SkPDF: Optionally output PDF/A-2b archive format.

src/pdf/SkPDFMetadata.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkPDFMetadata.h"
+#include "SkPDFTypes.h"
+
+#ifdef SK_PDF_GENERATE_PDFA
+#include "SkMD5.h"
+#endif
+
+static SkString pdf_date(const SkTime::DateTime& dt) {
+    int timeZoneMinutes = SkToInt(dt.fTimeZoneMinutes);
+    char timezoneSign = timeZoneMinutes >= 0 ? '+' : '-';
+    int timeZoneHours = SkTAbs(timeZoneMinutes) / 60;
+    timeZoneMinutes = SkTAbs(timeZoneMinutes) % 60;
+    return SkStringPrintf(
+            "D:%04u%02u%02u%02u%02u%02u%c%02d'%02d'",
+            static_cast<unsigned>(dt.fYear), static_cast<unsigned>(dt.fMonth),
+            static_cast<unsigned>(dt.fDay), static_cast<unsigned>(dt.fHour),
+            static_cast<unsigned>(dt.fMinute),
+            static_cast<unsigned>(dt.fSecond), timezoneSign, timeZoneHours,
+            timeZoneMinutes);
+}
+
+SkPDFObject* SkPDFMetadata::createDocumentInformationDict() const {
+    SkAutoTUnref<SkPDFDict> dict(new SkPDFDict);
+    static const char* keys[] = {
+            "Title", "Author", "Subject", "Keywords", "Creator"};
+    for (const char* key : keys) {
+        for (const SkDocument::Attribute& keyValue : fInfo) {
+            if (keyValue.fKey.equals(key)) {
+                dict->insertString(key, keyValue.fValue);
+            }
+        }
+    }
+    dict->insertString("Producer", "Skia/PDF");
+    if (fCreation) {
+        dict->insertString("CreationDate", pdf_date(*fCreation.get()));
+    }
+    if (fModified) {
+        dict->insertString("ModDate", pdf_date(*fModified.get()));
+    }
+    return dict.detach();
+}
+
+#ifdef SK_PDF_GENERATE_PDFA
+SkPDFMetadata::UUID SkPDFMetadata::uuid() const {
+    // The main requirement is for the UUID to be unique; the exact
+    // format of the data that will be hashed is not important.
+    SkMD5 md5;
+    const char uuidNamespace[] = "org.skia.pdf\n";
+    md5.write(uuidNamespace, strlen(uuidNamespace));
+    SkMSec msec = SkTime::GetMSecs();
+    md5.write(&msec, sizeof(msec));
+    SkTime::DateTime dateTime;
+    SkTime::GetDateTime(&dateTime);
+    md5.write(&dateTime, sizeof(dateTime));
+    if (fCreation) {
+        md5.write(fCreation.get(), sizeof(fCreation));
+    }
+    if (fModified) {
+        md5.write(fModified.get(), sizeof(fModified));
+    }
+    for (const auto& kv : fInfo) {
+        md5.write(kv.fKey.c_str(), kv.fKey.size());
+        md5.write("\037", 1);
+        md5.write(kv.fValue.c_str(), kv.fValue.size());
+        md5.write("\036", 1);
+    }
+    SkMD5::Digest digest;
+    md5.finish(digest);
+    // See RFC 4122, page 6-7.
+    digest.data[6] = (digest.data[6] & 0x0F) | 0x30;
+    digest.data[8] = (digest.data[6] & 0x3F) | 0x80;
+    static_assert(sizeof(digest) == sizeof(UUID), "uuid_size");
+    SkPDFMetadata::UUID uuid;
+    memcpy(&uuid, &digest, sizeof(digest));
+    return uuid;
+}
+
+SkPDFObject* SkPDFMetadata::CreatePdfId(const UUID& doc, const UUID& instance) {
+    // /ID [ <81b14aafa313db63dbd6f981e49f94f4>
+    //       <81b14aafa313db63dbd6f981e49f94f4> ]
+    SkAutoTUnref<SkPDFArray> array(new SkPDFArray);
+    static_assert(sizeof(UUID) == 16, "uuid_size");
+    array->appendString(
+            SkString(reinterpret_cast<const char*>(&doc), sizeof(UUID)));
+    array->appendString(
+            SkString(reinterpret_cast<const char*>(&instance), sizeof(UUID)));
+    return array.detach();
+}
+
+// Improvement on SkStringPrintf to allow for arbitrarily long output.
+// TODO: replace SkStringPrintf.
+static SkString sk_string_printf(const char* format, ...) {
+#ifdef SK_BUILD_FOR_WIN
+    va_list args;
+    va_start(args, format);
+    char buffer[1024];
+    int length = _vsnprintf_s(buffer, sizeof(buffer), _TRUNCATE, format, args);
+    va_end(args);
+    if (length >= 0 && length < (int)sizeof(buffer)) {
+        return SkString(buffer, length);
+    }
+    va_start(args, format);
+    length = _vscprintf(format, args);
+    va_end(args);
+
+    SkString string((size_t)length);
+    va_start(args, format);
+    SkDEBUGCODE(int check = ) _vsnprintf_s(string.writable_str(), length + 1,
+                                           _TRUNCATE, format, args);
+    va_end(args);
+    SkASSERT(check == length);
+    SkASSERT(string[length] == '\0');
+    return skstd::move(string);
+#else  // C99/C++11 standard vsnprintf
+    // TODO: When all compilers support this, remove windows-specific code.
+    va_list args;
+    va_start(args, format);
+    char buffer[1024];
+    int length = vsnprintf(buffer, sizeof(buffer), format, args);
+    va_end(args);
+    if (length < 0) {
+        return SkString();
+    }
+    if (length < (int)sizeof(buffer)) {
+        return SkString(buffer, length);
+    }
+    SkString string((size_t)length);
+    va_start(args, format);
+    SkDEBUGCODE(int check = )
+            vsnprintf(string.writable_str(), length + 1, format, args);
+    va_end(args);
+    SkASSERT(check == length);
+    SkASSERT(string[length] == '\0');
+    return skstd::move(string);
+#endif
+}
+
+static const SkString get(const SkTArray<SkDocument::Attribute>& info,
+                          const char* key) {
+    for (const auto& keyValue : info) {
+        if (keyValue.fKey.equals(key)) {
+            return keyValue.fValue;
+        }
+    }
+    return SkString();
+}
+
+#define HEXIFY(INPUT_PTR, OUTPUT_PTR, HEX_STRING, BYTE_COUNT) \
+    do {                                                      \
+        for (int i = 0; i < (BYTE_COUNT); ++i) {              \
+            uint8_t value = *(INPUT_PTR)++;                   \
+            *(OUTPUT_PTR)++ = (HEX_STRING)[value >> 4];       \
+            *(OUTPUT_PTR)++ = (HEX_STRING)[value & 0xF];      \
+        }                                                     \
+    } while (false)
+static SkString uuid_to_string(const SkPDFMetadata::UUID& uuid) {
+    //  8-4-4-4-12
+    char buffer[36];  // [32 + 4]
+    static const char gHex[] = "0123456789abcdef";
+    SkASSERT(strlen(gHex) == 16);
+    char* ptr = buffer;
+    const uint8_t* data = uuid.fData;
+    HEXIFY(data, ptr, gHex, 4);
+    *ptr++ = '-';
+    HEXIFY(data, ptr, gHex, 2);
+    *ptr++ = '-';
+    HEXIFY(data, ptr, gHex, 2);
+    *ptr++ = '-';
+    HEXIFY(data, ptr, gHex, 2);
+    *ptr++ = '-';
+    HEXIFY(data, ptr, gHex, 6);
+    SkASSERT(ptr == buffer + 36);
+    SkASSERT(data == uuid.fData + 16);
+    return SkString(buffer, 36);
+}
+#undef HEXIFY
+
+namespace {
+class PDFXMLObject : public SkPDFObject {
+public:
+    PDFXMLObject(SkString xml) : fXML(skstd::move(xml)) {}
+    void emitObject(SkWStream* stream,
+                    const SkPDFObjNumMap& omap,
+                    const SkPDFSubstituteMap& smap) const override {
+        SkPDFDict dict("Metadata");
+        dict.insertName("Subtype", "XML");
+        dict.insertInt("Length", fXML.size());
+        dict.emitObject(stream, omap, smap);
+        static const char streamBegin[] = " stream\n";
+        stream->write(streamBegin, strlen(streamBegin));
+        // Do not compress this.  The standard requires that a
+        // program that does not understand PDF can grep for
+        // "<?xpacket" and extracť the entire XML.
+        stream->write(fXML.c_str(), fXML.size());
+        static const char streamEnd[] = "\nendstream";
+        stream->write(streamEnd, strlen(streamEnd));
+    }
+
+private:
+    const SkString fXML;
+};
+}  // namespace
+
+static int count_xml_escape_size(const SkString& input) {
+    int extra = 0;
+    for (size_t i = 0; i < input.size(); ++i) {
+        if (input[i] == '&') {
+            extra += 4;  // strlen("&amp;") - strlen("&")
+        } else if (input[i] == '<') {
+            extra += 3;  // strlen("&lt;") - strlen("<")
+        }
+    }
+    return extra;
+}
+
+const SkString escape_xml(const SkString& input,
+                          const char* before = nullptr,
+                          const char* after = nullptr) {
+    if (input.size() == 0) {
+        return input;
+    }
+    // "&" --> "&amp;" and  "<" --> "&lt;"
+    // text is assumed to be in UTF-8
+    // all strings are xml content, not attribute values.
+    size_t beforeLen = before ? strlen(before) : 0;
+    size_t afterLen = after ? strlen(after) : 0;
+    int extra = count_xml_escape_size(input);
+    SkString output(input.size() + extra + beforeLen + afterLen);
+    char* out = output.writable_str();
+    if (before) {
+        strncpy(out, before, beforeLen);
+        out += beforeLen;
+    }
+    static const char kAmp[] = "&amp;";
+    static const char kLt[] = "&lt;";
+    for (size_t i = 0; i < input.size(); ++i) {
+        if (input[i] == '&') {
+            strncpy(out, kAmp, strlen(kAmp));
+            out += strlen(kAmp);
+        } else if (input[i] == '<') {
+            strncpy(out, kLt, strlen(kLt));
+            out += strlen(kLt);
+        } else {
+            *out++ = input[i];
+        }
+    }
+    if (after) {
+        strncpy(out, after, afterLen);
+        out += afterLen;
+    }
+    // Validate that we haven't written outside of our string.
+    SkASSERT(out == &output.writable_str()[output.size()]);
+    *out = '\0';
+    return skstd::move(output);
+}
+
+SkPDFObject* SkPDFMetadata::createXMPObject(const UUID& doc,
+                                            const UUID& instance) const {
+    static const char templateString[] =
+            "<?xpacket begin=\"\" id=\"W5M0MpCehiHzreSzNTczkc9d\"?>\n"
+            "<x:xmpmeta xmlns:x=\"adobe:ns:meta/\"\n"
+            " x:xmptk=\"Adobe XMP Core 5.4-c005 78.147326, "
+            "2012/08/23-13:03:03\">\n"
+            "<rdf:RDF "
+            "xmlns:rdf=\"http://www.w3.org/1999/02/22-rdf-syntax-ns#\">\n"
+            "<rdf:Description rdf:about=\"\"\n"
+            " xmlns:xmp=\"http://ns.adobe.com/xap/1.0/\"\n"
+            " xmlns:dc=\"http://purl.org/dc/elements/1.1/\"\n"
+            " xmlns:xmpMM=\"http://ns.adobe.com/xap/1.0/mm/\"\n"
+            " xmlns:pdf=\"http://ns.adobe.com/pdf/1.3/\"\n"
+            " xmlns:pdfaid=\"http://www.aiim.org/pdfa/ns/id/\">\n"
+            "<pdfaid:part>2</pdfaid:part>\n"
+            "<pdfaid:conformance>B</pdfaid:conformance>\n"
+            "%s"  // ModifyDate
+            "%s"  // CreateDate
+            "%s"  // MetadataDate
+            "%s"  // xmp:CreatorTool
+            "<dc:format>application/pdf</dc:format>\n"
+            "%s"  // dc:title
+            "%s"  // dc:description
+            "%s"  // author
+            "%s"  // keywords
+            "<xmpMM:DocumentID>uuid:%s</xmpMM:DocumentID>\n"
+            "<xmpMM:InstanceID>uuid:%s</xmpMM:InstanceID>\n"
+            "<pdf:Producer>Skia/PDF</pdf:Producer>\n"
+            "%s"  // pdf:Keywords
+            "</rdf:Description>\n"
+            "</rdf:RDF>\n"
+            "</x:xmpmeta>\n"  // Note:  the standard suggests 4k of padding.
+            "<?xpacket end=\"w\"?>\n";
+
+    SkString creationDate;
+    SkString modificationDate;
+    SkString metadataDate;
+    if (fCreation) {
+        SkString tmp;
+        fCreation->toISO8601(&tmp);
+        SkASSERT(0 == count_xml_escape_size(tmp));
+        // YYYY-mm-ddTHH:MM:SS[+|-]ZZ:ZZ; no need to escape
+        creationDate = sk_string_printf("<xmp:CreateDate>%s</xmp:CreateDate>\n",
+                                        tmp.c_str());
+    }
+    if (fModified) {
+        SkString tmp;
+        fModified->toISO8601(&tmp);
+        SkASSERT(0 == count_xml_escape_size(tmp));
+        modificationDate = sk_string_printf(
+                "<xmp:ModifyDate>%s</xmp:ModifyDate>\n", tmp.c_str());
+        metadataDate = sk_string_printf(
+                "<xmp:MetadataDate>%s</xmp:MetadataDate>\n", tmp.c_str());
+    }
+
+    SkString title =
+            escape_xml(get(fInfo, "Title"), "<dc:title><rdf:Alt><rdf:li>",
+                       "</rdf:li></rdf:Alt></dc:title>\n");
+    SkString author =
+            escape_xml(get(fInfo, "Author"), "<dc:creator><rdf:Bag><rdf:li>",
+                       "</rdf:li></rdf:Bag></dc:creator>\n");
+    // TODO: in theory, XMP can support multiple authors.  Split on a delimiter?
+    SkString subject = escape_xml(get(fInfo, "Subject"),
+                                  "<dc:description><rdf:Alt><rdf:li>",
+                                  "</rdf:li></rdf:Alt></dc:description>\n");
+    SkString keywords1 =
+            escape_xml(get(fInfo, "Keywords"), "<dc:subject><rdf:Bag><rdf:li>",
+                       "</rdf:li></rdf:Bag></dc:subject>\n");
+    SkString keywords2 = escape_xml(get(fInfo, "Keywords"), "<pdf:Keywords>",
+                                    "</pdf:Keywords>\n");
+
+    // TODO: in theory, keywords can be a list too.
+    SkString creator = escape_xml(get(fInfo, "Creator"), "<xmp:CreatorTool>",
+                                  "</xmp:CreatorTool>\n");
+    SkString documentID = uuid_to_string(doc);  // no need to escape
+    SkASSERT(0 == count_xml_escape_size(documentID));
+    SkString instanceID = uuid_to_string(instance);
+    SkASSERT(0 == count_xml_escape_size(instanceID));
+    return new PDFXMLObject(sk_string_printf(
+            templateString, modificationDate.c_str(), creationDate.c_str(),
+            metadataDate.c_str(), creator.c_str(), title.c_str(),
+            subject.c_str(), author.c_str(), keywords1.c_str(),
+            documentID.c_str(), instanceID.c_str(), keywords2.c_str()));
+}
+
+#endif  // SK_PDF_GENERATE_PDFA