty())
|
|
return err;
|
|
|
|
auto root_ref = pdf.trailer.find("Root");
|
|
if (root_ref == pdf.trailer.end() || root_ref->second.type != pdf_object::REFERENCE)
|
|
return "trailer does not contain a reference to Root";
|
|
auto root = pdf.get(root_ref->second.n, root_ref->second.generation);
|
|
if (root.type != pdf_object::DICT)
|
|
return "invalid Root dictionary reference";
|
|
|
|
// 8.7 Digital Signatures - /signature dictionary/
|
|
auto sigdict_n = pdf.allocate();
|
|
size_t byterange_off = 0, byterange_len = 0, sign_off = 0, sign_len = 0;
|
|
pdf.update(sigdict_n, [&] {
|
|
// The timestamp is important for Adobe Acrobat Reader DC. The ideal would be to use RFC 3161.
|
|
pdf.document.append("<< /Type/Sig /Filter/Adobe.PPKLite /SubFilter/adbe.pkcs7.detached\n"
|
|
" /M" + pdf_serialize(pdf_date(time(nullptr))) + " /ByteRange ");
|
|
byterange_off = pdf.document.size();
|
|
pdf.document.append((byterange_len = 32 /* fine for a gigabyte */), ' ');
|
|
pdf.document.append("\n /Contents <");
|
|
sign_off = pdf.document.size();
|
|
pdf.document.append((sign_len = reservation * 2), '0');
|
|
pdf.document.append("> >>");
|
|
|
|
// We actually need to exclude the hexstring quotes from signing
|
|
sign_off -= 1;
|
|
sign_len += 2;
|
|
});
|
|
|
|
// 8.6.3 Field Types - Signature Fields
|
|
pdf_object sigfield{pdf_object::DICT};
|
|
sigfield.dict.insert({"FT", {pdf_object::NAME, "Sig"}});
|
|
sigfield.dict.insert({"V", {pdf_object::REFERENCE, sigdict_n, 0}});
|
|
// 8.4.5 Annotations Types - Widget Annotations
|
|
// We can merge the Signature Annotation and omit Kids here
|
|
sigfield.dict.insert({"Subtype", {pdf_object::NAME, "Widget"}});
|
|
sigfield.dict.insert({"F", {pdf_object::NUMERIC, 2 /* Hidden */}});
|
|
sigfield.dict.insert({"T", {pdf_object::STRING, "Signature1"}});
|
|
sigfield.dict.insert({"Rect", {std::vector<pdf_object>{
|
|
{pdf_object::NUMERIC, 0},
|
|
{pdf_object::NUMERIC, 0},
|
|
{pdf_object::NUMERIC, 0},
|
|
{pdf_object::NUMERIC, 0},
|
|
}}});
|
|
|
|
auto sigfield_n = pdf.allocate();
|
|
pdf.update(sigfield_n, [&] { pdf.document += pdf_serialize(sigfield); });
|
|
|
|
auto pages_ref = root.dict.find("Pages");
|
|
if (pages_ref == root.dict.end() || pages_ref->second.type != pdf_object::REFERENCE)
|
|
return "invalid Pages reference";
|
|
auto page = pdf_get_first_page(pdf, pages_ref->second.n, pages_ref->second.generation);
|
|
if (page.type != pdf_object::DICT)
|
|
return "invalid or unsupported page tree";
|
|
|
|
auto& annots = page.dict["Annots"];
|
|
if (annots.type != pdf_object::ARRAY) {
|
|
// TODO indirectly referenced arrays might not be that hard to support
|
|
if (annots.type != pdf_object::END)
|
|
return "unexpected Annots";
|
|
|
|
annots = {pdf_object::ARRAY};
|
|
}
|
|
annots.array.emplace_back(pdf_object::REFERENCE, sigfield_n, 0);
|
|
pdf.update(page.n, [&] { pdf.document += pdf_serialize(page); });
|
|
|
|
// 8.6.1 Interactive Form Dictionary
|
|
if (root.dict.count("AcroForm"))
|
|
return "the document already contains forms, they would be overwritten";
|
|
|
|
root.dict["AcroForm"] = {std::map<std::string, pdf_object>{
|
|
{"Fields", {std::vector<pdf_object>{
|
|
{pdf_object::REFERENCE, sigfield_n, 0}
|
|
}}},
|
|
{"SigFlags", {pdf_object::NUMERIC, 3 /* SignaturesExist | AppendOnly */}}
|
|
}};
|
|
|
|
// Upgrade the document version for SHA-256 etc.
|
|
if (pdf.version(root) < 16)
|
|
root.dict["Version"] = {pdf_object::NAME, "1.6"};
|
|
|
|
pdf.update(root_ref->second.n, [&] { pdf.document += pdf_serialize(root); });
|
|
pdf.flush_updates();
|
|
|
|
// Now that we know the length of everything, store byte ranges of what we're about to sign,
|
|
// which must be everything but the resulting signature itself
|
|
size_t tail_off = sign_off + sign_len, tail_len = pdf.document.size() - tail_off;
|
|
auto ranges = ssprintf("[0 %zu %zu %zu]", sign_off, tail_off, tail_len);
|
|
if (ranges.length() > byterange_len)
|
|
return "not enough space reserved for /ByteRange";
|
|
pdf.document.replace(byterange_off, std::min(ranges.length(), byterange_len), ranges);
|
|
return pdf_fill_in_signature(pdf.document, sign_off, sign_len);
|
|
}
|
|
|
|
// -------------------------------------------------------------------------------------------------
|
|
|
|
__attribute__((format(printf, 2, 3)))
|
|
static void die(int status, const char* format, ...) {
|
|
va_list ap;
|
|
va_start(ap, format);
|
|
if (isatty(fileno(stderr)))
|
|
vfprintf(stderr, ssprintf("\x1b[31m%s\x1b[0m\n", format).c_str(), ap);
|
|
else
|
|
vfprintf(stderr, format, ap);
|
|
va_end(ap);
|
|
exit(status);
|
|
}
|
|
|
|
int main(int argc, char* argv[]) {
|
|
auto invocation_name = argv[0];
|
|
auto usage = [=] {
|
|
die(1, "Usage: %s [-h] [-r RESERVATION] INPUT-FILENAME OUTPUT-FILENAME PKCS12-PATH PKCS12-PASS",
|
|
invocation_name);
|
|
};
|
|
|
|
static struct option opts[] = {
|
|
{"help", no_argument, 0, 'h'},
|
|
{"version", no_argument, 0, 'V'},
|
|
{"reservation", required_argument, 0, 'r'},
|
|
{nullptr, 0, 0, 0},
|
|
};
|
|
|
|
// Reserved space in bytes for the certificate, digest, encrypted digest, ...
|
|
long reservation = 4096;
|
|
while (1) {
|
|
int option_index = 0;
|
|
auto c = getopt_long(argc, const_cast<char* const*>(argv), "hVr:", opts, &option_index);
|
|
if (c == -1)
|
|
break;
|
|
|
|
char* end = nullptr;
|
|
switch (c) {
|
|
case 'r':
|
|
errno = 0, reservation = strtol(optarg, &end, 10);
|
|
if (errno || *end || reservation <= 0 || reservation > USHRT_MAX)
|
|
die(1, "%s: must be a positive number", optarg);
|
|
break;
|
|
case 'V':
|
|
die(0, "%s", PROJECT_NAME " " PROJECT_VERSION);
|
|
break;
|
|
case 'h':
|
|
default:
|
|
usage();
|
|
}
|
|
}
|
|
|
|
argv += optind;
|
|
argc -= optind;
|
|
|
|
if (argc != 4)
|
|
usage();
|
|
|
|
const char* input_path = argv[0];
|
|
const char* output_path = argv[1];
|
|
pkcs12_path = argv[2];
|
|
pkcs12_pass = argv[3];
|
|
|
|
std::string pdf_document;
|
|
if (auto fp = fopen(input_path, "rb")) {
|
|
int c;
|
|
while ((c = fgetc(fp)) != EOF)
|
|
pdf_document += c;
|
|
if (ferror(fp))
|
|
die(1, "%s: %s", input_path, strerror(errno));
|
|
fclose(fp);
|
|
} else {
|
|
die(1, "%s: %s", input_path, strerror(errno));
|
|
}
|
|
|
|
auto err = pdf_sign(pdf_document, ushort(reservation));
|
|
if (!err.empty()) {
|
|
die(2, "Error: %s", err.c_str());
|
|
}
|
|
|
|
if (auto fp = fopen(output_path, "wb")) {
|
|
auto written = fwrite(pdf_document.c_str(), pdf_document.size(), 1, fp);
|
|
if (fclose(fp) || written != 1) {
|
|
(void) unlink(output_path);
|
|
die(3, "%s: %s", output_path, strerror(errno));
|
|
}
|
|
} else {
|
|
die(3, "%s: %s", output_path, strerror(errno));
|
|
}
|
|
return 0;
|
|
}
|