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Support PDF 2.0 dates and tighten date validation #631

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214 changes: 82 additions & 132 deletions app/src/main/java/app/grapheneos/pdfviewer/Utils.java
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Original file line number Diff line number Diff line change
@@ -1,15 +1,46 @@
package app.grapheneos.pdfviewer;

import android.text.TextUtils;

import java.math.RoundingMode;
import java.text.DateFormat;
import java.text.DecimalFormat;
import java.text.ParseException;
import java.util.Calendar;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Utils {

// PDF date string format. Based on the format described in section 7.9.4 of
// the PDF 32000-2:2020 specification:
//
// D:YYYYMMDDHHmmSSOHH'mm
//
// The PDF 1.7 reference defined the same format with a terminating
// apostrophe, and PDF processors are recommended to accept date strings
// that follow that older convention. The apostrophe between HH and mm is
// also tolerated as missing for additional leniency, matching pdf.js.
private static final Pattern PDF_DATE_PATTERN = Pattern.compile(
"^D:" +
"(\\d{4})" + // Year (required)
"(\\d{2})?" + // Month (optional)
"(\\d{2})?" + // Day (optional)
"(\\d{2})?" + // Hours (optional)
"(\\d{2})?" + // Minutes (optional)
"(\\d{2})?" + // Seconds (optional)
"(?:" +
" ([Z+\\-])" + // Universal time relation
" (?:" +
" (\\d{2})" + // Offset hours
" '?" + // Splitting apostrophe (optional)
" (?:" +
" (\\d{2})" + // Offset minutes
" '?" + // Trailing apostrophe (optional, PDF <= 1.7)
" )?" +
" )?" +
")?$",
Pattern.COMMENTS
);

private static int parseIntSafely(String field) throws ParseException {
try {
return Integer.parseInt(field);
Expand All @@ -18,163 +49,82 @@ private static int parseIntSafely(String field) throws ParseException {
}
}

// Parse date as per PDF spec (complies with PDF v1.4 to v1.7)
public static String parseDate(String date) throws ParseException {
int position = 0;
private static int parseGroup(Matcher matcher, int group, int defaultValue) throws ParseException {
final String field = matcher.group(group);
return field == null ? defaultValue : parseIntSafely(field);
}

// D: prefix is optional for PDF < v1.7; required for PDF v1.7
// Parse date as per PDF spec (complies with PDF v1.4 to v2.0)
public static String parseDate(String date) throws ParseException {
// D: prefix is optional for PDF < v1.7; required for PDF v1.7+
if (!date.startsWith("D:")) {
date = "D:" + date;
}
if (date.length() < 6 || date.length() > 23) {
throw new ParseException("Invalid datetime length", position);

final Matcher matcher = PDF_DATE_PATTERN.matcher(date);
if (!matcher.matches()) {
throw new ParseException("Invalid date format", 0);
}

final Calendar calendar = Calendar.getInstance();
final int currentYear = calendar.get(Calendar.YEAR);

// Year is required
String field = date.substring(position += 2, 6);
if (!TextUtils.isDigitsOnly(field)) {
throw new ParseException("Invalid year", position);
}
int year = parseIntSafely(field);
int year = parseIntSafely(matcher.group(1));
if (year > currentYear) {
year = currentYear;
}

position += 4;

// Default value for month and day shall be 1 (calendar month starts at 0 in Java 7),
// all others default to 0
int month = 0;
int day = 1;
int hours = 0;
int minutes = 0;
int seconds = 0;

// All succeeding fields are optional, but each preceding field must be present
if (date.length() >= 8) {
field = date.substring(position, 8);
if (!TextUtils.isDigitsOnly(field)) {
throw new ParseException("Invalid month", position);
}
month = parseIntSafely(field) - 1;
if (month > 11) {
throw new ParseException("Invalid month", position);
}
position += 2;
// Calendar month starts at 0 in Java; defaults for month and day are 1
// per the spec, all other fields default to 0.
final int month = parseGroup(matcher, 2, 1) - 1;
if (month < 0 || month > 11) {
throw new ParseException("Invalid month", 0);
}
if (date.length() >= 10) {
field = date.substring(8, 10);
if (!TextUtils.isDigitsOnly(field)) {
throw new ParseException("Invalid day", position);
}
day = parseIntSafely(field);
if (day > 31) {
throw new ParseException("Invalid day", position);
}
position += 2;
final int day = parseGroup(matcher, 3, 1);
if (day < 1 || day > 31) {
throw new ParseException("Invalid day", 0);
}
if (date.length() >= 12) {
field = date.substring(10, 12);
if (!TextUtils.isDigitsOnly(field)) {
throw new ParseException("Invalid hours", position);
}
hours = parseIntSafely(field);
if (hours > 23) {
throw new ParseException("Invalid hours", position);
}
position += 2;
int hours = parseGroup(matcher, 4, 0);
if (hours > 23) {
throw new ParseException("Invalid hours", 0);
}
if (date.length() >= 14) {
field = date.substring(12, 14);
if (!TextUtils.isDigitsOnly(field)) {
throw new ParseException("Invalid minutes", position);
}
minutes = parseIntSafely(field);
if (minutes > 59) {
throw new ParseException("Invalid minutes", position);
}
position += 2;
int minutes = parseGroup(matcher, 5, 0);
if (minutes > 59) {
throw new ParseException("Invalid minutes", 0);
}
if (date.length() >= 16) {
field = date.substring(14, 16);
if (!TextUtils.isDigitsOnly(field)) {
throw new ParseException("Invalid seconds", position);
}
seconds = parseIntSafely(field);
if (seconds > 59) {
throw new ParseException("Invalid seconds", position);
}
position += 2;
final int seconds = parseGroup(matcher, 6, 0);
if (seconds > 59) {
throw new ParseException("Invalid seconds", 0);
}


if (date.length() > position) {
int offsetHours = 0;
int offsetMinutes = 0;

final char utRel = date.charAt(position);
if (utRel != '\u002D' && utRel != '\u002B' && utRel != '\u005A') {
throw new ParseException("Invalid UT relation", position);
final String utRel = matcher.group(7);
if (utRel != null) {
final int offsetHours = parseGroup(matcher, 8, 0);
final int offsetMinutes = parseGroup(matcher, 9, 0);
if (offsetMinutes > 59) {
throw new ParseException("Invalid UTC offset minutes", 0);
}

position++;

if (date.length() > position + 2) {
field = date.substring(position, position + 2);
if (!TextUtils.isDigitsOnly(field)) {
throw new ParseException("Invalid UTC offset hours", position);
}
offsetHours = parseIntSafely(field);
final int offsetHoursMinutes = offsetHours * 100 + offsetMinutes;

// Validate UTC offset (UTC-12:00 to UTC+14:00)
if ((utRel == '\u002D' && offsetHoursMinutes > 1200) ||
(utRel == '\u002B' && offsetHoursMinutes > 1400)) {
throw new ParseException("Invalid UTC offset hours", position);
}

position += 2;

// Apostrophe shall succeed HH and precede mm
if (date.charAt(position) != '\'') {
throw new ParseException("Expected apostrophe", position);
}

position++;

if (date.length() > position + 2) {
field = date.substring(position, position + 2);
if (!TextUtils.isDigitsOnly(field)) {
throw new ParseException("Invalid UTC offset minutes", position);
}
offsetMinutes = parseIntSafely(field);
if (offsetMinutes > 59) {
throw new ParseException("Invalid UTC offset minutes", position);
}
position += 2;

// Apostrophe shall succeed mm
if (date.charAt(position) != '\'') {
throw new ParseException("Expected apostrophe", position);
}
}
}


final int offsetHoursMinutes = offsetHours * 100 + offsetMinutes;
// Validate UTC offset (UTC-12:00 to UTC+14:00; "Z" means UTC)
switch (utRel) {
case '\u002D':
case "-":
if (offsetHoursMinutes > 1200) {
throw new ParseException("Invalid UTC offset", 0);
}
hours -= offsetHours;
minutes -= offsetMinutes;
break;
case '\u002B':
case "+":
if (offsetHoursMinutes > 1400) {
throw new ParseException("Invalid UTC offset", 0);
}
hours += offsetHours;
minutes += offsetMinutes;
break;
default:
// "Z" means equal to UTC
case "Z":
if (offsetHoursMinutes != 0) {
throw new ParseException("UTC indicator 'Z' must not have a non-zero offset", 0);
}
break;
}
}
Expand Down