libwiretap: make wtap_wtap_encap_to_pcap_encap() private to the library.

Only a tiny amount of code outside libwiretap needs to know about
pcap/pcapng LINKTYPE_ values, and all that code needs to know is, for a
given LINKTYPE_ value, what the corresponding WTAP_ENCAP_ value is.
Nothing should need to know, for a given WTAP_ENCAP_ value, what its
LINKTYPE_ value is.

Make it the case that nothing *does* need to know, for a given
WTAP_ENCAP_ value, what its LINKTYPE_ value is.  Export
wtap_dump_can_write_encap() and use *that*, in the "import hex dump"
code, what formats can be written to a pcap file.

debian/libwiretap0.symbols

@@ -68,6 +68,7 @@ libwiretap.so.0 libwiretap0 #MINVER#
  wtap_dump_can_compress@Base 1.9.1
  wtap_dump_can_open@Base 1.9.1
  wtap_dump_can_write@Base 1.9.1
+ wtap_dump_can_write_encap@Base 3.5.0
  wtap_dump_close@Base 1.9.1
  wtap_dump_discard_decryption_secrets@Base 3.0.0
  wtap_dump_fdopen@Base 1.9.1
@@ -156,4 +157,3 @@ libwiretap.so.0 libwiretap0 #MINVER#
  wtap_strerror@Base 1.9.1
  wtap_tsprec_string@Base 1.99.9
  wtap_write_shb_comment@Base 1.9.1
- wtap_wtap_encap_to_pcap_encap@Base 1.9.1

ui/qt/import_text_dialog.cpp

@@ -56,6 +56,7 @@ ImportTextDialog::ImportTextDialog(QWidget *parent) :
 {
     int encap;
     int i;
+    int pcap_file_type_subtype;
 
     ti_ui_->setupUi(this);
     setWindowTitle(wsApp->windowTitleString(tr("Import From Hex Dump")));
@@ -85,8 +86,16 @@ ImportTextDialog::ImportTextDialog(QWidget *parent) :
         if (rb) encap_buttons_.append(rb);
     }
 
-    /* Scan all Wiretap encapsulation types */
+    /*
+     * Scan all Wiretap encapsulation types.
+     *
+     * XXX - this "knows" that WTAP_ENCAP_ETHERNET is the first encapsulation
+     * type, skipping the special non-types WTAP_ENCAP_PER_PACKET and
+     * WTAP_ENCAP_UNKNOWN.  We need a better way to express the notion
+     * of "for (all encapsulation types)".
+     */
     import_info_.encapsulation = WTAP_ENCAP_ETHERNET;
+    pcap_file_type_subtype = wtap_pcap_file_type_subtype();
     for (encap = import_info_.encapsulation; encap < wtap_get_num_encap_types(); encap++)
     {
         /* Check if we can write to a PCAP file
@@ -95,7 +104,8 @@ ImportTextDialog::ImportTextDialog(QWidget *parent) :
          * because we won't setup one from the text we import and
          * wiretap doesn't allow us to write 'raw' frames
          */
-        if ((wtap_wtap_encap_to_pcap_encap(encap) > 0) && !wtap_encap_requires_phdr(encap)) {
+        if (wtap_dump_can_write_encap(pcap_file_type_subtype, encap) &&
+            !wtap_encap_requires_phdr(encap)) {
             const char *name;
             /* If it has got a name */
             if ((name = wtap_encap_description(encap)))

wiretap/file_access.c

@@ -1433,24 +1433,25 @@ wtap_dump_file_encap_type(const GArray *file_encaps)
 	return encap;
 }
 
-static gboolean
-wtap_dump_can_write_encap(int filetype, int encap)
+gboolean
+wtap_dump_can_write_encap(int file_type_subtype, int encap)
 {
 	int result = 0;
 
-	if (filetype < 0 || filetype >= (int)file_type_subtype_table_arr->len ||
-	    file_type_subtype_table[filetype].can_write_encap == NULL)
+	if (file_type_subtype < 0 ||
+	    file_type_subtype >= (int)file_type_subtype_table_arr->len ||
+	    file_type_subtype_table[file_type_subtype].can_write_encap == NULL)
 		return FALSE;
 
-	result = (*file_type_subtype_table[filetype].can_write_encap)(encap);
+	result = (*file_type_subtype_table[file_type_subtype].can_write_encap)(encap);
 
 	if (result != 0) {
 		/* if the err said to check wslua's can_write_encap, try that */
 		if (result == WTAP_ERR_CHECK_WSLUA
-			&& file_type_subtype_table[filetype].wslua_info != NULL
-			&& file_type_subtype_table[filetype].wslua_info->wslua_can_write_encap != NULL) {
+			&& file_type_subtype_table[file_type_subtype].wslua_info != NULL
+			&& file_type_subtype_table[file_type_subtype].wslua_info->wslua_can_write_encap != NULL) {
 
-			result = (*file_type_subtype_table[filetype].wslua_info->wslua_can_write_encap)(encap, file_type_subtype_table[filetype].wslua_info->wslua_data);
+			result = (*file_type_subtype_table[file_type_subtype].wslua_info->wslua_can_write_encap)(encap, file_type_subtype_table[file_type_subtype].wslua_info->wslua_data);
 
 		}
 

wiretap/pcap-encap.h

@@ -21,7 +21,7 @@ extern "C" {
 #endif /* __cplusplus */
 
 WS_DLL_PUBLIC int wtap_pcap_encap_to_wtap_encap(int encap);
-WS_DLL_PUBLIC int wtap_wtap_encap_to_pcap_encap(int encap);
+int wtap_wtap_encap_to_pcap_encap(int encap);
 WS_DLL_PUBLIC gboolean wtap_encap_requires_phdr(int encap);
 
 #ifdef __cplusplus

wiretap/wtap.h

@@ -1978,11 +1978,18 @@ WS_DLL_PUBLIC
 int wtap_dump_file_encap_type(const GArray *file_encaps);
 
 /**
- * Return TRUE if we can write this capture file format out in
+ * Return TRUE if we can write this encapsulation type in this
+ * capture file type/subtype, FALSE if not.
+ */
+WS_DLL_PUBLIC
+gboolean wtap_dump_can_write_encap(int file_type_subtype, int encap);
+
+/**
+ * Return TRUE if we can write this capture file type/subtype out in
  * compressed form, FALSE if not.
  */
 WS_DLL_PUBLIC
-gboolean wtap_dump_can_compress(int filetype);
+gboolean wtap_dump_can_compress(int file_type_subtype);
 
 /**
  * Initialize the per-file information based on an existing file. Its