/*
  * Decryption protocol handler
  * Copyright (c) 2011 Martin Storsjo
  *
  * This file is part of Libav.
  *
  * Libav is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * Libav is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with Libav; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 #include "avformat.h"
 #include "libavutil/aes.h"
 #include "libavutil/avstring.h"
 #include "libavutil/opt.h"
 #include "internal.h"
 #include "url.h"
 
 #define MAX_BUFFER_BLOCKS 150
 #define BLOCKSIZE 16
 
 typedef struct {
     const AVClass *class;
     URLContext *hd;
     uint8_t inbuffer [BLOCKSIZE*MAX_BUFFER_BLOCKS],
             outbuffer[BLOCKSIZE*MAX_BUFFER_BLOCKS];
     uint8_t *outptr;
     int indata, indata_used, outdata;
     int eof;
     uint8_t *key;
     int keylen;
     uint8_t *iv;
     int ivlen;
     struct AVAES *aes;
 } CryptoContext;
 
 #define OFFSET(x) offsetof(CryptoContext, x)

 #define D AV_OPT_FLAG_DECODING_PARAM

 static const AVOption options[] = {

     {"key", "AES decryption key", OFFSET(key), AV_OPT_TYPE_BINARY, .flags = D },

     {"iv",  "AES decryption initialization vector", OFFSET(iv), AV_OPT_TYPE_BINARY, .flags = D },

     { NULL }
 };
 
 static const AVClass crypto_class = {

     .class_name     = "crypto",
     .item_name      = av_default_item_name,
     .option         = options,
     .version        = LIBAVUTIL_VERSION_INT,

 };
 

 static int crypto_open2(URLContext *h, const char *uri, int flags, AVDictionary **options)

 {
     const char *nested_url;

     int ret = 0;

     CryptoContext *c = h->priv_data;
 
     if (!av_strstart(uri, "crypto+", &nested_url) &&
         !av_strstart(uri, "crypto:", &nested_url)) {
         av_log(h, AV_LOG_ERROR, "Unsupported url %s\n", uri);
         ret = AVERROR(EINVAL);
         goto err;
     }
 
     if (c->keylen < BLOCKSIZE || c->ivlen < BLOCKSIZE) {
         av_log(h, AV_LOG_ERROR, "Key or IV not set\n");
         ret = AVERROR(EINVAL);
         goto err;
     }
     if (flags & AVIO_FLAG_WRITE) {
         av_log(h, AV_LOG_ERROR, "Only decryption is supported currently\n");
         ret = AVERROR(ENOSYS);
         goto err;
     }

     if ((ret = ffurl_open(&c->hd, nested_url, AVIO_FLAG_READ,

                           &h->interrupt_callback, options)) < 0) {

         av_log(h, AV_LOG_ERROR, "Unable to open input\n");
         goto err;
     }

     c->aes = av_aes_alloc();

     if (!c->aes) {
         ret = AVERROR(ENOMEM);
         goto err;
     }
 
     av_aes_init(c->aes, c->key, 128, 1);
 
     h->is_streamed = 1;
 
 err:
     return ret;
 }
 
 static int crypto_read(URLContext *h, uint8_t *buf, int size)
 {
     CryptoContext *c = h->priv_data;
     int blocks;
 retry:
     if (c->outdata > 0) {
         size = FFMIN(size, c->outdata);
         memcpy(buf, c->outptr, size);
         c->outptr  += size;
         c->outdata -= size;
         return size;
     }
     // We avoid using the last block until we've found EOF,
     // since we'll remove PKCS7 padding at the end. So make
     // sure we've got at least 2 blocks, so we can decrypt
     // at least one.
     while (c->indata - c->indata_used < 2*BLOCKSIZE) {
         int n = ffurl_read(c->hd, c->inbuffer + c->indata,
                            sizeof(c->inbuffer) - c->indata);
         if (n <= 0) {
             c->eof = 1;
             break;
         }
         c->indata += n;
     }
     blocks = (c->indata - c->indata_used) / BLOCKSIZE;
     if (!blocks)
         return AVERROR_EOF;
     if (!c->eof)
         blocks--;
     av_aes_crypt(c->aes, c->outbuffer, c->inbuffer + c->indata_used, blocks,
                  c->iv, 1);
     c->outdata      = BLOCKSIZE * blocks;
     c->outptr       = c->outbuffer;
     c->indata_used += BLOCKSIZE * blocks;
     if (c->indata_used >= sizeof(c->inbuffer)/2) {
         memmove(c->inbuffer, c->inbuffer + c->indata_used,
                 c->indata - c->indata_used);
         c->indata     -= c->indata_used;
         c->indata_used = 0;
     }
     if (c->eof) {
         // Remove PKCS7 padding at the end
         int padding = c->outbuffer[c->outdata - 1];
         c->outdata -= padding;
     }
     goto retry;
 }
 
 static int crypto_close(URLContext *h)
 {
     CryptoContext *c = h->priv_data;
     if (c->hd)
         ffurl_close(c->hd);

     av_freep(&c->aes);

     return 0;
 }
 
 URLProtocol ff_crypto_protocol = {
     .name            = "crypto",

     .url_open2       = crypto_open2,

     .url_read        = crypto_read,
     .url_close       = crypto_close,
     .priv_data_size  = sizeof(CryptoContext),
     .priv_data_class = &crypto_class,
     .flags           = URL_PROTOCOL_FLAG_NESTED_SCHEME,
 };