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134 lines
2.9 KiB
134 lines
2.9 KiB
/************************************************************************
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** 此文件实现了 URLProtocol 抽象层广义文件操作函数，
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** 由于 URLProtocol 是底层其他具体文件(file,pipe 等)的简单封装，
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** 这一层只是一个中转站，大部分函数都是简单中转到底层的具体实现函数
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/************************************************************************/
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#include "../berrno.h"
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#include "avformat.h"
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/* ffmpeg可以支持多种协议，用链表把所有支持的协议串起来 */
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URLProtocol *first_protocol = NULL;
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/* 注册协议（所谓协议就是输入数据的载体：文件、套接字等形式） */
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int register_protocol(URLProtocol *protocol)
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{
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URLProtocol **p;
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p = &first_protocol;
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while (*p != NULL)
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p = &(*p)->next;
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*p = protocol;
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protocol->next = NULL;
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return 0;
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}
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/* 打开URL */
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int url_open(URLContext **puc, const char *filename, int flags)
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{
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// 上下文
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URLContext *uc;
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// 协议及操作
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URLProtocol *up;
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const char *p;
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// 协议字符串
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char proto_str[128], *q;
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int err;
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p = filename;
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q = proto_str;
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// 确定协议的名字
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while (*p != '\0' && *p != ':')
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{
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if (!isalpha(*p)) // protocols can only contain alphabetic chars
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goto file_proto;
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if ((q - proto_str) < sizeof(proto_str) - 1)
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*q++ = *p;
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p++;
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}
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// if the protocol has length 1, we consider it is a dos drive
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if (*p == '\0' || (q - proto_str) <= 1)
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{
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file_proto:
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strcpy(proto_str, "file");
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}
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else
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{
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*q = '\0';
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}
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up = first_protocol;
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// 寻找合适协议
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while (up != NULL)
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{
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if (!strcmp(proto_str, up->name))
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goto found;
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up = up->next;
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}
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err = - ENOENT;
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goto fail;
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found:
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// URL上下文
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uc = av_malloc(sizeof(URLContext) + strlen(filename));
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if (!uc)
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{
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err = - ENOMEM;
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goto fail;
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}
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strcpy(uc->filename, filename);
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uc->prot = up;
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uc->flags = flags;
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uc->max_packet_size = 0; // default: stream file
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// 打开URL
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err = up->url_open(uc, filename, flags);
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if (err < 0)
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{
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av_free(uc);
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*puc = NULL;
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return err;
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}
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*puc = uc;
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return 0;
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fail:
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*puc = NULL;
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return err;
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}
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/* 读取数据 */
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int url_read(URLContext *h, unsigned char *buf, int size)
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{
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int ret;
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if (h->flags &URL_WRONLY)
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return AVERROR_IO;
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ret = h->prot->url_read(h, buf, size);
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return ret;
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}
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/* 在广义文件中跳转 */
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offset_t url_seek(URLContext *h, offset_t pos, int whence)
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{
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offset_t ret;
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if (!h->prot->url_seek)
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return - EPIPE;
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ret = h->prot->url_seek(h, pos, whence);
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return ret;
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}
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/* 关闭URL */
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int url_close(URLContext *h)
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{
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int ret;
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ret = h->prot->url_close(h);
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av_free(h);
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return ret;
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}
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int url_get_max_packet_size(URLContext *h)
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{
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return h->max_packet_size;
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}
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