Implement JSONHandler for recursively processing JSON

include/qpdf/JSON.hh

@@ -30,7 +30,10 @@
 // create temporary JSON objects on the stack, add them to other
 // objects, and let them go out of scope safely. It also means that if
 // the json JSON object is added in more than one place, all copies
-// share underlying data.
+// share underlying data. This makes them similar in structure and
+// behavior to QPDFObjectHandle and may feel natural within the QPDF
+// codebase, but it is also a good reason not to use this as a
+// general-purpose JSON package.
 
 #include <qpdf/DLL.h>
 #include <qpdf/PointerHolder.hh>
@@ -38,6 +41,7 @@
 #include <map>
 #include <vector>
 #include <list>
+#include <functional>
 
 class JSON
 {
@@ -77,6 +81,24 @@ class JSON
     QPDF_DLL
     bool isDictionary() const;
 
+    // Accessors. Accessor behavior:
+    //
+    // - If argument is wrong type, including null, return false
+    // - If argument is right type, return true and initialize the value
+    QPDF_DLL
+    bool getString(std::string& utf8) const;
+    QPDF_DLL
+    bool getNumber(std::string& value) const;
+    QPDF_DLL
+    bool getBool(bool& value) const;
+    QPDF_DLL
+    bool isNull() const;
+    QPDF_DLL
+    bool forEachDictItem(
+        std::function<void(std::string const& key, JSON value)> fn) const;
+    QPDF_DLL
+    bool forEachArrayItem(std::function<void(JSON value)> fn) const;
+
     // Check this JSON object against a "schema". This is not a schema
     // according to any standard. It's just a template of what the
     // JSON is supposed to contain. The checking does the following:
@@ -129,6 +151,7 @@ class JSON
         JSON_string(std::string const& utf8);
         virtual ~JSON_string();
         virtual std::string unparse(size_t depth) const;
+        std::string utf8;
         std::string encoded;
     };
     struct JSON_number: public JSON_value

include/qpdf/JSONHandler.hh

@@ -0,0 +1,142 @@
+// Copyright (c) 2005-2021 Jay Berkenbilt
+//
+// This file is part of qpdf.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Versions of qpdf prior to version 7 were released under the terms
+// of version 2.0 of the Artistic License. At your option, you may
+// continue to consider qpdf to be licensed under those terms. Please
+// see the manual for additional information.
+
+#ifndef JSONHANDLER_HH
+#define JSONHANDLER_HH
+
+#include <qpdf/DLL.h>
+#include <qpdf/PointerHolder.hh>
+#include <qpdf/JSON.hh>
+#include <string>
+#include <map>
+#include <functional>
+#include <stdexcept>
+#include <memory>
+
+class JSONHandler
+{
+  public:
+    // Error exception is thrown if there are any errors validating
+    // the JSON object.
+    class QPDF_DLL_CLASS Error: public std::runtime_error
+    {
+      public:
+        QPDF_DLL
+        Error(std::string const&);
+    };
+
+    QPDF_DLL
+    JSONHandler();
+
+    QPDF_DLL
+    ~JSONHandler() = default;
+
+    // Based on the type of handler, expect the object to be of a
+    // certain type. JSONHandler::Error is thrown otherwise. Multiple
+    // handlers may be registered, which allows the object to be of
+    // various types. If an anyHandler is added, no other handler will
+    // be called.
+
+    typedef std::function<void(
+        std::string const& path, JSON value)> json_handler_t;
+    typedef std::function<void(
+        std::string const& path)> void_handler_t;
+    typedef std::function<void(
+        std::string const& path, std::string const& value)> string_handler_t;
+    typedef std::function<void(
+        std::string const& path, bool value)> bool_handler_t;
+
+    // If an any handler is added, it will be called for any value
+    // including null, and no other handler will be called.
+    QPDF_DLL
+    void addAnyHandler(json_handler_t fn);
+
+    // If any of the remaining handlers are registered, each
+    // registered handle will be called.
+    QPDF_DLL
+    void addNullHandler(void_handler_t fn);
+    QPDF_DLL
+    void addStringHandler(string_handler_t fn);
+    QPDF_DLL
+    void addNumberHandler(string_handler_t fn);
+    QPDF_DLL
+    void addBoolHandler(bool_handler_t fn);
+
+    // Returns a reference to a map: keys are expected object keys,
+    // and values are handlers for that object.
+    QPDF_DLL
+    std::map<std::string, std::shared_ptr<JSONHandler>>& addDictHandlers();
+
+    // Apply the given handler to any key not explicitly in dict
+    // handlers.
+    QPDF_DLL
+    void addFallbackDictHandler(std::shared_ptr<JSONHandler>);
+
+    // Apply the given handler to each element of the array.
+    QPDF_DLL
+    void addArrayHandler(std::shared_ptr<JSONHandler>);
+
+    // Apply handlers recursively to a JSON object.
+    QPDF_DLL
+    void handle(std::string const& path, JSON j);
+
+  private:
+    JSONHandler(JSONHandler const&) = delete;
+
+    struct Handlers
+    {
+        Handlers() :
+            any_handler(nullptr),
+            null_handler(nullptr),
+            string_handler(nullptr),
+            number_handler(nullptr),
+            bool_handler(nullptr)
+        {
+        }
+
+        json_handler_t any_handler;
+        void_handler_t null_handler;
+        string_handler_t string_handler;
+        string_handler_t number_handler;
+        bool_handler_t bool_handler;
+        std::map<std::string, std::shared_ptr<JSONHandler>> dict_handlers;
+        std::shared_ptr<JSONHandler> fallback_dict_handler;
+        std::shared_ptr<JSONHandler> array_handler;
+    };
+
+    class Members
+    {
+        friend class JSONHandler;
+
+      public:
+        QPDF_DLL
+        ~Members() = default;
+
+      private:
+        Members();
+        Members(Members const&) = delete;
+
+        Handlers h;
+    };
+    PointerHolder<Members> m;
+};
+
+#endif // JSONHANDLER_HH

libqpdf/JSON.cc

@@ -90,6 +90,7 @@ std::string JSON::JSON_array::unparse(size_t depth) const
 }
 
 JSON::JSON_string::JSON_string(std::string const& utf8) :
+    utf8(utf8),
     encoded(encode_string(utf8))
 {
 }
@@ -311,6 +312,83 @@ JSON::isDictionary() const
         this->m->value.getPointer());
 }
 
+bool
+JSON::getString(std::string& utf8) const
+{
+    auto v = dynamic_cast<JSON_string const*>(this->m->value.getPointer());
+    if (v == nullptr)
+    {
+        return false;
+    }
+    utf8 = v->utf8;
+    return true;
+}
+
+bool
+JSON::getNumber(std::string& value) const
+{
+    auto v = dynamic_cast<JSON_number const*>(this->m->value.getPointer());
+    if (v == nullptr)
+    {
+        return false;
+    }
+    value = v->encoded;
+    return true;
+}
+
+bool
+JSON::getBool(bool& value) const
+{
+    auto v = dynamic_cast<JSON_bool const*>(this->m->value.getPointer());
+    if (v == nullptr)
+    {
+        return false;
+    }
+    value = v->value;
+    return true;
+}
+
+bool
+JSON::isNull() const
+{
+    if (dynamic_cast<JSON_null const*>(this->m->value.getPointer()))
+    {
+        return true;
+    }
+    return false;
+}
+
+bool
+JSON::forEachDictItem(
+    std::function<void(std::string const& key, JSON value)> fn) const
+{
+    auto v = dynamic_cast<JSON_dictionary const*>(this->m->value.getPointer());
+    if (v == nullptr)
+    {
+        return false;
+    }
+    for (auto const& k: v->members)
+    {
+        fn(k.first, JSON(k.second));
+    }
+    return true;
+}
+
+bool
+JSON::forEachArrayItem(std::function<void(JSON value)> fn) const
+{
+    auto v = dynamic_cast<JSON_array const*>(this->m->value.getPointer());
+    if (v == nullptr)
+    {
+        return false;
+    }
+    for (auto const& i: v->elements)
+    {
+        fn(JSON(i));
+    }
+    return true;
+}
+
 bool
 JSON::checkSchema(JSON schema, std::list<std::string>& errors)
 {

libqpdf/JSONHandler.cc

@@ -0,0 +1,160 @@
+#include <qpdf/JSONHandler.hh>
+#include <qpdf/QUtil.hh>
+#include <qpdf/QTC.hh>
+
+JSONHandler::Error::Error(std::string const& msg) :
+    std::runtime_error(msg)
+{
+}
+
+JSONHandler::JSONHandler() :
+    m(new Members())
+{
+}
+
+JSONHandler::Members::Members()
+{
+}
+
+void
+JSONHandler::addAnyHandler(json_handler_t fn)
+{
+    this->m->h.any_handler = fn;
+}
+
+void
+JSONHandler::addNullHandler(void_handler_t fn)
+{
+    this->m->h.null_handler = fn;
+}
+
+void
+JSONHandler::addStringHandler(string_handler_t fn)
+{
+    this->m->h.string_handler = fn;
+}
+
+void
+JSONHandler::addNumberHandler(string_handler_t fn)
+{
+    this->m->h.number_handler = fn;
+}
+
+void
+JSONHandler::addBoolHandler(bool_handler_t fn)
+{
+    this->m->h.bool_handler = fn;
+}
+
+std::map<std::string, std::shared_ptr<JSONHandler>>&
+JSONHandler::addDictHandlers()
+{
+    return this->m->h.dict_handlers;
+}
+
+void
+JSONHandler::addFallbackDictHandler(std::shared_ptr<JSONHandler> fdh)
+{
+    this->m->h.fallback_dict_handler = fdh;
+}
+
+void
+JSONHandler::addArrayHandler(std::shared_ptr<JSONHandler> ah)
+{
+    this->m->h.array_handler = ah;
+}
+
+void
+JSONHandler::handle(std::string const& path, JSON j)
+{
+    if (this->m->h.any_handler)
+    {
+        this->m->h.any_handler(path, j);
+        return;
+    }
+    bool handled = false;
+    bool bvalue = false;
+    std::string svalue;
+    if (this->m->h.null_handler && j.isNull())
+    {
+        this->m->h.null_handler(path);
+        handled = true;
+    }
+    if (this->m->h.string_handler && j.getString(svalue))
+    {
+        this->m->h.string_handler(path, svalue);
+        handled = true;
+    }
+    if (this->m->h.number_handler && j.getNumber(svalue))
+    {
+        this->m->h.number_handler(path, svalue);
+        handled = true;
+    }
+    if (this->m->h.bool_handler && j.getBool(bvalue))
+    {
+        this->m->h.bool_handler(path, bvalue);
+        handled = true;
+    }
+    if ((this->m->h.fallback_dict_handler.get() ||
+         (! this->m->h.dict_handlers.empty())) && j.isDictionary())
+    {
+        std::string path_base = path;
+        if (path_base != ".")
+        {
+            path_base += ".";
+        }
+        j.forEachDictItem([&path, &path_base, this](
+                              std::string const& k, JSON v) {
+            auto i = this->m->h.dict_handlers.find(k);
+            if (i == this->m->h.dict_handlers.end())
+            {
+                if (this->m->h.fallback_dict_handler.get())
+                {
+                    this->m->h.fallback_dict_handler->handle(
+                        path_base + k, v);
+                }
+                else
+                {
+                    QTC::TC("libtests", "JSONHandler unexpected key");
+                    throw Error(
+                        "JSON handler found unexpected key " + k +
+                        " in object at " + path);
+                }
+            }
+            else
+            {
+                i->second->handle(path_base + k, v);
+            }
+        });
+
+        // Set handled = true even if we didn't call any handlers.
+        // This dictionary could have been empty, but it's okay since
+        // it's a dictionary like it's supposed to be.
+        handled = true;
+    }
+    if (this->m->h.array_handler.get())
+    {
+        size_t i = 0;
+        j.forEachArrayItem([&i, &path, this](JSON v) {
+            this->m->h.array_handler->handle(
+                path + "[" + QUtil::uint_to_string(i) + "]", v);
+            ++i;
+        });
+        // Set handled = true even if we didn't call any handlers.
+        // This could have been an empty array.
+        handled = true;
+    }
+
+    if (! handled)
+    {
+        // It would be nice to include information about what type the
+        // object was and what types were allowed, but we're relying
+        // on schema validation to make sure input is properly
+        // structured before calling the handlers. It would be
+        // different if this code were trying to be part of a
+        // general-purpose JSON package.
+        QTC::TC("libtests", "JSONHandler unhandled value");
+        throw Error("JSON handler: value at " + path +
+                    " is not of expected type");
+    }
+}

libqpdf/build.mk

@@ -38,6 +38,7 @@ SRCS_libqpdf = \
 	libqpdf/InputSource.cc \
 	libqpdf/InsecureRandomDataProvider.cc \
 	libqpdf/JSON.cc \
+	libqpdf/JSONHandler.cc \
 	libqpdf/MD5.cc \
 	libqpdf/NNTree.cc \
 	libqpdf/OffsetInputSource.cc \

libtests/build.mk

@@ -13,6 +13,7 @@ BINS_libtests = \
 	hex \
 	input_source \
 	json \
+	json_handler \
 	json_parse \
 	lzw \
 	main_from_wmain \

libtests/json.cc

@@ -1,7 +1,7 @@
 #include <qpdf/JSON.hh>
 #include <qpdf/QPDFObjectHandle.hh>
 #include <iostream>
-#include <assert.h>
+#include <cassert>
 
 static void check(JSON const& j, std::string const& exp)
 {
@@ -20,12 +20,25 @@ static void test_main()
           "\\u0003\\t\\b\\r\\n<4>\"");
     JSON jnull = JSON::makeNull();
     check(jnull, "null");
+    assert(jnull.isNull());
+    std::string value;
+    assert(! jnull.getNumber(value));
     JSON jarr = JSON::makeArray();
     check(jarr, "[]");
     JSON jstr2 = JSON::makeString("a\tb");
+    assert(jstr2.getString(value));
+    assert(value == "a\tb");
+    assert(! jstr2.getNumber(value));
     JSON jint = JSON::makeInt(16059);
     JSON jdouble = JSON::makeReal(3.14159);
     JSON jexp = JSON::makeNumber("2.1e5");
+    JSON jbool1 = JSON::makeBool(true);
+    JSON jbool2 = JSON::makeBool(false);
+    bool bvalue = false;
+    assert(jbool1.getBool(bvalue));
+    assert(bvalue);
+    assert(jbool2.getBool(bvalue));
+    assert(! bvalue);
     jarr.addArrayElement(jstr2);
     jarr.addArrayElement(jnull);
     jarr.addArrayElement(jint);
@@ -39,6 +52,18 @@ static void test_main()
           "  3.14159,\n"
           "  2.1e5\n"
           "]");
+    std::vector<std::string> avalue;
+    assert(jarr.forEachArrayItem([&avalue](JSON j) {
+        avalue.push_back(j.unparse());
+    }));
+    std::vector<std::string> xavalue = {
+        "\"a\\tb\"",
+        "null",
+        "16059",
+        "3.14159",
+        "2.1e5",
+    };
+    assert(avalue == xavalue);
     JSON jmap = JSON::makeDictionary();
     check(jmap, "{}");
     jmap.addDictionaryMember("b", jstr2);
@@ -73,6 +98,18 @@ static void test_main()
     check(QPDFObjectHandle::newReal(".34").getJSON(), "0.34");
     check(QPDFObjectHandle::newReal("-0.56").getJSON(), "-0.56");
     check(QPDFObjectHandle::newReal("-.78").getJSON(), "-0.78");
+    JSON jmap2 = JSON::parse(R"({"a": 1, "b": "two", "c": [true]})");
+    std::map<std::string, std::string> dvalue;
+    assert(jmap2.forEachDictItem([&dvalue]
+                                 (std::string const& k, JSON j) {
+        dvalue[k] = j.unparse();
+    }));
+    std::map<std::string, std::string> xdvalue = {
+        {"a", "1"},
+        {"b", "\"two\""},
+        {"c", "[\n  true\n]"},
+    };
+    assert(dvalue == xdvalue);
 }
 
 static void check_schema(JSON& obj, JSON& schema, bool exp,

libtests/json_handler.cc

@@ -0,0 +1,128 @@
+#include <qpdf/JSONHandler.hh>
+#include <qpdf/QUtil.hh>
+#include <iostream>
+#include <cassert>
+
+static void print_null(std::string const& path)
+{
+    std::cout << path << ": null" << std::endl;
+}
+
+static void print_string(std::string const& path, std::string const& value)
+{
+    std::cout << path << ": string: " << value << std::endl;
+}
+
+static void print_number(std::string const& path, std::string const& value)
+{
+    std::cout << path << ": number: " << value << std::endl;
+}
+
+static void print_bool(std::string const& path, bool value)
+{
+    std::cout << path << ": bool: " << (value ? "true" : "false") << std::endl;
+}
+
+static void print_json(std::string const& path, JSON value)
+{
+    std::cout << path << ": json: " << value.unparse() << std::endl;
+}
+
+static void test_scalar()
+{
+    std::cout << "-- scalar --" << std::endl;
+    JSONHandler h;
+    h.addStringHandler(print_string);
+    JSON j = JSON::parse("\"potato\"");
+    h.handle(".", j);
+}
+
+static std::shared_ptr<JSONHandler> make_all_handler()
+{
+    auto h = std::make_shared<JSONHandler>();
+    auto& m = h->addDictHandlers();
+    auto h1 = std::make_shared<JSONHandler>();
+    h1->addStringHandler(print_string);
+    m["one"] = h1;
+    auto h2 = std::make_shared<JSONHandler>();
+    h2->addNumberHandler(print_number);
+    m["two"] = h2;
+    auto h3 = std::make_shared<JSONHandler>();
+    h3->addBoolHandler(print_bool);
+    m["three"] = h3;
+    auto h4 = std::make_shared<JSONHandler>();
+    h4->addAnyHandler(print_json);
+    m["four"] = h4;
+    m["phour"] = h4;           // share h4
+    auto h5 = std::make_shared<JSONHandler>();
+    // Allow to be either string or bool
+    h5->addBoolHandler(print_bool);
+    h5->addStringHandler(print_string);
+    h5->addNullHandler(print_null);
+    auto h5s = std::make_shared<JSONHandler>();
+    m["five"] = h5s;
+    h5s->addArrayHandler(h5);
+    auto h6 = std::make_shared<JSONHandler>();
+    auto& m6 = h6->addDictHandlers();
+    auto h6a = std::make_shared<JSONHandler>();
+    m6["a"] = h6a;
+    auto& m6a = h6a->addDictHandlers();
+    auto h6ab = std::make_shared<JSONHandler>();
+    m6a["b"] = h6ab;
+    auto h6ax = std::make_shared<JSONHandler>();
+    h6ax->addAnyHandler(print_json);
+    h6a->addFallbackDictHandler(h6ax);
+    m6["b"] = h6ab;             // share
+    h6ab->addStringHandler(print_string);
+    m["six"] = h6;
+    return h;
+}
+
+static void test_all()
+{
+    std::cout << "-- all --" << std::endl;
+    auto h = make_all_handler();
+    JSON j = JSON::parse(R"({
+   "one": "potato",
+   "two": 3.14,
+   "three": true,
+   "four": ["a", 1],
+   "five": ["x", false, "y", null, true],
+   "phour": null,
+   "six": {"a": {"b": "quack", "Q": "baaa"}, "b": "moo"}
+})");
+    h->handle(".", j);
+}
+
+static void test_errors()
+{
+    std::cout << "-- errors --" << std::endl;
+    auto h = make_all_handler();
+    auto t = [h](std::string const& msg, std::function<void()> fn) {
+        try
+        {
+            fn();
+            assert(false);
+        }
+        catch (JSONHandler::Error& e)
+        {
+            std::cout << msg << ": " << e.what() << std::endl;
+        }
+    };
+
+    t("bad type at top", [&h](){
+        h->handle(".", JSON::makeString("oops"));
+    });
+    t("unexpected key", [&h](){
+        JSON j = JSON::parse(R"({"x": "y"})");
+        h->handle(".", j);
+    });
+}
+
+int main(int argc, char* argv[])
+{
+    test_scalar();
+    test_all();
+    test_errors();
+    return 0;
+}

libtests/libtests.testcov

@@ -87,3 +87,5 @@ JSON parse leading zero 0
 JSON parse number no digits 0
 JSON parse premature end of u 0
 JSON parse bad hex after u 0
+JSONHandler unhandled value 0
+JSONHandler unexpected key 0

libtests/qtest/json_handler.test

@@ -0,0 +1,17 @@
+#!/usr/bin/env perl
+require 5.008;
+use warnings;
+use strict;
+
+chdir("json_handler") or die "chdir testdir failed: $!\n";
+
+require TestDriver;
+
+my $td = new TestDriver('json_handler');
+
+$td->runtest("JSON handler",
+             {$td->COMMAND => "json_handler"},
+             {$td->FILE => "json_handler.out", $td->EXIT_STATUS => 0},
+             $td->NORMALIZE_NEWLINES);
+
+$td->report(1);

libtests/qtest/json_handler/json_handler.out

@@ -0,0 +1,22 @@
+-- scalar --
+.: string: potato
+-- all --
+.five[0]: string: x
+.five[1]: bool: false
+.five[2]: string: y
+.five[3]: null
+.five[4]: bool: true
+.four: json: [
+  "a",
+  1
+]
+.one: string: potato
+.phour: json: null
+.six.a.Q: json: "baaa"
+.six.a.b: string: quack
+.six.b: string: moo
+.three: bool: true
+.two: number: 3.14
+-- errors --
+bad type at top: JSON handler: value at . is not of expected type
+unexpected key: JSON handler found unexpected key x in object at .