Enable opening mailto URLs under Android

* doc/emacs/android.texi (Android Startup): Mention how mailto
URLs are treated by the emacsclient wrapper.

* java/AndroidManifest.xml.in: Register `mailto' scheme filters
for EmacsOpenActivity.

* java/org/gnu/emacs/EmacsOpenActivity.java (startEmacsClient):
Extract code that starts Emacs when it isn't already running,
and take a list of arguments rather than a single file name.
(onCreate): If the scheme is `mailto', escape the URI and call
`message-mailto'.

2 files changed, 66 insertions, 23 deletions

diff --git a/java/AndroidManifest.xml.in b/java/AndroidManifest.xml.in
index 9044725640d..d4017a055dd 100644
--- a/java/AndroidManifest.xml.in
+++ b/java/AndroidManifest.xml.in
@@ -122,6 +122,21 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>. -->
         <category android:name="android.intent.category.BROWSABLE"/>
         <data android:scheme="org-protocol"/>
       </intent-filter>
+
+      <!-- And also mailto links.  -->
+
+      <intent-filter>
+        <action android:name="android.intent.action.VIEW"/>
+        <category android:name="android.intent.category.DEFAULT"/>
+        <category android:name="android.intent.category.BROWSABLE"/>
+        <data android:scheme="mailto"/>
+      </intent-filter>
+
+      <intent-filter>
+        <action android:name="android.intent.action.SENDTO"/>
+        <data android:scheme="mailto"/>
+        <category android:name="android.intent.category.DEFAULT"/>
+      </intent-filter>
     </activity>
 
     <activity android:name="org.gnu.emacs.EmacsMultitaskActivity"
diff --git a/java/org/gnu/emacs/EmacsOpenActivity.java b/java/org/gnu/emacs/EmacsOpenActivity.java
index 00503b6cbcc..d27139e98bc 100644
--- a/java/org/gnu/emacs/EmacsOpenActivity.java
+++ b/java/org/gnu/emacs/EmacsOpenActivity.java
@@ -342,8 +342,14 @@ public final class EmacsOpenActivity extends Activity
       });
   }
 
+  /* Start `emacsclient' with the provided list of ARGUMENTS, after
+     ARGUMENTS[0] is replaced with the name of the emacsclient binary.
+
+     Create a new thread to await its completion, subsequently
+     reporting any errors that arise to the user.  */
+
   public void
-  startEmacsClient (String fileName)
+  startEmacsClient (String[] arguments)
   {
     String libDir;
     ProcessBuilder builder;
@@ -352,23 +358,10 @@ public final class EmacsOpenActivity extends Activity
     File file;
     Intent intent;
 
-    /* If the Emacs service is not running, then start Emacs and make
-       it open this file.  */
-
-    if (EmacsService.SERVICE == null)
-      {
-        fileToOpen = fileName;
-        intent = new Intent (EmacsOpenActivity.this,
-                             EmacsActivity.class);
-        finish ();
-        startActivity (intent);
-        return;
-      }
-
     libDir = EmacsService.getLibraryDirectory (this);
-    builder = new ProcessBuilder (libDir + "/libemacsclient.so",
-                                  fileName, "--reuse-frame",
-                                  "--timeout=10", "--no-wait");
+    arguments[0] = libDir + "/libemacsclient.so";
+
+    builder = new ProcessBuilder (arguments);
 
     /* Redirection is unfortunately not possible in Android 7 and
        earlier.  */
@@ -413,7 +406,7 @@ public final class EmacsOpenActivity extends Activity
     ContentResolver resolver;
     ParcelFileDescriptor fd;
     byte[] names;
-    String errorBlurb;
+    String errorBlurb, scheme;
 
     super.onCreate (savedInstanceState);
 
@@ -431,7 +424,8 @@ public final class EmacsOpenActivity extends Activity
 
     if (action.equals ("android.intent.action.VIEW")
         || action.equals ("android.intent.action.EDIT")
-        || action.equals ("android.intent.action.PICK"))
+        || action.equals ("android.intent.action.PICK")
+        || action.equals ("android.intent.action.SENDTO"))
       {
         /* Obtain the URI of the action.  */
         uri = intent.getData ();
@@ -442,15 +436,35 @@ public final class EmacsOpenActivity extends Activity
             return;
           }
 
+        scheme = uri.getScheme ();
+
+        /* If URL is a mailto URI, call `message-mailto' much the same
+           way emacsclient-mail.desktop does.  */
+
+        if (scheme.equals ("mailto"))
+          {
+            /* Escape the special characters $ and " before enclosing
+               the string within the `message-mailto' wrapper.  */
+            fileName = uri.toString ();
+            fileName.replace ("\"", "\\\"").replace ("$", "\\$");
+            fileName = "(message-mailto \"" + fileName + "\")";
+
+            /* Execute emacsclient in order to execute this code.  */
+            currentActivity = this;
+            startEmacsClient (new String[] { "--timeout=10", "--no-wait",
+                                             "--eval", fileName, });
+            return;
+          }
+
         /* Now, try to get the file name.  */
 
-        if (uri.getScheme ().equals ("file"))
+        if (scheme.equals ("file"))
           fileName = uri.getPath ();
         else
           {
             fileName = null;
 
-            if (uri.getScheme ().equals ("content"))
+            if (scheme.equals ("content"))
               {
                 /* This is one of the annoying Android ``content''
                    URIs.  Most of the time, there is actually an
@@ -501,7 +515,7 @@ public final class EmacsOpenActivity extends Activity
                       }
                   }
               }
-            else if (uri.getScheme ().equals ("org-protocol"))
+            else if (scheme.equals ("org-protocol"))
               /* URL is an org-protocol:// link, which is meant to be
                  directly relayed to emacsclient.  */
               fileName = uri.toString ();
@@ -516,11 +530,25 @@ public final class EmacsOpenActivity extends Activity
               }
           }
 
+        /* If the Emacs service is not running, then start Emacs and make
+           it open this file.  */
+
+        if (EmacsService.SERVICE == null)
+          {
+            fileToOpen = fileName;
+            intent = new Intent (EmacsOpenActivity.this,
+                                 EmacsActivity.class);
+            finish ();
+            startActivity (intent);
+            return;
+          }
+
         /* And start emacsclient.  Set `currentActivity' to this now.
            Presumably, it will shortly become capable of displaying
            dialogs.  */
         currentActivity = this;
-        startEmacsClient (fileName);
+        startEmacsClient (new String[] { "--timeout=10", "--no-wait",
+                                         "--reuse-frame", fileName, });
       }
     else
       finish ();