/*
  * Decryption protocol handler
  * Copyright (c) 2011 Martin Storsjo
  *

  * This file is part of FFmpeg.

  *

  * FFmpeg 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.
  *

  * FFmpeg 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 FFmpeg; 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"
 

 // encourage reads of 4096 bytes - 1 block is always retained.
 #define MAX_BUFFER_BLOCKS 257

 #define BLOCKSIZE 16
 

 typedef struct CryptoContext {

     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;

     int64_t position;  // position in file - used in seek
     int flags;

     int eof;
     uint8_t *key;
     int keylen;
     uint8_t *iv;
     int ivlen;

     uint8_t *decrypt_key;
     int decrypt_keylen;
     uint8_t *decrypt_iv;
     int decrypt_ivlen;
     uint8_t *encrypt_key;
     int encrypt_keylen;
     uint8_t *encrypt_iv;
     int encrypt_ivlen;
     struct AVAES *aes_decrypt;
     struct AVAES *aes_encrypt;

     uint8_t *write_buf;
     unsigned int write_buf_size;

     uint8_t pad[BLOCKSIZE];
     int pad_len;

 } CryptoContext;
 
 #define OFFSET(x) offsetof(CryptoContext, x)

 #define D AV_OPT_FLAG_DECODING_PARAM

 #define E AV_OPT_FLAG_ENCODING_PARAM

 static const AVOption options[] = {

     {"key", "AES encryption/decryption key",                   OFFSET(key),         AV_OPT_TYPE_BINARY, .flags = D|E },
     {"iv",  "AES encryption/decryption initialization vector", OFFSET(iv),          AV_OPT_TYPE_BINARY, .flags = D|E },
     {"decryption_key", "AES decryption key",                   OFFSET(decrypt_key), AV_OPT_TYPE_BINARY, .flags = D },
     {"decryption_iv",  "AES decryption initialization vector", OFFSET(decrypt_iv),  AV_OPT_TYPE_BINARY, .flags = D },
     {"encryption_key", "AES encryption key",                   OFFSET(encrypt_key), AV_OPT_TYPE_BINARY, .flags = E },
     {"encryption_iv",  "AES encryption initialization vector", OFFSET(encrypt_iv),  AV_OPT_TYPE_BINARY, .flags = E },

     { NULL }
 };
 
 static const AVClass crypto_class = {

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

 };
 

 static int set_aes_arg(URLContext *h, uint8_t **buf, int *buf_len,

                        uint8_t *default_buf, int default_buf_len,
                        const char *desc)
 {
     if (!*buf_len) {
         if (!default_buf_len) {

             av_log(h, AV_LOG_ERROR, "%s not set\n", desc);

             return AVERROR(EINVAL);
         } else if (default_buf_len != BLOCKSIZE) {

             av_log(h, AV_LOG_ERROR,

                    "invalid %s size (%d bytes, block size is %d)\n",
                    desc, default_buf_len, BLOCKSIZE);
             return AVERROR(EINVAL);
         }

         *buf = av_memdup(default_buf, default_buf_len);

         if (!*buf)
             return AVERROR(ENOMEM);
         *buf_len = default_buf_len;
     } else if (*buf_len != BLOCKSIZE) {

         av_log(h, AV_LOG_ERROR,

                "invalid %s size (%d bytes, block size is %d)\n",
                desc, *buf_len, BLOCKSIZE);
         return AVERROR(EINVAL);
     }
     return 0;
 }
 

 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;

     c->flags = flags;

 
     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 (flags & AVIO_FLAG_READ) {

         if ((ret = set_aes_arg(h, &c->decrypt_key, &c->decrypt_keylen,

                                c->key, c->keylen, "decryption key")) < 0)
             goto err;

         if ((ret = set_aes_arg(h, &c->decrypt_iv, &c->decrypt_ivlen,

                                c->iv, c->ivlen, "decryption IV")) < 0)

             goto err;

     }

     if (flags & AVIO_FLAG_WRITE) {

         if ((ret = set_aes_arg(h, &c->encrypt_key, &c->encrypt_keylen,

                                c->key, c->keylen, "encryption key")) < 0)
         if (ret < 0)
             goto err;

         if ((ret = set_aes_arg(h, &c->encrypt_iv, &c->encrypt_ivlen,

                                c->iv, c->ivlen, "encryption IV")) < 0)

             goto err;

     }

     if ((ret = ffurl_open_whitelist(&c->hd, nested_url, flags,
                                     &h->interrupt_callback, options,

                                     h->protocol_whitelist, h->protocol_blacklist, h)) < 0) {

         av_log(h, AV_LOG_ERROR, "Unable to open resource: %s\n", nested_url);

         goto err;
     }

 
     if (flags & AVIO_FLAG_READ) {
         c->aes_decrypt = av_aes_alloc();
         if (!c->aes_decrypt) {
             ret = AVERROR(ENOMEM);
             goto err;
         }

         ret = av_aes_init(c->aes_decrypt, c->decrypt_key, BLOCKSIZE * 8, 1);

         if (ret < 0)
             goto err;

 
         // pass back information about the context we openned
         if (c->hd->is_streamed)
             h->is_streamed = c->hd->is_streamed;

     }
 

     if (flags & AVIO_FLAG_WRITE) {
         c->aes_encrypt = av_aes_alloc();
         if (!c->aes_encrypt) {
             ret = AVERROR(ENOMEM);
             goto err;
         }

         ret = av_aes_init(c->aes_encrypt, c->encrypt_key, BLOCKSIZE * 8, 0);

         if (ret < 0)
             goto err;

         // for write, we must be streamed
         // - linear write only for crytpo aes-128-cbc
         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;

         c->position = c->position + 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_decrypt, c->outbuffer, c->inbuffer + c->indata_used,
                  blocks, c->decrypt_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 int64_t crypto_seek(URLContext *h, int64_t pos, int whence)
 {
     CryptoContext *c = h->priv_data;
     int64_t block;
     int64_t newpos;
 
     if (c->flags & AVIO_FLAG_WRITE) {
         av_log(h, AV_LOG_ERROR,
             "Crypto: seek not supported for write\r\n");
         /* seems the most appropriate error to return */
         return AVERROR(ESPIPE);
     }
 
     // reset eof, else we won't read it correctly if we already hit eof.
     c->eof = 0;
 
     switch (whence) {
     case SEEK_SET:
         break;
     case SEEK_CUR:
         pos = pos + c->position;
         break;
     case SEEK_END: {
         int64_t newpos = ffurl_seek( c->hd, pos, AVSEEK_SIZE );
         if (newpos < 0) {
             av_log(h, AV_LOG_ERROR,
                 "Crypto: seek_end - can't get file size (pos=%lld)\r\n", (long long int)pos);
             return newpos;
         }
         pos = newpos - pos;
         }
         break;
     case AVSEEK_SIZE: {
         int64_t newpos = ffurl_seek( c->hd, pos, AVSEEK_SIZE );
         return newpos;
         }
         break;
     default:
         av_log(h, AV_LOG_ERROR,
             "Crypto: no support for seek where 'whence' is %d\r\n", whence);
         return AVERROR(EINVAL);
     }
 
     c->outdata = 0;
     c->indata = 0;
     c->indata_used = 0;
     c->outptr = c->outbuffer;
 
     // identify the block containing the IV for the
     // next block we will decrypt
     block = pos/BLOCKSIZE;
     if (block == 0) {
         // restore the iv to the seed one - this is the iv for the FIRST block
         memcpy( c->decrypt_iv, c->iv, c->ivlen );
         c->position = 0;
     } else {
         // else, go back one block - we will get av_cyrpt to read this block
         // which it will then store use as the iv.
         // note that the DECRYPTED result will not be correct,
         // but will be discarded
         block--;
         c->position = (block * BLOCKSIZE);
     }
 
     newpos = ffurl_seek( c->hd, c->position, SEEK_SET );
     if (newpos < 0) {
         av_log(h, AV_LOG_ERROR,
             "Crypto: nested protocol no support for seek or seek failed\n");
         return newpos;
     }
 
     // read and discard from here up to required position
     // (which will set the iv correctly to it).
     if (pos - c->position) {
         uint8_t buff[BLOCKSIZE*2]; // maximum size of pos-c->position
         int len = pos - c->position;
         int res;
 
         while (len > 0) {
             // note: this may not return all the bytes first time
             res = crypto_read(h, buff, len);
             if (res < 0)
                 break;
             len -= res;
         }
 
         // if we did not get all the bytes
         if (len != 0) {
             char errbuf[100] = "unknown error";
             av_strerror(res, errbuf, sizeof(errbuf));
             av_log(h, AV_LOG_ERROR,
                 "Crypto: discard read did not get all the bytes (%d remain) - read returned (%d)-%s\n",
                 len, res, errbuf);
             return AVERROR(EINVAL);
         }
     }
 
     return c->position;
 }
 

 static int crypto_write(URLContext *h, const unsigned char *buf, int size)
 {
     CryptoContext *c = h->priv_data;
     int total_size, blocks, pad_len, out_size;
     int ret = 0;
 
     total_size = size + c->pad_len;
     pad_len = total_size % BLOCKSIZE;
     out_size = total_size - pad_len;
     blocks = out_size / BLOCKSIZE;
 
     if (out_size) {

         av_fast_malloc(&c->write_buf, &c->write_buf_size, out_size);
 
         if (!c->write_buf)

             return AVERROR(ENOMEM);
 
         if (c->pad_len) {
             memcpy(&c->pad[c->pad_len], buf, BLOCKSIZE - c->pad_len);

             av_aes_crypt(c->aes_encrypt, c->write_buf, c->pad, 1, c->encrypt_iv, 0);

             blocks--;
         }
 

         av_aes_crypt(c->aes_encrypt,
                      &c->write_buf[c->pad_len ? BLOCKSIZE : 0],
                      &buf[c->pad_len ? BLOCKSIZE - c->pad_len : 0],
                      blocks, c->encrypt_iv, 0);

         ret = ffurl_write(c->hd, c->write_buf, out_size);

         if (ret < 0)
             return ret;
 
         memcpy(c->pad, &buf[size - pad_len], pad_len);
     } else
         memcpy(&c->pad[c->pad_len], buf, size);
 
     c->pad_len = pad_len;
 
     return size;
 }
 

 static int crypto_close(URLContext *h)
 {
     CryptoContext *c = h->priv_data;

     int ret = 0;

 
     if (c->aes_encrypt) {

         uint8_t out_buf[BLOCKSIZE];
         int pad = BLOCKSIZE - c->pad_len;
 

         memset(&c->pad[c->pad_len], pad, pad);
         av_aes_crypt(c->aes_encrypt, out_buf, c->pad, 1, c->encrypt_iv, 0);

         ret = ffurl_write(c->hd, out_buf, BLOCKSIZE);

     }
 

     if (c->hd)
         ffurl_close(c->hd);

     av_freep(&c->aes_decrypt);
     av_freep(&c->aes_encrypt);

     av_freep(&c->write_buf);
     return ret;

 }
 

 const URLProtocol ff_crypto_protocol = {

     .name            = "crypto",

     .url_open2       = crypto_open2,

     .url_seek        = crypto_seek,

     .url_read        = crypto_read,

     .url_write       = crypto_write,

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