Add Pipe::prepend_filter

Fixes #1402

2 files changed, 32 insertions, 1 deletions

diff --git a/src/lib/filters/pipe.cpp b/src/lib/filters/pipe.cpp
index ed6abbad8..0bba81bf2 100644
--- a/src/lib/filters/pipe.cpp
+++ b/src/lib/filters/pipe.cpp
@@ -214,6 +214,19 @@ void Pipe::append_filter(Filter* filter)
    do_append(filter);
    }
 
+void Pipe::prepend(Filter* filter)
+   {
+   do_prepend(filter);
+   }
+
+void Pipe::prepend_filter(Filter* filter)
+   {
+   if(m_outputs->message_count() != 0)
+      throw Invalid_State("Cannot call Pipe::prepend_filter after start_msg");
+
+   do_prepend(filter);
+   }
+
 /*
 * Append a Filter to the Pipe
 */
@@ -238,7 +251,7 @@ void Pipe::do_append(Filter* filter)
 /*
 * Prepend a Filter to the Pipe
 */
-void Pipe::prepend(Filter* filter)
+void Pipe::do_prepend(Filter* filter)
    {
    if(m_inside_msg)
       throw Invalid_State("Cannot prepend to a Pipe while it is processing");
diff --git a/src/lib/filters/pipe.h b/src/lib/filters/pipe.h
index 9ba299024..03b516083 100644
--- a/src/lib/filters/pipe.h
+++ b/src/lib/filters/pipe.h
@@ -270,6 +270,9 @@ class BOTAN_PUBLIC_API(2,0) Pipe final : public DataSource
 
       /**
       * Insert a new filter at the front of the pipe
+      * Deprecated because runtime modification of Pipes is deprecated.
+      * You can instead use prepend_filter which only works before the first
+      * message is processed.
       * @param filt the new filter to insert
       */
       BOTAN_DEPRECATED("Runtime modification of Pipe deprecated")
@@ -277,6 +280,9 @@ class BOTAN_PUBLIC_API(2,0) Pipe final : public DataSource
 
       /**
       * Insert a new filter at the back of the pipe
+      * Deprecated because runtime modification of Pipes is deprecated.
+      * You can instead use append_filter which only works before the first
+      * message is processed.
       * @param filt the new filter to insert
       */
       BOTAN_DEPRECATED("Runtime modification of Pipe deprecated")
@@ -306,6 +312,17 @@ class BOTAN_PUBLIC_API(2,0) Pipe final : public DataSource
       void append_filter(Filter* filt);
 
       /**
+      * Prepend 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 prepend) is not deprecated, as it allows
+      * only modification of the pipe at initialization (before use)
+      * rather than after messages have been processed.
+      */
+      void prepend_filter(Filter* filt);
+
+      /**
       * Construct a Pipe of up to four filters. The filters are set up
       * in the same order as the arguments.
       */
@@ -325,6 +342,7 @@ class BOTAN_PUBLIC_API(2,0) Pipe final : public DataSource
    private:
       void destruct(Filter*);
       void do_append(Filter* filt);
+      void do_prepend(Filter* filt);
       void find_endpoints(Filter*);
       void clear_endpoints(Filter*);