Correctly handle non-BMP characters in Android content file names

* lisp/term/android-win.el (android-encode-jni)
(android-decode-jni, android-jni): New coding system, for
Android file names and runtime data.

* src/androidterm.h (syms_of_androidvfs): New function.

* src/androidvfs.c (struct android_special_vnode): New field
special_coding_system.
(android_saf_tree_readdir): Decode the file name using the
android-jni coding system.
(special_vnodes): <contents>: Specify a file name coding system.
(android_vfs_convert_name): New function.
(android_root_name): If a special coding system be specified for
a special vnode, convert components to it before invoking its
name function.
(syms_of_androidvfs): New symbol Qandroid_jni.

* src/emacs.c (android_emacs_init): Call syms_of_androidvfs.

3 files changed, 126 insertions, 17 deletions

diff --git a/src/androidterm.h b/src/androidterm.h
index ca6929bef0e..fd4cc99f641 100644
--- a/src/androidterm.h
+++ b/src/androidterm.h
@@ -461,7 +461,7 @@ extern void sfntfont_android_shrink_scanline_buffer (void);
 extern void init_sfntfont_android (void);
 extern void syms_of_sfntfont_android (void);
 
-/* Defined in androidselect.c  */
+/* Defined in androidselect.c.  */
 
 #ifndef ANDROID_STUBIFY
 
@@ -473,6 +473,9 @@ extern void android_notification_action (struct android_notification_event *,
 extern void init_androidselect (void);
 extern void syms_of_androidselect (void);
 
+/* Defined in androidvfs.c.  */
+extern void syms_of_androidvfs (void);
+
 #endif
 
 
diff --git a/src/androidvfs.c b/src/androidvfs.c
index 9e3d5cab8cf..6a9ddb33c56 100644
--- a/src/androidvfs.c
+++ b/src/androidvfs.c
@@ -38,8 +38,10 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <linux/ashmem.h>
 
 #include "android.h"
+#include "androidterm.h"
 #include "systime.h"
 #include "blockinput.h"
+#include "coding.h"
 
 #if __ANDROID_API__ >= 9
 #include <android/asset_manager.h>
@@ -248,8 +250,14 @@ struct android_special_vnode
   /* Function called to create the initial vnode from the rest of the
      component.  */
   struct android_vnode *(*initial) (char *, size_t);
+
+  /* If non-nil, an encoding system into which file name buffers are to
+     be re-encoded before being handed to VFS functions.  */
+  Lisp_Object special_coding_system;
 };
 
+verify (NIL_IS_ZERO); /* special_coding_system above.  */
+
 enum android_vnode_type
   {
     ANDROID_VNODE_UNIX,
@@ -3867,7 +3875,8 @@ android_saf_root_readdir (struct android_vdir *vdir)
                                                   NULL);
   android_exception_check_nonnull ((void *) chars, string);
 
-  /* Figure out how large it is, and then resize dirent to fit.  */
+  /* Figure out how large it is, and then resize dirent to fit--this
+     string is always ASCII.  */
   length = strlen (chars) + 1;
   size   = offsetof (struct dirent, d_name) + length;
   dirent = xrealloc (dirent, size);
@@ -5479,6 +5488,7 @@ android_saf_tree_readdir (struct android_vdir *vdir)
   jmethodID method;
   size_t length, size;
   const char *chars;
+  struct coding_system coding;
 
   dir = (struct android_saf_tree_vdir *) vdir;
 
@@ -5526,9 +5536,25 @@ android_saf_tree_readdir (struct android_vdir *vdir)
                                                   NULL);
   android_exception_check_nonnull ((void *) chars, d_name);
 
-  /* Figure out how large it is, and then resize dirent to fit.  */
+  /* Decode this JNI string into utf-8-emacs; see
+     android_vfs_convert_name for considerations regarding coding
+     systems.  */
+  length = strlen (chars);
+  setup_coding_system (Qandroid_jni, &coding);
+  coding.mode |= CODING_MODE_LAST_BLOCK;
+  coding.source = (const unsigned char *) chars;
+  coding.dst_bytes = 0;
+  coding.destination = NULL;
+  decode_coding_object (&coding, Qnil, 0, 0, length, length, Qnil);
+
+  /* Release the string data and the local reference to STRING.  */
+  (*android_java_env)->ReleaseStringUTFChars (android_java_env,
+                                              (jstring) d_name,
+                                              chars);
+
+  /* Resize dirent to accommodate the decoded text.  */
   length = strlen (chars) + 1;
-  size   = offsetof (struct dirent, d_name) + length;
+  size   = offsetof (struct dirent, d_name) + 1 + coding.produced;
   dirent = xrealloc (dirent, size);
 
   /* Clear dirent.  */
@@ -5540,12 +5566,12 @@ android_saf_tree_readdir (struct android_vdir *vdir)
   dirent->d_off = 0;
   dirent->d_reclen = size;
   dirent->d_type = d_type ? DT_DIR : DT_UNKNOWN;
-  strcpy (dirent->d_name, chars);
+  memcpy (dirent->d_name, coding.destination, coding.produced);
+  dirent->d_name[coding.produced] = '\0';
+
+  /* Free the coding system destination buffer.  */
+  xfree (coding.destination);
 
-  /* Release the string data and the local reference to STRING.  */
-  (*android_java_env)->ReleaseStringUTFChars (android_java_env,
-                                              (jstring) d_name,
-                                              chars);
   ANDROID_DELETE_LOCAL_REF (d_name);
   return dirent;
 }
@@ -6531,9 +6557,35 @@ static struct android_vops root_vfs_ops =
 static struct android_special_vnode special_vnodes[] =
   {
     { "assets",  6, android_afs_initial,        },
-    { "content", 7, android_content_initial,    },
+    { "content", 7, android_content_initial,
+      LISPSYM_INITIALLY (Qandroid_jni),         },
   };
 
+/* Convert the file name NAME from Emacs's internal character encoding
+   to CODING, and return a Lisp string with the data so produced.
+
+   Calling this function creates an implicit assumption that
+   file-name-coding-system is compatible with utf-8-emacs, which is not
+   unacceptable as users with cause to modify file-name-coding-system
+   should be aware and prepared for consequences towards files stored on
+   different filesystems, including virtual ones.  */
+
+static Lisp_Object
+android_vfs_convert_name (const char *name, Lisp_Object coding)
+{
+  Lisp_Object src_coding, name1;
+
+  src_coding = Qutf_8_emacs;
+
+  /* Convert the contents of the buffer after BUFFER_END
+     from the file name coding system to
+     special->special_coding_system.  */
+  AUTO_STRING (file_name, name);
+  name1 = code_convert_string_norecord (file_name, src_coding, false);
+  name1 = code_convert_string (name1, coding, Qt, true, true, true);
+  return name1;
+}
+
 static struct android_vnode *
 android_root_name (struct android_vnode *vnode, char *name,
                    size_t length)
@@ -6541,6 +6593,8 @@ android_root_name (struct android_vnode *vnode, char *name,
   char *component_end;
   struct android_special_vnode *special;
   size_t i;
+  Lisp_Object file_name;
+  struct android_vnode *vp;
 
   /* Skip any leading separator in NAME.  */
 
@@ -6567,8 +6621,29 @@ android_root_name (struct android_vnode *vnode, char *name,
 
       if (component_end - name == special->length
           && !memcmp (special->name, name, special->length))
-        return (*special->initial) (component_end,
-                                    length - special->length);
+        {
+          if (!NILP (special->special_coding_system))
+            {
+              USE_SAFE_ALLOCA;
+
+              file_name
+                = android_vfs_convert_name (component_end,
+                                            special->special_coding_system);
+
+              /* Allocate a buffer and copy file_name into the same.  */
+              length = SBYTES (file_name) + 1;
+              name = SAFE_ALLOCA (length + 1);
+
+              /* Copy the trailing NULL byte also.  */
+              memcpy (name, SDATA (file_name), length);
+              vp = (*special->initial) (name, length - 1);
+              SAFE_FREE ();
+              return vp;
+            }
+
+          return (*special->initial) (component_end,
+                                      length - special->length);
+        }
 
       /* Detect the case where a special is named with a trailing
          directory separator.  */
@@ -6576,9 +6651,30 @@ android_root_name (struct android_vnode *vnode, char *name,
       if (component_end - name == special->length + 1
           && !memcmp (special->name, name, special->length)
           && name[special->length] == '/')
-        /* Make sure to include the directory separator.  */
-        return (*special->initial) (component_end - 1,
-                                    length - special->length);
+        {
+          if (!NILP (special->special_coding_system))
+            {
+              USE_SAFE_ALLOCA;
+
+              file_name
+                = android_vfs_convert_name (component_end - 1,
+                                            special->special_coding_system);
+
+              /* Allocate a buffer and copy file_name into the same.  */
+              length = SBYTES (file_name) + 1;
+              name = SAFE_ALLOCA (length + 1);
+
+              /* Copy the trailing NULL byte also.  */
+              memcpy (name, SDATA (file_name), length);
+              vp = (*special->initial) (name, length - 1);
+              SAFE_FREE ();
+              return vp;
+            }
+
+          /* Make sure to include the directory separator.  */
+          return (*special->initial) (component_end - 1,
+                                      length - special->length);
+        }
     }
 
   /* Otherwise, continue searching for a vnode normally.  */
@@ -6589,8 +6685,9 @@ android_root_name (struct android_vnode *vnode, char *name,
 
 /* File system lookup.  */
 
-/* Look up the vnode that designates NAME, a file name that is at
-   least N bytes.
+/* Look up the vnode that designates NAME, a file name that is at least
+   N bytes, converting between different file name coding systems as
+   necessary.
 
    NAME may be either an absolute file name or a name relative to the
    current working directory.  It must not be longer than EMACS_PATH_MAX
@@ -7605,3 +7702,11 @@ android_closedir (struct android_vdir *dirp)
 {
   return (*dirp->closedir) (dirp);
 }
+
+
+
+void
+syms_of_androidvfs (void)
+{
+  DEFSYM (Qandroid_jni, "android-jni");
+}
diff --git a/src/emacs.c b/src/emacs.c
index f4bfb9a6bbd..87f12d3fa86 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -2444,6 +2444,7 @@ Using an Emacs configured with --with-x-toolkit=lucid does not have this problem
 #if !defined ANDROID_STUBIFY
       syms_of_androidfont ();
       syms_of_androidselect ();
+      syms_of_androidvfs ();
       syms_of_sfntfont ();
       syms_of_sfntfont_android ();
 #endif /* !ANDROID_STUBIFY */