streaming: filter cascading

This implements an internal "cascade" filter mechanism that plugs
two filters in series.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/convert.c b/convert.c
index 0c42bcb524e2f67e50900d6d045c6dfcebb1d14d..85939c29be67d4179a2afb9069b575afed4d8bb2 100644 (file)
--- a/convert.c
+++ b/convert.c
@@ -914,6 +914,112 @@ static struct stream_filter lf_to_crlf_filter_singleton = {
 };
 
 
+/*
+ * Cascade filter
+ */
+#define FILTER_BUFFER 1024
+struct cascade_filter {
+       struct stream_filter filter;
+       struct stream_filter *one;
+       struct stream_filter *two;
+       char buf[FILTER_BUFFER];
+       int end, ptr;
+};
+
+static int cascade_filter_fn(struct stream_filter *filter,
+                            const char *input, size_t *isize_p,
+                            char *output, size_t *osize_p)
+{
+       struct cascade_filter *cas = (struct cascade_filter *) filter;
+       size_t filled = 0;
+       size_t sz = *osize_p;
+       size_t to_feed, remaining;
+
+       /*
+        * input -- (one) --> buf -- (two) --> output
+        */
+       while (filled < sz) {
+               remaining = sz - filled;
+
+               /* do we already have something to feed two with? */
+               if (cas->ptr < cas->end) {
+                       to_feed = cas->end - cas->ptr;
+                       if (stream_filter(cas->two,
+                                         cas->buf + cas->ptr, &to_feed,
+                                         output + filled, &remaining))
+                               return -1;
+                       cas->ptr += (cas->end - cas->ptr) - to_feed;
+                       filled = sz - remaining;
+                       continue;
+               }
+
+               /* feed one from upstream and have it emit into our buffer */
+               to_feed = input ? *isize_p : 0;
+               if (input && !to_feed)
+                       break;
+               remaining = sizeof(cas->buf);
+               if (stream_filter(cas->one,
+                                 input, &to_feed,
+                                 cas->buf, &remaining))
+                       return -1;
+               cas->end = sizeof(cas->buf) - remaining;
+               cas->ptr = 0;
+               if (input) {
+                       size_t fed = *isize_p - to_feed;
+                       *isize_p -= fed;
+                       input += fed;
+               }
+
+               /* do we know that we drained one completely? */
+               if (input || cas->end)
+                       continue;
+
+               /* tell two to drain; we have nothing more to give it */
+               to_feed = 0;
+               remaining = sz - filled;
+               if (stream_filter(cas->two,
+                                 NULL, &to_feed,
+                                 output + filled, &remaining))
+                       return -1;
+               if (remaining == (sz - filled))
+                       break; /* completely drained two */
+               filled = sz - remaining;
+       }
+       *osize_p -= filled;
+       return 0;
+}
+
+static void cascade_free_fn(struct stream_filter *filter)
+{
+       struct cascade_filter *cas = (struct cascade_filter *)filter;
+       free_stream_filter(cas->one);
+       free_stream_filter(cas->two);
+       free(filter);
+}
+
+static struct stream_filter_vtbl cascade_vtbl = {
+       cascade_filter_fn,
+       cascade_free_fn,
+};
+
+static struct stream_filter *cascade_filter(struct stream_filter *one,
+                                           struct stream_filter *two)
+{
+       struct cascade_filter *cascade;
+
+       if (!one || is_null_stream_filter(one))
+               return two;
+       if (!two || is_null_stream_filter(two))
+               return one;
+
+       cascade = xmalloc(sizeof(*cascade));
+       cascade->one = one;
+       cascade->two = two;
+       cascade->end = cascade->ptr = 0;
+       cascade->filter.vtbl = &cascade_vtbl;
+       return (struct stream_filter *)cascade;
+}
+
 /*
  * ident filter
  */
@@ -1083,20 +1189,12 @@ struct stream_filter *get_stream_filter(const char *path, const unsigned char *s
        crlf_action = input_crlf_action(ca.crlf_action, ca.eol_attr);
 
        if ((crlf_action == CRLF_BINARY) || (crlf_action == CRLF_INPUT) ||
-           (crlf_action == CRLF_GUESS && auto_crlf == AUTO_CRLF_FALSE)) {
-               if (filter) {
-                       free_stream_filter(filter);
-                       return NULL;
-               }
-               return &null_filter_singleton;
-       } else if (output_eol(crlf_action) == EOL_CRLF &&
-                  !(crlf_action == CRLF_AUTO || crlf_action == CRLF_GUESS)) {
-               if (filter) {
-                       free_stream_filter(filter);
-                       return NULL;
-               }
-               return &lf_to_crlf_filter_singleton;
-       }
+           (crlf_action == CRLF_GUESS && auto_crlf == AUTO_CRLF_FALSE))
+               filter = cascade_filter(filter, &null_filter_singleton);
+
+       else if (output_eol(crlf_action) == EOL_CRLF &&
+                !(crlf_action == CRLF_AUTO || crlf_action == CRLF_GUESS))
+               filter = cascade_filter(filter, &lf_to_crlf_filter_singleton);
 
        return filter;
 }