filter: allow returning exit code from filter

Filters can now indicate a status back to cgit by means of the exit code
for exec, or the return value from close for Lua.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

3 files changed, 12 insertions, 6 deletions

diff --git a/cgitrc.5.txt b/cgitrc.5.txt
index d8f7d0e..170e825 100644
--- a/cgitrc.5.txt
+++ b/cgitrc.5.txt
@@ -590,7 +590,8 @@ specification with the relevant string; available values are:
                 This is called whenever cgit writes data to the webpage.
         'filter_close()'::
                 This is called when the current filtering operation is
-                completed.
+                completed. It must return an integer value. Usually 0
+                indicates success.
         
         Additionally, cgit exposes to the Lua the following built-in functions:
 
diff --git a/filter.c b/filter.c
index 4d4acaf..0cce7bb 100644
--- a/filter.c
+++ b/filter.c
@@ -106,7 +106,7 @@ static int open_exec_filter(struct cgit_filter *base, va_list ap)
 static int close_exec_filter(struct cgit_filter *base)
 {
         struct cgit_exec_filter *filter = (struct cgit_exec_filter *)base;
-        int i, exit_status;
+        int i, exit_status = 0;
 
         chk_non_negative(dup2(filter->old_stdout, STDOUT_FILENO),
                 "Unable to restore STDOUT");
@@ -114,14 +114,14 @@ static int close_exec_filter(struct cgit_filter *base)
         if (filter->pid < 0)
                 goto done;
         waitpid(filter->pid, &exit_status, 0);
-        if (WIFEXITED(exit_status) && !WEXITSTATUS(exit_status))
+        if (WIFEXITED(exit_status))
                 goto done;
         die("Subprocess %s exited abnormally", filter->cmd);
 
 done:
         for (i = 0; i < filter->base.argument_count; i++)
                 filter->argv[i + 1] = NULL;
-        return 0;
+        return WEXITSTATUS(exit_status);
 
 }
 
@@ -315,10 +315,14 @@ static int close_lua_filter(struct cgit_filter *base)
         int ret = 0;
 
         lua_getglobal(filter->lua_state, "filter_close");
-        if (lua_pcall(filter->lua_state, 0, 0, 0)) {
+        if (lua_pcall(filter->lua_state, 0, 1, 0)) {
                 error_lua_filter(filter);
-                ret = 1;
+                ret = -1;
+        } else {
+                ret = lua_tonumber(filter->lua_state, -1);
+                lua_pop(filter->lua_state, 1);
         }
+
         unhook_write();
         return ret;
 }
diff --git a/filters/email-gravatar.lua b/filters/email-gravatar.lua
index 22f0641..c80b63e 100644
--- a/filters/email-gravatar.lua
+++ b/filters/email-gravatar.lua
@@ -16,6 +16,7 @@ end
 
 function filter_close()
         html("<img src='//www.gravatar.com/avatar/" .. md5 .. "?s=13&amp;d=retro' style='height:10pt;width:10pt' alt='Gravatar' /> " .. buffer)
+        return 0
 end
 
 function filter_write(str)