Add Pipe::append_filter

Similar to append but it only allows modfication before start_msg.
See GH #1306

3 files changed, 36 insertions, 13 deletions

diff --git a/src/lib/filters/pipe.cpp b/src/lib/filters/pipe.cpp
index ff3cb599b..ed6abbad8 100644
--- a/src/lib/filters/pipe.cpp
+++ b/src/lib/filters/pipe.cpp
@@ -40,7 +40,10 @@ Pipe::Pipe(Filter* f1, Filter* f2, Filter* f3, Filter* f4) :
 */
 Pipe::Pipe(std::initializer_list<Filter*> args)
    {
-   init();
+   m_outputs.reset(new Output_Buffers);
+   m_pipe = nullptr;
+   m_default_read = 0;
+   m_inside_msg = false;
 
    for(auto i = args.begin(); i != args.end(); ++i)
       do_append(*i);
@@ -55,17 +58,6 @@ Pipe::~Pipe()
    }
 
 /*
-* Initialize the Pipe
-*/
-void Pipe::init()
-   {
-   m_outputs.reset(new Output_Buffers);
-   m_pipe = nullptr;
-   m_default_read = 0;
-   m_inside_msg = false;
-   }
-
-/*
 * Reset the Pipe
 */
 void Pipe::reset()
@@ -214,6 +206,14 @@ void Pipe::append(Filter* filter)
    do_append(filter);
    }
 
+void Pipe::append_filter(Filter* filter)
+   {
+   if(m_outputs->message_count() != 0)
+      throw Invalid_State("Cannot call Pipe::append_filter after start_msg");
+
+   do_append(filter);
+   }
+
 /*
 * Append a Filter to the Pipe
 */
diff --git a/src/lib/filters/pipe.h b/src/lib/filters/pipe.h
index cd446bd7e..9ba299024 100644
--- a/src/lib/filters/pipe.h
+++ b/src/lib/filters/pipe.h
@@ -295,6 +295,17 @@ class BOTAN_PUBLIC_API(2,0) Pipe final : public DataSource
       void reset();
 
       /**
+      * Append a new filter onto the filter sequence. This may only be
+      * called immediately after initial construction, before _any_
+      * calls to start_msg have been made.
+      *
+      * This function (unlike append) is not deprecated, as it allows
+      * only modification of the pipe at initialization (before use)
+      * rather than after messages have been processed.
+      */
+      void append_filter(Filter* filt);
+
+      /**
       * Construct a Pipe of up to four filters. The filters are set up
       * in the same order as the arguments.
       */
@@ -312,7 +323,6 @@ class BOTAN_PUBLIC_API(2,0) Pipe final : public DataSource
 
       ~Pipe();
    private:
-      void init();
       void destruct(Filter*);
       void do_append(Filter* filt);
       void find_endpoints(Filter*);
diff --git a/src/tests/test_filters.cpp b/src/tests/test_filters.cpp
index 26d13e0bc..b8a4ee9f0 100644
--- a/src/tests/test_filters.cpp
+++ b/src/tests/test_filters.cpp
@@ -198,6 +198,7 @@ class Filter_Tests final : public Test
 
          Botan::Pipe pipe;
 
+         pipe.append_filter(nullptr); // ignored
          pipe.append(nullptr); // ignored
          pipe.prepend(nullptr); // ignored
          pipe.pop(); // empty pipe, so ignored
@@ -213,11 +214,19 @@ class Filter_Tests final : public Test
                             "Invalid argument Pipe::prepend: SecureQueue cannot be used",
                             [&]() { pipe.prepend(queue_filter.get()); });
 
+         pipe.append_filter(new Botan::BitBucket); // succeeds
+         pipe.pop();
+
          pipe.start_msg();
 
          std::unique_ptr<Botan::Filter> filter(new Botan::BitBucket);
 
          // now inside a message, cannot modify pipe structure
+
+         result.test_throws("pipe error",
+                            "Cannot call Pipe::append_filter after start_msg",
+                            [&]() { pipe.append_filter(filter.get()); });
+
          result.test_throws("pipe error",
                             "Cannot append to a Pipe while it is processing",
                             [&]() { pipe.append(filter.get()); });
@@ -233,6 +242,10 @@ class Filter_Tests final : public Test
          pipe.end_msg();
 
          result.test_throws("pipe error",
+                            "Cannot call Pipe::append_filter after start_msg",
+                            [&]() { pipe.append_filter(filter.get()); });
+
+         result.test_throws("pipe error",
                             "Invalid argument Pipe::read: Invalid message number 100",
                             [&]() { uint8_t b; size_t got = pipe.read(&b, 1, 100); BOTAN_UNUSED(got); });