Gzip: use zlib to write header and trailer.

When nginx is used with zlib patched with [1], which provides
integration with the future IBM Z hardware deflate acceleration, it ends
up computing CRC32 twice: one time in hardware, which always does this,
and one time in software by explicitly calling crc32().

crc32() calls were added in changesets 133:b27548f540ad ("nginx-0.0.1-
2003-09-24-23:51:12 import") and 134:d57c6835225c ("nginx-0.0.1-
2003-09-26-09:45:21 import") as part of gzip wrapping feature - back
then zlib did not support it.

However, since then gzip wrapping was implemented in zlib v1.2.0.4,
and it's already being used by nginx for log compression.

This patch replaces hand-written gzip wrapping with the one provided by
zlib. It simplifies the code, and makes it avoid computing CRC32 twice
when using hardware acceleration.

[1] madler/zlib#410

Author: iii-i

src/http/modules/ngx_http_gzip_filter_module.c

@@ -55,44 +55,23 @@ typedef struct {
     unsigned             redo:1;
     unsigned             done:1;
     unsigned             nomem:1;
-    unsigned             gzheader:1;
     unsigned             buffering:1;
     unsigned             intel:1;
 
     size_t               zin;
     size_t               zout;
 
-    uint32_t             crc32;
     z_stream             zstream;
     ngx_http_request_t  *request;
 } ngx_http_gzip_ctx_t;
 
 
-#if (NGX_HAVE_LITTLE_ENDIAN && NGX_HAVE_NONALIGNED)
-
-struct gztrailer {
-    uint32_t  crc32;
-    uint32_t  zlen;
-};
-
-#else /* NGX_HAVE_BIG_ENDIAN || !NGX_HAVE_NONALIGNED */
-
-struct gztrailer {
-    u_char  crc32[4];
-    u_char  zlen[4];
-};
-
-#endif
-
-
 static void ngx_http_gzip_filter_memory(ngx_http_request_t *r,
     ngx_http_gzip_ctx_t *ctx);
 static ngx_int_t ngx_http_gzip_filter_buffer(ngx_http_gzip_ctx_t *ctx,
     ngx_chain_t *in);
 static ngx_int_t ngx_http_gzip_filter_deflate_start(ngx_http_request_t *r,
     ngx_http_gzip_ctx_t *ctx);
-static ngx_int_t ngx_http_gzip_filter_gzheader(ngx_http_request_t *r,
-    ngx_http_gzip_ctx_t *ctx);
 static ngx_int_t ngx_http_gzip_filter_add_data(ngx_http_request_t *r,
     ngx_http_gzip_ctx_t *ctx);
 static ngx_int_t ngx_http_gzip_filter_get_buf(ngx_http_request_t *r,
@@ -446,12 +425,6 @@ ngx_http_gzip_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
             return ctx->busy ? NGX_AGAIN : NGX_OK;
         }
 
-        if (!ctx->gzheader) {
-            if (ngx_http_gzip_filter_gzheader(r, ctx) != NGX_OK) {
-                goto failed;
-            }
-        }
-
         rc = ngx_http_next_body_filter(r, ctx->out);
 
         if (rc == NGX_ERROR) {
@@ -643,7 +616,7 @@ ngx_http_gzip_filter_deflate_start(ngx_http_request_t *r,
     ctx->zstream.opaque = ctx;
 
     rc = deflateInit2(&ctx->zstream, (int) conf->level, Z_DEFLATED,
-                      - ctx->wbits, ctx->memlevel, Z_DEFAULT_STRATEGY);
+                      ctx->wbits + 16, ctx->memlevel, Z_DEFAULT_STRATEGY);
 
     if (rc != Z_OK) {
         ngx_log_error(NGX_LOG_ALERT, r->connection->log, 0,
@@ -652,45 +625,12 @@ ngx_http_gzip_filter_deflate_start(ngx_http_request_t *r,
     }
 
     ctx->last_out = &ctx->out;
-    ctx->crc32 = crc32(0L, Z_NULL, 0);
     ctx->flush = Z_NO_FLUSH;
 
     return NGX_OK;
 }
 
 
-static ngx_int_t
-ngx_http_gzip_filter_gzheader(ngx_http_request_t *r, ngx_http_gzip_ctx_t *ctx)
-{
-    ngx_buf_t      *b;
-    ngx_chain_t    *cl;
-    static u_char  gzheader[10] =
-                               { 0x1f, 0x8b, Z_DEFLATED, 0, 0, 0, 0, 0, 0, 3 };
-
-    b = ngx_calloc_buf(r->pool);
-    if (b == NULL) {
-        return NGX_ERROR;
-    }
-
-    b->memory = 1;
-    b->pos = gzheader;
-    b->last = b->pos + 10;
-
-    cl = ngx_alloc_chain_link(r->pool);
-    if (cl == NULL) {
-        return NGX_ERROR;
-    }
-
-    cl->buf = b;
-    cl->next = ctx->out;
-    ctx->out = cl;
-
-    ctx->gzheader = 1;
-
-    return NGX_OK;
-}
-
-
 static ngx_int_t
 ngx_http_gzip_filter_add_data(ngx_http_request_t *r, ngx_http_gzip_ctx_t *ctx)
 {
@@ -743,14 +683,9 @@ ngx_http_gzip_filter_add_data(ngx_http_request_t *r, ngx_http_gzip_ctx_t *ctx)
 
     } else if (ctx->in_buf->flush) {
         ctx->flush = Z_SYNC_FLUSH;
-    }
-
-    if (ctx->zstream.avail_in) {
 
-        ctx->crc32 = crc32(ctx->crc32, ctx->zstream.next_in,
-                           ctx->zstream.avail_in);
-
-    } else if (ctx->flush == Z_NO_FLUSH) {
+    } else if (ctx->zstream.avail_in == 0) {
+        /* ctx->flush == Z_NO_FLUSH */
         return NGX_AGAIN;
     }
 
@@ -932,13 +867,11 @@ static ngx_int_t
 ngx_http_gzip_filter_deflate_end(ngx_http_request_t *r,
     ngx_http_gzip_ctx_t *ctx)
 {
-    int                rc;
-    ngx_buf_t         *b;
-    ngx_chain_t       *cl;
-    struct gztrailer  *trailer;
+    int           rc;
+    ngx_chain_t  *cl;
 
     ctx->zin = ctx->zstream.total_in;
-    ctx->zout = 10 + ctx->zstream.total_out + 8;
+    ctx->zout = ctx->zstream.total_out;
 
     rc = deflateEnd(&ctx->zstream);
 
@@ -960,50 +893,7 @@ ngx_http_gzip_filter_deflate_end(ngx_http_request_t *r,
     *ctx->last_out = cl;
     ctx->last_out = &cl->next;
 
-    if (ctx->zstream.avail_out >= 8) {
-        trailer = (struct gztrailer *) ctx->out_buf->last;
-        ctx->out_buf->last += 8;
-        ctx->out_buf->last_buf = 1;
-
-    } else {
-        b = ngx_create_temp_buf(r->pool, 8);
-        if (b == NULL) {
-            return NGX_ERROR;
-        }
-
-        b->last_buf = 1;
-
-        cl = ngx_alloc_chain_link(r->pool);
-        if (cl == NULL) {
-            return NGX_ERROR;
-        }
-
-        cl->buf = b;
-        cl->next = NULL;
-        *ctx->last_out = cl;
-        ctx->last_out = &cl->next;
-        trailer = (struct gztrailer *) b->pos;
-        b->last += 8;
-    }
-
-#if (NGX_HAVE_LITTLE_ENDIAN && NGX_HAVE_NONALIGNED)
-
-    trailer->crc32 = ctx->crc32;
-    trailer->zlen = ctx->zin;
-
-#else
-
-    trailer->crc32[0] = (u_char) (ctx->crc32 & 0xff);
-    trailer->crc32[1] = (u_char) ((ctx->crc32 >> 8) & 0xff);
-    trailer->crc32[2] = (u_char) ((ctx->crc32 >> 16) & 0xff);
-    trailer->crc32[3] = (u_char) ((ctx->crc32 >> 24) & 0xff);
-
-    trailer->zlen[0] = (u_char) (ctx->zin & 0xff);
-    trailer->zlen[1] = (u_char) ((ctx->zin >> 8) & 0xff);
-    trailer->zlen[2] = (u_char) ((ctx->zin >> 16) & 0xff);
-    trailer->zlen[3] = (u_char) ((ctx->zin >> 24) & 0xff);
-
-#endif
+    ctx->out_buf->last_buf = 1;
 
     ctx->zstream.avail_in = 0;
     ctx->zstream.avail_out = 0;