Add new procedure QUtil::read_file_into_string

include/qpdf/QUtil.hh

@@ -485,6 +485,11 @@ namespace QUtil
     void read_file_into_memory(
         char const* filename, std::shared_ptr<char>& file_buf, size_t& size);
 
+    QPDF_DLL
+    std::string read_file_into_string(char const* filename);
+    QPDF_DLL
+    std::string read_file_into_string(FILE* f, std::string_view filename = "");
+
     // This used to be called strcasecmp, but that is a macro on some
     // platforms, so we have to give it a name that is not likely to
     // be a macro anywhere.

libqpdf/QPDFJob_config.cc

@@ -760,11 +760,9 @@ QPDFJob::Config::showObject(std::string const& parameter)
 QPDFJob::Config*
 QPDFJob::Config::jobJsonFile(std::string const& parameter)
 {
-    std::shared_ptr<char> file_buf;
-    size_t size;
-    QUtil::read_file_into_memory(parameter.c_str(), file_buf, size);
     try {
-        o.initializeFromJson(std::string(file_buf.get(), size), true);
+        o.initializeFromJson(
+            QUtil::read_file_into_string(parameter.c_str()), true);
     } catch (std::exception& e) {
         throw std::runtime_error(
             "error with job-json file " + std::string(parameter) + ": " +

libqpdf/QUtil.cc

@@ -1243,6 +1243,37 @@ QUtil::read_file_into_memory(
     }
 }
 
+std::string
+QUtil::read_file_into_string(char const* filename)
+{
+    FILE* f = safe_fopen(filename, "rb");
+    FileCloser fc(f);
+    return read_file_into_string(f, filename);
+}
+
+std::string
+QUtil::read_file_into_string(FILE* f, std::string_view filename)
+{
+    fseek(f, 0, SEEK_END);
+    auto size = QIntC::to_size(QUtil::tell(f));
+    fseek(f, 0, SEEK_SET);
+    std::string result(size, '\0');
+    if (auto read = fread(result.data(), 1, size, f); read != size) {
+        if (ferror(f)) {
+            throw std::runtime_error(
+                std::string("failure reading file ") + std::string(filename) +
+                " into memory: read " + uint_to_string(read) + "; wanted " +
+                uint_to_string(size));
+        } else {
+            throw std::runtime_error(
+                std::string("premature eof reading file ") +
+                std::string(filename) + " into memory: read " +
+                uint_to_string(read) + "; wanted " + uint_to_string(size));
+        }
+    }
+    return result;
+}
+
 static bool
 read_char_from_FILE(char& ch, FILE* f)
 {

libtests/qutil.cc

@@ -576,6 +576,12 @@ read_from_file_test()
     auto buf2 = b2.getBufferSharedPointer();
     assert(buf2->getSize() == size);
     assert(memcmp(buf2->getBuffer(), p, size) == 0);
+
+    auto s = QUtil::read_file_into_string("other-file");
+    std::cout << "read " << s.size() << " bytes" << std::endl;
+    assert(s.size() == 24652);
+    assert(s.substr(0, 36) == "This file is used for qutil testing.");
+    assert(s.substr(24641, 10) == "very long.");
 }
 
 void