Add Pl_Buffer::getMallocBuffer

ChangeLog

@@ -1,3 +1,8 @@
+2021-12-17  Jay Berkenbilt  <ejb@ql.org>
+
+	* Add Pl_Buffer::getMallocBuffer() to initialize a buffer with
+	malloc in support of the C API
+
 2021-12-16  Jay Berkenbilt  <ejb@ql.org>
 
 	* Add several functions to the C API for working with pages. C

include/qpdf/Pl_Buffer.hh

@@ -55,6 +55,15 @@ class Pl_Buffer: public Pipeline
     QPDF_DLL
     Buffer* getBuffer();
 
+    // getMallocBuffer behaves in the same was as getBuffer except the
+    // buffer is allocated with malloc(), making it suitable for use
+    // when calling from other languages. If there is no data, *buf is
+    // set to a null pointer and *len is set to 0. Otherwise, *buf is
+    // a buffer of size *len allocated with malloc(). It is the
+    // caller's responsibility to call free() on the buffer.
+    QPDF_DLL
+    void getMallocBuffer(unsigned char **buf, size_t* len);
+
   private:
     class Members
     {

libqpdf/Pl_Buffer.cc

@@ -3,6 +3,7 @@
 #include <algorithm>
 #include <assert.h>
 #include <string.h>
+#include <stdlib.h>
 
 Pl_Buffer::Members::Members() :
     ready(true),
@@ -80,3 +81,25 @@ Pl_Buffer::getBuffer()
     this->m = new Members();
     return b;
 }
+
+void
+Pl_Buffer::getMallocBuffer(unsigned char **buf, size_t* len)
+{
+    if (! this->m->ready)
+    {
+	throw std::logic_error(
+            "Pl_Buffer::getMallocBuffer() called when not ready");
+    }
+
+    *len = this->m->total_size;
+    if (this->m->total_size > 0)
+    {
+        *buf = reinterpret_cast<unsigned char*>(malloc(this->m->total_size));
+        memcpy(*buf, this->m->data->getBuffer(), this->m->total_size);
+    }
+    else
+    {
+        *buf = nullptr;
+    }
+    this->m = new Members();
+}

libtests/buffer.cc

@@ -6,6 +6,7 @@
 #include <stdexcept>
 #include <iostream>
 #include <cassert>
+#include <cstring>
 
 static unsigned char* uc(char const* s)
 {
@@ -98,6 +99,31 @@ int main()
         b = bp3.getBuffer();
         std::cout << "size: " << b->getSize() << std::endl;
         delete b;
+
+        // Malloc buffer should behave similarly.
+        Pl_Buffer bp4("bp4");
+        bp4.write(uc("asdf"), 4);
+        unsigned char* mbuf;
+        size_t len;
+        try
+        {
+            bp4.getMallocBuffer(&mbuf, &len);
+            assert(false);
+        }
+        catch (std::logic_error& e)
+        {
+            std::cout << "malloc buffer logic error: " << e.what() << std::endl;
+        }
+        bp4.finish();
+        bp4.getMallocBuffer(&mbuf, &len);
+        assert(len == 4);
+        assert(memcmp(mbuf, uc("asdf"), 4) == 0);
+        free(mbuf);
+        bp4.write(uc(""), 0);
+        bp4.finish();
+        bp4.getMallocBuffer(&mbuf, &len);
+        assert(mbuf == nullptr);
+        assert(len == 0);
     }
     catch (std::exception& e)
     {

libtests/qtest/buffer/buffer.out

@@ -11,4 +11,5 @@ data: mooquack
 size: 0
 size: 0
 size: 0
+malloc buffer logic error: Pl_Buffer::getMallocBuffer() called when not ready
 done

manual/index.rst

@@ -3622,10 +3622,14 @@ For a detailed list of changes, please see the file
       object is not of the expected type. These warnings now have an
       error code of ``qpdf_e_object`` instead of
       ``qpdf_e_damaged_pdf``. Also, comments have been added to
-      :file:`QPDFObjectHandle.hh` to explain in
+      :file:`QPDFObjectHandle.hh` to explain in more detail what the
-      more detail what the behavior is. See :ref:`ref.object-accessors` for a more in-depth
+      behavior is. See :ref:`ref.object-accessors` for a more in-depth
       discussion.
 
+    - Add ``Pl_Buffer::getMallocBuffer()`` to initialize a buffer
+      allocated with ``malloc()`` for better cross-language
+      interoperability.
+
   - C API Enhancements
 
     - Overhaul error handling for the object handle functions