Add feature list to connection banner.

This allows us to test for features explicitly rather than relying on
the protocol version number, allowing us to fall back gracefully if a
feature is not supported.

This will be needed for the upcoming shell upgrades for stdout/stderr
separation and exit code reporting.

Change-Id: Ibb1d8ad2611f7209901ee76d51346b453e9c5873
diff --git a/adb/adb.cpp b/adb/adb.cpp
index a8737f5..180954b 100644
--- a/adb/adb.cpp
+++ b/adb/adb.cpp
@@ -58,6 +58,8 @@
 #if !ADB_HOST
 const char* adb_device_banner = "device";
 static android::base::LogdLogger gLogdLogger;
+#else
+const char* adb_device_banner = "host";
 #endif
 
 void AdbLogger(android::base::LogId id, android::base::LogSeverity severity,
@@ -305,45 +307,50 @@
     send_packet(p, t);
 }
 
-static size_t fill_connect_data(char *buf, size_t bufsize)
-{
-#if ADB_HOST
-    return snprintf(buf, bufsize, "host::") + 1;
-#else
-    static const char *cnxn_props[] = {
+std::string get_connection_string() {
+    std::vector<std::string> connection_properties;
+
+#if !ADB_HOST
+    static const char* cnxn_props[] = {
         "ro.product.name",
         "ro.product.model",
         "ro.product.device",
     };
-    static const int num_cnxn_props = ARRAY_SIZE(cnxn_props);
-    int i;
-    size_t remaining = bufsize;
-    size_t len;
 
-    len = snprintf(buf, remaining, "%s::", adb_device_banner);
-    remaining -= len;
-    buf += len;
-    for (i = 0; i < num_cnxn_props; i++) {
+    for (const auto& prop_name : cnxn_props) {
         char value[PROPERTY_VALUE_MAX];
-        property_get(cnxn_props[i], value, "");
-        len = snprintf(buf, remaining, "%s=%s;", cnxn_props[i], value);
-        remaining -= len;
-        buf += len;
+        property_get(prop_name, value, "");
+        connection_properties.push_back(
+            android::base::StringPrintf("%s=%s", prop_name, value));
     }
-
-    return bufsize - remaining + 1;
 #endif
+
+    connection_properties.push_back(android::base::StringPrintf(
+        "features=%s", android::base::Join(supported_features(), ',').c_str()));
+
+    return android::base::StringPrintf(
+        "%s::%s", adb_device_banner,
+        android::base::Join(connection_properties, ';').c_str());
 }
 
-void send_connect(atransport *t)
-{
+void send_connect(atransport* t) {
     D("Calling send_connect \n");
-    apacket *cp = get_apacket();
+    apacket* cp = get_apacket();
     cp->msg.command = A_CNXN;
     cp->msg.arg0 = t->get_protocol_version();
     cp->msg.arg1 = t->get_max_payload();
-    cp->msg.data_length = fill_connect_data((char *)cp->data,
-                                            MAX_PAYLOAD_V1);
+
+    std::string connection_str = get_connection_string();
+    // Connect and auth packets are limited to MAX_PAYLOAD_V1 because we don't
+    // yet know how much data the other size is willing to accept.
+    if (connection_str.length() > MAX_PAYLOAD_V1) {
+        LOG(FATAL) << "Connection banner is too long (length = "
+                   << connection_str.length() << ")";
+    }
+
+    memcpy(cp->data, connection_str.c_str(), connection_str.length());
+    cp->msg.data_length = connection_str.length();
+
     send_packet(cp, t);
 }
 
@@ -356,8 +363,8 @@
     *dst = strdup(src.c_str());
 }
 
-void parse_banner(const char* banner, atransport* t) {
-    D("parse_banner: %s\n", banner);
+void parse_banner(const std::string& banner, atransport* t) {
+    D("parse_banner: %s\n", banner.c_str());
 
     // The format is something like:
     // "device::ro.product.name=x;ro.product.model=y;ro.product.device=z;".
@@ -380,6 +387,10 @@
                 qual_overwrite(&t->model, value);
             } else if (key == "ro.product.device") {
                 qual_overwrite(&t->device, value);
+            } else if (key == "features") {
+                for (const auto& feature : android::base::Split(value, ",")) {
+                    t->add_feature(feature);
+                }
             }
         }
     }
@@ -407,6 +418,29 @@
     }
 }
 
+static void handle_new_connection(atransport* t, apacket* p) {
+    if (t->connection_state != kCsOffline) {
+        t->connection_state = kCsOffline;
+        handle_offline(t);
+    }
+
+    t->update_version(p->msg.arg0, p->msg.arg1);
+    std::string banner(reinterpret_cast<const char*>(p->data),
+                       p->msg.data_length);
+    parse_banner(banner, t);
+
+#if ADB_HOST
+    handle_online(t);
+#else
+    if (!auth_required) {
+        handle_online(t);
+        send_connect(t);
+    } else {
+        send_auth_request(t);
+    }
+#endif
+}
+
 void handle_packet(apacket *p, atransport *t)
 {
     asocket *s;
@@ -431,25 +465,8 @@
         }
         return;
 
-    case A_CNXN: /* CONNECT(version, maxdata, "system-id-string") */
-        if(t->connection_state != kCsOffline) {
-            t->connection_state = kCsOffline;
-            handle_offline(t);
-        }
-
-        t->update_version(p->msg.arg0, p->msg.arg1);
-        parse_banner(reinterpret_cast<const char*>(p->data), t);
-
-#if ADB_HOST
-        handle_online(t);
-#else
-        if (!auth_required) {
-            handle_online(t);
-            send_connect(t);
-        } else {
-            send_auth_request(t);
-        }
-#endif
+    case A_CNXN:  // CONNECT(version, maxdata, "system-id-string")
+        handle_new_connection(t, p);
         break;
 
     case A_AUTH: