src/http/modules/ngx_http_image_filter_module.c

/*
 * Copyright (C) Igor Sysoev
 */


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_http.h>

#include <gd.h>


#define NGX_HTTP_IMAGE_OFF       0
#define NGX_HTTP_IMAGE_TEST      1
#define NGX_HTTP_IMAGE_SIZE      2
#define NGX_HTTP_IMAGE_RESIZE    3
#define NGX_HTTP_IMAGE_CROP      4


#define NGX_HTTP_IMAGE_START     0
#define NGX_HTTP_IMAGE_READ      1
#define NGX_HTTP_IMAGE_PROCESS   2
#define NGX_HTTP_IMAGE_PASS      3
#define NGX_HTTP_IMAGE_DONE      4


#define NGX_HTTP_IMAGE_NONE      0
#define NGX_HTTP_IMAGE_JPEG      1
#define NGX_HTTP_IMAGE_GIF       2
#define NGX_HTTP_IMAGE_PNG       3


#define NGX_HTTP_IMAGE_BUFFERED  0x08


typedef struct {
    ngx_uint_t                   filter;
    ngx_uint_t                   width;
    ngx_uint_t                   height;

    size_t                       buffer_size;
} ngx_http_image_filter_conf_t;


typedef struct {
    u_char                      *image;
    u_char                      *last;

    size_t                       length;

    ngx_uint_t                   width;
    ngx_uint_t                   height;

    ngx_uint_t                   phase;
    ngx_uint_t                   type;
} ngx_http_image_filter_ctx_t;


static ngx_int_t ngx_http_image_send(ngx_http_request_t *r,
    ngx_http_image_filter_ctx_t *ctx, ngx_chain_t *in);
static ngx_uint_t ngx_http_image_test(ngx_http_request_t *r, ngx_chain_t *in);
static ngx_int_t ngx_http_image_read(ngx_http_request_t *r, ngx_chain_t *in);
static ngx_buf_t *ngx_http_image_process(ngx_http_request_t *r);
static ngx_buf_t *ngx_http_image_json(ngx_http_request_t *r,
    ngx_http_image_filter_ctx_t *ctx);
static ngx_buf_t *ngx_http_image_asis(ngx_http_request_t *r,
    ngx_http_image_filter_ctx_t *ctx);
static void ngx_http_image_length(ngx_http_request_t *r, ngx_buf_t *b);
static ngx_int_t ngx_http_image_size(ngx_http_request_t *r,
    ngx_http_image_filter_ctx_t *ctx);

static ngx_buf_t *ngx_http_image_resize(ngx_http_request_t *r,
    ngx_http_image_filter_ctx_t *ctx);
static gdImagePtr ngx_http_image_source(ngx_http_request_t *r,
    ngx_http_image_filter_ctx_t *ctx);
static gdImagePtr ngx_http_image_new(ngx_http_request_t *r, int w, int h,
    int colors);
static u_char *ngx_http_image_out(ngx_http_request_t *r, ngx_uint_t type,
    gdImagePtr img, int *size);
static void ngx_http_image_cleanup(void *data);


static void *ngx_http_image_filter_create_conf(ngx_conf_t *cf);
static char *ngx_http_image_filter_merge_conf(ngx_conf_t *cf, void *parent,
    void *child);
static char *ngx_http_image_filter(ngx_conf_t *cf, ngx_command_t *cmd,
    void *conf);
static ngx_int_t ngx_http_image_filter_init(ngx_conf_t *cf);


static ngx_command_t  ngx_http_image_filter_commands[] = {

    { ngx_string("image_filter"),
      NGX_HTTP_LOC_CONF|NGX_CONF_TAKE13,
      ngx_http_image_filter,
      NGX_HTTP_LOC_CONF_OFFSET,
      0,
      NULL },

    { ngx_string("image_filter_buffer"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_size_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_image_filter_conf_t, buffer_size),
      NULL },

      ngx_null_command
};


static ngx_http_module_t  ngx_http_image_filter_module_ctx = {
    NULL,                                  /* preconfiguration */
    ngx_http_image_filter_init,            /* postconfiguration */

    NULL,                                  /* create main configuration */
    NULL,                                  /* init main configuration */

    NULL,                                  /* create server configuration */
    NULL,                                  /* merge server configuration */

    ngx_http_image_filter_create_conf,     /* create location configuration */
    ngx_http_image_filter_merge_conf       /* merge location configuration */
};


ngx_module_t  ngx_http_image_filter_module = {
    NGX_MODULE_V1,
    &ngx_http_image_filter_module_ctx,     /* module context */
    ngx_http_image_filter_commands,        /* module directives */
    NGX_HTTP_MODULE,                       /* module type */
    NULL,                                  /* init master */
    NULL,                                  /* init module */
    NULL,                                  /* init process */
    NULL,                                  /* init thread */
    NULL,                                  /* exit thread */
    NULL,                                  /* exit process */
    NULL,                                  /* exit master */
    NGX_MODULE_V1_PADDING
};


static ngx_http_output_header_filter_pt  ngx_http_next_header_filter;
static ngx_http_output_body_filter_pt    ngx_http_next_body_filter;


static ngx_str_t  ngx_http_image_types[] = {
    ngx_string("image/jpeg"),
    ngx_string("image/gif"),
    ngx_string("image/png")
};


static ngx_int_t
ngx_http_image_header_filter(ngx_http_request_t *r)
{
    off_t                          len;
    ngx_http_image_filter_ctx_t   *ctx;
    ngx_http_image_filter_conf_t  *conf;

    if (r->headers_out.status == NGX_HTTP_NOT_MODIFIED) {
        return ngx_http_next_header_filter(r);
    }

    ctx = ngx_http_get_module_ctx(r, ngx_http_image_filter_module);

    if (ctx) {
        ngx_http_set_ctx(r, NULL, ngx_http_image_filter_module);
        return ngx_http_next_header_filter(r);
    }

    conf = ngx_http_get_module_loc_conf(r, ngx_http_image_filter_module);

    if (conf->filter == NGX_HTTP_IMAGE_OFF) {
        return ngx_http_next_header_filter(r);
    }

    if (r->headers_out.content_type.len
            >= sizeof("multipart/x-mixed-replace") - 1
        && ngx_strncasecmp(r->headers_out.content_type.data,
                           (u_char *) "multipart/x-mixed-replace",
                           sizeof("multipart/x-mixed-replace") - 1)
           == 0)
    {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                      "image filter: multipart/x-mixed-replace response");

        return NGX_ERROR;
    }

    ctx = ngx_pcalloc(r->pool, sizeof(ngx_http_image_filter_ctx_t));
    if (ctx == NULL) {
        return NGX_ERROR;
    }

    ngx_http_set_ctx(r, ctx, ngx_http_image_filter_module);

    len = r->headers_out.content_length_n;

    if (len != -1 && len > (off_t) conf->buffer_size) {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                      "image filter: too big response: %O", len);

        return NGX_ERROR;
    }

    if (len == -1) {
        ctx->length = conf->buffer_size;

    } else {
        ctx->length = (size_t) len;
    }

    if (r->headers_out.refresh) {
        r->headers_out.refresh->hash = 0;
    }

    r->main_filter_need_in_memory = 1;
    r->allow_ranges = 0;

    return NGX_OK;
}


static ngx_int_t
ngx_http_image_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
    ngx_int_t                      rc;
    ngx_str_t                     *ct;
    ngx_chain_t                    out;
    ngx_http_image_filter_ctx_t   *ctx;
    ngx_http_image_filter_conf_t  *conf;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0, "image filter");

    if (in == NULL) {
        return ngx_http_next_body_filter(r, in);
    }

    ctx = ngx_http_get_module_ctx(r, ngx_http_image_filter_module);

    if (ctx == NULL) {
        return ngx_http_next_body_filter(r, in);
    }

    switch (ctx->phase) {

    case NGX_HTTP_IMAGE_START:

        ctx->type = ngx_http_image_test(r, in);

        conf = ngx_http_get_module_loc_conf(r, ngx_http_image_filter_module);

        if (ctx->type == NGX_HTTP_IMAGE_NONE) {

            if (conf->filter == NGX_HTTP_IMAGE_SIZE) {
                out.buf = ngx_http_image_json(r, NULL);

                if (out.buf) {
                    out.next = NULL;
                    ctx->phase = NGX_HTTP_IMAGE_DONE;

                    return ngx_http_image_send(r, ctx, &out);
                }
            }

            return ngx_http_filter_finalize_request(r,
                                              &ngx_http_image_filter_module,
                                              NGX_HTTP_UNSUPPORTED_MEDIA_TYPE);
        }

        /* override content type */

        ct = &ngx_http_image_types[ctx->type - 1];
        r->headers_out.content_type_len = ct->len;
        r->headers_out.content_type = *ct;

        if (conf->filter == NGX_HTTP_IMAGE_TEST) {
            ctx->phase = NGX_HTTP_IMAGE_PASS;

            return ngx_http_image_send(r, ctx, in);
        }

        ctx->phase = NGX_HTTP_IMAGE_READ;

        /* fall through */

    case NGX_HTTP_IMAGE_READ:

        rc = ngx_http_image_read(r, in);

        if (rc == NGX_AGAIN) {
            return NGX_OK;
        }

        if (rc == NGX_ERROR) {
            return ngx_http_filter_finalize_request(r,
                                              &ngx_http_image_filter_module,
                                              NGX_HTTP_UNSUPPORTED_MEDIA_TYPE);
        }

        /* fall through */

    case NGX_HTTP_IMAGE_PROCESS:

        out.buf = ngx_http_image_process(r);

        if (out.buf == NULL) {
            return ngx_http_filter_finalize_request(r,
                                              &ngx_http_image_filter_module,
                                              NGX_HTTP_UNSUPPORTED_MEDIA_TYPE);
        }

        out.next = NULL;
        ctx->phase = NGX_HTTP_IMAGE_PASS;

        return ngx_http_image_send(r, ctx, &out);

    case NGX_HTTP_IMAGE_PASS:

        return ngx_http_next_body_filter(r, in);

    default: /* NGX_HTTP_IMAGE_DONE */

        rc = ngx_http_next_body_filter(r, NULL);

        /* NGX_ERROR resets any pending data */
        return (rc == NGX_OK) ? NGX_ERROR : rc;
    }
}


static ngx_int_t
ngx_http_image_send(ngx_http_request_t *r, ngx_http_image_filter_ctx_t *ctx,
    ngx_chain_t *in)
{
    ngx_int_t  rc;

    rc = ngx_http_next_header_filter(r);

    if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) {
        return NGX_ERROR;
    }

    rc = ngx_http_next_body_filter(r, in);

    if (ctx->phase == NGX_HTTP_IMAGE_DONE) {
        /* NGX_ERROR resets any pending data */
        return (rc == NGX_OK) ? NGX_ERROR : rc;
    }

    return rc;
}


static ngx_uint_t
ngx_http_image_test(ngx_http_request_t *r, ngx_chain_t *in)
{
    u_char  *p;

    p = in->buf->pos;

    if (in->buf->last - p < 16) {
        return NGX_HTTP_IMAGE_NONE;
    }

    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "image filter: \"%c%c\"", p[0], p[1]);

    if (p[0] == 0xff && p[1] == 0xd8) {

        /* JPEG */

        return NGX_HTTP_IMAGE_JPEG;

    } else if (p[0] == 'G' && p[1] == 'I' && p[2] == 'F' && p[3] == '8'
               && p[4] == '9' && p[5] == 'a')
    {
        /* GIF */

        return NGX_HTTP_IMAGE_GIF;

    } else if (p[0] == 0x89 && p[1] == 'P' && p[2] == 'N' && p[3] == 'G'
               && p[4] == 0x0d && p[5] == 0x0a && p[6] == 0x1a && p[7] == 0x0a)
    {
        /* PNG */

        return NGX_HTTP_IMAGE_PNG;
    }

    return NGX_HTTP_IMAGE_NONE;
}


static ngx_int_t
ngx_http_image_read(ngx_http_request_t *r, ngx_chain_t *in)
{
    u_char                       *p;
    size_t                        size, rest;
    ngx_buf_t                    *b;
    ngx_chain_t                  *cl;
    ngx_http_image_filter_ctx_t  *ctx;

    ctx = ngx_http_get_module_ctx(r, ngx_http_image_filter_module);

    if (ctx->image == NULL) {
        ctx->image = ngx_palloc(r->pool, ctx->length);
        if (ctx->image == NULL) {
            return NGX_ERROR;
        }

        ctx->last = ctx->image;
    }

    p = ctx->last;

    for (cl = in; cl; cl = cl->next) {

        b = cl->buf;
        size = b->last - b->pos;

        ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                       "image buf: %uz", size);

        rest = ctx->image + ctx->length - p;
        size = (rest < size) ? rest : size;

        p = ngx_cpymem(p, b->pos, size);
        b->pos += size;

        if (b->last_buf) {
            ctx->last = p;
            return NGX_OK;
        }
    }

    ctx->last = p;
    r->connection->buffered |= NGX_HTTP_IMAGE_BUFFERED;

    return NGX_AGAIN;
}


static ngx_buf_t *
ngx_http_image_process(ngx_http_request_t *r)
{
    ngx_buf_t                     *b;
    ngx_int_t                      rc;
    ngx_http_image_filter_ctx_t   *ctx;
    ngx_http_image_filter_conf_t  *conf;

    r->connection->buffered &= ~NGX_HTTP_IMAGE_BUFFERED;

    ctx = ngx_http_get_module_ctx(r, ngx_http_image_filter_module);

    rc = ngx_http_image_size(r, ctx);

    conf = ngx_http_get_module_loc_conf(r, ngx_http_image_filter_module);

    if (conf->filter == NGX_HTTP_IMAGE_SIZE) {

        b = ngx_http_image_json(r, rc == NGX_OK ? ctx : NULL);

    } else if (rc == NGX_OK
               && ctx->width <= conf->width
               && ctx->height <= conf->height)
    {
        b = ngx_http_image_asis(r, ctx);

    } else {
        b = ngx_http_image_resize(r, ctx);
    }

    return b;
}


static ngx_buf_t *
ngx_http_image_json(ngx_http_request_t *r, ngx_http_image_filter_ctx_t *ctx)
{
    size_t      len;
    ngx_buf_t  *b;

    b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t));
    if (b == NULL) {
        return NULL;
    }

    b->memory = 1;
    b->last_buf = 1;

    ngx_http_clean_header(r);

    r->headers_out.status = NGX_HTTP_OK;
    r->headers_out.content_type.len = sizeof("text/plain") - 1;
    r->headers_out.content_type.data = (u_char *) "text/plain";

    if (ctx == NULL) {
        b->pos = (u_char *) "{}" CRLF;
        b->last = b->pos + sizeof("{}" CRLF) - 1;

        ngx_http_image_length(r, b);

        return b;
    }

    len = sizeof("{ \"img\" : "
                 "{ \"width\": , \"height\": , \"type\": \"jpeg\" } }" CRLF) - 1
          + 2 * NGX_SIZE_T_LEN;

    b->pos = ngx_pnalloc(r->pool, len);
    if (b->pos == NULL) {
        return NULL;
    }

    b->last = ngx_sprintf(b->pos,
                          "{ \"img\" : "
                                       "{ \"width\": %uz,"
                                        " \"height\": %uz,"
                                        " \"type\": \"%s\" } }" CRLF,
                          ctx->width, ctx->height,
                          ngx_http_image_types[ctx->type - 1].data + 6);

    ngx_http_image_length(r, b);

    return b;
}


static ngx_buf_t *
ngx_http_image_asis(ngx_http_request_t *r, ngx_http_image_filter_ctx_t *ctx)
{
    ngx_buf_t  *b;

    b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t));
    if (b == NULL) {
        return NULL;
    }

    b->pos = ctx->image;
    b->last = ctx->last;
    b->memory = 1;
    b->last_buf = 1;

    ngx_http_image_length(r, b);

    return b;
}


static void
ngx_http_image_length(ngx_http_request_t *r, ngx_buf_t *b)
{
    r->headers_out.content_length_n = b->last - b->pos;

    if (r->headers_out.content_length) {
        r->headers_out.content_length->hash = 0;
    }

    r->headers_out.content_length = NULL;
}


static ngx_int_t
ngx_http_image_size(ngx_http_request_t *r, ngx_http_image_filter_ctx_t *ctx)
{
    u_char      *p, *last;
    ngx_uint_t   width, height;

    p = ctx->image;

    switch (ctx->type) {

    case NGX_HTTP_IMAGE_JPEG:

        p += 2;
        last = ctx->image + ctx->length - 10;

        while (p < last) {

            if (p[0] == 0xff && p[1] != 0xff) {

                ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                               "JPEG: %02xd %02xd", *p, *(p + 1));

                p++;

                if (*p == 0xc0 || *p == 0xc1 || *p == 0xc2 || *p == 0xc3
                    || *p == 0xc9 || *p == 0xca || *p == 0xcb)
                {
                    goto found;
                }

                ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                               "JPEG: %02xd %02xd", p[1], p[2]);

                p += p[1] * 256 + p[2];

                continue;
            }

            p++;
        }

        return NGX_DECLINED;

    found:

        width = p[6] * 256 + p[7];
        height = p[4] * 256 + p[5];

        break;

    case NGX_HTTP_IMAGE_GIF:

        if (ctx->length < 10) {
            return NGX_DECLINED;
        }

        width = p[7] * 256 + p[6];
        height = p[9] * 256 + p[8];

        break;

    case NGX_HTTP_IMAGE_PNG:

        if (ctx->length < 24) {
            return NGX_DECLINED;
        }

        width = p[18] * 256 + p[19];
        height = p[22] * 256 + p[23];

        break;

    default:

        return NGX_DECLINED;
    }

    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "image size: %d x %d", width, height);

    ctx->width = width;
    ctx->height = height;

    return NGX_OK;
}


static ngx_buf_t *
ngx_http_image_resize(ngx_http_request_t *r, ngx_http_image_filter_ctx_t *ctx)
{
    int                            sx, sy, dx, dy, ox, oy,
                                   colors, transparent, size;
    u_char                        *out;
    ngx_buf_t                     *b;
    ngx_uint_t                     resize;
    gdImagePtr                     src, dst;
    ngx_pool_cleanup_t            *cln;
    ngx_http_image_filter_conf_t  *conf;

    src = ngx_http_image_source(r, ctx);

    if (src == NULL) {
        return NULL;
    }

    sx = gdImageSX(src);
    sy = gdImageSY(src);

    conf = ngx_http_get_module_loc_conf(r, ngx_http_image_filter_module);

    if ((ngx_uint_t) sx <= conf->width && (ngx_uint_t) sy <= conf->height) {
        gdImageDestroy(src);
        return ngx_http_image_asis(r, ctx);
    }

    colors = gdImageColorsTotal(src);
    transparent = gdImageGetTransparent(src);

    dx = sx;
    dy = sy;

    if (conf->filter == NGX_HTTP_IMAGE_RESIZE) {

        if ((ngx_uint_t) dx > conf->width) {
            dy = dy * conf->width / dx;
            dy = dy ? dy : 1;
            dx = conf->width;
        }

        if ((ngx_uint_t) dy > conf->height) {
            dx = dx * conf->height / dy;
            dx = dx ? dx : 1;
            dy = conf->height;
        }

        resize = 1;

    } else { /* NGX_HTTP_IMAGE_CROP */

        resize = 0;

        if ((ngx_uint_t) (dx * 100 / dy) < conf->width * 100 / conf->height) {

            if ((ngx_uint_t) dx > conf->width) {
                dy = dy * conf->width / dx;
                dy = dy ? dy : 1;
                dx = conf->width;
                resize = 1;
            }

        } else {
            if ((ngx_uint_t) dy > conf->height) {
                dx = dx * conf->height / dy;
                dx = dx ? dx : 1;
                dy = conf->height;
                resize = 1;
            }
        }
    }

    if (resize) {
        dst = ngx_http_image_new(r, dx, dy, colors);
        if (dst == NULL) {
            gdImageDestroy(src);
            return NULL;
        }

        gdImageCopyResampled(dst, src, 0, 0, 0, 0, dx, dy, sx, sy);

        gdImageDestroy(src);

    } else {
        dst = src;
    }

    if (conf->filter == NGX_HTTP_IMAGE_CROP) {

        src = dst;

        if ((ngx_uint_t) dx > conf->width) {
            ox = dx - conf->width;

        } else {
            ox = 0;
        }

        if ((ngx_uint_t) dy > conf->height) {
            oy = dy - conf->height;

        } else {
            oy = 0;
        }

        if (ox || oy) {

            dst = ngx_http_image_new(r, dx - ox, dy - oy, colors);

            if (dst == NULL) {
                gdImageDestroy(src);
                return NULL;
            }

            ox /= 2;
            oy /= 2;

            ngx_log_debug4(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                           "image crop: %d x %d @ %d x %d",
                           dx, dy, ox, oy);

            gdImageCopy(dst, src, 0, 0, ox, oy, dx - ox, dy - oy);

            gdImageDestroy(src);
        }
    }

    gdImageColorTransparent(dst, transparent);

    out = ngx_http_image_out(r, ctx->type, dst, &size);

    ngx_log_debug3(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "image: %d x %d %d", sx, sy, colors);

    gdImageDestroy(dst);
    ngx_pfree(r->pool, ctx->image);

    if (out == NULL) {
        return NULL;
    }

    cln = ngx_pool_cleanup_add(r->pool, 0);
    if (cln == NULL) {
        gdFree(out);
        return NULL;
    }

    b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t));
    if (b == NULL) {
        gdFree(out);
        return NULL;
    }

    cln->handler = ngx_http_image_cleanup;
    cln->data = out;

    b->pos = out;
    b->last = out + size;
    b->memory = 1;
    b->last_buf = 1;

    ngx_http_image_length(r, b);

    return b;
}


static gdImagePtr
ngx_http_image_source(ngx_http_request_t *r, ngx_http_image_filter_ctx_t *ctx)
{
    char        *failed;
    gdImagePtr   img;

    img = NULL;

    switch (ctx->type) {

    case NGX_HTTP_IMAGE_JPEG:
        img = gdImageCreateFromJpegPtr(ctx->length, ctx->image);
        failed = "gdImageCreateFromJpegPtr() failed";
        break;

    case NGX_HTTP_IMAGE_GIF:
        img = gdImageCreateFromGifPtr(ctx->length, ctx->image);
        failed = "gdImageCreateFromGifPtr() failed";
        break;

    case NGX_HTTP_IMAGE_PNG:
        img = gdImageCreateFromPngPtr(ctx->length, ctx->image);
        failed = "gdImageCreateFromPngPtr() failed";
        break;

    default:
        failed = "unknown image type";
        break;
    }

    if (img == NULL) {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, failed);
    }

    return img;
}


static gdImagePtr
ngx_http_image_new(ngx_http_request_t *r, int w, int h, int colors)
{
    gdImagePtr  img;

    if (colors == 0) {
        img = gdImageCreateTrueColor(w, h);

        if (img == NULL) {
            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                          "gdImageCreateTrueColor() failed");
            return NULL;
        }

    } else {
        img = gdImageCreate(w, h);

        if (img == NULL) {
            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                          "gdImageCreate() failed");
            return NULL;
        }
    }

    return img;
}


static u_char *
ngx_http_image_out(ngx_http_request_t *r, ngx_uint_t type, gdImagePtr img,
    int *size)
{
    char    *failed;
    u_char  *out;

    out = NULL;

    switch (type) {

    case NGX_HTTP_IMAGE_JPEG:
        out = gdImageJpegPtr(img, size, /* default quality */ -1);
        failed = "gdImageJpegPtr() failed";
        break;

    case NGX_HTTP_IMAGE_GIF:
        out = gdImageGifPtr(img, size);
        failed = "gdImageGifPtr() failed";
        break;

    case NGX_HTTP_IMAGE_PNG:
        out = gdImagePngPtr(img, size);
        failed = "gdImagePngPtr() failed";
        break;

    default:
        failed = "unknown image type";
        break;
    }

    if (out == NULL) {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, failed);
    }

    return out;
}


static void
ngx_http_image_cleanup(void *data)
{
    gdFree(data);
}


static void *
ngx_http_image_filter_create_conf(ngx_conf_t *cf)
{
    ngx_http_image_filter_conf_t  *conf;

    conf = ngx_pcalloc(cf->pool, sizeof(ngx_http_image_filter_conf_t));
    if (conf == NULL) {
        return NGX_CONF_ERROR;
    }

    conf->filter = NGX_CONF_UNSET_UINT;
    conf->buffer_size = NGX_CONF_UNSET_SIZE;

    return conf;
}


static char *
ngx_http_image_filter_merge_conf(ngx_conf_t *cf, void *parent, void *child)
{
    ngx_http_image_filter_conf_t *prev = parent;
    ngx_http_image_filter_conf_t *conf = child;

    if (conf->filter == NGX_CONF_UNSET_UINT) {

        if (prev->filter == NGX_CONF_UNSET_UINT) {
            conf->filter = NGX_HTTP_IMAGE_OFF;

        } else {
            conf->filter = prev->filter;
            conf->width = prev->width;
            conf->height = prev->height;
        }
    }

    ngx_conf_merge_size_value(conf->buffer_size, prev->buffer_size,
                              1 * 1024 * 1024);

    return NGX_CONF_OK;
}


static char *
ngx_http_image_filter(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_image_filter_conf_t *imcf = conf;

    ngx_str_t   *value;
    ngx_int_t    n;
    ngx_uint_t   i;

    value = cf->args->elts;

    i = 1;

    if (cf->args->nelts == 2) {
        if (ngx_strcmp(value[i].data, "off") == 0) {
            imcf->filter = NGX_HTTP_IMAGE_OFF;

        } else if (ngx_strcmp(value[i].data, "test") == 0) {
            imcf->filter = NGX_HTTP_IMAGE_TEST;

        } else if (ngx_strcmp(value[i].data, "size") == 0) {
            imcf->filter = NGX_HTTP_IMAGE_SIZE;

        } else {
            goto failed;
        }

        return NGX_CONF_OK;
    }

    if (ngx_strcmp(value[i].data, "resize") == 0) {
        imcf->filter = NGX_HTTP_IMAGE_RESIZE;

    } else if (ngx_strcmp(value[i].data, "crop") == 0) {
        imcf->filter = NGX_HTTP_IMAGE_CROP;

    } else {
        goto failed;
    }

    i++;

    if (value[i].len == 1 && value[i].data[0] == '-') {
        imcf->width = (ngx_uint_t) -1;

    } else {
        n = ngx_atoi(value[i].data, value[i].len);
        if (n == NGX_ERROR) {
            goto failed;
        }

        imcf->width = (ngx_uint_t) n;
    }

    i++;

    if (value[i].len == 1 && value[i].data[0] == '-') {
        imcf->height = (ngx_uint_t) -1;

    } else {
        n = ngx_atoi(value[i].data, value[i].len);
        if (n == NGX_ERROR) {
            goto failed;
        }

        imcf->height = (ngx_uint_t) n;
    }

    return NGX_CONF_OK;

failed:

    ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "invalid parameter \"%V\"",
                       &value[i]);

    return NGX_CONF_ERROR;
}


static ngx_int_t
ngx_http_image_filter_init(ngx_conf_t *cf)
{
    ngx_http_next_header_filter = ngx_http_top_header_filter;
    ngx_http_top_header_filter = ngx_http_image_header_filter;

    ngx_http_next_body_filter = ngx_http_top_body_filter;
    ngx_http_top_body_filter = ngx_http_image_body_filter;

    return NGX_OK;
}