Add next to Pl_String and fix comments

4 files changed, 25 insertions, 7 deletions

diff --git a/include/qpdf/Pl_String.hh b/include/qpdf/Pl_String.hh
index a858257c..327598da 100644
--- a/include/qpdf/Pl_String.hh
+++ b/include/qpdf/Pl_String.hh
@@ -19,11 +19,23 @@
 // continue to consider qpdf to be licensed under those terms. Please
 // see the manual for additional information.
 
-// End-of-line pipeline that simply writes its data to a stdio FILE* object.
-
 #ifndef PL_STRING_HH
 #define PL_STRING_HH
 
+// This pipeline accumulates the data passed to it into a std::string,
+// a reference to which is passed in at construction. Each subsequent
+// use of this pipeline appends to the data accumulated so far.
+//
+// For this pipeline, "next" may be null. If a next pointer is
+// provided, this pipeline will also pass the data through to it and
+// will forward finish() to it.
+//
+// It is okay to not call finish() on this pipeline. This makes it
+// easy to stick this in front of another pipeline to capture data
+// that is written to the other pipeline without interfering with when
+// finish is called on the other pipeline and without having to put a
+// Pl_Concatenate after it.
+
 #include <qpdf/Pipeline.hh>
 
 #include <string>
@@ -32,7 +44,7 @@ class QPDF_DLL_CLASS Pl_String: public Pipeline
 {
   public:
     QPDF_DLL
-    Pl_String(char const* identifier, std::string& s);
+    Pl_String(char const* identifier, Pipeline* next, std::string& s);
     QPDF_DLL
     virtual ~Pl_String();
 
diff --git a/libqpdf/JSON.cc b/libqpdf/JSON.cc
index 8549b7ed..31675a42 100644
--- a/libqpdf/JSON.cc
+++ b/libqpdf/JSON.cc
@@ -200,7 +200,7 @@ std::string
 JSON::unparse() const
 {
     std::string s;
-    Pl_String p("unparse", s);
+    Pl_String p("unparse", nullptr, s);
     write(&p, 0);
     return s;
 }
diff --git a/libqpdf/Pl_String.cc b/libqpdf/Pl_String.cc
index c9392821..d946a652 100644
--- a/libqpdf/Pl_String.cc
+++ b/libqpdf/Pl_String.cc
@@ -9,8 +9,8 @@ Pl_String::Members::Members(std::string& s) :
 {
 }
 
-Pl_String::Pl_String(char const* identifier, std::string& s) :
-    Pipeline(identifier, 0),
+Pl_String::Pl_String(char const* identifier, Pipeline* next, std::string& s) :
+    Pipeline(identifier, next),
     m(new Members(s))
 {
 }
@@ -25,9 +25,15 @@ void
 Pl_String::write(unsigned char const* buf, size_t len)
 {
     this->m->s.append(reinterpret_cast<char const*>(buf), len);
+    if (getNext(true)) {
+        getNext()->write(buf, len);
+    }
 }
 
 void
 Pl_String::finish()
 {
+    if (getNext(true)) {
+        getNext()->finish();
+    }
 }
diff --git a/qpdf/test_driver.cc b/qpdf/test_driver.cc
index 79744162..849eb4a0 100644
--- a/qpdf/test_driver.cc
+++ b/qpdf/test_driver.cc
@@ -437,7 +437,7 @@ test_6(QPDF& pdf, char const* arg2)
         throw std::logic_error("test 6 run on file with no metadata");
     }
     std::string buf;
-    Pl_String bufpl("buffer", buf);
+    Pl_String bufpl("buffer", nullptr, buf);
     metadata.pipeStreamData(&bufpl, 0, qpdf_dl_none);
     bool cleartext = false;
     if (buf.substr(0, 9) == "<?xpacket") {