Initial working version as independent repo

3 files changed, 674 insertions, 0 deletions

diff --git a/hook-plugin/CMakeLists.txt b/hook-plugin/CMakeLists.txt
new file mode 100644
index 0000000..329b2ef
--- /dev/null
+++ b/hook-plugin/CMakeLists.txt
@@ -0,0 +1,37 @@
+###########################################################################
+# Copyright 2015, 2016, 2017 IoT.bzh
+#
+# author: Fulup Ar Foll <fulup@iot.bzh>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+###########################################################################
+
+# Activate ALSA  dynamic build build mode get resolve "snd_dlsym_start"
+add_compile_options(-DPIC)
+
+PROJECT_TARGET_ADD(policy_hook_cb)
+
+    # Define targets
+    ADD_LIBRARY(${TARGET_NAME} MODULE PolicyHookCb.c)
+
+    # Alsa Plugin properties
+    SET_TARGET_PROPERTIES(${TARGET_NAME} PROPERTIES
+	PREFIX ""
+        OUTPUT_NAME ${TARGET_NAME}
+    )
+
+    # Library dependencies (include updates automatically)
+    TARGET_LINK_LIBRARIES(${TARGET_NAME}
+        ${link_libraries}
+    )
+    install(TARGETS ${TARGET_NAME} LIBRARY DESTINATION lib)
diff --git a/hook-plugin/PolicyHookCb.c b/hook-plugin/PolicyHookCb.c
new file mode 100644
index 0000000..fdec61d
--- /dev/null
+++ b/hook-plugin/PolicyHookCb.c
@@ -0,0 +1,560 @@
+/*
+ * Copyright (C) 2016 "IoT.bzh"
+ * Author Fulup Ar Foll <fulup@iot.bzh>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * AfbCallBack (snd_ctl_hal_t *handle, int numid, void **response);
+ *  AlsaHookInit is mandatory and called with numid=0
+ *
+ * Syntax in .asoundrc file
+ *   CrlLabel    { cb MyFunctionName name "My_Second_Control" }
+ *
+ * Testing:
+ *   aplay -DAlsaHook /usr/share/sounds/alsa/test.wav
+ *
+ * References:
+ *  https://www.spinics.net/lists/alsa-devel/msg54235.html
+ *  https://github.com/shivdasgujare/utilities/blob/master/nexuss/alsa-scenario-hook/src/alsa-wrapper.c
+ */
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <alsa/asoundlib.h>
+#include <alsa/conf.h>
+#include <alsa/pcm.h>
+
+#include <systemd/sd-event.h>
+#include <json-c/json.h>
+
+#include "afb/afb-wsj1.h"
+#include "afb/afb-ws-client.h"
+#include <pthread.h>
+#include <semaphore.h>
+
+
+#define PLUGIN_ENTRY_POINT AlsaInstallHook
+    // Fulup Note: What ever you may find on Internet you should use
+    // SND_CONFIG_DLSYM_VERSION_HOOK and not SND_CONFIG_DLSYM_VERSION_HOOK
+    SND_DLSYM_BUILD_VERSION(PLUGIN_ENTRY_POINT, SND_PCM_DLSYM_VERSION)
+
+// this should be more than enough
+#define MAX_API_CALL 10
+#define MAX_EVT_CALL 10
+
+// timeout in ms
+#define REQUEST_DEFAULT_TIMEOUT 500
+#ifndef MAINLOOP_WATCHDOG
+#define MAINLOOP_WATCHDOG 100000
+#endif
+
+// closing message is added to query when PCM is closed
+#define CLOSING_MSG ",\"source\":-1}"
+
+// Currently not implemented
+#define UNUSED_ARG(x) UNUSED_ ## x __attribute__((__unused__))
+void OnRequestCB(void* UNUSED_ARG(handle) , const char* UNUSED_ARG(api), const char* UNUSED_ARG(verb), struct afb_wsj1_msg*UNUSED_ARG(msg)) {}
+
+typedef struct {
+    const char *api;
+    const char *openVerb;
+    const char *closeVerb;
+    long timeout;
+    char *query;
+    size_t length;
+
+    sd_event_source *evtSource;
+    char *callIdTag;
+    void *afbClient;
+} afbRequestT;
+
+typedef struct {
+    const char *name;
+    int  signal;
+} afbEventT;
+
+typedef struct {
+    snd_pcm_t *pcm;
+    const char *uri;
+    struct afb_wsj1 *wsj1;
+    sd_event *sdLoop;
+    int verbose;
+    sem_t semaphore;
+    int count;
+    int error;
+    afbRequestT **request;
+    afbEventT **event;
+} afbClientT;
+
+
+
+static void *LoopInThread(void *handle) {
+    afbClientT *afbClient = (afbClientT*) handle;
+    int count=0;
+    int watchdog= MAINLOOP_WATCHDOG *1000;
+
+    /* loop until end */
+    for (;;) {
+
+        if (afbClient->verbose) printf("ON-MAINLOOP ping=%d\n", count++);
+        sd_event_run(afbClient->sdLoop, watchdog);
+    }
+
+    return NULL;
+}
+
+// lost connect with the AudioDaemon
+static void OnHangupCB(void *handle, struct afb_wsj1 *wsj1) {
+
+    afbClientT *afbClient = (afbClientT*) handle;
+    SNDERR("(Hoops) Lost Connection to %s", afbClient->uri);
+
+    // try to close PCM when impossible terminate client
+    int err = snd_pcm_close (afbClient->pcm);
+    if (err) exit(1);
+}
+
+typedef enum {
+    HOOK_INSTALL,
+    HOOK_CLOSE,
+} hookActionT;
+
+
+void OnEventCB(void *handle, const char *event, struct afb_wsj1_msg *msg) {
+    afbClientT *afbClient = (afbClientT*) handle;
+    afbEventT **afbEvent = afbClient->event;
+    json_object *eventJ, *tmpJ, *dataJ;
+    const char *label;
+    int value, done, index;
+
+    eventJ = afb_wsj1_msg_object_j(msg);
+    done= json_object_object_get_ex(eventJ,"data", &dataJ);
+    if (!done) {
+        SNDERR ("PCM_HOOK: uri=%s empty event label", afbClient->uri);
+        goto OnErrorExit;
+    }
+
+    json_object_object_get_ex(dataJ,"signal", &tmpJ);
+    label=json_object_get_string(tmpJ);
+
+    json_object_object_get_ex(dataJ,"value", &tmpJ);
+    value=json_object_get_int(tmpJ);
+
+    for (index=0; afbEvent[index]!= NULL; index++) {
+        if (!strcmp(afbEvent[index]->name, label)) break;
+    }
+
+    if (!afbEvent[index] || !afbEvent[index]->signal) {
+        SNDERR ("PCM_HOOK: Unsupported uri=%s label=%s", afbClient->uri, label);
+        return;
+    }
+
+    // send signal to self process
+    kill (getpid(), afbEvent[index]->signal);
+
+    if (afbClient->verbose) printf("ON-EVENT label=%s signal=%d\n", label, value);
+    return;
+
+OnErrorExit:
+    SNDERR("ON-EVENT %s(%s)\n", event, afb_wsj1_msg_object_s(msg));
+    return;
+}
+
+// callback interface for wsj1
+static struct afb_wsj1_itf itf = {
+    .on_hangup = OnHangupCB,
+    .on_call = OnRequestCB,
+    .on_event = OnEventCB
+};
+
+void OnResponseCB(void *handle, struct afb_wsj1_msg *msg) {
+    afbRequestT *afbRequest= (afbRequestT*)handle;
+    afbClientT *afbClient=(afbClientT*)afbRequest->afbClient;
+
+    if (afbClient->verbose) printf("ON-RESPONSE call=%s response=%s\n", afbRequest->callIdTag, afb_wsj1_msg_object_s(msg));
+
+    // Cancel timeout for this request
+    sd_event_source_unref(afbRequest->evtSource);
+
+    if (! afb_wsj1_msg_is_reply_ok(msg)) goto OnErrorExit;
+
+    // When not more waiting call release semaphore
+    afbClient->count--;
+    if (afbClient->count == 0) {
+        if (afbClient->verbose) printf("ON-RESPONSE No More Waiting Request\n");
+        afbClient->error=0;
+        sem_post (&afbClient->semaphore);
+    }
+    return;
+
+OnErrorExit:
+    fprintf(stderr, "ON-RESPONSE ERROR call=%s response=%s\n", afbRequest->callIdTag, afb_wsj1_msg_object_s(msg));
+   afbClient->error=1;
+    sem_post (&afbClient->semaphore);
+}
+
+int OnTimeoutCB (sd_event_source* source, uint64_t timer, void* handle) {
+    afbClientT *afbClient= (afbClientT*)handle;
+
+    SNDERR("\nON-TIMEOUT Call Request Fail URI=%s\n", afbClient->uri);
+
+    // Close PCM and release waiting client
+    afbClient->error=1;
+    sem_post (&afbClient->semaphore);
+
+    return 0;
+}
+
+// Call AGL binder asynchronously by with a timeout
+static int CallWithTimeout(afbClientT *afbClient, afbRequestT *afbRequest, int count, hookActionT action) {
+    uint64_t usec;
+    const char * apiVerb;
+    int err;
+
+    // create a unique tag for request
+    (void) asprintf(&afbRequest->callIdTag, "%d:%s/%s", count, afbRequest->api, afbRequest->openVerb);
+
+    // create a timer with ~250us accuracy
+    sd_event_now(afbClient->sdLoop, CLOCK_MONOTONIC, &usec);
+    sd_event_add_time(afbClient->sdLoop, &afbRequest->evtSource, CLOCK_MONOTONIC, usec+afbRequest->timeout*1000, 250, OnTimeoutCB, afbClient);
+
+
+    // on PCM close replace last '}' by CLOSING_MSG
+    if (action == HOOK_CLOSE) apiVerb= afbRequest->closeVerb;
+    else apiVerb= afbRequest->openVerb;
+
+    // release action is optional
+    if (apiVerb) {    
+        if (afbClient->verbose) printf("CALL-REQUEST api=%s/%s tag=%s\n", afbRequest->api, apiVerb, afbRequest->callIdTag);
+        err = afb_wsj1_call_s(afbClient->wsj1, afbRequest->api, apiVerb, afbRequest->query, OnResponseCB, afbRequest);
+        if (err) goto OnErrorExit;        
+    }
+    // save client handle in request
+    afbRequest->afbClient = afbClient;
+    afbClient->count ++;
+
+    return 0;
+
+OnErrorExit:
+    fprintf(stderr, "LaunchCallRequest: Fail call %s//%s/%s&%s", afbClient->uri, afbRequest->api, apiVerb, afbRequest->query);
+    return 1;
+}
+
+static int LaunchCallRequest(afbClientT *afbClient, hookActionT action) {
+
+    pthread_t tid;
+    int err, idx;
+    afbRequestT **afbRequest= afbClient->request;
+
+    if (action == HOOK_INSTALL) {
+        // init waiting counting semaphore
+        if (sem_init(&afbClient->semaphore, 1, 0) == -1) {
+           fprintf(stderr, "LaunchCallRequest: Fail Semaphore Init: %s\n", afbClient->uri);
+        }
+
+        // Create a main loop
+        err = sd_event_default(&afbClient->sdLoop);
+        if (err < 0) {
+            fprintf(stderr, "LaunchCallRequest: Connection to default event loop failed: %s\n", strerror(-err));
+            goto OnErrorExit;
+        }
+
+        // start a thread with a mainloop to monitor Audio-Agent
+        err = pthread_create(&tid, NULL, &LoopInThread, afbClient);
+        if (err) goto OnErrorExit;
+
+        // connect the websocket wsj1 to the uri given by the first argument
+        afbClient->wsj1 = afb_ws_client_connect_wsj1(afbClient->sdLoop, afbClient->uri, &itf, afbClient);
+        if (afbClient->wsj1 == NULL) {
+            fprintf(stderr, "LaunchCallRequest: Connection to %s failed\n", afbClient->uri);
+            goto OnErrorExit;
+        }
+    }
+
+    // send call request to audio-agent asynchronously (respond with thread mainloop context)
+    for (idx = 0; afbRequest[idx] != NULL; idx++) {
+        err = CallWithTimeout(afbClient, afbRequest[idx], idx, action);
+        if (err) goto OnErrorExit;
+    }
+
+    // launch counter to keep track of waiting request call
+    afbClient->count=idx;
+
+    return 0;
+
+OnErrorExit:
+    return -1;
+}
+
+static int AlsaCloseHook(snd_pcm_hook_t *hook) {
+
+    afbClientT *afbClient = (afbClientT*) snd_pcm_hook_get_private (hook);
+
+    // launch call request and create a waiting mainloop thread
+    int err = LaunchCallRequest(afbClient, HOOK_CLOSE);
+    if (err < 0) {
+        fprintf (stderr, "PCM Fail to Enter Mainloop\n");
+        goto OnErrorExit;
+    }
+
+    // wait for all call request to return
+    sem_wait(&afbClient->semaphore);
+    if (afbClient->error) {
+        fprintf (stderr, "AlsaCloseHook: Notice exit before audio-4a response\n");
+        goto OnErrorExit;
+    }
+
+    if (afbClient->verbose) fprintf(stdout, "\nAlsaHook Close Success PCM=%s URI=%s\n", snd_pcm_name(afbClient->pcm), afbClient->uri);
+    return 0;
+
+OnErrorExit:
+    fprintf(stderr, "\nAlsaPcmHook Plugin Close Fail PCM=%s\n", snd_pcm_name(afbClient->pcm));
+    return 0;
+}
+
+// Function call when Plugin PCM is OPEN
+int PLUGIN_ENTRY_POINT (snd_pcm_t *pcm, snd_config_t *conf) {
+    snd_pcm_hook_t *h_close = NULL;
+    snd_config_iterator_t it, next;
+    afbClientT *afbClient = malloc(sizeof (afbClientT));
+    afbRequestT **afbRequest = malloc(MAX_API_CALL * sizeof(afbRequestT*));
+    afbEventT **afbEvent= malloc(MAX_EVT_CALL * sizeof(afbEventT*));
+    int err;
+
+    // start populating client handle
+    afbClient->pcm = pcm;
+    afbClient->verbose = 0;
+    afbClient->request = afbRequest;
+
+    // Get PCM arguments from asoundrc
+    snd_config_for_each(it, next, conf) {
+        snd_config_t *node = snd_config_iterator_entry(it);
+        const char *id;
+
+        // ignore comment en empty lines
+        if (snd_config_get_id(node, &id) < 0) continue;
+        if (strcmp(id, "comment") == 0 || strcmp(id, "hint") == 0) continue;
+
+        if (strcmp(id, "uri") == 0) {
+            const char *uri;
+            if (snd_config_get_string(node, &uri) < 0) {
+                SNDERR("Invalid String for %s", id);
+                goto OnErrorExit;
+            }
+            afbClient->uri=strdup(uri);
+            continue;
+        }
+
+        if (strcmp(id, "verbose") == 0) {
+            afbClient->verbose= snd_config_get_bool(node);
+            if (afbClient->verbose < 0) {
+                SNDERR("Invalid Boolean for %s", id);
+                goto OnErrorExit;
+            }
+            continue;
+        }
+
+        if (strcmp(id, "request") == 0) {
+            const char *callConf, *callLabel;
+            snd_config_type_t ctype;
+            snd_config_iterator_t currentCall, follow;
+            snd_config_t *itemConf;
+            int callCount=0;
+
+            ctype = snd_config_get_type(node);
+            if (ctype != SND_CONFIG_TYPE_COMPOUND) {
+                snd_config_get_string(node, &callConf);
+                SNDERR("Invalid compound type for %s", callConf);
+                goto OnErrorExit;
+            }
+
+
+            // loop on each call
+            snd_config_for_each(currentCall, follow, node) {
+                snd_config_t *ctlconfig = snd_config_iterator_entry(currentCall);
+
+                // ignore empty line
+                if (snd_config_get_id(ctlconfig, &callLabel) < 0) continue;
+
+                // each clt should be a valid config compound
+                ctype = snd_config_get_type(ctlconfig);
+                if (ctype != SND_CONFIG_TYPE_COMPOUND) {
+                    snd_config_get_string(node, &callConf);
+                    SNDERR("Invalid call element for %s value=%s", callLabel, callConf);
+                    goto OnErrorExit;
+                }
+
+                // allocate an empty call request
+                afbRequest[callCount] = calloc(1, sizeof (afbRequestT));
+
+
+                err = snd_config_search(ctlconfig, "api", &itemConf);
+                if (!err) {
+                    const char *api;
+                    if (snd_config_get_string(itemConf, &api) < 0) {
+                        SNDERR("Invalid api string for %s", callLabel);
+                        goto OnErrorExit;
+                    }
+                    afbRequest[callCount]->api=strdup(api);
+                }
+
+                err = snd_config_search(ctlconfig, "request", &itemConf);
+                if (!err) {
+                    const char *verb;
+                    if (snd_config_get_string(itemConf, &verb) < 0) {
+                        SNDERR("Invalid open verb string %s", id);
+                        goto OnErrorExit;
+                    }
+                    afbRequest[callCount]->openVerb=strdup(verb);
+                }
+
+                err = snd_config_search(ctlconfig, "release", &itemConf);
+                if (!err) {
+                    const char *verb;
+                    if (snd_config_get_string(itemConf, &verb) < 0) {
+                        SNDERR("Invalid close verb string %s", id);
+                        goto OnErrorExit;
+                    }
+                    afbRequest[callCount]->closeVerb=strdup(verb);
+                }
+
+                err = snd_config_search(ctlconfig, "timeout", &itemConf);
+                if (!err) {
+                    if (snd_config_get_integer(itemConf, &afbRequest[callCount]->timeout) < 0) {
+                        SNDERR("Invalid timeout Integer %s", id);
+                        goto OnErrorExit;
+                    }
+                }
+
+                err = snd_config_search(ctlconfig, "args", &itemConf);
+                if (!err) {
+                    const char *query;
+                    if (snd_config_get_string(itemConf, &query) < 0) {
+                        SNDERR("Invalid args string %s", id);
+                        goto OnErrorExit;
+                    }
+                    // reserve enough space to ad closing message
+                    afbRequest[callCount]->length= strlen(query);
+                    afbRequest[callCount]->query = malloc (afbRequest[callCount]->length+strlen(CLOSING_MSG)+1);
+                    strcpy (afbRequest[callCount]->query, query);
+
+                    // cleanup string for json_tokener
+                    for (int idx = 0; query[idx] != '\0'; idx++) {
+                        if (query[idx] == '\'') afbRequest[callCount]->query[idx] = '"';
+                        else afbRequest[callCount]->query[idx] = query[idx];
+                    }
+                    json_object *queryJ = json_tokener_parse(afbRequest[callCount]->query);
+                    if (!queryJ) {
+                        SNDERR("Invalid Json %s args=%s should be args=\"{'tok1':'val1', 'tok2':'val2'}\" ", id, afbRequest[callCount]->query);
+                        goto OnErrorExit;
+                    }
+                }
+
+                // Simple check on call request validity
+                if (!afbRequest[callCount]->query)   afbRequest[callCount]->query= "";
+                if (!afbRequest[callCount]->timeout) afbRequest[callCount]->timeout=REQUEST_DEFAULT_TIMEOUT ;
+                if (!afbRequest[callCount]->openVerb || !afbRequest[callCount]->api) {
+                    SNDERR("Missing api/open(verb)/close(verb) %s in asoundrc", callLabel);
+                    goto OnErrorExit;
+                }
+
+                // move to next call if any
+                callCount ++;
+                if (callCount == MAX_API_CALL) {
+                    SNDERR("Too Many call MAX_API_CALL=%d", MAX_API_CALL);
+                    goto OnErrorExit;
+                }
+                afbRequest[callCount]=NULL; // afbRequest array is NULL terminated
+
+            }
+            continue;
+        }
+        if (strcmp(id, "event") == 0) {
+            const char *callConf, *callLabel;
+            snd_config_type_t ctype;
+            snd_config_iterator_t currentCall, follow;
+            int callCount=0;
+
+            ctype = snd_config_get_type(node);
+            if (ctype != SND_CONFIG_TYPE_COMPOUND) {
+                snd_config_get_string(node, &callConf);
+                SNDERR("Invalid compound type for %s", callConf);
+                goto OnErrorExit;
+            }
+
+
+            // loop on each call
+            snd_config_for_each(currentCall, follow, node) {
+                snd_config_t *ctlconfig = snd_config_iterator_entry(currentCall);
+                long sigval;
+
+                // ignore empty line
+                if (snd_config_get_id(ctlconfig, &callLabel) < 0) continue;
+
+                // each clt should be a valid config compound
+                ctype = snd_config_get_type(ctlconfig);
+                if (ctype != SND_CONFIG_TYPE_INTEGER) {
+                    snd_config_get_string(ctlconfig, &callConf);
+                    SNDERR("Invalid signal number for %s value=%s", callLabel, callConf);
+                    goto OnErrorExit;
+                }
+
+                // allocate an empty call request
+                snd_config_get_integer(ctlconfig, &sigval);
+                afbEvent[callCount] = calloc(1, sizeof (afbEventT));
+                afbEvent[callCount]->name=strdup(callLabel);
+                afbEvent[callCount]->signal= (int)sigval;
+
+                // move to next call if any
+                callCount ++;
+                if (callCount == MAX_EVT_CALL) {
+                    SNDERR("Too Many call MAX_EVT_CALL=%d", MAX_EVT_CALL);
+                    goto OnErrorExit;
+                }
+                afbEvent[callCount]=NULL; // afbEvent array is NULL terminated
+
+            }
+            continue;
+        }
+    }
+
+    if (afbClient->verbose) fprintf(stdout, "\nAlsaHook Install Start PCM=%s URI=%s\n", snd_pcm_name(afbClient->pcm), afbClient->uri);
+
+    err = snd_pcm_hook_add(&h_close, afbClient->pcm, SND_PCM_HOOK_TYPE_CLOSE, AlsaCloseHook, afbClient);
+    if (err < 0) goto OnErrorExit;
+
+    // launch call request and create a waiting mainloop thread
+    err = LaunchCallRequest(afbClient, HOOK_INSTALL);
+    if (err < 0) {
+        fprintf (stderr, "PCM Fail to Enter Mainloop\n");
+        goto OnErrorExit;
+    }
+
+    // wait for all call request to return
+    sem_wait(&afbClient->semaphore);
+    if (afbClient->error) {
+        fprintf (stderr, "PCM Authorisation Deny from AAAA Controller (AGL Advanced Audio Agent)\n");
+        goto OnErrorExit;
+    }
+
+    if (afbClient->verbose) fprintf(stdout, "\nAlsaHook Install Success PCM=%s URI=%s\n", snd_pcm_name(afbClient->pcm), afbClient->uri);
+    return 0;
+
+OnErrorExit:
+    fprintf(stderr, "\nAlsaPcmHook Plugin Install Fail PCM=%s\n", snd_pcm_name(pcm));
+    if (h_close)
+        snd_pcm_hook_remove(h_close);
+
+    return -EINVAL;
+}
+
diff --git a/hook-plugin/README.md b/hook-plugin/README.md
new file mode 100644
index 0000000..0472c7b
--- /dev/null
+++ b/hook-plugin/README.md
@@ -0,0 +1,77 @@
+Alsa-Hook-Plugin
+
+Object: Provide a Hook on Alsa PCM to check permission again AGL Advance Audio Agent
+Status: Release Candidate
+Author: Fulup Ar Foll fulup@iot.bzh
+Date  : August-2017
+
+Functionalities:
+ - Execute a set of websocket RPC request again AGL binders to allow/deny access
+ - Keep websocket open in an idepandant thread on order to monitor event receive from AGL audio agent
+
+Installation
+ - Alsaplugins are typically search in /usr/share/alsa-lib. Nevertheless a full path might be given
+ - This plugin implement a hook on a slave PCM. Typically this slave PCM is a dedicated virtual channel (eg: navigation, emergency,...)
+ - Config should be place in ~/.asoundrc (see config sample in PROJECT_ROOT/conf.d/alsa)
+
+Test
+ - Install a full .asoundrc from conf.d/project/alsa.d
+ - speaker-test -DMyNavigationHook -c2 -twav
+
+Config
+```
+# Define sharelib location and entry point
+# -----------------------------------------
+pcm_hook_type.MyHookPlugin {
+    install "AlsaInstallHook"
+    lib "/home/fulup/Workspace/AGL-AppFW/audio-bindings-dev/build/Alsa-Plugin/Alsa-Hook-Callback/alsa_hook_cb.so"
+}
+
+# Create PCM HOOK with corresponding request calls to AGL Audio Agent
+# --------------------------------------------------------------------
+pcm.MyNavigationHook {
+    type hooks
+    slave.pcm "MyMixerPCM"
+
+    # Defined used hook sharelib and provide arguments/config to install func
+    hooks.0 {
+        type "MyHookPlugin"
+        hook_args {
+            verbose true # print few log messages (default false);
+
+            # Every Call should return OK in order PCM to open (default timeout 100ms)
+            uri   "ws://localhost:1234/api?token='audio-agent-token'"
+            request {
+                # Request authorisation to write on navigation
+                navigation-ctl {
+                    api     "pol4a"
+                    request "navigation-role"
+                    release "navigation-role"
+                    args    "{'uid':'alsa-hook-navigation'}"
+                }
+                # subscribe to Audio Agent Event map them to signal
+                subscribe-evt {
+                    api   "pol4a"
+                    verb  "subscribe"
+                }
+            }
+            # map event reception to self generated signal
+            event {
+                pause  30
+                resume 31
+                stop   3
+            }
+        }
+    }
+}
+
+```
+
+NOTE:
+
+* Hook plugin is loaded by Alsa libasound within player context. It inherits client process attributes, as UID/GID or
+the SMACK label on AGL. This smack label is tested by AGL security framework when requested a call on the audio-agent binder.
+As a result the call will only succeed it the permission attached the application in Cynara matches.
+
+* Hook plugin keep a connection with the Audio-Agent until PCM is closed by the application. This connection allow the
+Audio-Agent to send events. eg: pause, quit, mute, ...
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