关于android:修改linphonesdkandroid下篇

前言

接上篇批改 linphone-sdk-android- 上篇

接中篇批改 linphone-sdk-android- 中篇

本文是下篇，本篇记录在上篇中提到的问题 1 排查过程及修复计划，尽量形容排查问题过程中的思路与方向

上篇中说问题 1 当初认为是 linphone 的 bug，前面看源码及查资料发现可能不是 bug，本篇将记录集体的了解

问题

这里再形容下问题 1：关上音频编解码 G722、G729 等时，发动呼叫的 INVITE SDP 中，没有 G722、G729 的rtpmap

m=audio 7078 RTP/AVP 96 0 8 9 18 101 97
a=fmtp:18 annexb=yes
a=rtpmap:101 telephone-event/48000
a=rtpmap:97 telephone-event/8000
a=rtcp-fb:* trr-int 1000
a=rtcp-fb:* ccm tmmbr

剖析

这里先理解下 SDP 协定，参考 The Session Description Protocol (SDP) (3cx.com)

rtpmap是 Session attribute lines，即为会话属性行，是对Payload Type 的补充阐明，Payload Type既是 m=audio 7078 RTP/AVP 96 0 8 9 18 101 97 中AVP前面的数字，这些数字是音频编解码对应的代码，对应关系如下：

下表源自 Real-Time Transport Protocol (RTP) Parameters (iana.org)

从表中理解到，Payload Type(PT) code 0 – 95 为动态类型，即 code 对应固定的 codec(编解码器)，96 – 127 为动静 codec，即须要在 SDP 协商过程中确定

接下来追踪下源码，看看 SDP 中为什么没有rtpmap

先找到 Java 层发动呼叫的代码，在 Core.java 中有 4 个发动呼叫的办法

@Nullable
Call invite(@NonNull String var1);

@Nullable
Call inviteAddress(@NonNull Address var1);

@Nullable
Call inviteAddressWithParams(@NonNull Address var1, @NonNull CallParams var2);

@Nullable
Call inviteWithParams(@NonNull String var1, @NonNull CallParams var2);

具体实现在 CoreImpl.java 中，查看这个 public Call inviteAddress(@NonNull Address addr); 办法吧

private native Call inviteAddress(long nativePtr, Address addr);

@Override @Nullable
synchronized public Call inviteAddress(@NonNull Address addr)  {return (Call)inviteAddress(nativePtr, addr);
}

Java层调用了 native 层代码，关上编译后生成的 linphone_jni.cc，找到Java_org_linphone_core_CoreImpl_inviteAddress 办法

JNIEXPORT jobject JNICALL Java_org_linphone_core_CoreImpl_inviteAddress(JNIEnv *env, jobject thiz, jlong ptr, jobject addr) {LinphoneCore *cptr = (LinphoneCore*)ptr;
    if (cptr == nullptr) {bctbx_error("Java_org_linphone_core_CoreImpl_inviteAddress's LinphoneCore C ptr is null!");
        return 0;
    }
    
    LinphoneAddress* c_addr = nullptr;
    if (addr) c_addr = (LinphoneAddress*)GetObjectNativePtr(env, addr);
    
    jobject jni_result = (jobject)getCall(env, (LinphoneCall *)linphone_core_invite_address(cptr, c_addr), TRUE);
    return jni_result;
}

在 native 层调用了 linphone_core_invite_address 这个办法，在 IDE 中，能够通过 Ctrl+ 左键点击进行跳转，linphone_core_invite_address位于 linphonecore.c 中

LinphoneCall * linphone_core_invite_address(LinphoneCore *lc, const LinphoneAddress *addr){
    LinphoneCall *call;
    LinphoneCallParams *p=linphone_core_create_call_params(lc, NULL);
    linphone_call_params_enable_video(p, linphone_call_params_video_enabled(p) && !!lc->video_policy.automatically_initiate);
    call=linphone_core_invite_address_with_params (lc,addr,p);
    linphone_call_params_unref(p);
    return call;
}

在 linphone_core_invite_address 办法中调用了 linphone_core_invite_address_with_params 发动呼叫，这个办法较长，删减一些不关怀的代码

LinphoneCall * linphone_core_invite_address_with_params(LinphoneCore *lc, const LinphoneAddress *addr, const LinphoneCallParams *params){
    const char *from=NULL;
    LinphoneCall *call;
    
    if (!addr) {ms_error("Can't invite a NULL address");
        return NULL;
    }

    parsed_url2=linphone_address_new(from);
    call=linphone_call_new_outgoing(lc,parsed_url2,addr,cp,proxy);
    
    bool defer = Call::toCpp(call)->initiateOutgoing();
    if (!defer) {if (Call::toCpp(call)->startInvite(nullptr) != 0) {
            /* The call has already gone to error and released state, so do not return it */
            call = nullptr;
        }
    }

    return call;
}

在 linphone_core_invite_address_with_params 办法中调用 linphone_call_new_outgoing 办法创立 Call 对象，调用 initiateOutgoing 办法初始化发动呼叫并设置以后状态为 OutgoingInit，接下来调用startInvite 办法发动呼叫，startInvite办法位于 call.cpp 中，在其中又调用 getActiveSession 办法获取 CallSession，调用CallSession::startInvite 办法

int Call::startInvite (const Address *destination) {return getActiveSession()->startInvite(destination, "");
}

CallSession::startInvite办法位于 call-session.cpp 中，在这个办法中找了半天，没见有与 SDP 发送相干的逻辑，先去头文件中看看办法原型吧

找了半天也是有点播种的，剖析出调用 addAdditionalLocalBody 去组装自定义扩大头数据

int CallSession::startInvite (const Address *destination, const string &subject, const Content *content) {L_D();
    d->subject = subject;
    /* Try to be best-effort in giving real local or routable contact address */
    d->setContactOp();
    string destinationStr;
    char *realUrl = nullptr;
    if (destination)
        destinationStr = destination->asString();
    else {realUrl = linphone_address_as_string(d->log->to);
        destinationStr = realUrl;
        ms_free(realUrl);
    }
    char *from = linphone_address_as_string(d->log->from);
    /* Take a ref because sal_call() may destroy the CallSession if no SIP transport is available */
    shared_ptr<CallSession> ref = getSharedFromThis();
    if (content)
        d->op->setLocalBody(*content);

    // If a custom Content has been set in the call params, create a multipart body for the INVITE
    for (auto& content : d->params->getCustomContents()) {d->op->addAdditionalLocalBody(content);
    }

    int result = d->op->call(from, destinationStr, subject);
    ms_free(from);
    if (result < 0) {if ((d->state != CallSession::State::Error) && (d->state != CallSession::State::Released)) {// sal_call() may invoke call_failure() and call_released() SAL callbacks synchronously,
            // in which case there is no need to perform a state change here.
            d->setState(CallSession::State::Error, "Call failed");
        }
    } else {linphone_call_log_set_call_id(d->log, d->op->getCallId().c_str()); /* Must be known at that time */
        d->setState(CallSession::State::OutgoingProgress, "Outgoing call in progress");
    }
    return result;
}

CallSession::startInvite办法原型为，

virtual int startInvite (const Address *destination, const std::string &subject = "", const Content *content = nullptr);

是个 virtual 虚函数，阐明有函数复写，在 IDE 中搜寻发现 MediaSession 类继承自 CallSession，好的，找到MediaSession 复写的 startInvite 办法，办法较长，删除一些不关怀的代码

int MediaSession::startInvite (const Address *destination, const string &subject, const Content *content) {L_D();
    
    // 删除不关怀的代码

    d->op->setLocalMediaDescription(d->localDesc);

    int result = CallSession::startInvite(destination, subject, content);
    if (result < 0) {if (d->state == CallSession::State::Error)
            d->stopStreams();
        return result;
    }
    return result;
}

在 MediaSession::startInvite 中调用 setLocalMediaDescription 办法组装本地媒体形容信息，最初再调用父类的 CallSession::startInvite 办法持续发动呼叫，好的，当初只关怀 setLocalMediaDescription 办法，其中 op 是SalCallOp，在 IDE 中关上 call-op.cpp，找到setLocalMediaDescription 办法，删减一些不关怀的代码

int SalCallOp::setLocalMediaDescription (SalMediaDescription *desc) {if (desc) {sal_media_description_ref(desc);
        belle_sip_error_code error;
        belle_sdp_session_description_t *sdp = media_description_to_sdp(desc);
        vector<char> buffer = marshalMediaDescription(sdp, error);
        belle_sip_object_unref(sdp);
        if (error != BELLE_SIP_OK)
            return -1;

        mLocalBody.setContentType(ContentType::Sdp);
        mLocalBody.setBody(move(buffer));
    } else {mLocalBody = Content();
    }
    return 0;
}

到这里终于发现与 SDP 相干的办法了 media_description_to_sdp，持续查看media_description_to_sdp 办法，此办法位于 sal_sdp.c 中，办法较长，次要是组装 SDP 协定数据，比方设置版本、创立源信息，创立会话等，这里删减一些不关怀的代码

belle_sdp_session_description_t * media_description_to_sdp(const SalMediaDescription *desc) {belle_sdp_session_description_t* session_desc=belle_sdp_session_description_new();
    bool_t inet6;
    belle_sdp_origin_t* origin;
    int i;
    char *escaped_username = belle_sip_uri_to_escaped_username(desc->username);

    if (strchr ( desc->addr,':') !=NULL ) {inet6=1;} else inet6=0;
    belle_sdp_session_description_set_version (session_desc,belle_sdp_version_create ( 0) );

    origin = belle_sdp_origin_create ( escaped_username
                                      ,desc->session_id
                                      ,desc->session_ver
                                      ,"IN"
                                      , inet6 ? "IP6" :"IP4"
                                      ,desc->addr );
    bctbx_free(escaped_username);

    belle_sdp_session_description_set_origin (session_desc,origin);

    belle_sdp_session_description_set_session_name ( session_desc,
        belle_sdp_session_name_create (desc->name[0]!='\0' ? desc->name : "Talk" ) );

    // 删减不关怀的代码

    for (i=0; i<desc->nb_streams; i++) {stream_description_to_sdp(session_desc, desc, &desc->streams[i]);
    }
    return session_desc;
}

剖析 media_description_to_sdp 办法找到在 stream_description_to_sdp 办法中组装数据流信息到 SDP 协定中，stream_description_to_sdp办法十分长，此办法次要是组装 SDP 协定中编解码相干的信息，这里删除大部分不关怀的代码

static void stream_description_to_sdp (belle_sdp_session_description_t *session_desc, const SalMediaDescription *md, const SalStreamDescription *stream) {
    
    // 删减不关怀的代码

    media_desc = belle_sdp_media_description_create (sal_stream_description_get_type_as_string(stream)
                 ,stream->rtp_port
                 ,1
                 ,sal_media_proto_to_string (stream->proto)
                 ,NULL );
    // 看到 payloads 字段
    if (stream->payloads) {for ( pt_it=stream->payloads; pt_it!=NULL; pt_it=pt_it->next) {pt= ( PayloadType*) pt_it->data;
            mime_param= belle_sdp_mime_parameter_create ( pt->mime_type
                    , payload_type_get_number (pt)
                    , pt->clock_rate
                    , pt->channels>0 ? pt->channels : -1 );
            belle_sdp_mime_parameter_set_parameters (mime_param,pt->recv_fmtp);
            if (stream->ptime>0) {belle_sdp_mime_parameter_set_ptime ( mime_param,stream->ptime);
            }
            // 锁定此办法
            belle_sdp_media_description_append_values_from_mime_parameter (media_desc,mime_param);
            belle_sip_object_unref (mime_param);
        }
    } else {
        /* to comply with SDP we cannot have an empty payload type number list */
        /* as it happens only when mline is declined with a zero port, it does not matter to put whatever codec*/
        belle_sip_list_t* format = belle_sip_list_append(NULL,0);
        belle_sdp_media_set_media_formats(belle_sdp_media_description_get_media(media_desc),format);
    }

    // 组装自定义 sdp 属性
    if (stream->custom_sdp_attributes) {belle_sdp_session_description_t *custom_desc = (belle_sdp_session_description_t *)stream->custom_sdp_attributes;
        belle_sip_list_t *l = belle_sdp_session_description_get_attributes(custom_desc);
        belle_sip_list_t *elem;
        for (elem = l; elem != NULL; elem = elem->next) {belle_sdp_media_description_add_attribute(media_desc, (belle_sdp_attribute_t *)elem->data);
        }
    }
    
    // 删减不关怀的代码
}

在 stream_description_to_sdp 办法中看到 payload 字段，马上就要找到了 happy~

通过剖析，锁定 belle_sdp_media_description_append_values_from_mime_parameter 办法，剖析此办法，在其中找到组装 rtpmap 的源码

void belle_sdp_media_description_append_values_from_mime_parameter(belle_sdp_media_description_t* media_description, const belle_sdp_mime_parameter_t* mime_parameter) {
    
#ifndef BELLE_SDP_FORCE_RTP_MAP /* defined to for RTP map even for static codec*/
    if (!mime_parameter_is_static(mime_parameter)) {
        /*dynamic payload*/
#endif
        if (belle_sdp_mime_parameter_get_channel_count(mime_parameter)>1) {
            snprintf(atribute_value,MAX_FMTP_LENGTH,"%i %s/%i/%i"
                    ,belle_sdp_mime_parameter_get_media_format(mime_parameter)
                    ,belle_sdp_mime_parameter_get_type(mime_parameter)
                    ,belle_sdp_mime_parameter_get_rate(mime_parameter)
                    ,belle_sdp_mime_parameter_get_channel_count(mime_parameter));
        } else {
            snprintf(atribute_value,MAX_FMTP_LENGTH,"%i %s/%i"
                    ,belle_sdp_mime_parameter_get_media_format(mime_parameter)
                    ,belle_sdp_mime_parameter_get_type(mime_parameter)
                    ,belle_sdp_mime_parameter_get_rate(mime_parameter));
        }
        belle_sdp_media_description_set_attribute_value(media_description,"rtpmap",atribute_value);
#ifndef BELLE_SDP_FORCE_RTP_MAP
    }
#endif
    
    // always include fmtp parameters if available
    if (belle_sdp_mime_parameter_get_parameters(mime_parameter)) {
        snprintf(atribute_value,MAX_FMTP_LENGTH,"%i %s"
                ,belle_sdp_mime_parameter_get_media_format(mime_parameter)
                ,belle_sdp_mime_parameter_get_parameters(mime_parameter));
        belle_sdp_media_description_set_attribute_value(media_description,"fmtp",atribute_value);
    }
}

这里先剖析下 mime_parameter_is_static 办法是干什么的？查看以下源码发现，噢~~，原来是用于判断编解码是否是动态类型(后面提到的 Payload Type)

const struct static_payload static_payload_list [] ={
    /*audio*/
    {0,1,"PCMU",8000},
    {3,1,"GSM",8000},
    {4,1,"G723",8000},
    {5,1,"DVI4",8000},
    {6,1,"DVI4",16000},
    {7,1,"LPC",8000},
    {8,1,"PCMA",8000},
    {9,1,"G722",8000},
    {10,2,"L16",44100},
    {11,1,"L16",44100},
    {12,1,"QCELP",8000},
    {13,1,"CN",8000},
    {14,1,"MPA",90000},
    {15,1,"G728",8000},
    {16,1,"DVI4",11025},
    {17,1,"DVI4",22050},
    {18,1,"G729",8000},
    /*video*/
    {25,0,"CelB",90000},
    {26,0,"JPEG",90000},
    {28,0,"nv",90000},
    {31,0,"H261",90000},
    {32,0,"MPV",90000},
    {33,0,"MP2T",90000},
    {34,0,"H263",90000}
};

static int mime_parameter_is_static(const belle_sdp_mime_parameter_t *param){
    const struct static_payload* iterator;
    size_t i;

    for (iterator = static_payload_list,i=0;i<payload_list_elements;i++,iterator++) {
        if (iterator->number == param->media_format &&
            strcasecmp(iterator->type,param->type)==0 &&
            iterator->channel_count==param->channel_count &&
            iterator->rate==param->rate ) {return TRUE;}
    }
    return FALSE;
}

当初再来剖析下 belle_sdp_media_description_append_values_from_mime_parameter 办法的意思，粗心如下：如果没有定义 BELLE_SDP_FORCE_RTP_MAP 这个宏就执行 if (!mime_parameter_is_static(mime_parameter)) 判断编解码是否是动态类型，如果定义了就不判断是否是动态类型

总结一下就是如果没有定义 BELLE_SDP_FORCE_RTP_MAP 这个宏，就不组装动态类型编解码的 rtpmap 信息，只组装动静类型编解码的 rtpmap 信息，终于找到源头了，真是拨云见日呀

到这里还没完，既然是依据宏定义做的判断，必定在编译的时候能够配置，先看看能不能找到定义宏的中央，在 IDE 中全局搜寻，在 belle-sip 下的 CMakeList.txt 中发现

option(ENABLE_RTP_MAP_ALWAYS_IN_SDP "Always include rtpmap in SDP." OFF)

if(ENABLE_RTP_MAP_ALWAYS_IN_SDP) 
    set(BELLE_SDP_FORCE_RTP_MAP 1)
endif()

bingo~，真的是到最初了

最初在编译时减少编译配置项

$ cd linphone-sdk/build/
$ cmake -DENABLE_RTP_MAP_ALWAYS_IN_SDP=ON ..
$ cmake --build . --parallel 8

从新编译后拷贝到 AS 中运行，发动呼叫查看 Logcat 输入

总结

在源码中看到通过 BELLE_SDP_FORCE_RTP_MAP 这个宏管制是否在 SDP 中蕴含动态类型编解码的 rtpmap 信息，集体猜想是动态类型的编解码信息，是协定中固定的，任何遵循协定的实现方，都能够依据动态类型编解码对应的 code 解析出相应的 rtpmap 信息，所以在 SDP 中去掉动态类型编解码器的 rtpmap 信息，同时也能够缩小发送数据包的大小，加重网络压力