QPDFJob: documentation

16 files changed, 589 insertions, 49 deletions

diff --git a/README-maintainer b/README-maintainer
index 7ea049dc..49dc643f 100644
--- a/README-maintainer
+++ b/README-maintainer
@@ -124,14 +124,32 @@ CODING RULES
 
 HOW TO ADD A COMMAND-LINE ARGUMENT
 
+QPDFJob is documented in three places:
+
+* This section provides a quick reminder for how to add a command-line
+  argument
+
+* generate_auto_job has a detailed explanation about how QPDFJob and
+  generate_auto_job work together
+
+* The manual ("QPDFJob Design" in qpdf-job.rst) discusses the design
+  approach, rationale, and evolution of QPDFJob.
+
 Command-line arguments are closely coupled with QPDFJob. To add a new
 command-line argument, add the option to the appropriate table in
 job.yml. This will automatically declare a method in the private
 ArgParser class in QPDFJob_argv.cc which you have to implement. The
-implementation should make calls to methods in QPDFJob. Then, add the
-same option to either the no-json section of job.yml if it is to be
-excluded from the job json structure, or add it under the json
-structure to the place where it should appear in the json structure.
+implementation should make calls to methods in QPDFJob via its Config
+classes. Then, add the same option to either the no-json section of
+job.yml if it is to be excluded from the job json structure, or add it
+under the json structure to the place where it should appear in the
+json structure.
+
+In most cases, adding a new option will automatically declare and call
+the appropriate Config method, which you then have to implement. If
+you need a manual handler, you have to declare the option as manual in
+job.yml and implement the handler yourself, though the automatically
+generated code will declare it for you.
 
 The build will fail until the new option is documented in
 manual/cli.rst. To do that, create documentation for the option by
@@ -148,6 +166,10 @@ When done, the following should happen:
 * qpdf --help=topic should list --new-option for the correct topic
 * --new-option should appear in the manual
 * --new-option should be in the command-line option index in the manual
+* A Config method (in Config or one of the other Config classes in
+  QPDFJob) should exist that corresponds to the command-line flag
+* The job JSON file should have a new key in the schema corresponding
+  to the new option
 
 
 RELEASE PREPARATION
diff --git a/cSpell.json b/cSpell.json
index aacb3051..688c9f1d 100644
--- a/cSpell.json
+++ b/cSpell.json
@@ -100,6 +100,7 @@
     "encodable",
     "encp",
     "endianness",
+    "endl",
     "endobj",
     "endstream",
     "enspliel",
@@ -128,6 +129,7 @@
     "fuzzer",
     "fuzzers",
     "fvisibility",
+    "iostream",
     "gajic",
     "gajić",
     "gcurl",
diff --git a/examples/build.mk b/examples/build.mk
index 5472fba5..b4366c1a 100644
--- a/examples/build.mk
+++ b/examples/build.mk
@@ -8,13 +8,13 @@ BINS_examples = \
 	pdf-filter-tokens \
 	pdf-invert-images \
 	pdf-mod-info \
-	pdf-job \
 	pdf-name-number-tree \
 	pdf-npages \
 	pdf-overlay-page \
 	pdf-parse-content \
 	pdf-set-form-values \
-	pdf-split-pages
+	pdf-split-pages \
+	qpdf-job
 CBINS_examples = \
 	pdf-c-objects \
 	pdf-linearize
diff --git a/examples/pdf-job.cc b/examples/qpdf-job.cc
index 41ee8603..41ee8603 100644
--- a/examples/pdf-job.cc
+++ b/examples/qpdf-job.cc
diff --git a/generate_auto_job b/generate_auto_job
index 5e1e7e8a..e56c0e60 100755
--- a/generate_auto_job
+++ b/generate_auto_job
@@ -9,6 +9,121 @@ import json
 import filecmp
 from contextlib import contextmanager
 
+# The purpose of this code is to automatically generate various parts
+# of the QPDFJob class. It is fairly complicated and extremely
+# bespoke, so understanding it is important if modifications are to be
+# made.
+
+# Documentation of QPDFJob is divided among three places:
+#
+# * "HOW TO ADD A COMMAND-LINE ARGUMENT" in README-maintainer provides
+#   a quick reminder for how to add a command-line argument
+#
+# * This file has a detailed explanation about how QPDFJob and
+#   generate_auto_job work together
+#
+# * The manual ("QPDFJob Design" in qpdf-job.rst) discusses the design
+#   approach, rationale, and evolution of QPDFJob.
+#
+# QPDFJob solved the problem of moving extensive functionality that
+# lived in qpdf.cc into the library. The QPDFJob class consists of
+# four major sections:
+#
+# * The run() method and its subsidiaries are responsible for
+#   performing the actual operations on PDF files. This is implemented
+#   in QPDFJob.cc
+#
+# * The nested Config class and the other classes it creates provide
+#   an API for setting up a QPDFJob instance and correspond to the
+#   command-line arguments of the qpdf executable. This is implemented
+#   in QPDFJob_config.cc
+#
+# * The argument parsing code reads an argv array and calls
+#   configuration methods. This is implemented in QPDFJob_argv.cc. The
+#   argument parsing logic itself is implemented in the QPDFArgParser
+#   class.
+#
+# * The job JSON handling code, which reads a QPDFJob JSON file and
+#   calls configuration methods. This is implemented in
+#   QPDFJob_json.cc. The JSON parsing code is in the JSON class. A
+#   sax-like JSON handler class that calls callbacks in response to
+#   items in the JSON is implemented in the JSONHandler class.
+#
+# This code has the job of ensuring that configuration, command-line
+# arguments, and JSON are all consistent and complete so that a
+# developer or user can freely move among those different ways of
+# interacting with QPDFJob in a predictable fashion. In addition, help
+# information for each option appears in manual/cli.rst, and that
+# information is used in creation of the job JSON schema and to supply
+# help text to QPDFArgParser. This code also ensures that there is an
+# exact match between options in job.yml and options in cli.rst.
+#
+# The job.yml file contains the data that drives this code. To
+# understand job.yml, here are some important concepts.
+#
+# QPDFArgParser option table. There is support for positional
+# arguments, options consisting of flags and optional parameters, and
+# subparsers that start with a regular parameterless flag, have their
+# own positional and option sections, and are terminated with -- by
+# itself. Examples of this include --encrypt and --pages. An "option
+# table" contains an optional positional argument handler and a list
+# of valid options with specifications about their parameters. There
+# are three kinds of option tables:
+#
+# * The built-in "help" option table contains help commands, like
+#   --help and --version, that are only valid when they appear as the
+#   single command-line argument.
+#
+# * The "main" option table contains the options that are valid
+#   starting at the beginning of argument parsing.
+#
+# * A named option table can be started manually by the argument
+#   parsing code to switch the argument parser's context. Switching
+#   the parser to a new option table is manual (via a call to
+#   selectOptionTable). Context reverts to the main option table
+#   automatically when -- is encountered.
+#
+# In QPDFJob.hh, there is a Config class for each option table except
+# help.
+#
+# Option type: bare, required/optional parameter, required/optional
+# choices. A bare argument is just a flag, like --qdf. A parameter
+# option takes an arbitrary parameter, like --password. A choices
+# option takes one of a fixed list of choices, like --object-streams.
+# If a parameter or choices option's parameter is option, the empty
+# string may be specified as an option, such as --collate (or
+# --collate=). For a bare option, --option= is always the same as just
+# --option. This makes it possible to switch an option from bare to
+# optional choice to optional parameter all without breaking
+# compatibility.
+#
+# JSON "schema". This is a qpdf-specific "schema" for JSON. It is not
+# related to any kind of standard JSON schema. It is described in
+# JSON.hh and in the manual. QPDFJob uses the JSON "schema" in a mode
+# in which keys in the schema are all optional in the JSON object.
+#
+# Here is the mapping between configuration, argv, and JSON.
+#
+# The help options table is implemented solely for argv processing and
+# has no counterpart in configuration or JSON.
+#
+# The config() method returns a shared pointer to a Config object.
+# Every command-line option in the main option table has a
+# corresponding method in Config whose name is the option converted to
+# camel case. For bare options and options with optional parameters, a
+# version exists that takes no arguments. For others, a version exists
+# that takes a char const*. For example, the --qdf flag implies a
+# qdf() method in Config, and the --object-streams flag implies an
+# objectStreams(char const*) method in Config. For flags in option
+# tables, the method is declared inside a config class specific to the
+# option table. The mapping between option tables and config classes
+# is explicit in job.yml. Positional arguments are handled
+# individually and manually -- see QPDFJob.hh in the CONFIGURATION
+# section for details. See examples/qpdf-job.cc for an example.
+#
+# To understand the rest, start at main and follow comments in the
+# code.
+
 whoami = os.path.basename(sys.argv[0])
 BANNER = f'''//
 // This file is automatically generated by {whoami}.
@@ -33,12 +148,18 @@ def write_file(filename):
 
 
 class Main:
+    # SOURCES is a list of source files whose contents are used by
+    # this program. If they change, we are out of date.
     SOURCES = [
         whoami,
         'manual/_ext/qpdf.py',
         'job.yml',
         'manual/cli.rst',
     ]
+    # DESTS is a map to the output files this code generates. These
+    # generated files, as well as those added to DESTS later in the
+    # code, are included in various places by QPDFJob.hh or any of the
+    # implementing QPDFJob*.cc files.
     DESTS = {
         'decl': 'libqpdf/qpdf/auto_job_decl.hh',
         'init': 'libqpdf/qpdf/auto_job_init.hh',
@@ -48,6 +169,11 @@ class Main:
         'json_init': 'libqpdf/qpdf/auto_job_json_init.hh',
         # Others are added in top
     }
+    # SUBS contains a checksum for each source and destination and is
+    # used to detect whether we're up to date without having to force
+    # recompilation all the time. This way the build can invoke this
+    # script unconditionally without causing stuff to rebuild every
+    # time.
     SUMS = 'job.sums'
 
     def main(self, args=sys.argv[1:], prog=whoami):
@@ -71,8 +197,17 @@ class Main:
     def top(self, options):
         with open('job.yml', 'r') as f:
             data = yaml.safe_load(f.read())
+        # config_decls maps a config key from an option in "options"
+        # (from job.yml) to a list of declarations. A declaration is
+        # generated for each config method for that option table.
         self.config_decls = {}
+        # Keep track of which configs we've declared since we can have
+        # option tables share a config class, as with the encryption
+        # tables.
         self.declared_configs = set()
+
+        # Update DESTS -- see above. This ensures that each config
+        # class's contents are included in job.sums.
         for o in data['options']:
             config = o.get('config', None)
             if config is not None:
@@ -257,12 +392,21 @@ class Main:
     def generate(self, data):
         warn(f'{whoami}: regenerating auto job files')
         self.validate(data)
-        # Add the built-in help options to tables that we populate as
-        # we read job.yml since we won't encounter these in job.yml
+
+        # Keep track of which options are help options since they are
+        # handled specially. Add the built-in help options to tables
+        # that we populate as we read job.yml since we won't encounter
+        # these in job.yml
         self.help_options = set(
             ['--completion-bash', '--completion-zsh', '--help']
         )
+        # Keep track of which options we have encountered but haven't
+        # seen help text for. This enables us to report if any option
+        # is missing help.
         self.options_without_help = set(self.help_options)
+
+        # Compute the information needed for generated files and write
+        # the files.
         self.prepare(data)
         with write_file(self.DESTS['decl']) as f:
             print(BANNER, file=f)
@@ -276,6 +420,11 @@ class Main:
             with open('manual/cli.rst', 'r') as df:
                 print(BANNER, file=f)
                 self.generate_doc(df, f)
+
+        # Compute the json files after the config and arg parsing
+        # files. We need to have full information about all the
+        # options before we can generate the schema. Generating the
+        # schema also generates the json header files.
         self.generate_schema(data)
         with write_file(self.DESTS['schema']) as f:
             print('static constexpr char const* JOB_SCHEMA_DATA = R"(' +
@@ -301,6 +450,9 @@ class Main:
         # DON'T ADD CODE TO generate AFTER update_hashes
 
     def handle_trivial(self, i, identifier, cfg, prefix, kind, v):
+        # A "trivial" option is one whose handler does nothing other
+        # than to call the config method with the same name (switched
+        # to camelCase).
         decl_arg = 1
         decl_arg_optional = False
         if kind == 'bare':
@@ -341,11 +493,18 @@ class Main:
                 # strategy enables us to change an option from bare to
                 # optional_parameter or optional_choices without
                 # breaking binary compatibility. The overloaded
-                # methods both have to be implemented manually.
+                # methods both have to be implemented manually. They
+                # are not automatically called, so if you forget,
+                # someone will get a link error if they try to call
+                # one.
                 self.config_decls[cfg].append(
                     f'QPDF_DLL {config_prefix}* {identifier}();')
 
     def handle_flag(self, i, identifier, kind, v):
+        # For flags that require manual handlers, declare the handler
+        # and register it. They have to be implemented manually in
+        # QPDFJob_argv.cc. You get compiler/linker errors for any
+        # missing methods.
         if kind == 'bare':
             self.decls.append(f'void {identifier}();')
             self.init.append(f'this->ap.addBare("{i}", '
@@ -371,14 +530,17 @@ class Main:
                              f', false, {v}_choices);')
 
     def prepare(self, data):
-        self.decls = []
-        self.init = []
-        self.json_decls = []
-        self.json_init = []
-        self.jdata = {}
-        self.by_table = {}
+        self.decls = []         # argv handler declarations
+        self.init = []          # initialize arg parsing code
+        self.json_decls = []    # json handler declarations
+        self.json_init = []     # initialize json handlers
+        self.jdata = {}         # running data used for json generate
+        self.by_table = {}      # table information by name for easy lookup
 
         def add_jdata(flag, table, details):
+            # Keep track of each flag and where it appears so we can
+            # check consistency between the json information and the
+            # options section.
             nonlocal self
             if table == 'help':
                 self.help_options.add(f'--{flag}')
@@ -389,6 +551,7 @@ class Main:
                     'tables': {table: details},
                 }
 
+        # helper functions
         self.init.append('auto b = [this](void (ArgParser::*f)()) {')
         self.init.append('    return QPDFArgParser::bindBare(f, this);')
         self.init.append('};')
@@ -396,6 +559,8 @@ class Main:
         self.init.append('    return QPDFArgParser::bindParam(f, this);')
         self.init.append('};')
         self.init.append('')
+
+        # static variables for each set of choices for choices options
         for k, v in data['choices'].items():
             s = f'static char const* {k}_choices[] = {{'
             for i in v:
@@ -406,6 +571,8 @@ class Main:
         self.init.append('')
         self.json_init.append('')
 
+        # constants for the table names to reduce hard-coding strings
+        # in the handlers
         for o in data['options']:
             table = o['table']
             if table in ('main', 'help'):
@@ -413,6 +580,20 @@ class Main:
             i = self.to_identifier(table, 'O', True)
             self.decls.append(f'static constexpr char const* {i} = "{table}";')
         self.decls.append('')
+
+        # Walk through all the options adding declarations for the
+        # option handlers and initialization code to register the
+        # handlers in QPDFArgParser. For "trivial" cases,
+        # QPDFArgParser will call the corresponding config method
+        # automatically. Otherwise, it will declare a handler that you
+        # have to explicitly implement.
+
+        # If you add a new option table, you have to set config to the
+        # name of a member variable that you declare in the ArgParser
+        # class in QPDFJob_argv.cc. Then there should be an option in
+        # the main table, also listed as manual in job.yml, that
+        # switches to it. See implementations of any of the existing
+        # options that do this for examples.
         for o in data['options']:
             table = o['table']
             config = o.get('config', None)
@@ -437,8 +618,8 @@ class Main:
                 self.decls.append(f'void {arg_prefix}Positional(char*);')
                 self.init.append('this->ap.addPositional('
                                  f'p(&ArgParser::{arg_prefix}Positional));')
-            flags = {}
 
+            flags = {}
             for i in o.get('bare', []):
                 flags[i] = ['bare', None]
             for i, v in o.get('required_parameter', {}).items():
@@ -462,6 +643,11 @@ class Main:
                     self.handle_trivial(
                         i, identifier, config, config_prefix, kind, v)
 
+            # Subsidiary options tables need end methods to do any
+            # final checking within the option table. Final checking
+            # for the main option table is handled by
+            # checkConfiguration, which is called explicitly in the
+            # QPDFJob code.
             if table not in ('main', 'help'):
                 identifier = self.to_identifier(table, 'argEnd', False)
                 self.decls.append(f'void {identifier}();')
@@ -510,6 +696,19 @@ class Main:
         return self.option_to_json_key(schema_key)
 
     def build_schema(self, j, path, flag, expected, options_seen):
+        # j: the part of data from "json" in job.yml as we traverse it
+        # path: a string representation of the path in the json
+        # flag: the command-line flag
+        # expected: a map of command-line options we expect to eventually see
+        # options_seen: which options we have seen so far
+
+        # As described in job.yml, the json can have keys that don't
+        # map to options. This includes keys whose values are
+        # dictionaries as well as keys that correspond to positional
+        # arguments. These start with _ and get their help from
+        # job.yml. Things that correspond to options get their help
+        # from the help text we gathered from cli.rst.
+
         if flag in expected:
             options_seen.add(flag)
         elif isinstance(j, str):
@@ -519,6 +718,19 @@ class Main:
         elif not (flag == '' or flag.startswith('_')):
             raise Exception(f'json: unknown key {flag}')
 
+        # The logic here is subtle and makes sense if you understand
+        # how our JSON schemas work. They are described in JSON.hh,
+        # but basically, if you see a dictionary, the schema should
+        # have a dictionary with the same keys whose values are
+        # descriptive. If you see an array, the array should have
+        # single member that describes each element of the array. See
+        # JSON.hh for details.
+
+        # See comments in QPDFJob_json.cc in the Handlers class
+        # declaration to understand how and why the methods called
+        # here work. The idea is that Handlers keeps a stack of
+        # JSONHandler shared pointers so that we can register our
+        # handlers in the right place as we go.
         if isinstance(j, dict):
             schema_value = {}
             if flag:
@@ -579,14 +791,20 @@ class Main:
 
     def generate_schema(self, data):
         # Check to make sure that every command-line option is
-        # represented in data['json'].
-
-        # Build a list of options that we expect. If an option appears
-        # once, we just expect to see it once. If it appears in more
-        # than one options table, we need to see a separate version of
-        # it for each option table. It is represented in job.yml
-        # prepended with the table prefix. The table prefix is removed
-        # in the schema.
+        # represented in data['json']. Build a list of options that we
+        # expect. If an option appears once, we just expect to see it
+        # once. If it appears in more than one options table, we need
+        # to see a separate version of it for each option table. It is
+        # represented in job.yml prepended with the table prefix. The
+        # table prefix is removed in the schema. Example: "password"
+        # appears multiple times, so the json section of job.yml has
+        # main.password, uo.password, etc. But most options appear
+        # only once, so we can just list them as they are. There is a
+        # nearly exact match between option tables and dictionary in
+        # the job json schema, but it's not perfect because of how
+        # positional arguments are handled, so we have to do this
+        # extra work. Information about which tables a particular
+        # option appeared in is gathered up in prepare().
         expected = {}
         for k, v in self.jdata.items():
             tables = v['tables']
@@ -600,7 +818,11 @@ class Main:
         # Walk through the json information building the schema as we
         # go. This verifies consistency between command-line options
         # and the json section of the data and builds up a schema by
-        # populating with help information as available.
+        # populating with help information as available. In addition
+        # to generating the schema, we declare and register json
+        # handlers that correspond with it. That way, we can first
+        # check a job JSON file against the schema, and if it matches,
+        # we have fewer error opportunities while calling handlers.
         self.schema = self.build_schema(
             data['json'], '', '', expected, options_seen)
         if options_seen != set(expected.keys()):
diff --git a/include/qpdf/QPDFJob.hh b/include/qpdf/QPDFJob.hh
index 5a8c88cc..64075bc1 100644
--- a/include/qpdf/QPDFJob.hh
+++ b/include/qpdf/QPDFJob.hh
@@ -62,10 +62,10 @@ class QPDFJob
     // the regular API. This is exposed in the C API, which makes it
     // easier to get certain high-level qpdf functionality from other
     // languages. If there are any command-line errors, this method
-    // will throw QPDFArgParser::Usage which is derived from
-    // std::runtime_error. Other exceptions may be thrown in some
-    // cases. Note that argc, and argv should be UTF-8 encoded. If you
-    // are calling this from a Windows Unicode-aware main (wmain), see
+    // will throw QPDFUsage which is derived from std::runtime_error.
+    // Other exceptions may be thrown in some cases. Note that argc,
+    // and argv should be UTF-8 encoded. If you are calling this from
+    // a Windows Unicode-aware main (wmain), see
     // QUtil::call_main_from_wmain for information about converting
     // arguments to UTF-8. This method will mutate arguments that are
     // passed to it.
@@ -76,7 +76,7 @@ class QPDFJob
     // Initialize a QPDFJob from json. Passing partial = true prevents
     // this method from doing the final checks (calling
     // checkConfiguration) after processing the json file. This makes
-    // it possible to initialze QPDFJob in stages using multiple json
+    // it possible to initialize QPDFJob in stages using multiple json
     // files or to have a json file that can be processed from the CLI
     // with --job-json-file and be combined with other arguments. For
     // example, you might include only encryption parameters, leaving
@@ -84,7 +84,11 @@ class QPDFJob
     // input and output files. initializeFromJson is called with
     // partial = true when invoked from the command line. To make sure
     // that the json file is fully valid on its own, just don't
-    // specify any other command-line flags.
+    // specify any other command-line flags. If there are any
+    // configuration errors, QPDFUsage is thrown. Some error messages
+    // may be CLI-centric. If an an exception tells you to use the
+    // "--some-option" option, set the "someOption" key in the JSON
+    // object instead.
     QPDF_DLL
     void initializeFromJson(std::string const& json, bool partial = false);
 
@@ -160,7 +164,7 @@ class QPDFJob
     // object. The Config object contains methods that correspond with
     // qpdf command-line arguments. You can use a fluent interface to
     // configure a QPDFJob object that would do exactly the same thing
-    // as a specific qpdf command. The example pdf-job.cc contains an
+    // as a specific qpdf command. The example qpdf-job.cc contains an
     // example of this usage. You can also use initializeFromJson or
     // initializeFromArgv to initialize a QPDFJob object.
 
@@ -180,6 +184,10 @@ class QPDFJob
     //   with references. Returning pointers instead of references
     //   makes for a more uniform interface.
 
+    // Maintainer documentation: see the section in README-maintainer
+    // called "HOW TO ADD A COMMAND-LINE ARGUMENT", which contains
+    // references to additional places in the documentation.
+
     class Config;
 
     class AttConfig
@@ -330,7 +338,10 @@ class QPDFJob
     // Return a top-level configuration item. See CONFIGURATION above
     // for details. If an invalid configuration is created (such as
     // supplying contradictory options, omitting an input file, etc.),
-    // QPDFUsage is thrown.
+    // QPDFUsage is thrown. Note that error messages are CLI-centric,
+    // but you can map them into config calls. For example, if an
+    // exception tells you to use the --some-option flag, you should
+    // call config()->someOption() instead.
     QPDF_DLL
     std::shared_ptr<Config> config();
 
diff --git a/job.sums b/job.sums
index 0c574cc1..d434c642 100644
--- a/job.sums
+++ b/job.sums
@@ -1,17 +1,17 @@
 # Generated by generate_auto_job
-generate_auto_job 1fdb113412a444aad67b0232f3f6c4f50d9e2a5701691e5146fd1b559039ef2e
+generate_auto_job 5d6ec1e4f0b94d8f73df665061d8a2188cbbe8f25ea42be78ec576547261d5ac
 include/qpdf/auto_job_c_att.hh 7ad43bb374c1370ef32ebdcdcb7b73a61d281f7f4e3f12755585872ab30fb60e
 include/qpdf/auto_job_c_copy_att.hh 32275d03cdc69b703dd7e02ba0bbe15756e714e9ad185484773a6178dc09e1ee
 include/qpdf/auto_job_c_enc.hh 72e138c7b96ed5aacdce78c1dec04b1c20d361faec4f8faf52f64c1d6be99265
 include/qpdf/auto_job_c_main.hh 69d5ea26098bcb6ec5b5e37ba0bca9e7d16a784d2618e0c05d635046848d5123
 include/qpdf/auto_job_c_pages.hh 931840b329a36ca0e41401190e04537b47f2867671a6643bfd8da74014202671
 include/qpdf/auto_job_c_uo.hh 0585b7de459fa479d9e51a45fa92de0ff6dee748efc9ec1cedd0dde6cee1ad50
-job.yml effc93a805fb74503be2213ad885238db21991ba3d084fbfeff01183c66cb002
+job.yml 9544c6e046b25d3274731fbcd07ba25b300fd67055021ac4364ad8a91f77c6b6
 libqpdf/qpdf/auto_job_decl.hh 9f79396ec459f191be4c5fe34cf88c265cf47355a1a945fa39169d1c94cf04f6
-libqpdf/qpdf/auto_job_help.hh 6002f503368f319a3d717484ac39d1558f34e67989d442f394791f6f6f5f0500
+libqpdf/qpdf/auto_job_help.hh 43184f01816b5210bbc981de8de48446546fb94f4fd6e63cfc7f2fbac3578e6b
 libqpdf/qpdf/auto_job_init.hh fd13b9f730e6275a39a15d193bd9af19cf37f4495699ec1886c2b208d7811ab1
 libqpdf/qpdf/auto_job_json_decl.hh c5e3fd38a3b0c569eb0c6b4c60953a09cd6bc7d3361a357a81f64fe36af2b0cf
 libqpdf/qpdf/auto_job_json_init.hh 3f86ce40931ca8f417d050fcd49104d73c1fa4e977ad19d54b372831a8ea17ed
 libqpdf/qpdf/auto_job_schema.hh 18a3780671d95224cb9a27dcac627c421cae509d59f33a63e6bda0ab53cce923
 manual/_ext/qpdf.py e9ac9d6c70642a3d29281ee5ad92ae2422dee8be9306fb8a0bc9dba0ed5e28f3
-manual/cli.rst 35289dbf593085016a62249f760cdcad50d5cce76d799ea4acf5dff58b78679a
+manual/cli.rst 3746df6c4f115387cca0d921f25619a6b8407fc10b0e4c9dcf40b0b1656c6f8a
diff --git a/job.yml b/job.yml
index eb6a6b01..eb5b7753 100644
--- a/job.yml
+++ b/job.yml
@@ -1,4 +1,11 @@
 # See "HOW TO ADD A COMMAND-LINE ARGUMENT" in README-maintainer.
+
+# REMEMBER: if you add an optional_choices or optional_parameter, you
+# have to explicitly remember to implement the overloaded config
+# method that takes no arguments. Since no generated code will call it
+# automatically, there is no automated reminder to do this. If you
+# forget, it will be a link error if someone tries to call it.
+
 choices:
   yn:
     - "y"
diff --git a/libqpdf/QPDFJob.cc b/libqpdf/QPDFJob.cc
index 1c6a16d6..a06f87bc 100644
--- a/libqpdf/QPDFJob.cc
+++ b/libqpdf/QPDFJob.cc
@@ -646,7 +646,6 @@ QPDFJob::createsOutput() const
 void
 QPDFJob::checkConfiguration()
 {
-    // QXXXQ messages are CLI-centric
     if (m->replace_input)
     {
         if (m->outfilename)
@@ -722,7 +721,8 @@ QPDFJob::checkConfiguration()
     {
         QTC::TC("qpdf", "qpdf same file error");
         usage("input file and output file are the same;"
-              " use --replace-input to intentionally overwrite the input file");
+              " use --replace-input to intentionally"
+              " overwrite the input file");
     }
 }
 
diff --git a/libqpdf/QPDFJob_config.cc b/libqpdf/QPDFJob_config.cc
index fb61924c..68eaf5c8 100644
--- a/libqpdf/QPDFJob_config.cc
+++ b/libqpdf/QPDFJob_config.cc
@@ -28,7 +28,6 @@ QPDFJob::Config::emptyInput()
 {
     if (o.m->infilename == 0)
     {
-        // QXXXQ decide whether to fix this or just leave the comment:
         // Various places in QPDFJob.cc know that the empty string for
         // infile means empty. This means that passing "" as the
         // argument to inputFile, or equivalently using "" as a
diff --git a/libqpdf/QPDFJob_json.cc b/libqpdf/QPDFJob_json.cc
index cc4e2ff7..c0de8666 100644
--- a/libqpdf/QPDFJob_json.cc
+++ b/libqpdf/QPDFJob_json.cc
@@ -29,6 +29,28 @@ namespace
         typedef std::function<void(char const*)> param_handler_t;
         typedef std::function<void(JSON)> json_handler_t;
 
+        // The code that calls these methods is automatically
+        // generated by generate_auto_job. This describes how we
+        // implement what it does. We keep a stack of handlers in
+        // json_handlers. The top of the stack is the "current" json
+        // handler, intially for the top-level object. Whenever we
+        // encounter a scalar, we add a handler using addBare,
+        // addParameter, or addChoices. Whenever we encounter a
+        // dictionary, we first add the dictionary handlers. Then we
+        // walk into the dictionary and, for each key, we register a
+        // dict key handler and push it to the stack, then do the same
+        // process for the key's value. Then we pop the key handler
+        // off the stack. When we encounter an array, we add the array
+        // handlers, push an item handler to the stack, call
+        // recursively for the array's single item (as this is what is
+        // expected in a schema), and pop the item handler. Note that
+        // we don't pop dictionary start/end handlers. The dictionary
+        // handlers and the key handlers are at the same level in
+        // JSONHandler. This logic is subtle and took several tries to
+        // get right. It's best understood by carefully understanding
+        // the behavior of JSONHandler, the JSON schema, and the code
+        // in generate_auto_job.
+
         void addBare(bare_handler_t);
         void addParameter(param_handler_t);
         void addChoices(char const** choices, bool required, param_handler_t);
diff --git a/libqpdf/qpdf/auto_job_help.hh b/libqpdf/qpdf/auto_job_help.hh
index 49ac3494..38d275b5 100644
--- a/libqpdf/qpdf/auto_job_help.hh
+++ b/libqpdf/qpdf/auto_job_help.hh
@@ -812,7 +812,8 @@ This option is repeatable. If given, only specified objects will
 be shown in the "objects" key of the JSON output. Otherwise, all
 objects will be shown.
 )");
-ap.addOptionHelp("--job-json-help", "json", "show format of job JSON", R"(Describe the format of the QPDFJob JSON input.
+ap.addOptionHelp("--job-json-help", "json", "show format of job JSON", R"(Describe the format of the QPDFJob JSON input used by
+--job-json-file.
 )");
 ap.addHelpTopic("testing", "options for testing or debugging", R"(The options below are useful when writing automated test code that
 includes files created by qpdf or when testing qpdf itself.
diff --git a/manual/cli.rst b/manual/cli.rst
index 7dd955c4..614be80d 100644
--- a/manual/cli.rst
+++ b/manual/cli.rst
@@ -167,9 +167,11 @@ Related Options
       description of the JSON input file format.
 
    Specify the name of a file whose contents are expected to contain a
-   QPDFJob JSON file. QXXXQ ref.  This file is read and treated as if
-   the equivalent command-line arguments were supplied. It can be
-   mixed freely with other options.
+   QPDFJob JSON file. This file is read and treated as if the
+   equivalent command-line arguments were supplied. It can be repeated
+   and mixed freely with other options. Run ``qpdf`` with
+   :qpdf:ref:`--job-json-help` for a description of the job JSON input
+   file format. For more information, see :ref:`qpdf-job`.
 
 .. _exit-status:
 
@@ -3200,9 +3202,12 @@ Related Options
 
    .. help: show format of job JSON
 
-      Describe the format of the QPDFJob JSON input.
+      Describe the format of the QPDFJob JSON input used by
+      --job-json-file.
 
-   Describe the format of the QPDFJob JSON input. QXXXQ doc ref.
+   Describe the format of the QPDFJob JSON input used by
+   :qpdf:ref:`--job-json-file`. For more information about QPDFJob,
+   see :ref:`qpdf-job`.
 
 .. _test-options:
 
diff --git a/manual/index.rst b/manual/index.rst
index 7f8b1483..5aa59346 100644
--- a/manual/index.rst
+++ b/manual/index.rst
@@ -28,6 +28,7 @@ documentation, please visit `https://qpdf.readthedocs.io
    weak-crypto
    json
    design
+   qpdf-job
    linearization
    object-streams
    encryption
diff --git a/manual/qpdf-job.rst b/manual/qpdf-job.rst
new file mode 100644
index 00000000..72e02305
--- /dev/null
+++ b/manual/qpdf-job.rst
@@ -0,0 +1,248 @@
+
+.. _qpdf-job:
+
+QPDFJob: a Job-Based Interface
+==============================
+
+All of the functionality from the :command:`qpdf` command-line
+executable is available from inside the C++ library using the
+``QPDFJob`` class. There are several ways to access this functionality:
+
+- Command-line options
+
+  - Run the :command:`qpdf` command line
+
+  - Use from the C++ API with ``QPDFJob::initializeFromArgv``
+
+  - Use from the C API with QXXXQ
+
+- The job JSON file format
+
+  - Use from the CLI with the :qpdf:ref:`--job-json-file` parameter
+
+  - Use from the C++ API with ``QPDFJob::initializeFromJson``
+
+  - Use from the C API with QXXXQ
+
+- The ``QPDFJob`` C++ API
+
+If you can understand how to use the :command:`qpdf` CLI, you can
+understand the ``QPDFJob`` class and the json file. qpdf guarantees
+that all of the above methods are in sync. Here's how it works:
+
+.. list-table:: QPDFJob Interfaces
+   :widths: 30 30 30
+   :header-rows: 1
+
+   - - CLI
+     - JSON
+     - C++
+
+   - - ``--some-option``
+     - ``"someOption": ""``
+     - ``config()->someOption()``
+
+   - - ``--some-option=value``
+     - ``"someOption": "value"``
+     - ``config()->someOption("value")``
+
+   - - positional argument
+     - ``"otherOption": "value"``
+     - ``config()->otherOption("value")``
+
+In the JSON file, the JSON structure is an object (dictionary) whose
+keys are command-line flags converted to camelCase. Positional
+arguments have some corresponding key, which you can find by running
+``qpdf`` with the :qpdf:ref:`--job-json-help` flag. For example, input
+and output files are named by positional arguments on the CLI. In the
+JSON, they are ``"inputFile"`` and ``"outputFile"``. The following are
+equivalent:
+
+.. It would be nice to have an automated test that these are all the
+   same, but we have so few live examples that it's not worth it for
+   now.
+
+CLI:
+  ::
+
+     qpdf infile.pdf outfile.pdf \
+        --pages . other.pdf --password=x 1-5 -- \
+        --encrypt user owner 256 --print=low -- \
+        --object-streams=generate
+
+Job JSON:
+  .. code-block:: json
+
+      {
+        "inputFile": "infile.pdf",
+        "outputFile": "outfile.pdf",
+        "pages": [
+          {
+            "file": "."
+          },
+          {
+            "file": "other.pdf",
+            "password": "x",
+            "range": "1-5"
+          }
+        ],
+        "encrypt": {
+          "userPassword": "user",
+          "ownerPassword": "owner",
+          "256bit": {
+            "print": "low"
+          }
+        },
+        "objectStreams": "generate"
+      }
+
+C++ code:
+  .. code-block:: c++
+
+      #include <qpdf/QPDFJob.hh>
+      #include <qpdf/QPDFUsage.hh>
+      #include <iostream>
+
+      int main(int argc, char* argv[])
+      {
+          try
+          {
+              QPDFJob j;
+              j.config()
+                  ->inputFile("infile.pdf")
+                  ->outputFile("outfile.pdf")
+                  ->pages()
+                  ->pageSpec(".", "1-z")
+                  ->pageSpec("other.pdf", "1-5", "x")
+                  ->endPages()
+                  ->encrypt(256, "user", "owner")
+                  ->print("low")
+                  ->endEncrypt()
+                  ->objectStreams("generate")
+                  ->checkConfiguration();
+              j.run();
+          }
+          catch (QPDFUsage& e)
+          {
+              std::cerr << "configuration error: " << e.what() << std::endl;
+              return 2;
+          }
+          catch (std::exception& e)
+          {
+              std::cerr << "other error: " << e.what() << std::endl;
+              return 2;
+          }
+          return 0;
+      }
+
+It is also possible to mix and match command-line options and json
+from the CLI. For example, you could create a file called
+:file:`my-options.json` containing the following:
+
+.. code-block:: json
+
+    {
+      "encrypt": {
+        "userPassword": "",
+        "ownerPassword": "owner",
+        "256bit": {
+        }
+      },
+      "objectStreams": "generate"
+    }
+
+and use it with other options to create 256-bit encrypted (but
+unrestricted) files with object streams while specifying other
+parameters on the command line, such as
+
+::
+
+   qpdf infile.pdf outfile.pdf --job-json-file=my-options.json
+
+.. _qpdfjob-design:
+
+See also :file:`examples/qpdf-job.cc` in the source distribution as
+well as comments in ``QPDFJob.hh``.
+
+
+QPDFJob Design
+--------------
+
+This section describes some of the design rationale and history behind
+``QPDFJob``.
+
+Documentation of ``QPDFJob`` is divided among three places:
+
+- "HOW TO ADD A COMMAND-LINE ARGUMENT" in :file:`README-maintainer`
+  provides a quick reminder for how to add a command-line argument
+
+- The source file :file:`generate_auto_job` has a detailed explanation
+  about how ``QPDFJob`` and ``generate_auto_job`` work together
+
+- This chapter of the manual has other details.
+
+Prior to qpdf version 10.6.0, the qpdf CLI executable had a lot of
+functionality built into the executable that was not callable from the
+library as such. This created a number of problems:
+
+- Some of the logic in :file:`qpdf.cc` was pretty complex, such as
+  image optimization, generating json output, and many of the page
+  manipulations. While those things could all be coded using the C++
+  API, there would be a lot of duplicated code.
+
+- Page splitting and merging will get more complicated over time as
+  qpdf supports a wider range of document-level options. It would be
+  nice to be able to expose this to library users instead of baking it
+  all into the CLI.
+
+- Users of other languages who just wanted an interface to do things
+  that the CLI could do didn't have a good way to do it, such as just
+  handling a library call a set of command-line options or an
+  equivalent JSON object that could be passed in as a string.
+
+- The qpdf CLI itself was almost 8,000 lines of code. It needed to be
+  refactored, cleaned up, and split.
+
+- Exposing a new feature via the command-line required making lots of
+  small edits to lots of small bits of code, and it was easy to forget
+  something. Adding a code generator, while complex in some ways,
+  greatly reduces the chances of error when extending qpdf.
+
+Here are a few notes on some design decisions about QPDFJob and its
+various interfaces.
+
+- Bare command-line options (flags with no parameter) map to config
+  functions that take no options and to json keys whose values are
+  required to be the empty string. The rationale is that we can later
+  change these bare options to options that take an optional parameter
+  without breaking backward compatibility in the CLI or the JSON.
+  Options that take optional parameters generate two config functions:
+  one has no arguments, and one that has a ``char const*`` argument.
+  This means that adding an optional parameter to a previously bare
+  option also doesn't break binary compatibility.
+
+- Adding a new argument to :file:`job.yml` automatically triggers
+  almost everything by declaring and referencing things that you have
+  to implement. This way, once you get the code to compile and link,
+  you know you haven't forgotten anything. There are two tricky cases:
+
+  - If an argument handler has to do something special, like call a
+    nested config method or select an option table, you have to
+    implement it manually. This is discussed in
+    :file:`generate_auto_job`.
+
+  - When you add an option that has optional parameters or choices,
+    both of the handlers described above are declared, but only the
+    one that takes an argument is referenced. You have to remember to
+    implement the one that doesn't take an argument or else people
+    will get a linker error if they try to call it. The assumption is
+    that things with optional parameters started out as bare, so the
+    argument-less version is already there.
+
+- If you have to add a new option that requires its own option table,
+  you will have to do some extra work including adding a new nested
+  Config class, adding a config member variable to ``ArgParser`` in
+  :file:`QPDFJob_argv.cc` and ``Handlers`` in :file:`QPDFJob_json.cc`,
+  and make sure that manually implemented handlers are consistent with
+  each other. It is best under the cases to explicit test cases for
+  all the various ways to get to the option.
diff --git a/manual/release-notes.rst b/manual/release-notes.rst
index 8c2af683..6b5b85f4 100644
--- a/manual/release-notes.rst
+++ b/manual/release-notes.rst
@@ -2303,9 +2303,9 @@ For a detailed list of changes, please see the file
     been added to the :command:`qpdf` command-line
     tool. See :ref:`page-selection`.
 
-  - Options have been added to the :command:`qpdf`
-    command-line tool for copying encryption parameters from another
-    file. (QXXXQ Link)
+  - The :qpdf:ref:`--copy-encryption` option have been added to the
+    :command:`qpdf` command-line tool for copying encryption
+    parameters from another file.
 
   - New methods have been added to the ``QPDF`` object for adding and
     removing pages. See :ref:`adding-and-remove-pages`.