Allow reading from fifo in readonly buffers

readonly is supposed to prevent the user from modifying the buffer
and it can be useful to generate a readonly fifo buffer.

Fixes #3398

2 files changed, 32 insertions, 24 deletions

diff --git a/src/buffer_utils.cc b/src/buffer_utils.cc
index cbead31d..0162822c 100644
--- a/src/buffer_utils.cc
+++ b/src/buffer_utils.cc
@@ -143,32 +143,38 @@ Buffer* create_fifo_buffer(String name, int fd, Buffer::Flags flags, bool scroll
             char data[buffer_size];
             BufferCoord insert_coord = m_buffer.back_coord();
             const int fifo = fd();
-            do
+
             {
-                const ssize_t count = ::read(fifo, data, buffer_size);
-                if (count <= 0)
+                auto restore_flags = on_scope_end([this, flags=m_buffer.flags()] { m_buffer.flags() = flags; });
+                m_buffer.flags() &= ~Buffer::Flags::ReadOnly;
+                do
                 {
-                    closed = true;
-                    break;
-                }
-
-                auto pos = m_buffer.back_coord();
-                const bool prevent_scrolling = pos == BufferCoord{0,0} and not m_scroll;
-                if (prevent_scrolling)
-                    pos = m_buffer.next(pos);
 
-                m_buffer.insert(pos, StringView(data, data+count));
-
-                if (prevent_scrolling)
-                {
-                    m_buffer.erase({0,0}, m_buffer.next({0,0}));
-                    // in the other case, the buffer will have automatically
-                    // inserted a \n to guarantee its invariant.
-                    if (data[count-1] == '\n')
-                        m_buffer.insert(m_buffer.end_coord(), "\n");
+                    const ssize_t count = ::read(fifo, data, buffer_size);
+                    if (count <= 0)
+                    {
+                        closed = true;
+                        break;
+                    }
+
+                    auto pos = m_buffer.back_coord();
+                    const bool prevent_scrolling = pos == BufferCoord{0,0} and not m_scroll;
+                    if (prevent_scrolling)
+                        pos = m_buffer.next(pos);
+
+                    m_buffer.insert(pos, StringView(data, data+count));
+
+                    if (prevent_scrolling)
+                    {
+                        m_buffer.erase({0,0}, m_buffer.next({0,0}));
+                        // in the other case, the buffer will have automatically
+                        // inserted a \n to guarantee its invariant.
+                        if (data[count-1] == '\n')
+                            m_buffer.insert(m_buffer.end_coord(), "\n");
+                    }
                 }
+                while (++loop < max_loop  and fd_readable(fifo));
             }
-            while (++loop < max_loop  and fd_readable(fifo));
 
             if (insert_coord != m_buffer.back_coord())
                 m_buffer.run_hook_in_own_context(
diff --git a/src/commands.cc b/src/commands.cc
index ee45bcde..09e73ce3 100644
--- a/src/commands.cc
+++ b/src/commands.cc
@@ -472,14 +472,16 @@ const ParameterDesc write_params{
 void do_write_buffer(Context& context, Optional<String> filename, WriteFlags flags, bool atomic = false)
 {
     Buffer& buffer = context.buffer();
+    const bool is_file = (bool)(buffer.flags() & Buffer::Flags::File);
 
-    if (not filename and !(buffer.flags() & Buffer::Flags::File))
+    if (not filename and !is_file)
         throw runtime_error("cannot write a non file buffer without a filename");
 
+    const bool is_readonly = (bool)(context.buffer().flags() & Buffer::Flags::ReadOnly);
     // if the buffer is in read-only mode and we try to save it directly
     // or we try to write to it indirectly using e.g. a symlink, throw an error
-    if ((context.buffer().flags() & Buffer::Flags::ReadOnly)
-        and (not filename or real_path(*filename) == buffer.name()))
+    if (is_file and is_readonly and 
+        (not filename or real_path(*filename) == buffer.name()))
         throw runtime_error("cannot overwrite the buffer when in readonly mode");
 
     auto effective_filename = not filename ? buffer.name() : parse_filename(*filename);