lpg: improve Picture sizing, clean up

Restraining a Picture in one dimension with a Frame should make it
report the right overall dimensions (keeping its aspect ratio).

Also applying the F.9 C++ Core Guideline.

LICENSE

@@ -1,4 +1,4 @@
-Copyright (c) 2017 - 2020, Přemysl Eric Janouch <p@janouch.name>
+Copyright (c) 2017 - 2025, Přemysl Eric Janouch <p@janouch.name>
 
 Permission to use, copy, modify, and/or distribute this software for any
 purpose with or without fee is hereby granted.

README.adoc

@@ -2,11 +2,19 @@ pdf-simple-sign
 ===============
 
 'pdf-simple-sign' is a simple PDF signer intended for documents produced by
-the Cairo library, GNU troff, ImageMagick, or similar.
+the Cairo library (≤ 1.17.4 or using PDF 1.4), GNU troff, ImageMagick,
+or similar.
 
 I don't aim to extend the functionality any further.  The project is fairly
 self-contained and it should be easy to grasp and change to suit to your needs.
 
+Packages
+--------
+Regular releases are sporadic.  git master should be stable enough.
+You can get a package with the latest development version using Arch Linux's
+https://aur.archlinux.org/packages/pdf-simple-sign-git[AUR],
+or as a https://git.janouch.name/p/nixexprs[Nix derivation].
+
 Documentation
 -------------
 See the link:pdf-simple-sign.adoc[man page] for information about usage.
@@ -25,9 +33,39 @@ Runtime dependencies: libcrypto (OpenSSL 1.1 API)
  $ cd builddir
  $ ninja
 
-In addition to the C++ version, also included is a native Go port:
+Go
+~~
+In addition to the C++ version, also included is a native Go port,
+which has enhanced PDF 1.5 support:
 
- $ go get janouch.name/pdf-simple-sign/cmd/pdf-simple-sign
+----
+$ go install janouch.name/pdf-simple-sign/cmd/pdf-simple-sign@master
+----
+
+and a crude external VFS for Midnight Commander, that may be used to extract
+all streams from a given PDF file:
+
+----
+$ GOBIN=$HOME/.local/share/mc/extfs.d \
+  go install janouch.name/pdf-simple-sign/cmd/extfs-pdf@master
+----
+
+To enable the VFS, edit your _~/.config/mc/mc.ext.ini_ to contain:
+
+----
+[pdf]
+Type=^PDF
+Open=%cd %p/extfs-pdf://
+----
+
+Lua PDF generator
+~~~~~~~~~~~~~~~~~
+Build dependencies: Meson, a C++17 compiler, pkg-config +
+Runtime dependencies: C++ Lua >= 5.3 (custom Meson wrap fallback),
+ cairo >= 1.15.4, pangocairo, libqrencode
+
+This is a parasitic subproject located in the _lpg_ subdirectory.
+It will generate its own documentation.
 
 Contributing and Support
 ------------------------

cmd/extfs-pdf/main.go

@@ -0,0 +1,141 @@
+//
+// Copyright (c) 2021 - 2024, Přemysl Eric Janouch <p@janouch.name>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+//
+
+// extfs-pdf is an external VFS plugin for Midnight Commander.
+// More serious image extractors should rewrite this to use pdfimages(1).
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"time"
+
+	"janouch.name/pdf-simple-sign/pdf"
+)
+
+func die(status int, format string, args ...interface{}) {
+	os.Stderr.WriteString(fmt.Sprintf(format+"\n", args...))
+	os.Exit(status)
+}
+
+func usage() {
+	die(1, "Usage: %s [-h] COMMAND DOCUMENT [ARG...]", os.Args[0])
+}
+
+func streamSuffix(o *pdf.Object) string {
+	if filter, _ := o.Dict["Filter"]; filter.Kind == pdf.Name {
+		switch filter.String {
+		case "JBIG2Decode":
+			// This is the file extension used by pdfimages(1).
+			// This is not a complete JBIG2 standalone file.
+			return "jb2e"
+		case "JPXDecode":
+			return "jp2"
+		case "DCTDecode":
+			return "jpg"
+		case "FlateDecode":
+			return "zz"
+		default:
+			return filter.String
+		}
+	}
+	return "stream"
+}
+
+func list(mtime time.Time, updater *pdf.Updater) {
+	stamp := mtime.Local().Format("01-02-2006 15:04:05")
+	for _, o := range updater.ListIndirect() {
+		object, err := updater.Get(o.N, o.Generation)
+		size := 0
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "%s\n", err)
+		} else {
+			// Accidental transformation, retrieving original data is more work.
+			size = len(object.Serialize())
+		}
+		fmt.Printf("-r--r--r-- 1 0 0 %d %s n%dg%d\n",
+			size, stamp, o.N, o.Generation)
+		if object.Kind == pdf.Stream {
+			fmt.Printf("-r--r--r-- 1 0 0 %d %s n%dg%d.%s\n", len(object.Stream),
+				stamp, o.N, o.Generation, streamSuffix(&object))
+		}
+	}
+}
+
+func copyout(updater *pdf.Updater, storedFilename, extractTo string) {
+	var (
+		n, generation uint
+		suffix        string
+	)
+	m, err := fmt.Sscanf(storedFilename, "n%dg%d%s", &n, &generation, &suffix)
+	if m < 2 {
+		die(3, "%s: %s", storedFilename, err)
+	}
+
+	object, err := updater.Get(n, generation)
+	if err != nil {
+		die(3, "%s: %s", storedFilename, err)
+	}
+
+	content := []byte(object.Serialize())
+	if suffix != "" {
+		content = object.Stream
+	}
+	if err = os.WriteFile(extractTo, content, 0666); err != nil {
+		die(3, "%s", err)
+	}
+}
+
+func main() {
+	flag.Usage = usage
+	flag.Parse()
+	if flag.NArg() < 2 {
+		usage()
+	}
+
+	command, documentPath := flag.Arg(0), flag.Arg(1)
+	doc, err := os.ReadFile(documentPath)
+	if err != nil {
+		die(1, "%s", err)
+	}
+
+	mtime := time.UnixMilli(0)
+	if info, err := os.Stat(documentPath); err == nil {
+		mtime = info.ModTime()
+	}
+
+	updater, err := pdf.NewUpdater(doc)
+	if err != nil {
+		die(2, "%s", err)
+	}
+
+	switch command {
+	default:
+		die(1, "unsupported command: %s", command)
+	case "list":
+		if flag.NArg() != 2 {
+			usage()
+		} else {
+			list(mtime, updater)
+		}
+	case "copyout":
+		if flag.NArg() != 4 {
+			usage()
+		} else {
+			copyout(updater, flag.Arg(2), flag.Arg(3))
+		}
+	}
+}

go.mod

@@ -3,6 +3,6 @@ module janouch.name/pdf-simple-sign
 go 1.17
 
 require (
-	go.mozilla.org/pkcs7 v0.0.0-20200128120323-432b2356ecb1
+	go.mozilla.org/pkcs7 v0.0.0-20210826202110-33d05740a352
-	golang.org/x/crypto v0.0.0-20200728195943-123391ffb6de
+	golang.org/x/crypto v0.10.0
 )

go.sum

@@ -1,8 +1,12 @@
 go.mozilla.org/pkcs7 v0.0.0-20200128120323-432b2356ecb1 h1:A/5uWzF44DlIgdm/PQFwfMkW0JX+cIcQi/SwLAmZP5M=
 go.mozilla.org/pkcs7 v0.0.0-20200128120323-432b2356ecb1/go.mod h1:SNgMg+EgDFwmvSmLRTNKC5fegJjB7v23qTQ0XLGUNHk=
+go.mozilla.org/pkcs7 v0.0.0-20210826202110-33d05740a352 h1:CCriYyAfq1Br1aIYettdHZTy8mBTIPo7We18TuO/bak=
+go.mozilla.org/pkcs7 v0.0.0-20210826202110-33d05740a352/go.mod h1:SNgMg+EgDFwmvSmLRTNKC5fegJjB7v23qTQ0XLGUNHk=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20200728195943-123391ffb6de h1:ikNHVSjEfnvz6sxdSPCaPt572qowuyMDMJLLm3Db3ig=
 golang.org/x/crypto v0.0.0-20200728195943-123391ffb6de/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
+golang.org/x/crypto v0.10.0 h1:LKqV2xt9+kDzSTfOhx4FrkEBcMrAgHSYgzywV9zcGmM=
+golang.org/x/crypto v0.10.0/go.mod h1:o4eNf7Ede1fv+hwOwZsTHl9EsPFO6q6ZvYR8vYfY45I=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=

lpg/.clang-format

@@ -0,0 +1,9 @@
+BasedOnStyle: LLVM
+ColumnLimit: 80
+IndentWidth: 4
+TabWidth: 4
+UseTab: ForContinuationAndIndentation
+SpaceAfterCStyleCast: true
+AlignAfterOpenBracket: DontAlign
+AlignOperands: DontAlign
+SpacesBeforeTrailingComments: 2

lpg/lpg.lua

@@ -0,0 +1,240 @@
+#!/usr/bin/env lpg
+local project_url = "https://git.janouch.name/p/pdf-simple-sign"
+
+function h1 (title)
+	return lpg.VBox {fontsize=18., fontweight=600,
+		title, lpg.HLine {2}, lpg.Filler {-1, 6}}
+end
+function h2 (title)
+	return lpg.VBox {fontsize=16., fontweight=600,
+		lpg.Filler {-1, 8}, title, lpg.HLine {1}, lpg.Filler {-1, 6}}
+end
+function h3 (title)
+	return lpg.VBox {fontsize=14., fontweight=600,
+		lpg.Filler {-1, 8}, title, lpg.HLine {.25}, lpg.Filler {-1, 6}}
+end
+function p (...)
+	return lpg.VBox {..., lpg.Filler {-1, 6}}
+end
+function code (...)
+	return lpg.VBox {
+		lpg.Filler {-1, 4},
+		lpg.HBox {
+			lpg.Filler {12},
+			lpg.VBox {"<tt>" .. table.concat {...} .. "</tt>"},
+			lpg.Filler {},
+		},
+		lpg.Filler {-1, 6},
+	}
+end
+function define (name, ...)
+	return lpg.VBox {
+		lpg.Filler {-1, 2},
+		lpg.Text {fontweight=600, name}, lpg.Filler {-1, 2},
+		lpg.HBox {lpg.Filler {12}, lpg.VBox {...}, lpg.Filler {}},
+		lpg.Filler {-1, 2},
+	}
+end
+function pad (widget)
+	return lpg.VBox {
+		lpg.Filler {-1, 2},
+		lpg.HBox {lpg.Filler {4}, widget, lpg.Filler {}, lpg.Filler {4}},
+		lpg.Filler {-1, 2},
+	}
+end
+
+local page1 = lpg.VBox {fontfamily="sans serif", fontsize=12.,
+	h1("lpg User Manual"),
+	p("<b>lpg</b> is a Lua-based PDF document generator, exposing a trivial " ..
+		"layouting engine on top of the Cairo graphics library, " ..
+		"with manual paging."),
+	p("The author has primarily been using this system to typeset invoices."),
+
+	h2("Synopsis"),
+	p("<b>lpg</b> <i>program.lua</i> [<i>args...</i>]"),
+
+	h2("API"),
+	p("The Lua program receives <b>lpg</b>'s and its own path joined " ..
+		"as <tt>arg[0]</tt>.  Any remaining sequential elements " ..
+		"of this table represent the passed <i>args</i>."),
+
+	h3("Utilities"),
+
+	define("lpg.cm (centimeters)",
+		p("Returns how many document points are needed " ..
+			"for the given physical length.")),
+
+	define("lpg.ntoa {number [, precision=…]\n" ..
+		"\t[, thousands_sep=…] [, decimal_point=…] [, grouping=…]}",
+		p("Formats a number using the C++ localization " ..
+			"and I/O libraries.  " ..
+			"For example, the following call results in “3 141,59”:"),
+		code("ntoa {3141.592, precision=2,\n" ..
+			"  thousands_sep=\" \", decimal_point=\",\", " ..
+			"grouping=\"\\003\"}")),
+
+	define("lpg.escape (values...)",
+		p("Interprets all values as strings, " ..
+			"and escapes them to be used as literal text—" ..
+			"all text within <b>lpg</b> is parsed as Pango markup, " ..
+			"which is a subset of XML.")),
+
+	h3("PDF documents"),
+
+	define("lpg.Document (filename, width, height [, margin])",
+		p("Returns a new <i>Document</i> object, whose pages are all " ..
+			"the same size in 72 DPI points, as specified by <b>width</b> " ..
+			"and <b>height</b>.  The <b>margin</b> is used by <b>show</b> " ..
+			"on all sides of pages."),
+		p("The file is finalized when the object is garbage collected.")),
+
+	define("<i>Document</i>.title, author, subject, keywords, " ..
+		"creator, create_date, mod_date",
+		p("Write-only PDF <i>Info</i> dictionary metadata strings.")),
+
+	define("<i>Document</i>:show ([widget...])",
+		p("Starts a new document page, and renders <i>Widget</i> trees over " ..
+		"the whole print area.")),
+
+	lpg.Filler {},
+}
+
+local page2 = lpg.VBox {fontfamily="sans serif", fontsize=12.,
+	h3("Widgets"),
+	p("The layouting system makes heavy use of composition, " ..
+		"and thus stays simple."),
+	p("For convenience, anywhere a <i>Widget</i> is expected but another " ..
+		"kind of value is received, <b>lpg.Text</b> widget will be invoked " ..
+		"on that value."),
+	p("Once a <i>Widget</i> is included in another <i>Widget</i>, " ..
+		"the original Lua object can no longer be used, " ..
+		"as its reference has been consumed."),
+	p("<i>Widgets</i> can be indexed by strings to get or set " ..
+		"their <i>attributes</i>.  All <i>Widget</i> constructor tables " ..
+		"also accept attributes, for convenience.  Attributes can be " ..
+		"either strings or numbers, mostly only act " ..
+		"on specific <i>Widget</i> kinds, and are hereditary.  " ..
+		"Prefix their names with an underscore to set them ‘privately’."),
+	p("<i>Widget</i> sizes can be set negative, which signals to their " ..
+		"container that they should take any remaining space, " ..
+		"after all their siblings’ requests have been satisfied.  " ..
+		"When multiple widgets make this request, that space is distributed " ..
+		"in proportion to these negative values."),
+
+	define("lpg.Filler {[width] [, height]}",
+		p("Returns a new blank widget with the given dimensions, " ..
+			"which default to -1, -1.")),
+	define("lpg.HLine {[thickness]}",
+		p("Returns a new widget that draws a simple horizontal line " ..
+			"of the given <b>thickness</b>.")),
+	define("lpg.VLine {[thickness]}",
+		p("Returns a new widget that draws a simple vertical line " ..
+			"of the given <b>thickness</b>.")),
+	define("lpg.Text {[value...]}",
+		p("Returns a new text widget that renders the concatenation of all " ..
+			"passed values filtered through Lua’s <b>tostring</b> " ..
+			"function.  Non-strings will additionally be escaped."),
+		define("<i>Text</i>.fontfamily, fontsize, fontweight, lineheight",
+			p("Various font properties, similar to their CSS counterparts."))),
+	define("lpg.Frame {widget}",
+		p("Returns a special container widget that can override " ..
+			"a few interesting properties."),
+		define("<i>Frame</i>.color",
+			p("Text and line colour, for example <tt>0xff0000</tt> for red.")),
+		define("<i>Frame</i>.w_override",
+			p("Forcefully changes the child <i>Widget</i>’s " ..
+				"requested width, such as to negative values.")),
+		define("<i>Frame</i>.h_override",
+			p("Forcefully changes the child <i>Widget</i>’s " ..
+				"requested height, such as to negative values."))),
+
+	lpg.Filler {},
+}
+
+local page3 = lpg.VBox {fontfamily="sans serif", fontsize=12.,
+	define("lpg.Link {target, widget}",
+		p("Returns a new hyperlink widget pointing to the <b>target</b>, " ..
+			"which is a URL.  The hyperlink applies " ..
+			"to the entire area of the child widget.  " ..
+			"It has no special appearance.")),
+	define("lpg.HBox {[widget...]}",
+		p("Returns a new container widget that places children " ..
+			"horizontally, from left to right."),
+		p("If any space remains after satisfying the children widgets’ " ..
+			"requisitions, it is distributed equally amongst all of them.  " ..
+			"Also see the note about negative sizes.")),
+	define("lpg.VBox {[widget...]}",
+		p("Returns a new container widget that places children " ..
+			"vertically, from top to bottom.")),
+	define("lpg.Picture {filename}",
+		p("Returns a new picture widget, showing the given <b>filename</b>, " ..
+			"which currently must be in the PNG format.  " ..
+			"Pictures are rescaled to fit, but keep their aspect ratio.")),
+	define("lpg.QR {contents, module}",
+		p("Returns a new QR code widget, encoding the <b>contents</b> " ..
+			"string using the given <b>module</b> size.  " ..
+			"The QR code version is chosen automatically.")),
+	
+	h2("Examples"),
+	p("See the source code of this user manual " ..
+		"for the general structure of scripts."),
+
+	h3("Size distribution and composition"),
+	lpg.VBox {
+		lpg.HLine {},
+		lpg.HBox {
+			lpg.VLine {}, lpg.Frame {_w_override=lpg.cm(3), pad "3cm"},
+			lpg.VLine {}, lpg.Frame {pad "Measured"},
+			lpg.VLine {}, lpg.Frame {_w_override=-1, pad "-1"},
+			lpg.VLine {}, lpg.Frame {_w_override=-2, pad "-2"},
+			lpg.VLine {},
+		},
+		lpg.HLine {},
+	},
+	lpg.Filler {-1, 6},
+	code([[
+<small><b>function</b> pad (widget)
+  <b>local function</b> f (...) <b>return</b> lpg.Filler {...} <b>end</b>
+  <b>return</b> lpg.VBox {f(-1, 2), lpg.HBox {f(4), w, f(), f(4)}, f(-1, 2)}
+<b>end</b>
+
+lpg.VBox {lpg.HLine {}, lpg.HBox {
+  lpg.VLine {}, lpg.Frame {_w_override=lpg.cm(3), pad "3cm"},
+  lpg.VLine {}, lpg.Frame {pad "Measured"},
+  lpg.VLine {}, lpg.Frame {_w_override=-1, pad "-1"},
+  lpg.VLine {}, lpg.Frame {_w_override=-2, pad "-2"},
+  lpg.VLine {},
+}, lpg.HLine {}}</small>]]),
+
+	h3("Clickable QR code link"),
+	lpg.HBox {
+		lpg.VBox {
+			p("Go here to report bugs, request features, " ..
+				"or submit pull requests:"),
+			code(([[
+url = "%s"
+lpg.Link {url, lpg.QR {url, 2.5}}]]):format(project_url)),
+		},
+		lpg.Filler {},
+		lpg.Link {project_url, lpg.QR {project_url, 2.5}},
+	},
+
+	lpg.Filler {},
+}
+
+if #arg < 1 then
+	io.stderr:write("Usage: " .. arg[0] .. " OUTPUT-PDF..." .. "\n")
+	os.exit(false)
+end
+local width, height, margin = lpg.cm(21), lpg.cm(29.7), lpg.cm(2.0)
+for i = 1, #arg do
+	local pdf = lpg.Document(arg[i], width, height, margin)
+	pdf.title = "lpg User Manual"
+	pdf.subject = "lpg User Manual"
+	pdf.author = "Přemysl Eric Janouch"
+	pdf.creator = ("lpg (%s)"):format(project_url)
+
+	pdf:show(page1)
+	pdf:show(page2)
+	pdf:show(page3)
+end

lpg/meson.build

@@ -0,0 +1,24 @@
+project('lpg', 'cpp', default_options : ['cpp_std=c++17'],
+	version : '1.1.1')
+
+conf = configuration_data()
+conf.set_quoted('PROJECT_NAME', meson.project_name())
+conf.set_quoted('PROJECT_VERSION', meson.project_version())
+configure_file(output : 'config.h', configuration : conf)
+
+luapp = dependency('lua++', allow_fallback : true)
+cairo = dependency('cairo')
+pangocairo = dependency('pangocairo')
+libqrencode = dependency('libqrencode')
+lpg_exe = executable('lpg', 'lpg.cpp',
+	install : true,
+	dependencies : [luapp, cairo, pangocairo, libqrencode])
+
+# XXX: https://github.com/mesonbuild/meson/issues/825
+docdir = get_option('datadir') / 'doc' / meson.project_name()
+lpg_pdf = custom_target('lpg.pdf',
+	output : 'lpg.pdf',
+	input : 'lpg.lua',
+	command : [lpg_exe, '@INPUT@', '@OUTPUT@'],
+	install_dir : docdir,
+	build_by_default : true)

lpg/subprojects/lua++.wrap

@@ -0,0 +1,10 @@
+[wrap-file]
+directory = lua-5.4.7
+source_url = https://github.com/lua/lua/archive/refs/tags/v5.4.7.tar.gz
+source_filename = lua-5.4.7.tar.gz
+source_hash = 5c39111b3fc4c1c9e56671008955a1730f54a15b95e1f1bd0752b868b929d8e3
+patch_directory = lua-5.4.7
+
+[provide]
+lua++-5.4 = lua_dep
+lua++ = lua_dep

lpg/subprojects/packagefiles/lua-5.4.7/LICENSE.build

@@ -0,0 +1,20 @@
+Copyright (c) 2025 Přemysl Eric Janouch <p@janouch.name>
+Copyright (c) 2021 The Meson development team
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

lpg/subprojects/packagefiles/lua-5.4.7/meson.build

@@ -0,0 +1,50 @@
+project(
+  'lua-5.4',
+  'cpp',
+  license : 'MIT',
+  meson_version : '>=0.49.2',
+  version : '5.4.7',
+  default_options : ['c_std=c99', 'warning_level=2'],
+)
+
+cxx = meson.get_compiler('cpp')
+
+# Skip bogus warning.
+add_project_arguments(cxx.get_supported_arguments(
+  '-Wno-string-plus-int', '-Wno-stringop-overflow'), language : 'cpp')
+
+# Platform-specific defines.
+is_posix = host_machine.system() in ['cygwin', 'darwin', 'dragonfly', 'freebsd',
+  'gnu', 'haiku', 'linux', 'netbsd', 'openbsd', 'sunos']
+if is_posix
+  add_project_arguments('-DLUA_USE_POSIX', language : 'cpp')
+endif
+
+# Library dependencies.
+lua_lib_deps = [cxx.find_library('m', required : false)]
+
+if meson.version().version_compare('>= 0.62')
+  dl_dep = dependency('dl', required : get_option('loadlib'))
+else
+  dl_dep = cxx.find_library('dl', required : get_option('loadlib'))
+endif
+
+if dl_dep.found()
+  lua_lib_deps += dl_dep
+  add_project_arguments('-DLUA_USE_DLOPEN', language : 'cpp')
+endif
+
+# Targets.
+add_project_arguments('-DMAKE_LIB', language : 'cpp')
+lua_lib = static_library(
+  'lua',
+  'onelua.cpp',
+  dependencies : lua_lib_deps,
+  implicit_include_directories : false,
+)
+
+inc = include_directories('.')
+lua_dep = declare_dependency(
+  link_with : lua_lib,
+  include_directories : inc,
+)

lpg/subprojects/packagefiles/lua-5.4.7/meson_options.txt

@@ -0,0 +1,4 @@
+option(
+  'loadlib', type : 'feature',
+  description : 'Allow Lua to "require" C extension modules'
+)

lpg/subprojects/packagefiles/lua-5.4.7/onelua.cpp

@@ -0,0 +1 @@
+#include "onelua.c"

pdf-simple-sign.adoc

@@ -14,7 +14,7 @@ Synopsis
 
 Description
 -----------
-'pdf-simple-sign' is a simple PDF signer intended for documents produced by
+*pdf-simple-sign* is a simple PDF signer intended for documents produced by
 the Cairo library, GNU troff, ImageMagick, or similar.  As such, it currently
 comes with some restrictions:
 

pdf-simple-sign.cpp

@@ -64,7 +64,7 @@ std::string ssprintf(const std::string& format, Args... args) {
 // -------------------------------------------------------------------------------------------------
 
 /// PDF token/object thingy.  Objects may be composed either from one or a sequence of tokens.
-/// The PDF Reference doesn't actually speak of tokens.
+/// The PDF Reference doesn't actually speak of tokens, though ISO 32000-1:2008 does.
 struct pdf_object {
   enum type {
     END, NL, COMMENT, NIL, BOOL, NUMERIC, KEYWORD, NAME, STRING,
@@ -543,8 +543,8 @@ std::string pdf_updater::initialize() {
     const auto prev_offset = trailer.dict.find("Prev");
     if (prev_offset == trailer.dict.end())
       break;
-    // FIXME we don't check for size_t over or underflow
+    // FIXME do not read offsets and sizes as floating point numbers
-    if (!prev_offset->second.is_integer())
+    if (!prev_offset->second.is_integer() || prev_offset->second.number < 0)
       return "invalid Prev offset";
     xref_offset = prev_offset->second.number;
   }

pdf/pdf.go

@@ -1,5 +1,5 @@
 //
-// Copyright (c) 2018 - 2020, Přemysl Eric Janouch <p@janouch.name>
+// Copyright (c) 2018 - 2024, Přemysl Eric Janouch <p@janouch.name>
 //
 // Permission to use, copy, modify, and/or distribute this software for any
 // purpose with or without fee is hereby granted.
@@ -18,6 +18,8 @@ package pdf
 
 import (
 	"bytes"
+	"compress/zlib"
+	"encoding/binary"
 	"encoding/hex"
 	"errors"
 	"fmt"
@@ -59,20 +61,22 @@ const (
 	// higher-level objects
 	Array
 	Dict
+	Stream
 	Indirect
 	Reference
 )
 
 // Object is a PDF token/object thingy. Objects may be composed either from
 // one or a sequence of tokens. The PDF Reference doesn't actually speak
-// of tokens.
+// of tokens, though ISO 32000-1:2008 does.
 type Object struct {
 	Kind ObjectKind
 
 	String        string            // Comment/Keyword/Name/String
 	Number        float64           // Bool, Numeric
 	Array         []Object          // Array, Indirect
-	Dict          map[string]Object // Dict, in the future also Stream
+	Dict          map[string]Object // Dict, Stream
+	Stream        []byte            // Stream
 	N, Generation uint              // Indirect, Reference
 }
 
@@ -118,6 +122,13 @@ func NewDict(d map[string]Object) Object {
 	return Object{Kind: Dict, Dict: d}
 }
 
+func NewStream(d map[string]Object, s []byte) Object {
+	if d == nil {
+		d = make(map[string]Object)
+	}
+	return Object{Kind: Stream, Dict: d, Stream: s}
+}
+
 func NewIndirect(o Object, n, generation uint) Object {
 	return Object{Kind: Indirect, N: n, Generation: generation,
 		Array: []Object{o}}
@@ -458,6 +469,10 @@ func (o *Object) Serialize() string {
 			fmt.Fprint(b, " /", k, " ", v.Serialize())
 		}
 		return "<<" + b.String() + " >>"
+	case Stream:
+		d := NewDict(o.Dict)
+		d.Dict["Length"] = NewNumeric(float64(len(o.Stream)))
+		return d.Serialize() + "\nstream\n" + string(o.Stream) + "\nendstream"
 	case Indirect:
 		return fmt.Sprintf("%d %d obj\n%s\nendobj", o.N, o.Generation,
 			o.Array[0].Serialize())
@@ -471,8 +486,9 @@ func (o *Object) Serialize() string {
 // -----------------------------------------------------------------------------
 
 type ref struct {
-	offset     int64 // file offset or N of the next free entry
+	offset     int64 // file offset, or N of the next free entry, or index
 	generation uint  // object generation
+	compressed *uint // PDF 1.5: N of the containing compressed object
 	nonfree    bool  // whether this N is taken (for a good zero value)
 }
 
@@ -497,6 +513,65 @@ type Updater struct {
 	Trailer map[string]Object
 }
 
+// ListIndirect returns the whole cross-reference table as Reference Objects.
+func (u *Updater) ListIndirect() []Object {
+	result := []Object{}
+	for i := 0; i < len(u.xref); i++ {
+		if u.xref[i].nonfree {
+			result = append(result, NewReference(uint(i), u.xref[i].generation))
+		}
+	}
+	return result
+}
+
+func (u *Updater) parseStream(lex *Lexer, stack *[]Object) (Object, error) {
+	lenStack := len(*stack)
+	if lenStack < 1 {
+		return newError("missing stream dictionary")
+	}
+	dict := (*stack)[lenStack-1]
+	if dict.Kind != Dict {
+		return newError("stream not preceded by a dictionary")
+	}
+
+	*stack = (*stack)[:lenStack-1]
+	length, ok := dict.Dict["Length"]
+	if !ok {
+		return newError("missing stream Length")
+	}
+	length, err := u.Dereference(length)
+	if err != nil {
+		return length, err
+	}
+	if !length.IsUint() || length.Number > math.MaxInt {
+		return newError("stream Length not an unsigned integer")
+	}
+
+	// Expect exactly one newline.
+	if nl, err := lex.Next(); err != nil {
+		return nl, err
+	} else if nl.Kind != NL {
+		return newError("stream does not start with a newline")
+	}
+
+	size := int(length.Number)
+	if len(lex.P) < size {
+		return newError("stream is longer than the document")
+	}
+
+	dict.Kind = Stream
+	dict.Stream = lex.P[:size]
+	lex.P = lex.P[size:]
+
+	// Skip any number of trailing newlines or comments.
+	if end, err := u.parse(lex, stack); err != nil {
+		return end, err
+	} else if end.Kind != Keyword || end.String != "endstream" {
+		return newError("improperly terminated stream")
+	}
+	return dict, nil
+}
+
 func (u *Updater) parseIndirect(lex *Lexer, stack *[]Object) (Object, error) {
 	lenStack := len(*stack)
 	if lenStack < 2 {
@@ -590,15 +665,11 @@ func (u *Updater) parse(lex *Lexer, stack *[]Object) (Object, error) {
 		}
 		return NewDict(dict), nil
 	case Keyword:
-		// Appears in the document body, typically needs
-		// to access the cross-reference table.
-		//
-		// TODO(p): Use the xref to read /Length etc. once we
-		// actually need to read such objects; presumably
-		// streams can use the Object.String member.
 		switch token.String {
 		case "stream":
-			return newError("streams are not supported yet")
+			// Appears in the document body,
+			// typically needs to access the cross-reference table.
+			return u.parseStream(lex, stack)
 		case "obj":
 			return u.parseIndirect(lex, stack)
 		case "R":
@@ -610,16 +681,159 @@ func (u *Updater) parse(lex *Lexer, stack *[]Object) (Object, error) {
 	}
 }
 
-func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) error {
+func (u *Updater) loadXrefEntry(
+	n uint, r ref, loadedEntries map[uint]struct{}) {
+	if _, ok := loadedEntries[n]; ok {
+		return
+	}
+	if lenXref := uint(len(u.xref)); n >= lenXref {
+		u.xref = append(u.xref, make([]ref, n-lenXref+1)...)
+	}
+	loadedEntries[n] = struct{}{}
+
+	u.xref[n] = r
+}
+
+func (u *Updater) loadXrefStream(
+	lex *Lexer, stack []Object, loadedEntries map[uint]struct{}) (
+	Object, error) {
+	var object Object
+	for {
+		var err error
+		if object, err = u.parse(lex, &stack); err != nil {
+			return New(End), fmt.Errorf("invalid xref table: %s", err)
+		} else if object.Kind == End {
+			return newError("invalid xref table")
+		}
+
+		// For the sake of simplicity, keep stacking until we find an object.
+		if object.Kind == Indirect {
+			break
+		}
+
+		stack = append(stack, object)
+	}
+
+	// ISO 32000-2:2020 7.5.8.2 Cross-reference stream dictionary
+	stream := object.Array[0]
+	if stream.Kind != Stream {
+		return newError("invalid xref table")
+	}
+	if typ, ok := stream.Dict["Type"]; !ok ||
+		typ.Kind != Name || typ.String != "XRef" {
+		return newError("invalid xref stream")
+	}
+
+	data, err := u.GetStreamData(stream)
+	if err != nil {
+		return New(End), fmt.Errorf("invalid xref stream: %s", err)
+	}
+
+	size, ok := stream.Dict["Size"]
+	if !ok || !size.IsUint() || size.Number <= 0 {
+		return newError("invalid or missing cross-reference stream Size")
+	}
+
+	type pair struct{ start, count uint }
+	pairs := []pair{}
+	if index, ok := stream.Dict["Index"]; !ok {
+		pairs = append(pairs, pair{0, uint(size.Number)})
+	} else {
+		if index.Kind != Array || len(index.Array)%2 != 0 {
+			return newError("invalid cross-reference stream Index")
+		}
+
+		a := index.Array
+		for i := 0; i < len(a); i += 2 {
+			if !a[i].IsUint() || !a[i+1].IsUint() {
+				return newError("invalid cross-reference stream Index")
+			}
+			pairs = append(pairs, pair{uint(a[i].Number), uint(a[i+1].Number)})
+		}
+	}
+
+	w, ok := stream.Dict["W"]
+	if !ok || w.Kind != Array || len(w.Array) != 3 ||
+		!w.Array[0].IsUint() || !w.Array[1].IsUint() || !w.Array[2].IsUint() {
+		return newError("invalid or missing cross-reference stream W")
+	}
+
+	w1 := uint(w.Array[0].Number)
+	w2 := uint(w.Array[1].Number)
+	w3 := uint(w.Array[2].Number)
+	if w2 == 0 {
+		return newError("invalid cross-reference stream W")
+	}
+
+	unit := w1 + w2 + w3
+	if uint(len(data))%unit != 0 {
+		return newError("invalid cross-reference stream length")
+	}
+
+	readField := func(data []byte, width uint) (uint, []byte) {
+		var n uint
+		for ; width != 0; width-- {
+			n = n<<8 | uint(data[0])
+			data = data[1:]
+		}
+		return n, data
+	}
+
+	// ISO 32000-2:2020 7.5.8.3 Cross-reference stream data
+	for _, pair := range pairs {
+		for i := uint(0); i < pair.count; i++ {
+			if uint(len(data)) < unit {
+				return newError("premature cross-reference stream EOF")
+			}
+
+			var f1, f2, f3 uint = 1, 0, 0
+			if w1 > 0 {
+				f1, data = readField(data, w1)
+			}
+			f2, data = readField(data, w2)
+			if w3 > 0 {
+				f3, data = readField(data, w3)
+			}
+
+			var r ref
+			switch f1 {
+			case 0:
+				r.offset = int64(f2)
+				r.generation = f3
+			case 1:
+				r.offset = int64(f2)
+				r.generation = f3
+				r.nonfree = true
+			case 2:
+				r.offset = int64(f3)
+				r.compressed = &f2
+				r.nonfree = true
+			default:
+				// TODO(p): It should be treated as a reference to
+				// the null object. We can't currently represent that.
+				return newError("unsupported cross-reference stream contents")
+			}
+
+			u.loadXrefEntry(pair.start+i, r, loadedEntries)
+		}
+	}
+
+	stream.Kind = Dict
+	stream.Stream = nil
+	return stream, nil
+}
+
+func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) (
+	Object, error) {
 	var throwawayStack []Object
-	if keyword, _ := u.parse(lex,
+	if object, _ := u.parse(lex,
-		&throwawayStack); keyword.Kind != Keyword || keyword.String != "xref" {
+		&throwawayStack); object.Kind != Keyword || object.String != "xref" {
-		return errors.New("invalid xref table")
+		return u.loadXrefStream(lex, []Object{object}, loadedEntries)
 	}
 	for {
 		object, _ := u.parse(lex, &throwawayStack)
 		if object.Kind == End {
-			return errors.New("unexpected EOF while looking for the trailer")
+			return newError("unexpected EOF while looking for the trailer")
 		}
 		if object.Kind == Keyword && object.String == "trailer" {
 			break
@@ -627,7 +841,7 @@ func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) error {
 
 		second, _ := u.parse(lex, &throwawayStack)
 		if !object.IsUint() || !second.IsUint() {
-			return errors.New("invalid xref section header")
+			return newError("invalid xref section header")
 		}
 
 		start, count := uint(object.Number), uint(second.Number)
@@ -639,33 +853,29 @@ func (u *Updater) loadXref(lex *Lexer, loadedEntries map[uint]struct{}) error {
 				off.Number > float64(len(u.Document)) ||
 				!gen.IsInteger() || gen.Number < 0 || gen.Number > 65535 ||
 				key.Kind != Keyword {
-				return errors.New("invalid xref entry")
+				return newError("invalid xref entry")
 			}
 
 			free := true
 			if key.String == "n" {
 				free = false
 			} else if key.String != "f" {
-				return errors.New("invalid xref entry")
+				return newError("invalid xref entry")
 			}
 
-			n := start + i
+			u.loadXrefEntry(start+i, ref{
-			if _, ok := loadedEntries[n]; ok {
-				continue
-			}
-			if lenXref := uint(len(u.xref)); n >= lenXref {
-				u.xref = append(u.xref, make([]ref, n-lenXref+1)...)
-			}
-			loadedEntries[n] = struct{}{}
-
-			u.xref[n] = ref{
 				offset:     int64(off.Number),
 				generation: uint(gen.Number),
 				nonfree:    !free,
+			}, loadedEntries)
 		}
 	}
+
+	trailer, _ := u.parse(lex, &throwawayStack)
+	if trailer.Kind != Dict {
+		return newError("invalid trailer dictionary")
 	}
-	return nil
+	return trailer, nil
 }
 
 // -----------------------------------------------------------------------------
@@ -695,7 +905,6 @@ func NewUpdater(document []byte) (*Updater, error) {
 	loadedXrefs := make(map[int64]struct{})
 	loadedEntries := make(map[uint]struct{})
 
-	var throwawayStack []Object
 	for {
 		if _, ok := loadedXrefs[xrefOffset]; ok {
 			return nil, errors.New("circular xref offsets")
@@ -705,24 +914,26 @@ func NewUpdater(document []byte) (*Updater, error) {
 		}
 
 		lex := Lexer{u.Document[xrefOffset:]}
-		if err := u.loadXref(&lex, loadedEntries); err != nil {
+		trailer, err := u.loadXref(&lex, loadedEntries)
+		if err != nil {
 			return nil, err
 		}
 
-		trailer, _ := u.parse(&lex, &throwawayStack)
-		if trailer.Kind != Dict {
-			return nil, errors.New("invalid trailer dictionary")
-		}
 		if len(loadedXrefs) == 0 {
 			u.Trailer = trailer.Dict
 		}
 		loadedXrefs[xrefOffset] = struct{}{}
 
+		// TODO(p): Descend into XRefStm here first, if present,
+		// which is also a linked list.
+
+		// We allow for mixed cross-reference tables and streams
+		// within a single Prev list, although this should never occur.
 		prevOffset, ok := trailer.Dict["Prev"]
 		if !ok {
 			break
 		}
-		// FIXME: We don't check for size_t over or underflow.
+		// FIXME: Do not read offsets and sizes as floating point numbers.
 		if !prevOffset.IsInteger() {
 			return nil, errors.New("invalid Prev offset")
 		}
@@ -764,18 +975,115 @@ func (u *Updater) Version(root *Object) int {
 	return 0
 }
 
+func (u *Updater) getFromObjStm(nObjStm, n uint) (Object, error) {
+	if nObjStm == n {
+		return newError("ObjStm recursion")
+	}
+
+	stream, err := u.Get(nObjStm, 0)
+	if err != nil {
+		return stream, err
+	}
+	if stream.Kind != Stream {
+		return newError("invalid ObjStm")
+	}
+	if typ, ok := stream.Dict["Type"]; !ok ||
+		typ.Kind != Name || typ.String != "ObjStm" {
+		return newError("invalid ObjStm")
+	}
+
+	data, err := u.GetStreamData(stream)
+	if err != nil {
+		return New(End), fmt.Errorf("invalid ObjStm: %s", err)
+	}
+	entryN, ok := stream.Dict["N"]
+	if !ok || !entryN.IsUint() || entryN.Number <= 0 {
+		return newError("invalid ObjStm N")
+	}
+	entryFirst, ok := stream.Dict["First"]
+	if !ok || !entryFirst.IsUint() || entryFirst.Number <= 0 {
+		return newError("invalid ObjStm First")
+	}
+
+	// NOTE: This means descending into that stream if n is not found here.
+	// It is meant to be an object reference.
+	if extends, ok := stream.Dict["Extends"]; ok && extends.Kind != Nil {
+		return newError("ObjStm extensions are unsupported")
+	}
+
+	count := uint(entryN.Number)
+	first := uint(entryFirst.Number)
+	if first > uint(len(data)) {
+		return newError("invalid ObjStm First")
+	}
+
+	lex1 := Lexer{data[:first]}
+	data = data[first:]
+
+	type pair struct{ n, offset uint }
+	pairs := []pair{}
+	for i := uint(0); i < count; i++ {
+		var throwawayStack []Object
+		objN, _ := u.parse(&lex1, &throwawayStack)
+		objOffset, _ := u.parse(&lex1, &throwawayStack)
+		if !objN.IsUint() || !objOffset.IsUint() {
+			return newError("invalid ObjStm pairs")
+		}
+		pairs = append(pairs, pair{uint(objN.Number), uint(objOffset.Number)})
+	}
+	for i, pair := range pairs {
+		if pair.offset > uint(len(data)) ||
+			i > 0 && pairs[i-1].offset >= pair.offset {
+			return newError("invalid ObjStm pairs")
+		}
+	}
+
+	for i, pair := range pairs {
+		if pair.n != n {
+			continue
+		}
+
+		if i+1 < len(pairs) {
+			data = data[pair.offset:pairs[i+1].offset]
+		} else {
+			data = data[pair.offset:]
+		}
+
+		lex2 := Lexer{data}
+		var stack []Object
+		for {
+			object, err := u.parse(&lex2, &stack)
+			if err != nil {
+				return object, err
+			} else if object.Kind == End {
+				break
+			} else {
+				stack = append(stack, object)
+			}
+		}
+		if len(stack) == 0 {
+			return newError("empty ObjStm object")
+		}
+		return stack[0], nil
+	}
+	return newError("object not found in ObjStm")
+}
+
 // Get retrieves an object by its number and generation--may return
 // Nil or End with an error.
-//
-// TODO(p): We should fix all uses of this not to eat the error.
 func (u *Updater) Get(n, generation uint) (Object, error) {
 	if n >= u.xrefSize {
 		return New(Nil), nil
 	}
 
 	ref := u.xref[n]
-	if !ref.nonfree || ref.generation != generation ||
+	if !ref.nonfree || ref.generation != generation {
-		ref.offset >= int64(len(u.Document)) {
+		return New(Nil), nil
+	}
+
+	if ref.compressed != nil {
+		return u.getFromObjStm(*ref.compressed, n)
+	} else if ref.offset >= int64(len(u.Document)) {
 		return New(Nil), nil
 	}
 
@@ -796,6 +1104,14 @@ func (u *Updater) Get(n, generation uint) (Object, error) {
 	}
 }
 
+// Derefence dereferences Reference objects, and passes the other kinds through.
+func (u *Updater) Dereference(o Object) (Object, error) {
+	if o.Kind != Reference {
+		return o, nil
+	}
+	return u.Get(o.N, o.Generation)
+}
+
 // Allocate allocates a new object number.
 func (u *Updater) Allocate() uint {
 	n := u.xrefSize
@@ -822,8 +1138,8 @@ type BytesWriter interface {
 	WriteString(s string) (n int, err error)
 }
 
-// Update appends an updated object to the end of the document. The fill
+// Update appends an updated object to the end of the document.
-// callback must write exactly one PDF object.
+// The fill callback must write exactly one PDF object.
 func (u *Updater) Update(n uint, fill func(buf BytesWriter)) {
 	oldRef := u.xref[n]
 	u.updated[n] = struct{}{}
@@ -843,20 +1159,62 @@ func (u *Updater) Update(n uint, fill func(buf BytesWriter)) {
 	u.Document = buf.Bytes()
 }
 
-// FlushUpdates writes an updated cross-reference table and trailer.
+func (u *Updater) flushXRefStm(updated []uint, buf *bytes.Buffer) {
-func (u *Updater) FlushUpdates() {
+	// The cross-reference stream has to point to itself.
-	updated := make([]uint, 0, len(u.updated))
+	// XXX: We only duplicate Update code here due to how we currently buffer.
-	for n := range u.updated {
+	n := u.Allocate()
 	updated = append(updated, n)
+
+	u.updated[n] = struct{}{}
+	u.xref[n] = ref{
+		offset:     int64(buf.Len() + 1),
+		generation: 0,
+		nonfree:    true,
 	}
-	sort.Slice(updated, func(i, j int) bool {
+
-		return updated[i] < updated[j]
+	index, b := []Object{}, []byte{}
+	write := func(f1 byte, f2, f3 uint64) {
+		b = append(b, f1)
+		b = binary.BigEndian.AppendUint64(b, f2)
+		b = binary.BigEndian.AppendUint64(b, f3)
+	}
+	for i := 0; i < len(updated); {
+		start, stop := updated[i], updated[i]+1
+		for i++; i < len(updated) && updated[i] == stop; i++ {
+			stop++
+		}
+
+		index = append(index,
+			NewNumeric(float64(start)), NewNumeric(float64(stop-start)))
+		for ; start < stop; start++ {
+			ref := u.xref[start]
+			if ref.compressed != nil {
+				write(2, uint64(*ref.compressed), uint64(ref.offset))
+			} else if ref.nonfree {
+				write(1, uint64(ref.offset), uint64(ref.generation))
+			} else {
+				write(0, uint64(ref.offset), uint64(ref.generation))
+			}
+		}
+	}
+
+	u.Trailer["Size"] = NewNumeric(float64(u.xrefSize))
+	u.Trailer["Index"] = NewArray(index)
+	u.Trailer["W"] = NewArray([]Object{
+		NewNumeric(1), NewNumeric(8), NewNumeric(8),
 	})
 
-	buf := bytes.NewBuffer(u.Document)
+	for _, key := range []string{
-	startXref := buf.Len() + 1
+		"Filter", "DecodeParms", "F", "FFilter", "FDecodeParms", "DL"} {
-	buf.WriteString("\nxref\n")
+		delete(u.Trailer, key)
+	}
 
+	stream := NewStream(u.Trailer, b)
+	fmt.Fprintf(buf, "\n%d 0 obj\n%s\nendobj", n, stream.Serialize())
+}
+
+func (u *Updater) flushXRefTable(updated []uint, buf *bytes.Buffer) {
+	buf.WriteString("\nxref\n")
 	for i := 0; i < len(updated); {
 		start, stop := updated[i], updated[i]+1
 		for i++; i < len(updated) && updated[i] == stop; i++ {
@@ -865,8 +1223,9 @@ func (u *Updater) FlushUpdates() {
 
 		fmt.Fprintf(buf, "%d %d\n", start, stop-start)
 		for ; start < stop; start++ {
+			// XXX: We should warn about any object streams here.
 			ref := u.xref[start]
-			if ref.nonfree {
+			if ref.nonfree && ref.compressed == nil {
 				fmt.Fprintf(buf, "%010d %05d n \n", ref.offset, ref.generation)
 			} else {
 				fmt.Fprintf(buf, "%010d %05d f \n", ref.offset, ref.generation)
@@ -883,10 +1242,38 @@ func (u *Updater) FlushUpdates() {
 
 	u.Trailer["Size"] = NewNumeric(float64(u.xrefSize))
 	trailer := NewDict(u.Trailer)
+	fmt.Fprintf(buf, "trailer\n%s", trailer.Serialize())
+}
 
-	fmt.Fprintf(buf, "trailer\n%s\nstartxref\n%d\n%%%%EOF\n",
+// FlushUpdates writes an updated cross-reference table and trailer, or stream.
-		trailer.Serialize(), startXref)
+func (u *Updater) FlushUpdates() {
+	updated := make([]uint, 0, len(u.updated))
+	for n := range u.updated {
+		updated = append(updated, n)
+	}
+	sort.Slice(updated, func(i, j int) bool {
+		return updated[i] < updated[j]
+	})
+
+	// It does not seem to be possible to upgrade a PDF file
+	// from trailer dictionaries to cross-reference streams,
+	// so keep continuity either way.
+	//
+	// (Downgrading from cross-reference streams using XRefStm would not
+	// create a true hybrid-reference file, although it should work.)
+	buf := bytes.NewBuffer(u.Document)
+	startXref := buf.Len() + 1 /* '\n' */
+	if typ, _ := u.Trailer["Type"]; typ.Kind == Name && typ.String == "XRef" {
+		u.flushXRefStm(updated, buf)
+	} else {
+		u.flushXRefTable(updated, buf)
+	}
+
+	fmt.Fprintf(buf, "\nstartxref\n%d\n%%%%EOF\n", startXref)
 	u.Document = buf.Bytes()
+	u.updated = make(map[uint]struct{})
+
+	u.Trailer["Prev"] = NewNumeric(float64(startXref))
 }
 
 // -----------------------------------------------------------------------------
@@ -904,17 +1291,47 @@ func NewDate(ts time.Time) Object {
 	return NewString(string(buf))
 }
 
+// GetStreamData returns the actual data stored in a stream object,
+// applying any filters.
+func (u *Updater) GetStreamData(stream Object) ([]byte, error) {
+	if f, ok := stream.Dict["F"]; ok && f.Kind != Nil {
+		return nil, errors.New("stream data in other files are unsupported")
+	}
+
+	// Support just enough to decode a common cross-reference stream.
+	if filter, ok := stream.Dict["Filter"]; !ok {
+		return stream.Stream, nil
+	} else if filter.Kind != Name || filter.String != "FlateDecode" {
+		return nil, errors.New("unsupported stream Filter")
+	}
+
+	// TODO(p): Support << /Columns N /Predictor 12 >>
+	// which usually appears in files with cross-reference streams.
+	if parms, ok := stream.Dict["DecodeParms"]; ok && parms.Kind != Nil {
+		return nil, errors.New("DecodeParms are not supported")
+	}
+
+	r, err := zlib.NewReader(bytes.NewReader(stream.Stream))
+	if err != nil {
+		return nil, err
+	}
+
+	var b bytes.Buffer
+	_, err = b.ReadFrom(r)
+	return b.Bytes(), err
+}
+
 // GetFirstPage retrieves the first page of the given page (sub)tree reference,
 // or returns a Nil object if unsuccessful.
-func (u *Updater) GetFirstPage(nodeN, nodeGeneration uint) Object {
+func (u *Updater) GetFirstPage(node Object) Object {
-	obj, _ := u.Get(nodeN, nodeGeneration)
+	obj, err := u.Dereference(node)
-	if obj.Kind != Dict {
+	if err != nil || obj.Kind != Dict {
 		return New(Nil)
 	}
 
 	// Out of convenience; these aren't filled normally.
-	obj.N = nodeN
+	obj.N = node.N
-	obj.Generation = nodeGeneration
+	obj.Generation = node.Generation
 
 	if typ, ok := obj.Dict["Type"]; !ok || typ.Kind != Name {
 		return New(Nil)
@@ -934,7 +1351,7 @@ func (u *Updater) GetFirstPage(nodeN, nodeGeneration uint) Object {
 	}
 
 	// XXX: Nothing prevents us from recursing in an evil circular graph.
-	return u.GetFirstPage(kids.Array[0].N, kids.Array[0].Generation)
+	return u.GetFirstPage(kids.Array[0])
 }
 
 // -----------------------------------------------------------------------------
@@ -1128,7 +1545,10 @@ func Sign(document []byte, key crypto.PrivateKey, certs []*x509.Certificate,
 	if !ok || rootRef.Kind != Reference {
 		return nil, errors.New("trailer does not contain a reference to Root")
 	}
-	root, _ := pdf.Get(rootRef.N, rootRef.Generation)
+	root, err := pdf.Dereference(rootRef)
+	if err != nil {
+		return nil, fmt.Errorf("Root dictionary retrieval failed: %s", err)
+	}
 	if root.Kind != Dict {
 		return nil, errors.New("invalid Root dictionary reference")
 	}
@@ -1182,7 +1602,7 @@ func Sign(document []byte, key crypto.PrivateKey, certs []*x509.Certificate,
 	if !ok || pagesRef.Kind != Reference {
 		return nil, errors.New("invalid Pages reference")
 	}
-	page := pdf.GetFirstPage(pagesRef.N, pagesRef.Generation)
+	page := pdf.GetFirstPage(pagesRef)
 	if page.Kind != Dict {
 		return nil, errors.New("invalid or unsupported page tree")
 	}
@@ -1204,7 +1624,7 @@ func Sign(document []byte, key crypto.PrivateKey, certs []*x509.Certificate,
 	})
 
 	// 8.6.1 Interactive Form Dictionary
-	if _, ok := root.Dict["AcroForm"]; ok {
+	if acroform, ok := root.Dict["AcroForm"]; ok && acroform.Kind != Nil {
 		return nil, errors.New("the document already contains forms, " +
 			"they would be overwritten")
 	}

test.sh

@@ -11,11 +11,15 @@ mkdir tmp
 
 # Create documents in various tools
 log "Creating source documents"
-inkscape --pipe --export-filename=tmp/cairo.pdf <<'EOF' 2>/dev/null || :
+inkscape --pipe --export-filename=tmp/cairo.pdf --export-pdf-version=1.4 \
+<<'EOF' 2>/dev/null || :
 <svg xmlns="http://www.w3.org/2000/svg"><text x="5" y="10">Hello</text></svg>
 EOF
 
-date | tee tmp/lowriter.txt | groff -T pdf > tmp/groff.pdf || :
+date > tmp/lowriter.txt
+if command -v gropdf >/dev/null
+then groff -T pdf < tmp/lowriter.txt > tmp/groff.pdf
+fi
 lowriter --convert-to pdf tmp/lowriter.txt --outdir tmp >/dev/null || :
 convert rose: tmp/imagemagick.pdf || :
 
@@ -45,7 +49,11 @@ openssl x509 -req -in tmp/cert.csr -out tmp/cert.pem \
 	-CA tmp/ca.cert.pem -CAkey tmp/ca.key.pem -set_serial 1 \
 	-extensions smime -extfile tmp/cert.cfg 2>/dev/null
 openssl verify -CAfile tmp/ca.cert.pem tmp/cert.pem >/dev/null
+
+# The second line accomodates the Go signer,
+# which doesn't support SHA-256 within pkcs12 handling
 openssl pkcs12 -inkey tmp/key.pem -in tmp/cert.pem \
+	-certpbe PBE-SHA1-3DES -keypbe PBE-SHA1-3DES -macalg sha1 \
 	-export -passout pass: -out tmp/key-pair.p12
 
 for tool in "$@"; do
@@ -55,6 +63,12 @@ for tool in "$@"; do
 		result=${source%.pdf}.signed.pdf
 		$tool "$source" "$result" tmp/key-pair.p12 ""
 		pdfsig -nssdir sql:tmp/nssdir "$result" | grep Validation
+
+		# Only some of our generators use PDF versions higher than 1.5
+		log "Testing $tool for version detection"
+		grep -q "/Version /1[.]6" "$result" \
+			|| grep -q "^%PDF-1[.][67]" "$result" \
+			|| die "Version detection seems to misbehave (no upgrade)"
 	done
 
 	log "Testing $tool for expected failures"
@@ -63,11 +77,6 @@ for tool in "$@"; do
 	$tool -r 1 "$source" "$source.fail.pdf" tmp/key-pair.p12 "" \
 		&& die "Too low reservations shouldn't succeed"
 
-	# Our generators do not use PDF versions higher than 1.5
-	log "Testing $tool for version detection"
-	grep -q "/Version /1.6" "$result" \
-		|| die "Version detection seems to misbehave (no upgrade)"
-
 	sed '1s/%PDF-1../%PDF-1.7/' "$source" > "$source.alt"
 	$tool "$source.alt" "$result.alt" tmp/key-pair.p12 ""
 	grep -q "/Version /1.6" "$result.alt" \