libopenarc: Wrap b= fields at the margin

Cleans up two XXXs.

Author: flowerysong

CHANGELOG.md

@@ -52,6 +52,7 @@ All notable changes to this project will be documented in this file.
   and `s=` tags.
 - libopenarc - `arc_eom()` propagates internal errors like memory allocation
   failure instead of marking the chain as failed.
+- libopenarc - Signature fields are wrapped at the configured margin.
 - milter - Use after free.
 - milter - Unlikely division by zero.
 - milter - Small memory leak during config loading.

libopenarc/arc.c

@@ -3599,9 +3599,7 @@ arc_getseal(ARC_MESSAGE         *msg,
     }
 
     /* append it to the stub */
-    arc_dstring_cat(dstr, (char *) b64sig);
-
-    /* XXX -- wrapping needs to happen here */
+    arc_dstring_cat_wrap(dstr, (char *) b64sig, msg->arc_margin);
 
     /* add it to the seal */
     h = ARC_MALLOC(sizeof hdr);
@@ -3700,9 +3698,7 @@ arc_getseal(ARC_MESSAGE         *msg,
     }
 
     /* append it to the stub */
-    arc_dstring_cat(dstr, (char *) b64sig);
-
-    /* XXX -- wrapping needs to happen here */
+    arc_dstring_cat_wrap(dstr, (char *) b64sig, msg->arc_margin);
 
     /* add it to the seal */
     h = ARC_MALLOC(sizeof hdr);

test/test_milter.py

@@ -50,6 +50,9 @@ def _run_miltertest(
             if msg[0] == miltertest.SMFIR_INSHEADER:
                 # Check for invalid characters
                 assert '\r' not in msg[1]['value']
+                # Check for proper wrapping
+                if msg[1]['name'] in ['ARC-Message-Signature', 'ARC-Seal']:
+                    assert not any(len(x) > 80 for x in msg[1]['value'].splitlines())
                 ins_headers.insert(msg[1]['index'], [msg[1]['name'], msg[1]['value']])
             elif msg[0] in miltertest.DISPOSITION_REPLIES:
                 assert msg[0] == miltertest.SMFIR_ACCEPT

util/arc-dstring.c

@@ -378,6 +378,84 @@ arc_dstring_catn(struct arc_dstring *dstr, const char *str, size_t nbytes)
     return true;
 }
 
+/**
+ *  Append a string to a dstring, wrapping at a specific column.
+ *
+ *  Parameters:
+ *      dstr: dstring to modify
+ *      str: string to append
+ *      margin: maximum line length, not including CRLF
+ *
+ *  Returns:
+ *      Whether the operation succeeded.
+ */
+bool
+arc_dstring_cat_wrap(struct arc_dstring *dstr, const char *str, size_t margin)
+{
+    size_t len;
+    size_t slen;
+
+    if (margin < 3)
+    {
+        /* margin is either disabled or nonsensical */
+        return arc_dstring_cat(dstr, str);
+    }
+
+    /* find the current line length */
+    len = 0;
+    for (char *p = dstr->ds_buf; *p; p++)
+    {
+        len++;
+        if (*p == '\n')
+        {
+            len = 0;
+        }
+    }
+
+    if (len >= margin)
+    {
+        len = 0;
+    }
+    else
+    {
+        len = margin - len;
+    }
+
+    slen = strlen(str);
+    if (len > slen)
+    {
+        len = slen;
+    }
+
+    if (len > 0)
+    {
+        if (!arc_dstring_catn(dstr, str, len))
+        {
+            return false;
+        }
+    }
+
+    for (const char *p = str + len; p < str + slen; p += margin - 2)
+    {
+        if (!arc_dstring_cat(dstr, "\r\n\t "))
+        {
+            return false;
+        }
+
+        len = strlen(p);
+        if (len > margin - 2)
+        {
+            len = margin - 2;
+        }
+
+        if (!arc_dstring_catn(dstr, p, len))
+        {
+            return false;
+        }
+    }
+    return true;
+}
+
 /*
 **  ARC_DSTRING_GET -- retrieve data in a dstring
 **

util/arc-dstring.h

@@ -27,6 +27,7 @@ extern void  arc_dstring_blank(struct arc_dstring *);
 extern bool  arc_dstring_cat(struct arc_dstring *, const char *);
 extern bool  arc_dstring_cat1(struct arc_dstring *, int);
 extern bool  arc_dstring_catn(struct arc_dstring *, const char *, size_t);
+extern bool  arc_dstring_cat_wrap(struct arc_dstring *, const char *, size_t);
 extern bool  arc_dstring_copy(struct arc_dstring *, const char *);
 extern void  arc_dstring_strip(struct arc_dstring *, const char *);
 extern void  arc_dstring_free(struct arc_dstring *);