From be852e39b25a4abbb7e5ecbe89d72f410ccfb3a8 Mon Sep 17 00:00:00 2001
From: Daniel Stenberg <daniel@haxx.se>
Date: Wed, 15 Oct 2025 08:42:20 +0200
Subject: [PATCH] tftp: check for trailing ";mode=" in URL without strstr

RFC 3617 defines two specific modes, "netascii" and "octet". This code
now checks only for those trailing ones - and not in the hostname since
they can't be there anymore.

Assisted-by: Jay Satiro
Closes #19070
---
 docs/cmdline-opts/use-ascii.md |  9 +++++----
 lib/tftp.c                     | 36 ++++++++++------------------------
 src/tool_listhelp.c            |  2 +-
 tests/data/test1093            |  4 ++--
 4 files changed, 18 insertions(+), 33 deletions(-)

diff --git a/docs/cmdline-opts/use-ascii.md b/docs/cmdline-opts/use-ascii.md
index 30cc860b0a..4dba446ffe 100644
--- a/docs/cmdline-opts/use-ascii.md
+++ b/docs/cmdline-opts/use-ascii.md
@@ -4,8 +4,8 @@ SPDX-License-Identifier: curl
 Short: B
 Long: use-ascii
 Help: Use ASCII/text transfer
-Protocols: FTP LDAP
-Category: ftp output ldap
+Protocols: FTP LDAP TFTP
+Category: ftp output ldap tftp
 Added: 5.0
 Multi: boolean
 See-also:
@@ -18,5 +18,6 @@ Example:
 # `--use-ascii`
 
 Enable ASCII transfer mode. For FTP, this can also be enforced by using a URL
-that ends with `;type=A`. This option causes data sent to stdout to be in text
-mode for Win32 systems.
+that ends with `;type=A`. For TFTP, this can also be enforced by using a URL
+that ends with `;mode=netascii`. This option causes data sent to stdout to be
+in text mode for Win32 systems.
diff --git a/lib/tftp.c b/lib/tftp.c
index 0a9b8a8e87..d9d978c24e 100644
--- a/lib/tftp.c
+++ b/lib/tftp.c
@@ -1379,35 +1379,19 @@ static CURLcode tftp_do(struct Curl_easy *data, bool *done)
 static CURLcode tftp_setup_connection(struct Curl_easy *data,
                                       struct connectdata *conn)
 {
-  char *type;
+  char *path = data->state.up.path;
+  size_t len = strlen(path);
 
   conn->transport_wanted = TRNSPRT_UDP;
 
-  /* TFTP URLs support an extension like ";mode=<typecode>" that
-   * we will try to get now! */
-  type = strstr(data->state.up.path, ";mode=");
-
-  if(!type)
-    type = strstr(conn->host.rawalloc, ";mode=");
-
-  if(type) {
-    char command;
-    *type = 0;                   /* it was in the middle of the hostname */
-    command = Curl_raw_toupper(type[6]);
-
-    switch(command) {
-    case 'A': /* ASCII mode */
-    case 'N': /* NETASCII mode */
-      data->state.prefer_ascii = TRUE;
-      break;
-
-    case 'O': /* octet mode */
-    case 'I': /* binary mode */
-    default:
-      /* switch off ASCII */
-      data->state.prefer_ascii = FALSE;
-      break;
-    }
+  /* TFTP URLs support a trailing ";mode=netascii" or ";mode=octet" */
+  if((len >= 14) && !memcmp(&path[len - 14], ";mode=netascii", 14)) {
+    data->state.prefer_ascii = TRUE;
+    path[len - 14] = 0; /* cut it there */
+  }
+  else if((len >= 11) && !memcmp(&path[len - 11], ";mode=octet", 11)) {
+    data->state.prefer_ascii = FALSE;
+    path[len - 11] = 0; /* cut it there */
   }
 
   return CURLE_OK;
diff --git a/src/tool_listhelp.c b/src/tool_listhelp.c
index c8e31e77a6..21019c7de1 100644
--- a/src/tool_listhelp.c
+++ b/src/tool_listhelp.c
@@ -834,7 +834,7 @@ const struct helptxt helptext[] = {
    CURLHELP_HTTP | CURLHELP_POST | CURLHELP_UPLOAD},
   {"-B, --use-ascii",
    "Use ASCII/text transfer",
-   CURLHELP_FTP | CURLHELP_OUTPUT | CURLHELP_LDAP},
+   CURLHELP_FTP | CURLHELP_OUTPUT | CURLHELP_LDAP | CURLHELP_TFTP},
   {"-u, --user <user:password>",
    "Server user and password",
    CURLHELP_IMPORTANT | CURLHELP_AUTH},
diff --git a/tests/data/test1093 b/tests/data/test1093
index 1bed99bec1..a135876ae0 100644
--- a/tests/data/test1093
+++ b/tests/data/test1093
@@ -25,10 +25,10 @@ returned
 tftp
 </server>
 <name>
-TFTP retrieve with mode=i
+TFTP retrieve with mode=octet
 </name>
 <command>
-"tftp://%HOSTIP:%TFTPPORT//%TESTNUMBER;mode=i" --use-ascii
+"tftp://%HOSTIP:%TFTPPORT//%TESTNUMBER;mode=octet" --use-ascii
 </command>
 </client>
 
-- 
2.47.3