From c9dae918fdf370367e2dfd92f3b19853783c9fc9 Mon Sep 17 00:00:00 2001
From: Roman Arutyunyan <arut@nginx.com>
Date: Sat, 2 Jul 2016 15:59:53 +0300
Subject: [PATCH] Sub filter: eliminate unnecessary buffering.

Previously, when a buffer was processed by the sub filter, its final bytes
could be buffered by the filter even if they don't match any pattern.
This happened because the Boyer-Moore algorithm, employed by the sub filter
since b9447fc457b4 (1.9.4), matches the last characters of patterns prior to
checking other characters.  If the last character is out of scope, initial
bytes of a potential match are buffered until the last character is available.

Now, after receiving a flush or recycled buffer, the filter performs
additional checks to reduce the number of buffered bytes.  The potential match
is checked against the initial parts of all patterns.  Non-matching bytes are
not buffered.  This improves processing of a chunked response from upstream
by sending the entire chunks without buffering unless a partial match is found
at the end of a chunk.
---
 src/http/modules/ngx_http_sub_filter_module.c | 41 +++++++++++++++++--
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/src/http/modules/ngx_http_sub_filter_module.c b/src/http/modules/ngx_http_sub_filter_module.c
index 62f8591ba..e8d1d801d 100644
--- a/src/http/modules/ngx_http_sub_filter_module.c
+++ b/src/http/modules/ngx_http_sub_filter_module.c
@@ -83,7 +83,7 @@ static ngx_uint_t ngx_http_sub_cmp_index;
 static ngx_int_t ngx_http_sub_output(ngx_http_request_t *r,
     ngx_http_sub_ctx_t *ctx);
 static ngx_int_t ngx_http_sub_parse(ngx_http_request_t *r,
-    ngx_http_sub_ctx_t *ctx);
+    ngx_http_sub_ctx_t *ctx, ngx_uint_t flush);
 static ngx_int_t ngx_http_sub_match(ngx_http_sub_ctx_t *ctx, ngx_int_t start,
     ngx_str_t *m);
 
@@ -287,6 +287,7 @@ ngx_http_sub_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
     ngx_int_t                  rc;
     ngx_buf_t                 *b;
     ngx_str_t                 *sub;
+    ngx_uint_t                 flush, last;
     ngx_chain_t               *cl;
     ngx_http_sub_ctx_t        *ctx;
     ngx_http_sub_match_t      *match;
@@ -328,6 +329,9 @@ ngx_http_sub_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
     ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                    "http sub filter \"%V\"", &r->uri);
 
+    flush = 0;
+    last = 0;
+
     while (ctx->in || ctx->buf) {
 
         if (ctx->buf == NULL) {
@@ -336,11 +340,19 @@ ngx_http_sub_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
             ctx->pos = ctx->buf->pos;
         }
 
+        if (ctx->buf->flush || ctx->buf->recycled) {
+            flush = 1;
+        }
+
+        if (ctx->in == NULL) {
+            last = flush;
+        }
+
         b = NULL;
 
         while (ctx->pos < ctx->buf->last) {
 
-            rc = ngx_http_sub_parse(r, ctx);
+            rc = ngx_http_sub_parse(r, ctx, last);
 
             ngx_log_debug4(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                            "parse: %i, looked: \"%V\" %p-%p",
@@ -592,7 +604,8 @@ ngx_http_sub_output(ngx_http_request_t *r, ngx_http_sub_ctx_t *ctx)
 
 
 static ngx_int_t
-ngx_http_sub_parse(ngx_http_request_t *r, ngx_http_sub_ctx_t *ctx)
+ngx_http_sub_parse(ngx_http_request_t *r, ngx_http_sub_ctx_t *ctx,
+    ngx_uint_t flush)
 {
     u_char                   *p, c;
     ngx_str_t                *m;
@@ -604,6 +617,7 @@ ngx_http_sub_parse(ngx_http_request_t *r, ngx_http_sub_ctx_t *ctx)
 
     slcf = ngx_http_get_module_loc_conf(r, ngx_http_sub_filter_module);
     tables = ctx->tables;
+    match = ctx->matches->elts;
 
     offset = ctx->offset;
     end = ctx->buf->last - ctx->pos;
@@ -630,7 +644,6 @@ ngx_http_sub_parse(ngx_http_request_t *r, ngx_http_sub_ctx_t *ctx)
         /* a potential match */
 
         start = offset - (ngx_int_t) tables->min_match_len + 1;
-        match = ctx->matches->elts;
 
         i = ngx_max(tables->index[c], ctx->index);
         j = tables->index[c + 1];
@@ -671,6 +684,26 @@ ngx_http_sub_parse(ngx_http_request_t *r, ngx_http_sub_ctx_t *ctx)
         ctx->index = 0;
     }
 
+    if (flush) {
+        for ( ;; ) {
+            start = offset - (ngx_int_t) tables->min_match_len + 1;
+
+            if (start >= end) {
+                break;
+            }
+
+            for (i = 0; i < ctx->matches->nelts; i++) {
+                m = &match[i].match;
+
+                if (ngx_http_sub_match(ctx, start, m) == NGX_AGAIN) {
+                    goto again;
+                }
+            }
+
+            offset++;
+        }
+    }
+
 again:
 
     ctx->offset = offset;