# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1615671513 -3600
# Node ID 54dcc50bf1930ff7717ad60d619feb9ac34b09a9
# Parent  14888a561fb945c98ac84f035815e1d525e48e93
Added convenience functions to access strings in mapped memory. Currently, the
opener context duplicates the string retrieval function internally.

diff -r 14888a561fb9 -r 54dcc50bf193 dstest_host_client.cc
--- a/dstest_host_client.cc	Sat Mar 13 17:49:23 2021 +0100
+++ b/dstest_host_client.cc	Sat Mar 13 22:38:33 2021 +0100
@@ -66,7 +66,7 @@
 
   /* Write the filename. */
 
-  strcpy(context.memory, filename);
+  file_string_set(&context, filename, 0);
 
   /* Invoke the open method to receive the file reference. */
 
diff -r 14888a561fb9 -r 54dcc50bf193 file.cc
--- a/file.cc	Sat Mar 13 17:49:23 2021 +0100
+++ b/file.cc	Sat Mar 13 22:38:33 2021 +0100
@@ -22,6 +22,8 @@
 #include <ipc/cap_alloc.h>
 #include <ipc/mem_ipc.h>
 
+#include <string.h>
+
 #include "dataspace_client.h"
 #include "opener_client.h"
 #include "opener_context_client.h"
@@ -76,6 +78,17 @@
   file->ref = L4_INVALID_CAP;
 }
 
+/* Open a file using the given structure and context. */
+
+long file_open(file_t *file, file_t *context)
+{
+  client_OpenerContext openercontext(context->ref);
+  file_init(file);
+  return openercontext.open(L4_FPAGE_RW, &file->size, &file->ref);
+}
+
+
+
 /* Map a region of the given file to a memory region. */
 
 long file_mmap(file_t *file, offset_t position, offset_t length)
@@ -86,16 +99,7 @@
   if (err)
     return err;
 
-  return ipc_attach_dataspace(file->ref, file->end_pos - file->start_pos, (void **) &file->memory);
-}
-
-/* Open a file using the given structure and context. */
-
-long file_open(file_t *file, file_t *context)
-{
-  client_OpenerContext openercontext(context->ref);
-  file_init(file);
-  return openercontext.open(L4_FPAGE_RW, &file->size, &file->ref);
+  return ipc_attach_dataspace(file->ref, file_span(file), (void **) &file->memory);
 }
 
 /* Return the amount of data in the mapped region for the given file. */
@@ -113,4 +117,50 @@
   return file->end_pos - file->start_pos;
 }
 
+
+
+/* Get a pointer to any terminated string at the given offset or NULL if the
+   data from offset is not terminated. */
+
+char *file_string_get(file_t *file, offset_t offset)
+{
+  offset_t limit = file_span(file) - offset;
+
+  if (strnlen(file->memory + offset, limit) < limit)
+    return file->memory + offset;
+  else
+    return NULL;
+}
+
+/* Copy a string to the mapped region at the given offset, returning the number
+   of copied characters excluding the zero terminator. */
+
+offset_t file_string_set(file_t *file, const char *data, offset_t offset)
+{
+  offset_t i, pos, limit = file_span(file) - 1;
+
+  /* Do not attempt to copy data with an invalid offset. */
+
+  if (offset > limit)
+    return 0;
+
+  /* Copy the data to the given offset, stopping before the final byte of the
+     region. */
+
+  for (i = 0, pos = offset; pos < limit; i++, pos++)
+  {
+    file->memory[pos] = data[i];
+
+    /* Terminator written, can return immediately. */
+
+    if (!data[i])
+      return pos - offset - 1;
+  }
+
+  /* Terminate the incomplete string at the end of the region. */
+
+  file->memory[limit] = '\0';
+  return limit - offset;
+}
+
 // vim: tabstop=2 expandtab shiftwidth=2
diff -r 14888a561fb9 -r 54dcc50bf193 file.h
--- a/file.h	Sat Mar 13 17:49:23 2021 +0100
+++ b/file.h	Sat Mar 13 22:38:33 2021 +0100
@@ -65,6 +65,11 @@
 offset_t file_populated_span(file_t *file);
 offset_t file_span(file_t *file);
 
+/* Convenience functions. */
+
+char *file_string_get(file_t *file, offset_t offset);
+offset_t file_string_set(file_t *file, const char *data, offset_t offset);
+
 EXTERN_C_END
 
 // vim: tabstop=2 expandtab shiftwidth=2