Add generic filter/plugin infrastructure

The functions cgit_open_filter() and cgit_close_filter() can be used to
execute filters on the output stream from cgit.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

3 files changed, 62 insertions, 0 deletions

diff --git a/cgit.c b/cgit.c
index 2039ab1..779a464 100644
--- a/cgit.c
+++ b/cgit.c
@@ -17,6 +17,21 @@
 
 const char *cgit_version = CGIT_VERSION;
 
+struct cgit_filter *new_filter(const char *cmd, int extra_args)
+{
+        struct cgit_filter *f;
+
+        if (!cmd)
+                return NULL;
+
+        f = xmalloc(sizeof(struct cgit_filter));
+        f->cmd = xstrdup(cmd);
+        f->argv = xmalloc((2 + extra_args) * sizeof(char *));
+        f->argv[0] = f->cmd;
+        f->argv[1] = NULL;
+        return f;
+}
+
 void config_cb(const char *name, const char *value)
 {
         if (!strcmp(name, "root-title"))
diff --git a/cgit.h b/cgit.h
index 8c64efe..d0fff1f 100644
--- a/cgit.h
+++ b/cgit.h
@@ -129,6 +129,15 @@ struct cgit_query {
         int showmsg;
 };
 
+struct cgit_filter {
+        char *cmd;
+        char **argv;
+        int old_stdout;
+        int pipe_fh[2];
+        int pid;
+        int exitstatus;
+};
+
 struct cgit_config {
         char *agefile;
         char *cache_root;
@@ -248,5 +257,8 @@ extern const char *cgit_repobasename(const char *reponame);
 
 extern int cgit_parse_snapshots_mask(const char *str);
 
+extern int cgit_open_filter(struct cgit_filter *filter);
+extern int cgit_close_filter(struct cgit_filter *filter);
+
 
 #endif /* CGIT_H */
diff --git a/shared.c b/shared.c
index cce0af4..288cfa2 100644
--- a/shared.c
+++ b/shared.c
@@ -355,3 +355,38 @@ int cgit_parse_snapshots_mask(const char *str)
         }
         return rv;
 }
+
+int cgit_open_filter(struct cgit_filter *filter)
+{
+
+        filter->old_stdout = chk_positive(dup(STDOUT_FILENO),
+                "Unable to duplicate STDOUT");
+        chk_zero(pipe(filter->pipe_fh), "Unable to create pipe to subprocess");
+        filter->pid = chk_non_negative(fork(), "Unable to create subprocess");
+        if (filter->pid == 0) {
+                close(filter->pipe_fh[1]);
+                chk_non_negative(dup2(filter->pipe_fh[0], STDIN_FILENO),
+                        "Unable to use pipe as STDIN");
+                execvp(filter->cmd, filter->argv);
+                die("Unable to exec subprocess %s: %s (%d)", filter->cmd,
+                        strerror(errno), errno);
+        }
+        close(filter->pipe_fh[0]);
+        chk_non_negative(dup2(filter->pipe_fh[1], STDOUT_FILENO),
+                "Unable to use pipe as STDOUT");
+        close(filter->pipe_fh[1]);
+        return 0;
+}
+
+int cgit_close_filter(struct cgit_filter *filter)
+{
+        chk_non_negative(dup2(filter->old_stdout, STDOUT_FILENO),
+                "Unable to restore STDOUT");
+        close(filter->old_stdout);
+        if (filter->pid < 0)
+                return 0;
+        waitpid(filter->pid, &filter->exitstatus, 0);
+        if (WIFEXITED(filter->exitstatus) && !WEXITSTATUS(filter->exitstatus))
+                return 0;
+        die("Subprocess %s exited abnormally", filter->cmd);
+}