In Nov 2019, I was unable to compile openbsd-netcat on a
uclibc-ng-1.0.32 based system.  Note: /I don't really write C and I
don't know what I'm doing/ but the following patch allowed me to compile
openbsd-netcat and run it.  I just pulled the bit from glibc (mostly
verbatim iirc) and added corresponding config parameter.  Hopefully it
will be useful even if incompetent.

I've been using openbsd-netcat with uclibc-ng 1.0.32 and 1.0.33 from
2019-11 to 2020-06 (now) on regular basis, and openbsd-netcat seems to
work fine.


--- a/include/resolv.h
+++ b/include/resolv.h
@@ -329,9 +329,12 @@
 #endif
 __END_DECLS
 
-#if 0
+
+#ifdef __UCLIBC_HAS_BSD_B64_NTOP_B64_PTON__
 #define b64_ntop               __b64_ntop
 #define b64_pton               __b64_pton
+#endif
+#if 0
 #define dn_count_labels                __dn_count_labels
 #endif
 #define dn_comp                        __dn_comp
@@ -384,8 +387,12 @@
 int            sym_ston (const struct res_sym *, const char *, int *) __THROW;
 const char *   sym_ntos (const struct res_sym *, int, int *) __THROW;
 const char *   sym_ntop (const struct res_sym *, int, int *) __THROW;
+#endif
+#ifdef __UCLIBC_HAS_BSD_B64_NTOP_B64_PTON__
 int            b64_ntop (u_char const *, size_t, char *, size_t) __THROW;
 int            b64_pton (char const *, u_char *, size_t) __THROW;
+#endif
+#if 0
 int            loc_aton (const char *ascii, u_char *binary) __THROW;
 const char *   loc_ntoa (const u_char *binary, char *ascii) __THROW;
 void           putlong (u_int32_t, u_char *) __THROW;

--- a/extra/Configs/Config.in
+++ b/extra/Configs/Config.in
@@ -1036,6 +1036,14 @@
 
          If unsure, say N.
 
+config UCLIBC_HAS_BSD_B64_NTOP_B64_PTON
+       bool "Support b64_ntop(), b64_pton() (bsd-compat)"
+       help
+         Answer Y if you need additional BSD compatibility
+          (e.g. for openbsd-netcat).
+
+         Most people will say N.
+
 config UCLIBC_HAS_OBSOLETE_SYSV_SIGNAL
        bool "SYSV obsolete signal functions"
        help

--- a/libc/inet/resolv.c
+++ b/libc/inet/resolv.c
@@ -3632,6 +3632,263 @@
 }
 #endif
 
+#ifdef __UCLIBC_HAS_BSD_B64_NTOP_B64_PTON__
+#define Assert(Cond) if (!(Cond)) abort()
+
+static const char Base64[] =
+       "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+static const char Pad64 = '=';
+
+/* (From RFC1521 and draft-ietf-dnssec-secext-03.txt)
+   The following encoding technique is taken from RFC 1521 by Borenstein
+   and Freed.  It is reproduced here in a slightly edited form for
+   convenience.
+
+   A 65-character subset of US-ASCII is used, enabling 6 bits to be
+   represented per printable character. (The extra 65th character, "=",
+   is used to signify a special processing function.)
+
+   The encoding process represents 24-bit groups of input bits as output
+   strings of 4 encoded characters. Proceeding from left to right, a
+   24-bit input group is formed by concatenating 3 8-bit input groups.
+   These 24 bits are then treated as 4 concatenated 6-bit groups, each
+   of which is translated into a single digit in the base64 alphabet.
+
+   Each 6-bit group is used as an index into an array of 64 printable
+   characters. The character referenced by the index is placed in the
+   output string.
+
+                         Table 1: The Base64 Alphabet
+
+      Value Encoding  Value Encoding  Value Encoding  Value Encoding
+          0 A            17 R            34 i            51 z
+          1 B            18 S            35 j            52 0
+          2 C            19 T            36 k            53 1
+          3 D            20 U            37 l            54 2
+          4 E            21 V            38 m            55 3
+          5 F            22 W            39 n            56 4
+          6 G            23 X            40 o            57 5
+          7 H            24 Y            41 p            58 6
+          8 I            25 Z            42 q            59 7
+          9 J            26 a            43 r            60 8
+         10 K            27 b            44 s            61 9
+         11 L            28 c            45 t            62 +
+         12 M            29 d            46 u            63 /
+         13 N            30 e            47 v
+         14 O            31 f            48 w         (pad) =
+         15 P            32 g            49 x
+         16 Q            33 h            50 y
+
+   Special processing is performed if fewer than 24 bits are available
+   at the end of the data being encoded.  A full encoding quantum is
+   always completed at the end of a quantity.  When fewer than 24 input
+   bits are available in an input group, zero bits are added (on the
+   right) to form an integral number of 6-bit groups.  Padding at the
+   end of the data is performed using the '=' character.
+
+   Since all base64 input is an integral number of octets, only the
+         -------------------------------------------------
+   following cases can arise:
+
+       (1) the final quantum of encoding input is an integral
+           multiple of 24 bits; here, the final unit of encoded
+          output will be an integral multiple of 4 characters
+          with no "=" padding,
+       (2) the final quantum of encoding input is exactly 8 bits;
+           here, the final unit of encoded output will be two
+          characters followed by two "=" padding characters, or
+       (3) the final quantum of encoding input is exactly 16 bits;
+           here, the final unit of encoded output will be three
+          characters followed by one "=" padding character.
+   */
+
+int
+b64_ntop(u_char const *src, size_t srclength, char *target, size_t targsize) {
+       size_t datalength = 0;
+       u_char input[3];
+       u_char output[4];
+       size_t i;
+
+       while (2 < srclength) {
+               input[0] = *src++;
+               input[1] = *src++;
+               input[2] = *src++;
+               srclength -= 3;
+
+               output[0] = input[0] >> 2;
+               output[1] = ((input[0] & 0x03) << 4) + (input[1] >> 4);
+               output[2] = ((input[1] & 0x0f) << 2) + (input[2] >> 6);
+               output[3] = input[2] & 0x3f;
+               Assert(output[0] < 64);
+               Assert(output[1] < 64);
+               Assert(output[2] < 64);
+               Assert(output[3] < 64);
+
+               if (datalength + 4 > targsize)
+                       return (-1);
+               target[datalength++] = Base64[output[0]];
+               target[datalength++] = Base64[output[1]];
+               target[datalength++] = Base64[output[2]];
+               target[datalength++] = Base64[output[3]];
+       }
+
+       /* Now we worry about padding. */
+       if (0 != srclength) {
+               /* Get what's left. */
+               input[0] = input[1] = input[2] = '\0';
+               for (i = 0; i < srclength; i++)
+                       input[i] = *src++;
+
+               output[0] = input[0] >> 2;
+               output[1] = ((input[0] & 0x03) << 4) + (input[1] >> 4);
+               output[2] = ((input[1] & 0x0f) << 2) + (input[2] >> 6);
+               Assert(output[0] < 64);
+               Assert(output[1] < 64);
+               Assert(output[2] < 64);
+
+               if (datalength + 4 > targsize)
+                       return (-1);
+               target[datalength++] = Base64[output[0]];
+               target[datalength++] = Base64[output[1]];
+               if (srclength == 1)
+                       target[datalength++] = Pad64;
+               else
+                       target[datalength++] = Base64[output[2]];
+               target[datalength++] = Pad64;
+       }
+       if (datalength >= targsize)
+               return (-1);
+       target[datalength] = '\0';      /* Returned value doesn't count \0. */
+       return (datalength);
+}
+/* libc_hidden_def (b64_ntop) */
+
+/* skips all whitespace anywhere.
+   converts characters, four at a time, starting at (or after)
+   src from base - 64 numbers into three 8 bit bytes in the target area.
+   it returns the number of data bytes stored at the target, or -1 on error.
+ */
+
+int
+b64_pton (char const *src, u_char *target, size_t targsize)
+{
+       int tarindex, state, ch;
+       char *pos;
+
+       state = 0;
+       tarindex = 0;
+
+       while ((ch = *src++) != '\0') {
+               if (isspace(ch))        /* Skip whitespace anywhere. */
+                       continue;
+
+               if (ch == Pad64)
+                       break;
+
+               pos = strchr(Base64, ch);
+               if (pos == 0)           /* A non-base64 character. */
+                       return (-1);
+
+               switch (state) {
+               case 0:
+                       if (target) {
+                               if ((size_t)tarindex >= targsize)
+                                       return (-1);
+                               target[tarindex] = (pos - Base64) << 2;
+                       }
+                       state = 1;
+                       break;
+               case 1:
+                       if (target) {
+                               if ((size_t)tarindex + 1 >= targsize)
+                                       return (-1);
+                               target[tarindex]   |=  (pos - Base64) >> 4;
+                               target[tarindex+1]  = ((pos - Base64) & 0x0f)
+                                                       << 4 ;
+                       }
+                       tarindex++;
+                       state = 2;
+                       break;
+               case 2:
+                       if (target) {
+                               if ((size_t)tarindex + 1 >= targsize)
+                                       return (-1);
+                               target[tarindex]   |=  (pos - Base64) >> 2;
+                               target[tarindex+1]  = ((pos - Base64) & 0x03)
+                                                       << 6;
+                       }
+                       tarindex++;
+                       state = 3;
+                       break;
+               case 3:
+                       if (target) {
+                               if ((size_t)tarindex >= targsize)
+                                       return (-1);
+                               target[tarindex] |= (pos - Base64);
+                       }
+                       tarindex++;
+                       state = 0;
+                       break;
+               default:
+                       abort();
+               }
+       }
+
+       /*
+        * We are done decoding Base-64 chars.  Let's see if we ended
+        * on a byte boundary, and/or with erroneous trailing characters.
+        */
+
+       if (ch == Pad64) {              /* We got a pad char. */
+               ch = *src++;            /* Skip it, get next. */
+               switch (state) {
+               case 0:         /* Invalid = in first position */
+               case 1:         /* Invalid = in second position */
+                       return (-1);
+
+               case 2:         /* Valid, means one byte of info */
+                       /* Skip any number of spaces. */
+                       for ((void)NULL; ch != '\0'; ch = *src++)
+                               if (!isspace(ch))
+                                       break;
+                       /* Make sure there is another trailing = sign. */
+                       if (ch != Pad64)
+                               return (-1);
+                       ch = *src++;            /* Skip the = */
+                       /* Fall through to "single trailing =" case. */
+                       /* FALLTHROUGH */
+
+               case 3:         /* Valid, means two bytes of info */
+                       /*
+                        * We know this char is an =.  Is there anything but
+                        * whitespace after it?
+                        */
+                       for ((void)NULL; ch != '\0'; ch = *src++)
+                               if (!isspace(ch))
+                                       return (-1);
+
+                       /*
+                        * Now make sure for cases 2 and 3 that the "extra"
+                        * bits that slopped past the last full byte were
+                        * zeros.  If we don't check them, they become a
+                        * subliminal channel.
+                        */
+                       if (target && target[tarindex] != 0)
+                               return (-1);
+               }
+       } else {
+               /*
+                * We ended by seeing the end of the string.  Make sure we
+                * have no partial bytes lying around.
+                */
+               if (state != 0)
+                       return (-1);
+       }
+
+       return (tarindex);
+}
+#endif
+
 /* This needs to be after the use of _res in res_init, above.  */
 #undef _res

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