LibPDF: Add implementation of the Standard security handler

Security handlers manage encryption and decription of PDF files. The
standard security handler uses RC4/MD5 to perform its crypto (AES as
well, but that is not yet implemented).

Tests/LibPDF/TestPDF.cpp

@@ -16,6 +16,7 @@ TEST_CASE(linearized_pdf)
     auto file = Core::MappedFile::map("linearized.pdf").release_value();
     auto document = PDF::Document::create(file->bytes());
     EXPECT(!document.is_error());
+    EXPECT(!document.value()->initialize().is_error());
     EXPECT_EQ(document.value()->get_page_count(), 1U);
 }
 
@@ -24,6 +25,7 @@ TEST_CASE(non_linearized_pdf)
     auto file = Core::MappedFile::map("non-linearized.pdf").release_value();
     auto document = PDF::Document::create(file->bytes());
     EXPECT(!document.is_error());
+    EXPECT(!document.value()->initialize().is_error());
     EXPECT_EQ(document.value()->get_page_count(), 1U);
 }
 
@@ -32,6 +34,7 @@ TEST_CASE(complex_pdf)
     auto file = Core::MappedFile::map("complex.pdf").release_value();
     auto document = PDF::Document::create(file->bytes());
     EXPECT(!document.is_error());
+    EXPECT(!document.value()->initialize().is_error());
     EXPECT_EQ(document.value()->get_page_count(), 3U);
 }
 

Userland/Applications/PDFViewer/PDFViewerWidget.cpp

@@ -160,6 +160,18 @@ void PDFViewerWidget::open_file(Core::File& file)
 
     auto document = maybe_document.release_value();
 
+    if (auto sh = document->security_handler(); !sh->has_user_password()) {
+        // FIXME: Prompt the user for a password
+        VERIFY_NOT_REACHED();
+    }
+
+    auto result = document->initialize();
+    if (result.is_error()) {
+        auto error = result.release_error();
+        GUI::MessageBox::show_error(nullptr, String::formatted("Couldn't load PDF {}:\n{}", file.filename(), error.message()));
+        return;
+    }
+
     m_viewer->set_document(document);
     m_total_page_label->set_text(String::formatted("of {}", document->get_page_count()));
 

Userland/Libraries/LibPDF/CMakeLists.txt

@@ -3,6 +3,7 @@ set(SOURCES
     CommonNames.cpp
     Document.cpp
     Encoding.cpp
+    Encryption.cpp
     Filter.cpp
     Fonts.cpp
     ObjectDerivatives.cpp
@@ -12,4 +13,4 @@ set(SOURCES
     )
 
 serenity_lib(LibPDF pdf)
-target_link_libraries(LibPDF LibC LibCore LibIPC LibGfx LibTextCodec)
+target_link_libraries(LibPDF LibC LibCore LibIPC LibGfx LibTextCodec LibCrypto)

Userland/Libraries/LibPDF/CommonNames.h

@@ -37,6 +37,8 @@
     A(Differences)                \
     A(E)                          \
     A(Encoding)                   \
+    A(Encrypt)                    \
+    A(EncryptMetadata)            \
     A(ExtGState)                  \
     A(F)                          \
     A(FL)                         \
@@ -61,6 +63,7 @@
     A(H)                          \
     A(HT)                         \
     A(HTO)                        \
+    A(ID)                         \
     A(JBIG2Decode)                \
     A(JPXDecode)                  \
     A(Kids)                       \
@@ -87,6 +90,7 @@
     A(Parent)                     \
     A(Pattern)                    \
     A(Prev)                       \
+    A(R)                          \
     A(RI)                         \
     A(Resources)                  \
     A(Root)                       \
@@ -103,6 +107,7 @@
     A(Title)                      \
     A(ToUnicode)                  \
     A(Type)                       \
+    A(U)                          \
     A(UCR)                        \
     A(UseBlackPTComp)             \
     A(UserUnit)                   \

Userland/Libraries/LibPDF/Document.cpp

@@ -41,9 +41,18 @@ PDFErrorOr<NonnullRefPtr<Document>> Document::create(ReadonlyBytes bytes)
 
     TRY(parser->initialize());
 
+    document->m_trailer = parser->trailer();
     document->m_catalog = TRY(parser->trailer()->get_dict(document, CommonNames::Root));
-    TRY(document->build_page_tree());
-    TRY(document->build_outline());
+
+    if (document->m_trailer->contains(CommonNames::Encrypt)) {
+        auto encryption_dict = TRY(document->m_trailer->get_dict(document, CommonNames::Encrypt));
+        document->m_security_handler = TRY(SecurityHandler::create(document, encryption_dict));
+
+        // Automatically attempt to unencrypt the document with the empty string. The
+        // result is not important; it is the caller's responsibility to ensure the
+        // document is unencrypted before calling initialize().
+        document->m_security_handler->try_provide_user_password("");
+    }
 
     return document;
 }
@@ -54,6 +63,17 @@ Document::Document(NonnullRefPtr<Parser> const& parser)
     m_parser->set_document(this);
 }
 
+PDFErrorOr<void> Document::initialize()
+{
+    if (m_security_handler)
+        VERIFY(m_security_handler->has_user_password());
+
+    TRY(build_page_tree());
+    TRY(build_outline());
+
+    return {};
+}
+
 PDFErrorOr<Value> Document::get_or_load_value(u32 index)
 {
     auto value = get_value(index);

Userland/Libraries/LibPDF/Document.h

@@ -11,6 +11,7 @@
 #include <AK/RefCounted.h>
 #include <AK/Weakable.h>
 #include <LibGfx/Color.h>
+#include <LibPDF/Encryption.h>
 #include <LibPDF/Error.h>
 #include <LibPDF/ObjectDerivatives.h>
 #include <LibPDF/Parser.h>
@@ -78,8 +79,17 @@ class Document final
 public:
     static PDFErrorOr<NonnullRefPtr<Document>> create(ReadonlyBytes bytes);
 
+    // If a security handler is present, it is the caller's responsibility to ensure
+    // this document is unencrypted before calling this function. The user does not
+    // need to handle the case where the user password is the empty string.
+    PDFErrorOr<void> initialize();
+
+    ALWAYS_INLINE RefPtr<SecurityHandler> const& security_handler() const { return m_security_handler; }
+
     ALWAYS_INLINE RefPtr<OutlineDict> const& outline() const { return m_outline; }
 
+    ALWAYS_INLINE RefPtr<DictObject> const& trailer() const { return m_trailer; }
+
     [[nodiscard]] PDFErrorOr<Value> get_or_load_value(u32 index);
 
     [[nodiscard]] u32 get_first_page_index() const;
@@ -139,10 +149,12 @@ private:
 
     NonnullRefPtr<Parser> m_parser;
     RefPtr<DictObject> m_catalog;
+    RefPtr<DictObject> m_trailer;
     Vector<u32> m_page_object_indices;
     HashMap<u32, Page> m_pages;
     HashMap<u32, Value> m_values;
     RefPtr<OutlineDict> m_outline;
+    RefPtr<SecurityHandler> m_security_handler;
 };
 
 }

Userland/Libraries/LibPDF/Encryption.cpp

@@ -0,0 +1,394 @@
+/*
+ * Copyright (c) 2022, Matthew Olsson <mattco@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/ByteBuffer.h>
+#include <LibCrypto/Hash/MD5.h>
+#include <LibPDF/CommonNames.h>
+#include <LibPDF/Document.h>
+#include <LibPDF/Encryption.h>
+
+namespace PDF {
+
+static constexpr Array<u8, 32> standard_encryption_key_padding_bytes = {
+    0x28,
+    0xBF,
+    0x4E,
+    0x5E,
+    0x4E,
+    0x75,
+    0x8A,
+    0x41,
+    0x64,
+    0x00,
+    0x4E,
+    0x56,
+    0xFF,
+    0xFA,
+    0x01,
+    0x08,
+    0x2E,
+    0x2E,
+    0x00,
+    0xB6,
+    0xD0,
+    0x68,
+    0x3E,
+    0x80,
+    0x2F,
+    0x0C,
+    0xA9,
+    0xFE,
+    0x64,
+    0x53,
+    0x69,
+    0x7A,
+};
+
+PDFErrorOr<NonnullRefPtr<SecurityHandler>> SecurityHandler::create(Document* document, NonnullRefPtr<DictObject> encryption_dict)
+{
+    auto filter = TRY(encryption_dict->get_name(document, CommonNames::Filter))->name();
+    if (filter == "Standard")
+        return TRY(StandardSecurityHandler::create(document, encryption_dict));
+
+    dbgln("Unrecognized security handler filter: {}", filter);
+    TODO();
+}
+
+PDFErrorOr<NonnullRefPtr<StandardSecurityHandler>> StandardSecurityHandler::create(Document* document, NonnullRefPtr<DictObject> encryption_dict)
+{
+    auto revision = encryption_dict->get_value(CommonNames::R).get<int>();
+    auto o = TRY(encryption_dict->get_string(document, CommonNames::O))->string();
+    auto u = TRY(encryption_dict->get_string(document, CommonNames::U))->string();
+    auto p = encryption_dict->get_value(CommonNames::P).get<int>();
+    auto length = encryption_dict->get_value(CommonNames::Length).get<int>() / 8;
+    bool encrypt_metadata = true;
+    if (encryption_dict->contains(CommonNames::EncryptMetadata))
+        encryption_dict->get_value(CommonNames::EncryptMetadata).get<bool>();
+    return adopt_ref(*new StandardSecurityHandler(document, revision, o, u, p, encrypt_metadata, length));
+}
+
+StandardSecurityHandler::StandardSecurityHandler(Document* document, size_t revision, String const& o_entry, String const& u_entry, u32 flags, bool encrypt_metadata, size_t length)
+    : m_document(document)
+    , m_revision(revision)
+    , m_o_entry(o_entry)
+    , m_u_entry(u_entry)
+    , m_flags(flags)
+    , m_encrypt_metadata(encrypt_metadata)
+    , m_length(length)
+{
+}
+
+template<>
+ByteBuffer StandardSecurityHandler::compute_user_password_value<true>(ByteBuffer password_string)
+{
+    // Algorithm 4: Computing the encryption dictionary's U (user password)
+    //              value (Security handlers of revision 2)
+
+    // a) Create an encryption key based on the user password string, as
+    //    described in [Algorithm 2]
+    auto encryption_key = compute_encryption_key(password_string);
+
+    // b) Encrypt the 32-byte padding string shown in step (a) of [Algorithm 2],
+    //    using an RC4 encryption function with the encryption key from the
+    //    preceding step.
+    RC4 rc4(encryption_key);
+    auto output = rc4.encrypt(standard_encryption_key_padding_bytes);
+
+    // c) Store the result of step (b) as the value of the U entry in the
+    //    encryption dictionary.
+    return output;
+}
+
+template<>
+ByteBuffer StandardSecurityHandler::compute_user_password_value<false>(ByteBuffer password_string)
+{
+    // Algorithm 5: Computing the encryption dictionary's U (user password)
+    //              value (Security handlers of revision 3 or greater)
+
+    // a) Create an encryption key based on the user password string, as
+    //    described in [Algorithm 2]
+    auto encryption_key = compute_encryption_key(password_string);
+
+    // b) Initialize the MD5 hash functino and pass the 32-byte padding string
+    //    shown in step (a) of [Algorithm 2] as input to this function
+    Crypto::Hash::MD5 md5;
+    md5.update(standard_encryption_key_padding_bytes);
+
+    // e) Pass the first element of the file's file identifier array to the MD5
+    //    hash function.
+    auto id_array = MUST(m_document->trailer()->get_array(m_document, CommonNames::ID));
+    auto first_element_string = MUST(id_array->get_string_at(m_document, 0))->string();
+    md5.update(first_element_string);
+
+    // d) Encrypt the 16-byte result of the hash, using an RC4 encryption function
+    //    with the encryption key from step (a).
+    RC4 rc4(encryption_key);
+    auto out = md5.peek();
+    auto buffer = rc4.encrypt(out.bytes());
+
+    // e) Do the following 19 times:
+    //
+    //    Take the output from the previous invocation of the RC4 function and pass
+    //    it as input to a new invocation of the function; use an encryption key generated
+    //    by taking each byte of the original encryption key obtained in step (a) and
+    //    performing an XOR operation between the that byte and the single-byte value of
+    //    the iteration counter (from 1 to 19).
+    auto new_encryption_key = MUST(ByteBuffer::create_uninitialized(encryption_key.size()));
+    for (size_t i = 1; i <= 19; i++) {
+        for (size_t j = 0; j < encryption_key.size(); j++)
+            new_encryption_key[j] = encryption_key[j] ^ i;
+
+        RC4 new_rc4(new_encryption_key);
+        buffer = new_rc4.encrypt(buffer);
+    }
+
+    // f) Append 16 bytes of the arbitrary padding to the output from the final invocation
+    //    of the RC4 function and store the 32-byte result as the value of the U entry in
+    //    the encryption dictionary.
+    VERIFY(buffer.size() == 16);
+    for (size_t i = 0; i < 16; i++)
+        buffer.append(0xab);
+
+    return buffer;
+}
+
+bool StandardSecurityHandler::try_provide_user_password(StringView password_string)
+{
+    // Algorithm 6: Authenticating the user password
+
+    // a) Perform all but the last step of [Algorithm 4] or [Algorithm 5] using the
+    //    supplied password string.
+    ByteBuffer password_buffer = MUST(ByteBuffer::copy(password_string.bytes()));
+    if (m_revision == 2) {
+        password_buffer = compute_user_password_value<true>(password_buffer);
+    } else {
+        password_buffer = compute_user_password_value<false>(password_buffer);
+    }
+
+    // b) If the result of step (a) is equal to the value of the encryption
+    //    dictionary's "U" entry (comparing the first 16 bytes in the case of security
+    //    handlers of revision 3 or greater), the password supplied is the correct user
+    //    password.
+    auto u_bytes = m_u_entry.bytes();
+    if (m_revision >= 3)
+        return u_bytes.slice(0, 16) == password_buffer.bytes().slice(0, 16);
+    return u_bytes == password_buffer.bytes();
+}
+
+ByteBuffer StandardSecurityHandler::compute_encryption_key(ByteBuffer password_string)
+{
+    // This function should never be called after we have a valid encryption key.
+    VERIFY(!m_encryption_key.has_value());
+
+    // 7.6.3.3 Encryption Key Algorithm
+
+    // Algorithm 2: Computing an encryption key
+
+    // a) Pad or truncate the password string to exactly 32 bytes. If the password string
+    //    is more than 32 bytes long, use only its first 32 bytes; if it is less than 32
+    //    bytes long, pad it by appending the required number of additional bytes from the
+    //    beginning of the following padding string: [omitted]
+
+    if (password_string.size() > 32) {
+        password_string.resize(32);
+    } else {
+        password_string.append(standard_encryption_key_padding_bytes.data(), 32 - password_string.size());
+    }
+
+    // b) Initialize the MD5 hash function and pass the result of step (a) as input to
+    //    this function.
+    Crypto::Hash::MD5 md5;
+    md5.update(password_string);
+
+    // c) Pass the value of the encryption dictionary's "O" entry to the MD5 hash function.
+    md5.update(m_o_entry);
+
+    // d) Convert the integer value of the P entry to a 32-bit unsigned binary number and pass
+    //    these bytes to the MD5 hash function, low-order byte first.
+    md5.update(reinterpret_cast<u8 const*>(&m_flags), sizeof(m_flags));
+
+    // e) Pass the first element of the file's file identifier array to the MD5 hash function.
+    auto id_array = MUST(m_document->trailer()->get_array(m_document, CommonNames::ID));
+    auto first_element_string = MUST(id_array->get_string_at(m_document, 0))->string();
+    md5.update(first_element_string);
+
+    // f) (Security handlers of revision 4 or greater) if the document metadata is not being
+    //    encrypted, pass 4 bytes with the value 0xffffffff to the MD5 hash function.
+    if (m_revision >= 4 && !m_encrypt_metadata) {
+        u32 value = 0xffffffff;
+        md5.update(reinterpret_cast<u8 const*>(&value), 4);
+    }
+
+    // g) Finish the hash.
+    // h) (Security handlers of revision 3 or greater) Do the following 50 times:
+    //
+    //    Take the output from the previous MD5 hash and pass the first n bytes
+    //    of the output as input into a new MD5 hash, where n is the number of
+    //    bytes of the encryption key as defined by the value of the encryption
+    //    dictionary's Length entry.
+    if (m_revision >= 3) {
+        ByteBuffer n_bytes;
+
+        for (u32 i = 0; i < 50; i++) {
+            Crypto::Hash::MD5 new_md5;
+            n_bytes.ensure_capacity(m_length);
+
+            while (n_bytes.size() < m_length) {
+                auto out = md5.peek().bytes();
+                for (size_t j = 0; j < out.size() && n_bytes.size() < m_length; j++)
+                    n_bytes.append(out[j]);
+            }
+
+            VERIFY(n_bytes.size() == m_length);
+            new_md5.update(n_bytes);
+            md5 = move(new_md5);
+            n_bytes.clear();
+        }
+    }
+
+    // i) Set the encryption key to the first n bytes of the output from the final MD5
+    //    hash, where n shall always be 5 for security handlers of revision 2 but, for
+    //    security handlers of revision 3 or greater, shall depend on the value of the
+    //    encryption dictionary's Length entry.
+    size_t n;
+    if (m_revision == 2) {
+        n = 5;
+    } else if (m_revision >= 3) {
+        n = m_length;
+    } else {
+        VERIFY_NOT_REACHED();
+    }
+
+    ByteBuffer encryption_key;
+    encryption_key.ensure_capacity(n);
+    while (encryption_key.size() < n) {
+        auto out = md5.peek();
+        for (size_t i = 0; encryption_key.size() < n && i < out.data_length(); i++)
+            encryption_key.append(out.bytes()[i]);
+    }
+
+    m_encryption_key = encryption_key;
+
+    return encryption_key;
+}
+
+void StandardSecurityHandler::encrypt(NonnullRefPtr<Object> object, Reference reference) const
+{
+    // 7.6.2 General Encryption Algorithm
+    // Algorithm 1: Encryption of data using the RC3 or AES algorithms
+
+    // FIXME: Support AES
+
+    VERIFY(m_encryption_key.has_value());
+
+    // a) Obtain the object number and generation number from the object identifier of
+    //    the string or stream to be encrypted. If the string is a direct object, use
+    //    the identifier of the indirect object containing it.
+    //
+    // Note: This is always passed in at parse time because objects don't know their own
+    //       object number.
+
+    // b) For all strings and streams with crypt filter specifier; treating the object
+    //    number as binary integers, extends the origin n-byte encryption key to n + 5
+    //    bytes by appending the low-order 3 bytes of the object number and the low-order
+    //    2 bytes of the generation number in that order, low-order byte first. ...
+
+    auto encryption_key = m_encryption_key.value();
+    ReadonlyBytes bytes;
+    Function<void(ByteBuffer const&)> assign;
+
+    if (object->is<StreamObject>()) {
+        auto stream = object->cast<StreamObject>();
+        bytes = stream->bytes();
+
+        assign = [&stream](ByteBuffer const& buffer) {
+            stream->buffer() = buffer;
+        };
+
+        if (stream->dict()->contains(CommonNames::Filter)) {
+            auto filter = MUST(stream->dict()->get_name(m_document, CommonNames::Filter))->name();
+            if (filter == "Crypt")
+                TODO();
+        }
+    } else if (object->is<StringObject>()) {
+        auto string = object->cast<StringObject>();
+        bytes = string->string().bytes();
+        assign = [&string](ByteBuffer const& buffer) {
+            string->set_string(String(buffer.bytes()));
+        };
+    } else {
+        VERIFY_NOT_REACHED();
+    }
+
+    auto index = reference.as_ref_index();
+    auto generation = reference.as_ref_generation_index();
+
+    encryption_key.append(index & 0xff);
+    encryption_key.append((index >> 8) & 0xff);
+    encryption_key.append((index >> 16) & 0xff);
+    encryption_key.append(generation & 0xff);
+    encryption_key.append((generation >> 8) & 0xff);
+
+    // c) Initialize the MD5 hash function and pass the result of step (b) as input to this
+    //    function.
+    Crypto::Hash::MD5 md5;
+    md5.update(encryption_key);
+
+    // d) Use the first (n + 5) bytes, up to a maximum of 16, of the output from the MD5
+    //    hash as the key for the RC4 or AES symmetric key algorithms, along with the string
+    //    or stream data to be encrypted.
+    auto key = MUST(ByteBuffer::copy(md5.peek().bytes()));
+
+    if (key.size() > min(encryption_key.size(), 16))
+        key.resize(encryption_key.size());
+
+    RC4 rc4(key);
+    auto output = rc4.encrypt(bytes);
+
+    assign(output);
+}
+
+void StandardSecurityHandler::decrypt(NonnullRefPtr<Object> object, Reference reference) const
+{
+    // AES and RC4 are both symmetric, so decryption is the same as encryption
+    encrypt(object, reference);
+}
+
+static constexpr auto identity_permutation = iota_array<size_t, 256>(0);
+
+RC4::RC4(ReadonlyBytes key)
+    : m_bytes(identity_permutation)
+{
+    size_t j = 0;
+    for (size_t i = 0; i < 256; i++) {
+        j = (j + m_bytes[i] + key[i % key.size()]) & 0xff;
+        swap(m_bytes[i], m_bytes[j]);
+    }
+}
+
+void RC4::generate_bytes(ByteBuffer& bytes)
+{
+    size_t i = 0;
+    size_t j = 0;
+
+    for (size_t count = 0; count < bytes.size(); count++) {
+        i = (i + 1) % 256;
+        j = (j + m_bytes[i]) % 256;
+        swap(m_bytes[i], m_bytes[j]);
+        bytes[count] = m_bytes[(m_bytes[i] + m_bytes[j]) % 256];
+    }
+}
+
+ByteBuffer RC4::encrypt(ReadonlyBytes bytes)
+{
+    auto output = MUST(ByteBuffer::create_uninitialized(bytes.size()));
+    generate_bytes(output);
+    for (size_t i = 0; i < bytes.size(); i++)
+        output[i] ^= bytes[i];
+    return output;
+}
+
+}

Userland/Libraries/LibPDF/Encryption.h

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2022, Matthew Olsson <mattco@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Span.h>
+#include <LibPDF/ObjectDerivatives.h>
+
+namespace PDF {
+
+class SecurityHandler : public RefCounted<SecurityHandler> {
+public:
+    static PDFErrorOr<NonnullRefPtr<SecurityHandler>> create(Document*, NonnullRefPtr<DictObject> encryption_dict);
+
+    virtual ~SecurityHandler() = default;
+
+    virtual bool try_provide_user_password(StringView password) = 0;
+    virtual bool has_user_password() const = 0;
+
+    virtual void encrypt(NonnullRefPtr<Object>, Reference reference) const = 0;
+    virtual void decrypt(NonnullRefPtr<Object>, Reference reference) const = 0;
+};
+
+class StandardSecurityHandler : public SecurityHandler {
+public:
+    static PDFErrorOr<NonnullRefPtr<StandardSecurityHandler>> create(Document*, NonnullRefPtr<DictObject> encryption_dict);
+
+    StandardSecurityHandler(Document*, size_t revision, String const& o_entry, String const& u_entry, u32 flags, bool encrypt_metadata, size_t length);
+
+    ~StandardSecurityHandler() override = default;
+
+    bool try_provide_user_password(StringView password_string) override;
+
+    bool has_user_password() const override { return m_encryption_key.has_value(); }
+
+protected:
+    void encrypt(NonnullRefPtr<Object>, Reference reference) const override;
+    void decrypt(NonnullRefPtr<Object>, Reference reference) const override;
+
+private:
+    template<bool is_revision_2>
+    ByteBuffer compute_user_password_value(ByteBuffer password_string);
+
+    ByteBuffer compute_encryption_key(ByteBuffer password_string);
+
+    Document* m_document;
+    size_t m_revision;
+    Optional<ByteBuffer> m_encryption_key;
+    String m_o_entry;
+    String m_u_entry;
+    u32 m_flags;
+    bool m_encrypt_metadata;
+    size_t m_length;
+};
+
+class RC4 {
+public:
+    RC4(ReadonlyBytes key);
+
+    void generate_bytes(ByteBuffer&);
+    ByteBuffer encrypt(ReadonlyBytes bytes);
+
+private:
+    Array<size_t, 256> m_bytes;
+};
+
+}

Userland/Libraries/LibPDF/ObjectDerivatives.h

@@ -29,6 +29,7 @@ public:
 
     [[nodiscard]] ALWAYS_INLINE String const& string() const { return m_string; }
     [[nodiscard]] ALWAYS_INLINE bool is_binary() const { return m_is_binary; }
+    void set_string(String string) { m_string = move(string); }
 
     const char* type_name() const override { return "string"; }
     String to_string(int indent) const override;
@@ -153,6 +154,7 @@ public:
 
     [[nodiscard]] ALWAYS_INLINE NonnullRefPtr<DictObject> dict() const { return m_dict; }
     [[nodiscard]] ReadonlyBytes bytes() const { return m_buffer.bytes(); };
+    [[nodiscard]] ByteBuffer& buffer() { return m_buffer; };
 
     const char* type_name() const override { return "stream"; }
     String to_string(int indent) const override;