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

src/buffer_utils.cc

@@ -143,8 +143,13 @@ 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();
+
+            {
+                auto restore_flags = on_scope_end([this, flags=m_buffer.flags()] { m_buffer.flags() = flags; });
+                m_buffer.flags() &= ~Buffer::Flags::ReadOnly;
                 do
                 {
+
                     const ssize_t count = ::read(fifo, data, buffer_size);
                     if (count <= 0)
                     {
@@ -169,6 +174,7 @@ Buffer* create_fifo_buffer(String name, int fd, Buffer::Flags flags, bool scroll
                     }
                 }
                 while (++loop < max_loop  and fd_readable(fifo));
+            }
 
             if (insert_coord != m_buffer.back_coord())
                 m_buffer.run_hook_in_own_context(

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)
+    if (is_file and is_readonly and 
-        and (not filename or real_path(*filename) == buffer.name()))
+        (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);

test/regression/3398-readonly-fifo-failure/cmd

@@ -0,0 +1 @@
+

test/regression/3398-readonly-fifo-failure/out

@@ -0,0 +1 @@
+blah

test/regression/3398-readonly-fifo-failure/rc

@@ -0,0 +1,2 @@
+nop %sh{ mkfifo test-fifo; ( printf 'blah' > test-fifo ) </dev/null >/dev/null 2>&1 & }
+edit -readonly -fifo test-fifo out

test/regression/3398-readonly-fifo-failure/script

@@ -0,0 +1,8 @@
+ui_out '{ "jsonrpc": "2.0", "method": "set_ui_options", "params": [{}] }'
+ui_out '{ "jsonrpc": "2.0", "method": "draw", "params": [[[{ "face": { "fg": "black", "bg": "cyan", "attributes": [] }, "contents": "\u000a" }]], { "fg": "default", "bg": "default", "attributes": [] }, { "fg": "blue", "bg": "default", "attributes": [] }] }'
+ui_out '{ "jsonrpc": "2.0", "method": "menu_hide", "params": [] }'
+ui_out '{ "jsonrpc": "2.0", "method": "info_hide", "params": [] }'
+ui_out '{ "jsonrpc": "2.0", "method": "draw_status", "params": [[], [{ "face": { "fg": "default", "bg": "default", "attributes": [] }, "contents": "out 1:1 " }, { "face": { "fg": "black", "bg": "yellow", "attributes": [] }, "contents": "[scratch][fifo]" }, { "face": { "fg": "default", "bg": "default", "attributes": [] }, "contents": " " }, { "face": { "fg": "blue", "bg": "default", "attributes": [] }, "contents": "1 sel" }, { "face": { "fg": "default", "bg": "default", "attributes": [] }, "contents": " - client0@[kak-tests]" }], { "fg": "cyan", "bg": "default", "attributes": [] }] }'
+ui_out '{ "jsonrpc": "2.0", "method": "set_cursor", "params": ["buffer", { "line": 0, "column": 0 }] }'
+ui_out '{ "jsonrpc": "2.0", "method": "refresh", "params": [true] }'
+ui_out '{ "jsonrpc": "2.0", "method": "draw", "params": [[[{ "face": { "fg": "black", "bg": "white", "attributes": [] }, "contents": "b" }, { "face": { "fg": "default", "bg": "default", "attributes": [] }, "contents": "lah\u000a" }]], { "fg": "default", "bg": "default", "attributes": [] }, { "fg": "blue", "bg": "default", "attributes": [] }] }'